Recycling doi: 10.3390/recycling11080153

Authors: Michael Carolan

Research on recycling and waste governance has produced extensive knowledge about the factors influencing environmentally responsible behavior. Studies examine strategies—including feedback systems, incentives, social norms, gamification, and certification schemes—to encourage recycling and waste reduction. Although these approaches differ in their theoretical foundations and intervention designs, many seek to make environmental actions visible, measurable, and feasible. Less attention has been devoted to how such actions acquire social meaning and become recognizable as worthy of evaluation, distinction, and acknowledgment. This study addresses that gap through a configurative review of 37 documents selected to represent diverse recycling and waste-governance intervention traditions. A comparative analysis reconstructed the recurring explanatory mechanisms through which environmental actions become evaluable. The findings show that intervention traditions commonly treated as distinct repeatedly rely on an evaluative architecture comprising five interacting components: visibility, evaluation, credibility, distinction, and embedding. These components constitute recognition infrastructures—governance arrangements that produce evaluability by rendering environmental actions observable, publicly meaningful, and sustainable over time. The framework identifies similarities across intervention traditions often studied separately and shifts attention from individual intervention tools to the broader arrangements that make environmental actions significant, while providing a practical lens for designing more durable recycling and waste-governance interventions.

Recycling doi: 10.3390/recycling11080152

Authors: Jorge Alberto Chagoya-Ramírez Alondra González-Segura Juan Rodrigo Laguna-Camacho Héctor Daniel López-Calderón Celia María Calderón-Ramón Paul Ramírez-Sánchez Javier Calderón-Sánchez Víctor Velázquez-Martínez

The increasing accumulation of polyethylene terephthalate (PET) bottles represents a significant environmental challenge due to their high consumption and limited recovery. The purpose of this study was to develop a sustainable alternative for reusing this waste by manufacturing educational test specimens for laboratory exercises in electrical mechanical engineering and industrial engineering programs. The proposed method was based on mechanical recycling and incorporated, as an innovation, a stage for measuring bottle parameters before processing to improve the quality and uniformity of the recycled material. The results were calculated with the participation of 6 students per test type, which showed that 66.66% of the specimens intended for impact tests and 83.33% of those intended for torsion tests exhibited adequate functional performance. Likewise, it was estimated that a weekly production of 1 kg of crushed PET would cover approximately half a week (three days) of laboratory practices, considering the large number of students. Therefore, it could use 60 to 80% of the total consumption during a standard 15-week course, depending on the situation, demonstrating that integrating recycling into academic activities supports the circular economy, reduces the environmental impact of plastic waste, and strengthens students’ practical training and professional skills.

Recycling doi: 10.3390/recycling11080151

Authors: Tonghe Du Tianzhi Wang Zhitao Li Yujie Zhao Chuangchuang Zhang

Food waste digestate is a high-moisture organic residue that requires effective stabilization before resource recovery or land application. This engineering-scale study compared high aeration (HA, 0.30 L·min−1·kg−1 dry matter), low aeration (LA, 0.15 L·min−1·kg−1 dry matter), and turning without forced bottom aeration (TG) during a 30-day food waste digestate–corn straw co-composting experiment. One engineering-scale pile was operated for each treatment. Physicochemical trajectories, bacterial succession, predicted functional potential, and microbial co-occurrence patterns were evaluated. All treatments rapidly entered the thermophilic phase. HA reached the highest temperature (63.70 °C) and remained above 55 °C for 340.8 h, but it also had the lowest final moisture reading (18.62%). LA achieved the greatest organic matter (OM) reduction (17.47%), compared with 13.47% in HA and 7.44% in TG, while retaining more moisture than HA at day 30. Bacillota became dominant in all treatments, although the intensity of thermophilic filtering and the pattern of late-stage succession differed among treatments. Functional predictions indicated the highest late-stage ureolysis potential in LA, whereas TG showed greater predicted representation of several nitrogen-transformation-related groups and the densest co-occurrence network. These findings suggest that engineering-scale composting performance depends on the balance among oxygen supply, heat accumulation, moisture conservation, and microbial organization rather than on thermophilic intensity alone. Under the tested conditions, LA provided the most favorable balance, particularly in terms of OM reduction and moisture retention.

Recycling doi: 10.3390/recycling11080149

Authors: Yan Zhang Yuanyuan Sun Yuting Li Shaohua Bian Li Meng Zhuang Li

Substantial dye wastewater from the textile industry poses serious ecological threats. Spent mushroom substrate (SMS) offers a cost-effective and eco-friendly decolorization option, yet traditional methods are hindered by prolonged processing times. This study introduces a column decolorization (CD) method using Auricularia cornea SMS, demonstrating markedly higher efficiency and practicality. The CD method achieved over 50% decolorization for 10 of 12 tested dyes, outperforming conventional approaches for six dyes. Analyses via SEM, FTIR, and isotherm measurements indicated that the high efficiency stems from the SMS microstructure and functional groups, with mechanisms including electrostatic attraction, hydrogen bonding, and π-π conjugation, following Langmuir monolayer adsorption. The process requires no specific conditions, avoids extraction steps, and reduces treatment time to 4% of traditional methods. HPLC analysis further revealed partial biodegradation of Malachite Green, reducing its cytotoxicity. This work provides the first systematic comparison of SMS decolorization methods and a mechanistic analysis, supporting SMS application in dye wastewater treatment.

Recycling doi: 10.3390/recycling11080148

Authors: Shuangxiang Zeng Lisha Dong Jingtao Shao Mohamed A. Deyab Xiangning Bu

Spent cathode carbon (SCC), a hazardous waste generated during primary aluminium production, contains valuable graphitic carbon resources but remains difficult to recycle because carbon purification is governed by complex interactions among multiple leaching parameters. Conventional process optimization relies on extensive laboratory experimentation, resulting in high chemical consumption, energy use, and development costs. This study presents an explainable machine learning framework for cleaner and more resource-efficient carbon purification from SCC under limited-data conditions. Six machine learning algorithms (GBDT, CatBoost, XGBoost, LightGBM, Random Forest, and Decision Tree) were evaluated using experimental data from alkaline leaching. The LightGBM model was systematically optimized by combining Response Surface Method (RSM), Orthogonal Experimental Design (OED), and local parameter optimization methods. The optimized model (min_child_samples = 2, num_leaves = 32, n_estimators = 500, and learning_rate = 0.5) achieved an R2 of 0.8015, RMSE of 0.9163, and MAE of 0.6599. SHAP analysis identified initial alkali concentration, liquid–solid ratio, stirring rate, and leaching time as the dominant factors controlling carbon purification, whereas temperature had a comparatively smaller influence within the investigated operating range. The results indicate that improving reagent utilization and hydrodynamic conditions offers greater potential for enhancing carbon purification than increasing thermal input alone. By integrating statistical experimental design with explainable machine learning, this study establishes an efficient, interpretable, and transferable decision-support framework for optimizing hazardous waste recycling and other resource recovery processes under limited-data conditions, thereby supporting cleaner production and circular economy practices.

Recycling doi: 10.3390/recycling11080150

Authors: Saw Shalton Roll Noppharit Sutthasil Sirintornthep Towprayoon Suthum Patumsawad Thapat Silalertruksa Sakulrat Sutthiprapa Abhisit Bhatsada Komsilp Wangyao

Mechanical treatment recovers combustible and recyclable fractions from mixed municipal solid waste (MSW), but full-scale performance is sensitive to front-end operation, line loading, and feedstock heterogeneity. This study examined material recovery trade-offs at a municipal mechanical treatment facility in Satun, Thailand. Four inverter-controlled regimes were assessed by adjusting the bag opener and trommel motor frequencies, giving measured line throughputs of 14.75, 13.45, 8.03, and 6.54 t·h−1. Output was classified as refuse-derived fuel (RDF), residual waste, recyclables, and bulky/loss material, with composition-based indicators of stream cleanliness and leakage. Each regime was a single short trial on waste from a different collection vehicle, without replication or input homogenization; no statistical comparison is possible, and results are reported as preliminary observations rather than isolated effects of inverter frequency. RDF yield fell from 42.06% of input at the highest throughput to 18.12% at the lowest, whereas recyclable recovery peaked at 4.95% under an intermediate regime that also returned the highest gross revenue. Residual-disposal methane generation potential was 7.78% higher under the lowest-throughput regime than under business-as-usual. Three trade-offs emerged: throughput against selectivity, RDF quantity against cleanliness, and recovery against leakage. The findings help operators select front-end settings on multi-criteria indicators rather than throughput alone.

Recycling doi: 10.3390/recycling11080147

Authors: Johan Montenegro Carmen Castaño María De Los Ángeles Ortega-Del-Rosario Ricardo Caballero Max Medina Dennis Keiser Michael Freitag

This systematic review evaluated technical evidence and system-level conditions for Distributed Recycling and Additive Manufacturing (DRAM) of post-consumer high-density polyethylene (HDPE) and polypropylene (PP). Peer-reviewed journal articles, conference papers, and reviews published from 2020 to 2025 were eligible when they addressed recycled-polymer preparation, feedstock conversion, extrusion-based additive manufacturing, printing performance, or circularity-related implementation; studies focused only on virgin polymers, outside the publication period, or lacking relevance were excluded. Scopus and Web of Science were searched on 17 October 2025 using four thematic strategies. Methodological completeness and applicability were appraised across six domains for the HDPE/PP material-specific evidence. Findings were synthesized narratively and thematically; meta-analysis was not performed because of substantial heterogeneity in feedstock, formulation, equipment, specimens, test methods, and outcomes. The final corpus comprised 119 unique sources: 28 material-specific sources (11 HDPE and 17 PP) and 91 contextual or system-level sources. Of the material-specific subset, 24 provided direct or partially direct recycled experimental evidence and four provided indirect or secondary evidence. Most appraised material-specific sources showed methodological concerns related to feedstock provenance, processing history, parameter reporting, replication, or test conditions. Recycled HDPE and PP could be converted into extrusion-based additive manufacturing feedstocks under study-specific conditions, but the evidence did not support universal processing windows, property ranges, degradation rates, cost competitiveness, environmental superiority, or generalized industrial readiness. Most evidence remained at laboratory or demonstrator scale. The Circular DRAM Viability Framework provides an evidence-informed structure intended to support application-specific diagnosis, monitoring, and qualification.

Recycling doi: 10.3390/recycling11080146

Authors: Napat Mahiwan Chatisa Kansomket Sumita Chailoi Natthicha Ma-Ud Sakhob Khumkoa Teerawut Tunnukij Tapany Patcharawit

Liquid Crystal Display (LCD) waste from various sources, such as TVs, desktop monitors, and computer notebooks, is increasing and has become an environmental issue, requiring legalized disposal and practical recycling technologies to address it. LCD screens generally contain Indium–Tin–Oxide (ITO), which are critical and valuable metals worth recovering. The aim of this research is to optimize the thermal–physical pretreatment of LCD screens after dismantling to effectively recover indium via leaching and solvent extraction at an acceptable recovery rate. A comparative study was conducted on the recovery of indium from LCD waste from TVs and a mixed waste stream, where the latter source represents the total proportion of LCD waste accumulation. This comparison aimed to identify key factors for effective recovery from TV and mixed waste streams, containing lower and higher amounts of indium, respectively. The recovery process consisted of waste pretreatment, leaching, and solvent extraction. In the first pretreatment, ethanol immersion was found to be the most practical for polarizing film removal for both streams in comparison with manual peeling, water immersion, surface heating, and calcination. Comminution in the second pretreatment aimed to increase the surface area for the subsequent chemical reaction. For both streams, HCl leaching allowed effective indium recovery of >99.9% at the optimal conditions of 5 M HCl with 10% H2O2 addition and an S/L ratio of 500 g/L under ultrasonication for 1 h. Subsequent purification via solvent extraction was conducted to exclude iron as the key impurity. In solvent extraction, D2EHPA concentration, pH, and the organic-to-aqueous ratio (O:A) was investigated. Optimal solvent extraction was achieved using 0.25 M D2EHPA at pH 1 and an O/A ratio of 1:5 for 5 min, while ascorbic acid was added to eliminate undesirable iron. Although both waste streams achieved >99.9% leaching efficiency, they exhibited different extraction behaviors after scrubbing and stripping. The TV waste stream achieved 74.32% solvent extraction efficiency. The higher indium recovery of 84.34% via solvent extraction through the stripping of the mixed stream might be due to the higher initial indium concentration reacting with D2EHPA. This led to the overall recovery of the two waste streams as 70.22% and 80.24% for TV and mixed waste streams, respectively, possibly due to higher amounts of indium in the initial waste stream. The findings of this study serve as research and practical guidance for indium recovery and EOL–LCD recycling.

Recycling doi: 10.3390/recycling11080145

Authors: Chunqing Gao Huifen Yang Jian Xu Ning Wang

Taking pickling sludge generated from the steel rolling process at a Chinese steel mill as the subject of study, this research investigates a combined mineral processing and metallurgical process involving gasification-reduction roasting, magnetic separation, and waste acid recovery. The main elements in this pickling sludge are Fe and Cl, with contents of 46.50% and 12.70%, respectively. The primary component is chlorine-containing iron oxide, and a significant amount of amorphous material is also present. The study investigated the effects of various calcination temperatures, calcination times, reducing agent dosages, and material thicknesses on gasification-reduction performance indicators. The results indicate that using a reduction calcination–grinding–magnetic separation process, with coal as the reducing agent, a calcination temperature of 1100 °C, a reducing agent dosage of 15%, and a calcination time of 2 h, the chlorine volatilization rate exceeds 97%. Furthermore, when the roasted ore is ground to a particle size where 85% passes through a −0.076 mm screen and is recovered via magnetic separation, an iron concentrate with a grade of over 69.50% can be obtained. This iron concentrate meets the quality requirements for high-grade iron concentrates used in direct reduced iron (DRI) production. The small amount of tailings from the iron concentration process can be utilized in the production of bricks, cement, and other products, thereby achieving the efficient comprehensive utilization of acid washing sludge.

Recycling doi: 10.3390/recycling11080144

Authors: Hélder Spínola Jacinta Fernandes Cátia Sousa Clarice Campos Sandra Mourato Lizete Heleno Maria Anunciação Mateus Ventura Sandra Caeiro Paula Bacelar-Nicolau Mahsa Mapar Ulisses M. Azeiteiro Sandra C. Guimarães Liliana Rodrigues Sílvia Mateus Carreira Rute Martins Sílvia Quadros

Waste management is essential for addressing local and global environmental challenges. Failure to manage waste effectively results in several consequences, including environmental degradation, public health risks, and economic costs. Besides the need for adequate and up-to-date waste management systems, citizens’ cooperation is crucial to achieving sustainable waste management in any community, which depends on their waste literacy levels, comprising the knowledge, attitudes, and behaviours required. This study assessed waste literacy among students completing compulsory education in Portugal to provide evidence regarding the outcomes of environmental education policies related to waste management. A representative sample of 1506 freshmen students was surveyed at the start of their undergraduate programmes. An online questionnaire was administered to the sample and the data were analyzed using statistical tests for assessing the influential factors associated with students’ waste knowledge, attitudes and behaviours. Results show that, on average, students demonstrated good levels of knowledge and practices on waste management, together with a predominantly ecocentric worldview. A higher performance in waste management knowledge and practices was observed among younger students, with higher grades and higher paternal educational attainment. Besides these variables, best practices were significantly more prevalent among those with a higher participation in environmental activities and holding membership in environmental organizations. The findings suggest that upon completing compulsory education in Portugal, students display generally high levels of waste literacy, while also revealing specific gaps in knowledge and practices that warrant further educational attention. The study identifies these areas for improvement, highlighting the potential value of more practical, participatory and community-based approaches to waste education.

Recycling doi: 10.3390/recycling11080143

Authors: Aritz Unamuno Garay Fernando Galera Pérez Ana Ibáñez-García Asunción Martínez-García María Dolores Samper

The recycling of post-industrial multilayer polyethylene terephthalate (mPET) packaging waste remains a major challenge due to the coexistence of incompatible polymeric phases and the deterioration of properties during reprocessing. In this work, different reactive compatibilization strategies were evaluated to improve the processability and performance of recycled multilayer PET scraps generated during industrial packaging manufacturing processes. Several functional compatibilizers were investigated, including poly(ethylene-co-acrylic acid) (EAA), poly(ethylene-alt-maleic anhydride) (EMA), poly(ethylene-co-glycidyl methacrylate) (EGMA), poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate) (EMAGMA), and maleic anhydride (MA). The influence of compatibilization on the thermal, mechanical, chemical, surface, and morphological properties of recycled mPET was systematically analyzed. Processing behavior revealed that EMA- and MA-based formulations could not be successfully injection molded. In contrast, EAA-, EGMA-, and EMAGMA-based formulations showed suitable processability and enabled the production of defect-free specimens. Thermogravimetric analysis revealed only minor changes in thermal degradation behavior after compatibilization. In contrast, differential scanning calorimetry revealed changes in the melting behavior of the recycled formulations, while tensile and impact tests demonstrated marked improvements in ductility and toughness for EGMA- and EMAGMA-modified systems. Among them, EMAGMA provided the highest elongation at break and impact resistance. Contact angle measurements showed moderate changes in surface wettability, whereas density and hardness remained largely unaffected. FESEM analysis revealed a more homogeneous phase distribution and reduced dispersed-domain size in the compatibilized formulations, particularly for EGMA, indicating improved interfacial compatibility. These results demonstrate that glycidyl methacrylate-based compatibilizers are effective reactive agents for upgrading post-industrial multilayer PET waste into higher-performance recycled materials for different applications.

Recycling doi: 10.3390/recycling11080142

Authors: Parinaz Seifollahzadeh Bettina Rutrecht Stefanie Lesiak Lalropuia Lalropuia Stephan Stuhr Lukas Schmidt Rebeka Frueholz Anna Sieber Sabine Spiess Markus Ellersdorfer Johannes Rieger Roland Pomberger

Recycling of lithium-ion batteries (LIBs) remains challenging due to high energy requirements, losses of key elements like lithium, and the heterogeneity of waste streams arising from different cathode chemistries. This study evaluates multiple recycling methods for LIBs black mass (BM), to recover critical raw materials and other valuable components. Three types of BM including nickel–manganese–cobalt (NMC), lithium iron phosphate (LFP) and a heterogeneous mixture of cell phones and laptops (HL; German: Handy/Laptops), were treated using froth flotation, pyrometallurgy, and biohydrometallurgy and their respective recovery efficiencies were assessed. The flotation results revealed that the HL sample had the lowest mis-recovery of non-ferrous metals into the froth product (around 10%), leading to further flotation only for HL. During screening, 94–99% of iron, phosphorus, and carbon in LFP-type BM were recovered in the fine fraction (<45 µm), while 92–99% of lithium, cobalt, manganese, nickel, and carbon in NMC-type BM were recovered in the same fraction. During precipitation, 99% of iron and 100% of phosphorus were recovered from LFP bioleachates at pH 3, while ~97–100% of dissolved cobalt, manganese, and nickel were recovered from NMC bioleachates. These findings confirm that no single recycling method is optimal for all battery chemistries.

Recycling doi: 10.3390/recycling11080141

Authors: Sutida Phitakwinai Wanich Nilnont

This study evaluated the technical viability and thermodynamic performance of an open-loop upcycled heat pump dryer, repurposed from a decommissioned window-type air conditioner, for thin-layer red dragon fruit (Selenicereus costaricensis) drying. Experiments were executed at 50 °C under controlled air velocities (0.5, 1.0, and 1.5 m/s), using open-sun drying as a control. Mathematical modeling revealed that the Wang and Singh model best described the drying process (R2: 0.996368–0.999539). Accounting for volumetric shrinkage via equivalent average thickness (Leq = 0.75 L0), corrected effective moisture diffusivity (Deff) ranged from 1.194 × 10−9 to 3.138 × 10−9 m2/s, while convective mass transfer coefficients (hm) ranged from 5.241 × 10−7 to 1.880 × 10−6 m/s, both peaking at 1.5 m/s due to thinned concentration boundary layers. Thermodynamic assessments showed a maximum COPhp of 3.41 at 1.0 m/s and a maximum SMER of 0.231 kg/kWh at 1.5 m/s. Individual statistical analysis of L*, a*, and b* parameters confirmed no statistically significant differences (p > 0.05) between heat-pump-dried and fresh samples. Concurrently, a remarkably low descriptive total color difference (ΔE = 1.24) was obtained, compared to open-sun drying (ΔE = 16.22), confirming high color retention. These findings highlight e-waste upcycling as an efficient and sustainable agricultural solution.

Recycling doi: 10.3390/recycling11080140

Authors: Mihaela Adriana Tița Cristina Maria Bătușaru Andreea Simina Porancea-Răulea Alina Rădoiu Ovidiu Tița

The adoption of circular economy (CE) in agri-food systems has been accelerated by rising environmental pressures and resource inefficiencies. This systematic review examines the thematic and conceptual evolution of CE research in agri-food systems between 2018 and 2025, focusing on the transition from waste management toward the strategic integration of circular principles across food value chains. By combining bibliometric mapping with a structured literature review, the study analyzes publication trends, intellectual structures, dominant research themes, and emerging directions within the field. The findings reveal a rapid growth in scientific output and a shift from conceptual frameworks toward applied management strategies, including performance measurement, organizational innovation, and decision-support tools. Technological solutions for waste valorization increasingly support regenerative food system models. Despite these advances, important research gaps remain, particularly regarding geographical concentration, the limited integration of consumer perspectives, and the need for broader assessment frameworks capable of evaluating the systemic impacts of circular strategies. Although nutrition-related aspects appear only marginally in the current literature, they represent a promising avenue for future interdisciplinary research rather than a dominant research theme. Overall, the field is evolving toward a more systemic and implementation-oriented perspective capable of supporting resilient and sustainable food systems.

Recycling doi: 10.3390/recycling11080139

Authors: Ramon Torres-Ortega Manuel Saba Jair Arrieta-Baldovino

The incorporation of supplementary cementitious materials derived from agro-industrial residues has emerged as a promising strategy to reduce the environmental impact associated with Portland cement production while promoting circular economy principles. This study investigates the influence of palm oil fuel ash (POFA) as a partial cement replacement on the mechanical and microstructural properties of concrete. Concrete mixtures containing 0%, 10%, 15%, and 20% POFA by mass of cement were produced using a constant water-to-binder ratio of 0.47. Compressive strength was evaluated at 7, 14, 28, and 56 days, while microstructural characterization was performed using scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS) to assess hydration products and the interfacial transition zone (ITZ). The incorporation of POFA resulted in lower compressive strength at early curing ages, with reductions of approximately 16–21% compared with the control mixture, reflecting the slower kinetics of pozzolanic reactions. However, prolonged curing promoted significant strength development. At 56 days, concretes containing 10% and 15% POFA exhibited compressive strengths 3.7% and 9.2% higher, respectively, than the control concrete, whereas the 20% replacement level resulted in a 14.6% reduction. SEM observations revealed a denser cementitious matrix, improved aggregate–paste bonding, and a more refined ITZ in mixtures containing 10–15% POFA. EDS analysis showed Ca/Si ratios of 1.22 and 1.08 for the 10% and 15% POFA mixtures, respectively, indicating the formation of silica-rich C–S–H gel associated with effective pozzolanic activity. The results demonstrate that POFA can be successfully utilized as a supplementary cementitious material in concrete. While the 15% replacement level produced the highest 56-day compressive strength, both the 10% and 15% mixtures exhibited favorable microstructural characteristics and effective pozzolanic activity, indicating that both replacement levels are suitable for sustainable concrete production.

Recycling doi: 10.3390/recycling11080138

Authors: Nafisa Tarannum Shahjalal Selim Nazimuddin M. Wasiuddin Andrew Peters

Increasing plastic waste and limited recycling rates underscore the need for value-added recycling applications. Polymers commonly present in plastic waste streams, including packaging films, bottles, caps, and rigid containers, may provide a practical pathway for developing plastic-modified asphalt binder (PMAB) systems. In this study, virgin high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) were selected as reference modifiers to evaluate their intrinsic effects on performance grade (PG) 58-28 and PG 67-22 base binders. Conventional high-, intermediate-, and low-temperature gradings were complemented by ΔTc, the Christensen–Anderson R-value (R-value), the Glover–Rowe (G-R) parameter, Linear Amplitude Sweep (LAS) fatigue analysis modeled via Viscoelastic Continuum Damage (VECD), rheological master curves, and extended Bending Beam Rheometer (BBR) testing. Modification improved high-temperature grading and LAS-based fatigue response while increasing master-curve stiffness. However, ΔTc, G-R parameter, and extended BBR results indicated increased low-temperature cracking susceptibility. High-temperature grades increased by 3.4 °C, 2.8 °C, and 2.3 °C per percent HDPE, LDPE, and PP, respectively, whereas low-temperature grade losses reached 7.8 °C; HDPE produced the highest high-temperature grade improvement, while LDPE showed the greatest extended BBR grade loss, and PP exhibited the fastest physical hardening rate. These results provide a controlled binder-level baseline for evaluating HDPE, LDPE, and PP as modifiers for future PMAB development.

Recycling doi: 10.3390/recycling11080137

Authors: Muhammad Imran Aamena Batool Nazish Hina Rao Taha Tauqeer Shaban Shahzad

Municipal waste composition is commonly measured at a single point, even though recovery, mixing and handling can alter the stream before disposal. This study examined municipal solid waste in Sialkot, Pakistan, during an eight-day campaign from 27 December 2021 to 3 January 2022. A total of 672 physical-characterization samples was obtained from residential, commercial, institutional, industrial and street-sweeping sources. Household generation was 0.42, 0.46 and 0.51 kg per person per day in low-, middle- and high-income proxy areas, respectively. Kitchen waste declined from 45.91% at the source to 34.20% at communal storage and 23.45% at the dumpsite. Recyclable paper and plastic also declined, whereas dust and fines increased from 2.05% at the source to 19.60% at storage and 21.78% at disposal. Six mixed-waste composites showed moisture contents of 30.72–53.06%, ash contents of 15.85–45.04% and gross calorific values of 2924–12,530 kcal kg−1. The results demonstrate that monitoring location materially affects estimated recycling and treatment potential. A multi-point monitoring protocol is therefore recommended for cities with mixed collection and informal material recovery.

Recycling doi: 10.3390/recycling11080136

Authors: Suraksha Baral Brian E. Roe

National recycling rates have stagnated at approximately 32 percent in the United States, suggesting that existing programs are not achieving desired levels of diversion. A growing body of field experiments has examined whether informational and norm-based messaging interventions can shift recycling behavior, though most studies rely on self-reported outcomes or stated preferences rather than objective behavioral measures. Using bin-level audit data from a randomized field trial among 200 voluntarily enrolled households in Columbus, Ohio, we find that norm-based and educational message framing produce statistically indistinguishable average effects on recycling fill level, participation, and contamination over a 29-week program. However, the analysis identifies that norm-based messaging outperforms educational messaging when adverse weather raises participation costs, while educational messaging holds up better during high-distraction community events. These patterns point toward adaptive messaging designs that condition content on observable contextual triggers as a promising direction for extracting greater behavioral returns from recycling outreach investment.

Recycling doi: 10.3390/recycling11080135

Authors: Javier Blázquez-Martín Marta Jiménez-Salcedo Jorge García-Barrasa María Teresa Tena

Seven bio-based solvents ((-)-β-pinene, α-phellandrene, α-terpinene, p-cymene, DL-limonene, γ-terpinene and terpinolene) are tested as environmentally friendly alternatives for use in a plastic recycling process based on dissolution–precipitation of post-consumer high-density polyethylene (PC-HDPE). In addition to evaluating cleaning performance, this work aims to develop and validate a new analytical method for the determination of residual bio-based solvents in the treated polymer, a critical aspect for evaluating the safety and quality of recycled materials. The suitability of the solvents for contaminant removal was assessed via challenge test, showing high cleaning efficiencies (>93.3%) for volatile, non-volatile, polar and non-polar compounds in most cases. To monitor residual solvent levels, a pressurized liquid extraction and gas chromatography–mass spectrometry (PLE-GC/MS) method was developed, optimized and validated. The method demonstrated adequate sensitivity (with LODs ranging between 2 and 4 mg kg−1), accuracy and precision (with intra- and inter-day relative standard deviations of less than 11 and 31%, respectively) for the simultaneous determination of the seven bio-based solvents in recycled HDPE. Overall, results demonstrate both the potential of bio-based solvents in polymer recycling and the importance of robust analytical tools to assess residual contamination, supporting the development of safer and more sustainable recycling processes.

Recycling doi: 10.3390/recycling11080134

Authors: Chiara Gnoffo Rossella Arrigo Valentina Piergrossi Letizia Tuccinardi Riccardo Tuffi Alberto Frache

This study evaluated the feasibility of mechanical recycling of plastic waste recovered from the disassembly of end-of-life lithium iron phosphate battery cases. In particular, the work focused on the case fraction, corresponding to the outer battery envelope, which represents the largest share of the plastic waste by weight. A preliminary characterization was carried out to determine the physico-chemical properties of the material and assess its suitability for mechanical recycling. The polymer matrix was found to consist of polypropylene, with glass fibers and calcium carbonate as inorganic fillers, each present at 18 wt%. X-ray fluorescence and elemental analysis confirmed the absence of elements of concern and subsequently, recycled material processability was investigated, with particular attention to injection molding, the same technology used to manufacture the original battery cases. Rheological analyses confirmed that the material exhibits Newtonian rheological behavior, suitable for injection molding, as also supported by a melt flow index value equal to 7.5 g/10 min (230 °C, 2.16 kg). The material was then reprocessed, and the resulting specimens were subjected to mechanical tests, with impact energy equal to 30.5 kJ/m2 and flexural strength amounting to 36.8 MPa. Overall, the recycled material exhibited adequate processability and mechanical performance after one reprocessing step, suggesting its potential for high-value mechanical recycling.

Recycling doi: 10.3390/recycling11070133

Authors: Thomas Langner Anja Rietig Jörg Acker

With the increasing prevalence of lithium–ion batteries, the recycling of battery materials is becoming increasingly important. Functional recycling represents a promising approach in this context, one that is often based on aqueous treatment steps. This study examines the aqueous treatment of positive electrodes coated with various cathode active materials and their mixtures. To this end, the electrodes were leached in two different broad-range buffer systems in the pH range of 5 to 11. The investigations focused on the temporal evolution of the pH value, the time-dependent leaching of the active material components, and the dissolution of the aluminum current collector. The results show that process parameters, particularly the initial pH value, the treatment duration, and the composition of the process medium, influence both the leaching of the active materials and the corrosion of the aluminum current collector. Furthermore, the coated electrodes studied show significant differences in the stability of the active materials, which sometimes deviate from the properties of the respective pure active materials described in the literature, suggesting additional interactions within the electrode structure. The results highlight the need for targeted process optimization to create the conditions for the successful functional recycling of active materials from lithium–ion batteries.

Recycling doi: 10.3390/recycling11070132

Authors: Kristaps Siltumens Inga Grinfelde

Textile waste represents a growing environmental challenge, while also offering opportunities for material recovery and the development of higher-value recycled products. This study investigated the potential of post-consumer textile waste for the production of sound-absorbing acoustic panels. Five textile fiber compositions were evaluated: cotton, polyester, wool, linen, and a mixed blend consisting of 50% polyester, 30% cotton, 10% wool, 5% linen, and 5% other fibers. The panels were produced using a biopolymer binder and tested using an AFD 1000 impedance tube. The measurement software generated frequency-resolved sound absorption data from 6.25 to 6393.75 Hz at 6.25 Hz intervals; however, only the validated frequency range of 100–4000 Hz was included in the analysis. Three cylindrical specimens with a diameter of 40 mm were prepared from each material type. Sound absorption coefficients were analyzed across low- (100–250 Hz), mid- (250–1000 Hz), and high-frequency (1000–4000 Hz) ranges, and statistical differences between materials were assessed using one-way ANOVA and Tukey’s HSD post hoc test. The results showed no statistically significant differences between fiber types at low frequencies. In contrast, significant differences were observed in the mid- and high-frequency ranges. Cotton achieved the highest mean absorption coefficient in the mid-frequency range (α = 0.747), while polyester and wool performed best at high frequencies, with mean absorption coefficients of 0.913 and 0.850, respectively. Polyester showed the highest overall acoustic performance across the analyzed frequency range, with a mean absorption coefficient of α = 0.824. These findings demonstrate that post-consumer textile waste can be upcycled into functional acoustic materials, supporting circular economy principles and offering a potential alternative to conventional mineral-based sound absorbers in interior and construction applications.

Recycling doi: 10.3390/recycling11070131

Authors: Gisela Inés Hernández-Contreras Laura Verónica Díaz-Archundia Marcel Szanto Narea Maria del Consuelo Mañon-Salas María del Consuelo Hernández-Berriel Fredy Cuellar-Robles

In most developing countries, the composition of municipal solid waste (MSW) arriving at final disposal sites (FDSs) differs from that at the source due to informal segregation of potentially recyclable waste (PRW) during its management, as well as because FDSs typically receive MSW from multiple municipalities. After exhaustively reviewing methods and studies of MSW characterization at their source, in collection trucks, and at FDSs, a lack of standardized methods for in situ characterization was identified, so this work proposes an innovative methodology to characterize MSW in situ at FDSs through the integration of geographic information systems to delimit the FDS or the selected cell(s) and the application of systematic sampling based on the NMX-AA-132-SCFI-2016 standard. To validate its applicability, MSW was sampled and characterized during the 2023 and 2024 dry (DS) and rainy seasons (RS) at a waste integral center in Tenango del Valle, Estado de México. The average compositions of organic waste were 15.3 ± 0.8% and 10.6 ± 0.1%; for PRW, they were 59.3 ± 5.4% and 50.5 ± 4.0%; and for the residual fraction, they were 25.4 ± 4.6% and 39.0 ± 4.1% in DS and RS, respectively; however, significant differences between seasonal or annual means could not be determined due to the limited sample size. The high percentages of PRW determined in situ are attributed to mixed household collection and show the potential to be recovered. The use of the proposed methodology enables representative in situ characterization of MSW after disposal with a lower level of significance, and it can be useful for decision-making regarding sustainable waste management projects.

Recycling doi: 10.3390/recycling11070130

Authors: Nizar Shbikat Omar M. Bwaliez Emad Alzubi Bassam Maali

This study aims to systematically investigate packaging waste repurposing in humanitarian logistics. It aims to bridge the theory–practice gap by providing a consolidated evidence-based analysis of how packaging is repurposed, the driving motivations, and the design characteristics that enable such transformations. A systematic review and thematic analysis of 34 documents from well-known international relief organizations was conducted. The documents were thoroughly reviewed, and codes were extracted and grouped into themes. The findings reveal that packaging repurposing is a widespread practice driven by three interconnected streams: (1) designer-led (top-down) initiatives rooted in Non-Governmental Organizations (NGOs) policies and design innovation, (2) user-led (bottom-up) initiatives that are induced by the survival and livelihood of affected communities, and (3) hybrid initiatives that involve the participation of the NGOs and affected people. Moreover, repurposing is highly dependent on specific design enablers, such as structural and material properties, to facilitate it. Lastly, a hierarchy of material transformation is proposed, ranging from low-energy mechanical adaptations to high-energy physio-chemical processes. This paper provides a novel integrated framework that links material, drivers, and design enablers for packaging repurposing in humanitarian logistics. It proposes a transformation spectrum to guide repurposing strategies based on resource and tool availability. This study consolidates fragmented knowledge across different sources and offers practical insights into the applicability of repurposing in various domains such as procurement, packaging design, and logistics planning.

Recycling doi: 10.3390/recycling11070129

Authors: María Paula Susunaga Ennio Marques Palmeira Ivonne Alejandra Gutiérrez Góngora Karla Yolima Rodriguez Rodríguez Juan Sebastián Perdomo Díaz

The growing generation of end-of-life tires and the structural deficiencies of tertiary road networks in developing regions represent two interconnected challenges that call for integrated engineering solutions. Although recycled tire geocells have been explored as a reinforcement alternative for unpaved roads, their mechanical performance has not been systematically compared against conventional high-density polyethylene (HDPE) geocells under controlled cyclic loading, nor has the material valorization potential been quantified in terms of waste diversion capacity. This study systematically evaluates and compares the deformation response, stress distribution, and aggregate degradation of both systems through large-scale laboratory testing. An instrumented steel chamber was used to apply up to 100,000 load cycles at 600 kPa contact pressure, across two cell heights (150 mm and 200 mm) and two granular infill qualities. The 200 mm recycled tire geocell reduced permanent surface deformation by up to 84% relative to the unreinforced condition, and Traffic Benefit Ratio values reached up to 1.6 times those recorded for HDPE geocells under lower-quality infill. The viscoelastic response of rubber promoted energy dissipation and limited aggregate particle breakage. Confinement performance was fully preserved after surface reconditioning, confirming the durability of the reinforcement system under maintenance cycles. The fabrication process requires no chemical transformation, valorizing approximately 16 end-of-life tires per square meter—equivalent to 56,000 tires per kilometer of reinforced road. These findings support the large-scale valorization of end-of-life tires as functional geotechnical materials, offering a circular economy pathway for solid waste diversion in regions where both road infrastructure deficits and tire disposal challenges coexist.

Recycling doi: 10.3390/recycling11070128

Authors: Sumita Chailoi Napat Mahiwan Chatisa Kansomket Thanapon Chandakhiaw Tapany Patcharawit Tanakorn Uthaiphetra Kiattisak Batsungnoen Sakhob Khumkoa

Rapidly increasing manufacturing waste intensifies the need for highly efficient and economically feasible waste-to-resource technologies. This research presented an upcycling strategy that transforms silver (Ag)-bearing waste into functional silver oxide nanoparticles (Ag2O NPs) for potential use in biomedical applications. A two-step process of silver purification and the bio–sonochemical synthesis of Ag2O NPs was employed. First, the sequential purification of Ag via melt-refining and electrorefining was utilized to efficiently achieve a silver purity of ≥99.90%. This purification encouraged the recycling of various forms of Ag-bearing waste. Subsequently, the purified Ag was prepared as the precursor for the bio–sonochemical synthesis of Ag2O NPs, using Cannabis sativa SUT CBD12 flower extract as a natural reducing agent. The optimal conditions were adapted from a preliminary test using AgNO3 as the precursor. At initial concentrations of 0.01 M Ag solution, 1 mM PVP solution, and 10 g dried weight of Cannabis sativa SUT CBD12 added to 100 mL DI water, the optimal condition was obtained at the capping agent:reducing agent:precursor volume ratio of 0.6:0.006:1, pH 10–12, under a short sonication time of 2 min. The purified Ag (waste-derived) and AgNO3-derived Ag2O NPs shared similar spherical shapes and sizes of ~100–130 nm. The Ag2O NPs showed antibacterial effectiveness against S. aureus (ZOI of 26–29 mm) and E. coli (ZOI of 16–20 mm). Preliminary observations into the incorporation of Ag2O NPs into polycaprolactone (PCL) to produce electrospun PCL/Ag2O NPs nano fabrics shows a bead-free morphology, raising the possibility of a potential use in wound dressing. Following these preliminary explorations into potential uses and emission controls, a circular design maximizing the use of recycled resources is emphasized.

Recycling doi: 10.3390/recycling11070127

Authors: Márcia A. D. Silva Liliana M. Martelo Belmira Neto Margarida M. S. M. Bastos Helena M. V. M. Soares

Integrated circuits (ICs), a major fraction of waste electrical and electronic equipment (WEEE), represent an important secondary source of gold (Au). However, recovering high-purity Au from ICs remains challenging due to the high silicon dioxide content that encapsulates Au within the IC core and the presence of complex base-metal mixtures that hinder selective purification. This study proposes a simplified end-to-end process that integrates mechanical liberation, magnetic separation, oxidative chlorination, ion-exchange purification and Au recovery from isolated ICs. Unlike conventional multi-stage comminution routes, the proposed pretreatment combines hydraulic pressing, milling/sieving and magnetic separation to maximize Au exposure while minimizing dust generation, metal losses and base-metal interference, which is subsequently subjected to oxidative leaching and purification. Optimal extraction conditions, determined through a Taguchi design (2.5 M HCl, 0.34 M NaClO, 40 °C, solid–liquid ratio 1 g/40 mL, 3 h), achieved a Au leaching efficiency of 89%. The resulting multi-metal leachate was treated with a strong anionic ion-exchange resin, increasing Au purity from 8% to 86% after thiourea elution in a sulfuric-acid medium. Final Au recovery was completed by reductive precipitation with sodium borohydride, yielding complete solidification (~100% efficiency). A comparative life-cycle assessment showed that this recycling route offers favourable environmental performance relative to primary mining. Beyond achieving efficient Au recovery, this work establishes an integrated recovery route for isolated ICs that combines process simplification with environmental positive impact, addressing an important gap in WEEE recycling.

Recycling doi: 10.3390/recycling11070126

Authors: Yasmine Boukhlouf Mohammed Benabdelhadi Hassan Tabyaoui Abderrahim Lahrach Abdallah Oulmekki Maryame El-Yazidi Zineb El Attar Soufi Omar Kassou

Construction and demolition waste valorization as recycled aggregates remains largely underdeveloped in North African urban contexts. This study presents the first normatively referenced characterization of recycled aggregates from ten sites in Fez, Morocco, combined with experimental C25/30 concrete formulation using the Dreux-Gorisse method. Physical, mechanical, and chemical analyses reveal high water absorption (9.98 ± 0.94%), low particle density (2197 kg/m3), sub-standard sand equivalent (39.4%), and elevated methylene blue (3.06 g/kg), all governed by attached cementitious mortar content. Principal component analysis identifies three groups: Cluster A (E2, E6, E8), directly valorizable for structural use; Cluster B (E3, E4, E7, E10), requiring fine-fraction removal (<80 µm) prior to concrete incorporation; and an intermediate group (E1, E5, E9), suitable for non-structural applications. Concrete mixes from a composite blend of all ten samples were experimentally validated on cylindrical specimens. At 25% substitution, the 28-day compressive strength reaches 22–28 MPa, achieving marginal C25/30 compliance when superplasticizer and pre-wetting correction (9.98 L/100 kg recycled aggregate) are applied; substitution at 50% and above does not meet structural requirements (18–24 MPa). Durability assessments confirm increasing carbonation depth (7–11 mm at 25%) and moderate-to-high chloride permeability, underscoring the need for source-selective sampling and pre-treatment in urban construction and demolition waste valorization programs, particularly in North African and Maghreb contexts where construction materials and building practices are broadly similar and demolition waste is typically processed without prior sorting.

Recycling doi: 10.3390/recycling11070125

Authors: Rosalia Ruiz-Ruiz Elia Mercedes Alonso-Guzman Hugo L. Chavez-Garcia Marco Antonio Navarrete-Seras Mauricio Arreola-Sánchez Judith Alejandra Velazquez-Perez Wilfrido Martinez-Molina

Concrete remains the most widely used construction material owing to its affordability, local availability, mechanical performance, durability, and versatility. However, its production has a significant environmental impact, and its service life may be reduced under aggressive exposure conditions, affecting both the functionality and cost of structures. This study presents a sustainability assessment based on a harmonized database of previously developed concrete mixtures, rather than a new experimental campaign. Waste-containing mixtures and their corresponding conventional or reference controls were considered to anchor the comparison to reference concretes, rather than only to the minimum values within the analyzed dataset. The objective was to compare the consistency among sustainability index formulations: KSB and KSB,C, associated with the Building Material Sustainability Potential (BMSP), and the Empathetic Added Sustainability Index (EASI). These formulations integrate functional and environmental performance, although they differ in their aggregation approach and in the treatment of economic variables, such as cost and eco-cost. The indicators considered include 28-day compressive strength, carbonation rate, global warming potential (GWP), gross energy requirement (GER), natural raw material consumption (NRMC), eco-cost, and material cost. The results show that mixtures with higher replacement levels of natural aggregates by recycled concrete aggregate and partial replacement of cement by locally sourced ashes exhibited the best integrated performance. The 300/100RCAg mixture stood out, with index values close to 3.43, 3.52, and 3.99, up to approximately four times those of the control. Sensitivity and uncertainty analyses showed that the highest-ranked mixtures generally maintained favorable positions across assessment methods and under ±20% input variability, although some alternatives exhibited substantial method-dependent ranking changes. The results demonstrate that local waste materials can improve concrete sustainability; however, their benefits depend on waste type, conditioning requirements, functional performance, and the selected sustainability assessment method.

Recycling doi: 10.3390/recycling11070124

Authors: Bobur Gayratov Bekhzod Gayratov Labone L. Godirilwe Gwiranai Danha Atsushi Shibayama

Copper smelter slag represents a significant secondary resource of critical metals, while flotation tailings serve as an abundant sulfur-bearing waste stream. This study investigated a waste-on-waste sulfation roasting approach for the selective recovery of Cu, Ni, and Co from fayalite copper smelter slag using flotation tailings as an in situ sulfur source and sodium metabisulfite (SMBS, Na2S2O5) as a sulfation promoter. The effects of roasting temperature, roasting time, slag-to-tailings ratio, SMBS dosage, and water-leaching conditions were systematically evaluated. Under the optimum conditions of a slag-to-tailings ratio of 1:1, roasting at 600 °C for 4 h with 30 wt% SMBS addition, followed by water leaching at 25 °C for 2 h, extraction efficiencies of 85.5% Cu, 81.6% Ni, and 87.1% Co were achieved, while Fe dissolution remained below 5%, demonstrating high selectivity. Phase and microstructural analyses by XRD, FTIR, SEM, and TG–DTA revealed that pyrite oxidation generated sulfur oxides required for metal sulfation, whereas SMBS promoted sulfur release and sulfate stabilization, enhancing sulfation efficiency. Thermodynamic analysis further confirmed the feasibility of sulfide oxidation and sulfate formation within the investigated temperature range. The results demonstrate that the synergistic use of tailings and SMBS enables efficient low-temperature sulfation roasting of fayalite slag and provides a promising route for the selective recovery of valuable metals from metallurgical waste materials.

Recycling doi: 10.3390/recycling11070123

Authors: Niccolò Rimbotti Daniele Sarri Jessica Scriva Andrea Pagliai Carolina Perna Federico Rotini Gianluca Bambi Leonardo Conti Giuseppe Rossi

Bio-based packaging is receiving increasing attention due to the environmental impact of fossil-based plastics. However, its practical implementation requires further evidence on material processing and functional performance. This study evaluated the thermal properties of expanded polylactic acid (E-PLA) prototypes blended with raw, minimally processed agroforestry residues. Specifically, spruce bark and grape stalks were used as waste wood fibers. This study focused primarily on the thermal characterization of the materials by measuring thermal conductivity and resistance. To evaluate the distribution of the two fractions (polymer and fibrous), samples were created with various volumetric ratios between the parts. Simultaneous pressure and microwave heating of the sample were used to stabilize the material. To characterize the raw materials used in this study, bulk density and moisture content were measured. To characterize the mixed materials samples, thermal conductivity and resistance, bulk density, and pressure were measured. To investigate the variables that influence thermal characteristics, statistical analyses such as regression models, ANCOVA, and Spearman correlation were applied. These analyses showed that increasing the biofiber content significantly reduced thermal resistance and increased thermal conductivity. However, negligible effects were observed for the type of fiber used and the duration of the heat treatment. These results describe the thermal properties of blends containing E-PLA and agroforestry residues. The results also show a marked effect of the biofiber content on thermal performance. This study does not provide a comprehensive characterization of the new materials, as it focuses on the prototyping methodology and the laboratory-scale production feasibility of E-PLA/agroforestry-residue prototypes.

Recycling doi: 10.3390/recycling11070122

Authors: Houssam Affan Laurent Fehr Ginan Al-Massri Farjallah Alassaad Amro Yaghi Hassan Ghanem

Conventional valorization of blast furnace slag commonly involves granulation, fine grinding, mechanical activation, or chemical activation, which increase energy demand and processing complexity. This study investigated a minimally processed blast furnace slag (MP-BFS), defined here as the fraction passing 64 µm obtained by sieving a 0–8 mm industrial material without grinding, additional granulation, thermal treatment, or chemical activation. MP-BFS replaced 10–50% of the cement by mass to reduce clinker in industrial mortars formulated at a constant flow spread of 23–24 cm and tested from 8 h to 90 d. Bulk density, water-accessible porosity, total and capillary water absorption, and compressive and flexural strengths were evaluated. Replacing 10% of the cement with slag improved compressive strength from the earliest test age and increased the 28-day compressive and flexural strengths by 5.1% and 9.5%, respectively, relative to the control mortar; this response coincided with a reduction in measured porosity from 8.95% to 8.01%. This improvement is consistent with a physical filling effect and improved particle packing, although these mechanisms were not directly verified by microstructural analyses. At higher replacement levels, water-accessible porosity increased, reaching 24.45% at 50% slag replacement, alongside greater water ingress and delayed strength development. Exploratory empirical regression analyses described associations among slag content, porosity, water transfer, and compressive strength within the investigated formulations. A simplified screening-level constituent-production-and-transport comparison per cubic meter, based on generic ICE factors and an assumed 50 km transport distance, estimated a maximum embodied carbon reduction of 44% at 50% replacement. Curing energy, use, carbonation, maintenance, and end-of-life stages were excluded. Overall, 10% MP-BFS replacement provided the most favorable performance–carbon content balance, whereas 30–50% achieved larger carbon reductions but showed early-age strength losses that limit their suitability for rapid-demolding applications under the investigated conditions.

Recycling doi: 10.3390/recycling11070121

Authors: Caterina Barbiero Anna Mazzi

The wood furniture sector, heavily reliant on wood panels, faces supply risks and generates significant waste, which can be managed through recycling or energy recovery. This study investigates the environmental impacts of wood waste end-of-life management and the use of virgin versus recycled raw materials in the wood furniture sector, aiming to identify the most sustainable scenario in wood manufacturing between wood waste recycling as output and recycled wood as input. Environmental impacts of four scenarios were analyzed and compared through the life cycle assessment with the “grave-to-cradle” approach. Inventory was supported by information and data from an Italian furniture company, while the impact assessment was performed using the ReCiPe method and the SimaPro software. The results from the impact assessment and gravity analysis show the main contribution of different scenarios due to the incineration of wood waste and the manufacturing of wood panels; the sensitivity analysis highlights how increasing recycling allows for greater performance improvement than increasing recycled inputs. Although limited by the assumptions related to the case study, this research enriches the discussion on the environmental convenience of recycling manufacturing waste and using recycled materials and confirms the importance of life cycle assessment for implementing circular economy strategies in companies.

Recycling doi: 10.3390/recycling11070120

Authors: Mehdi Golzar-Ahmadi Maria Holuszko

Urban mining is gaining importance as demand for critical metals continues to rise. Waste light-emitting diode (LED) lamps are a valuable secondary source of gallium, rare earth elements, precious metals, and base metals, yet accurately quantifying these metals remains challenging. In this work, various LED waste streams from a lamp recycler were subjected to critical metal characterization. The strengths and weaknesses of established metal assay techniques were evaluated to advance the determination of gallium, rare earth elements (Ho, Lu, Tb, Y, Er, Nd, Ce), and precious metals (Au, Ag, Pt, Pd) in LED waste. Metal assays, including alkaline fusion, four-acid digestion, aqua regia, a fire assay, and energy-dispersive X-ray fluorescence, were compared, and precision was assessed using a newly created LED lamp reference material and OREAS465. A metal-analysis-driven approach was developed to quantify the reduction in mining through recycling LED lamps using the rock-to-metal ratio metric. The economic value of LED waste streams, together with their recyclability and grindability, was assessed. The results indicate that LED strips can contain up to 147,484 g/t Cu, 452 g/t Ga, 367 g/t Lu, 89 g/t Tb, and 95 g/t of precious metals. Recycling one tonne of waste LEDs can offset mining 75.5 tonnes of rock and primary ore. The estimated economic value of mixed LED waste was USD 3351 per tonne, increasing to USD 4089 per tonne after physical separation. The results demonstrate the importance of robust analytical methods for accurate metal accounting and provide a stronger foundation for assessing the recycling potential of LED waste.

Recycling doi: 10.3390/recycling11070119

Authors: Huanjia Liu Pengpeng Zhang Zhaohan Zhang Kuokai Sun Weihua He Yujie Feng

To improve the efficiency of AD for tetracycline-containing wastewater, this study systematically investigated the effects of ZVI and PAC on pollutant removal, VFA metabolism, biogas production, and sludge physicochemical characteristics. RSM was employed to optimize the co-dosing conditions of ZVI and PAC. The results suggested that ZVI and PAC could significantly facilitate COD degradation, and the optimal dosages for COD removal were 1000 mg/L ZVI and 2000 mg/L PAC with a removal efficiency of 61.03% and 56.9%, respectively. Both additives effectively accelerated the catabolism of typical VFAs, thereby mitigating the accumulation of intermediate metabolites that may cause AD system instability. In terms of biogas production, 1000 mg/L ZVI and 2000 mg/L PAC enhanced methane yield by 55.9% and 35.0% compared to the control group, with ZVI exhibiting a more prominent enhancement effect. Mechanistic analysis suggested that ZVI and PAC reinforced the AD process through multiple pathways: enhancing the electrical conductivity of the AD system, possibly facilitating the electron transfer pathways, and stimulating the secretion of EPSs by anaerobic microbes. RSM optimization yielded the optimal co-dosing parameters: 1000 mg/L ZVI and 1200 mg/L PAC. Under these conditions, the methane yield was increased by 71.18% relative to the control group, and the model validation accuracy reached 97.94%. This study provides a viable technical strategy and theoretical basis for enhancing the efficiency of anaerobic treatment of tetracycline-containing wastewater.

Recycling doi: 10.3390/recycling11070118

Authors: Swapnil Gund Sandeep G. Thorat Sachin Pawar Prashant Paraye Anuj Prajapati

The transition to a circular economy (CE) in the automotive sector is increasingly critical amid rising resource pressures and climate imperatives. In India, this shift is influenced by regulatory initiatives, corporate sustainability goals, and life-cycle-wide environmental challenges. However, current studies remain fragmented, often neglecting the linkages between policy drivers, material issues, and firm-level responses. This study aims to evaluate how CE strategies are operationalized across the Indian automotive value chain using a Drivers–Materiality–Response (DMR) analytical framework. A multiple-case qualitative analysis was conducted involving six major automotive firms and associated ecosystem actors, with data sourced from corporate reports, national policies, and third-party assessments from 2018 to 2024. Semi-structured interviews with 11 industry experts were incorporated to strengthen triangulation, validate firm-level circular economy claims, and support the reliability of the DMR-based interpretation. Findings reveal strong alignment with national CE policies among leading firms, particularly Tata Motors and Mahindra, with comprehensive integration of electrification, battery reuse, zero-waste goals, and digital mobility solutions. However, challenges remain in end-of-life vehicle (ELV) formalization and circularity in downstream systems. The DMR model effectively bridges gaps in existing frameworks by offering a life-cycle-based lens that links Environmental, Social and Governance (ESG), Life Cycle Assessment (LCA), and policy–firm dynamics. The study contributes a scalable diagnostic tool for assessing CE maturity in emerging economies. While limited by reliance on secondary data, the triangulated approach enhances reliability and provides actionable insights for policymakers and industry leaders.

Recycling doi: 10.3390/recycling11070117

Authors: Dalia Perkumienė Ahmet Atalay Giedrė Adomavičienė Aidanas Perkumas Marius Mažeika

This study examines the transformation of environmental governance processes in recreational tourism in Turkey and Lithuania through artificial intelligence (AI)-supported waste management applications. The research focuses on the contributions of AI-based applications to sustainable destination management, environmental sustainability, and data-driven governance processes. A case study design was used within the framework of qualitative research methods. The dataset was obtained through semi-structured interviews with a total of 40 experts from Turkey and Lithuania. The data were analyzed using content analysis with the NVivo 14 program. The research findings reveal significant differences between the two countries in terms of digital infrastructure, institutional coordination, governance structures, and AI integration capacity. In Turkey, AI-supported waste management applications are still in their development phase; processes are largely shaped by managerial initiative, project-based approaches, financial constraints, and lack of institutional coordination. In contrast, Lithuania exhibits a more systematic and institutionalized digital governance structure thanks to EU-supported environmental and digitalization policies. However, data security, system sustainability, and high technology costs in small-scale recreation areas stand out as significant problem areas for Lithuania. This study addresses an underexplored intersection between artificial intelligence applications and environmental governance within recreational tourism contexts, contributing to the emerging literature on digital transformation in sustainable destination management. The findings reveal that AI-supported environmental management systems have significant potential to strengthen sustainable tourism management, increase operational efficiency, and support data-driven sustainable destination strategies. These findings offer practical implications for destination managers and policy makers by highlighting how AI-enabled environmental governance systems can enhance sustainability-oriented decision-making and improve operational efficiency in recreational tourism areas.

Recycling doi: 10.3390/recycling11070116

Authors: Dinusha Shiromala Dissanayake Thilina U. Jayawardena Dineth P. Nagahawatta

Due to large-scale macroalgal blooms, nutrient enrichment, and changes in ocean circulation brought on by climate change, beach-accumulated seaweed (BAS) has quickly become a global environmental and waste-governance concern. Despite degradation and contamination during beach stranding, BAS retains valuable bioactive compounds, including sulfated polysaccharides, phlorotannins, pigments, proteins, peptides, and lipids, which exhibit anti-inflammatory, antioxidant, antimicrobial, antiviral, immunomodulatory, anticancer, and metabolic regulatory activities. This review critically evaluates BAS as a sustainable bioresource by integrating current knowledge on biomass composition, degradation-associated challenges, bioactive properties, valorization pathways, advanced extraction technologies, safety validation, regulatory considerations, and emerging commercialization opportunities. Attention is given to sustainable valorization pathways, ranging from composting and bioenergy production to the recovery of high-value bioactives through enzyme-assisted, green, and advanced extraction technologies. The review further discusses policy and regulatory gaps, contamination challenges, safety validation requirements, and life-cycle sustainability considerations that currently limit industrial adoption. Finally, emerging opportunities involving metabolomics, microbial bioprocessing, artificial intelligence, automation, and nanotechnology are explored as future directions for transforming BAS into a standardized and economically viable feedstock within the circular blue bioeconomy. Establishing harmonized regulatory frameworks and integrating BAS management with Sustainable Development Goals (SDGs) 12 and 14 will be critical for enabling sustainable resource recovery and long-term coastal resilience.

Recycling doi: 10.3390/recycling11070115

Authors: Monica Keszler Martin Krengel Felix Grosswendt Doris Sebold Olivier Guillon Sebastian Weber Martin Bram

The particular microstructure of hot-deformed Nd-Fe-B magnets leads to difficulties in finding a direct recycling route. In this work, a combination of field-assisted sintering technology/spark plasma sintering (FAST/SPS) and spark plasma texturing (SPT) is used as pre-compaction and deformation techniques, respectively, for the consolidation of crushed, hot-deformed Nd-Fe-B scrap. Field-assisted sintering has the unique advantage of maintaining fine microstructures during material densification, making it an ideal candidate for direct recycling of this material. Recycled magnets, made from 100 wt% crushed magnet scrap, were able to achieve energy products of over 200 kJ m−3 after FAST/SPS pre-compaction and SPT deformation. These recycled magnets could then be smoothed and cut to the size of industrial bar magnets for testing in the motor of a water pump. When tested, the recycled magnets could achieve 95% of the electromotive force compared to industrial standard magnets.

Recycling doi: 10.3390/recycling11070114

Authors: Martin Jantson Rasmus Teppo Kerli Liivand

The increasing demand for lithium-ion batteries (LIBs) raises concerns about the security of critical raw material supply and the management of hazardous waste. Efficient recycling can alleviate these issues by transforming spent batteries into high-value secondary materials for the circular economy. Industrial recycling has traditionally focused on the recovery of nickel (Ni) and cobalt (Co), whereas lithium (Li) recovery has often been sidelined due to technical complexities and fluctuating economic incentives. To meet the European Union (EU) Batteries Regulation target of 80% lithium recovery by the end of 2031, technically effective and economically viable lithium recovery strategies are required. This study investigates the use of food-grade sucrose as an organic reductant for the targeted recovery of lithium from NMC622 and NCA battery materials. The process combines sucrose-assisted reductive roasting with selective water leaching. The effects of roasting temperature, holding time, sucrose dosage, and heating rate were systematically evaluated and optimised. Under the best conditions of 600 °C, 15 min, 15 wt% sucrose, and a heating rate of 20 °C/min, lithium leaching efficiencies of 93.2% and 87.6% were achieved for separated NMC622 cathode material and NMC622-derived black mass, respectively. The method was also applicable to NCA-based black mass, reaching 83.7% lithium recovery under the same conditions. Mechanistic analysis revealed that lithium release was strongly controlled by the extent of transition metal reduction. Cobalt was fully reduced to its metallic state under all tested conditions. However, maximum lithium recovery required nickel to be reduced to metallic Ni and manganese-containing phases to be converted to MnO. The sucrose-assisted roasting process was rapid and holding times longer than 15 min decreased lithium recovery. This decrease was caused by the formation of poorly soluble lithium-containing phases, such as LiF and Li3PO4. F composition analysis showed the black mass (1.06 wt%) and anode fractions (2.26 wt%) to contain significantly more F than the cathode fraction (0.46 wt%), hence leading to the 5% Li leaching efficiency difference between cathode and black mass fractions under most conditions tested. Overall, these results demonstrate that sucrose-assisted reductive roasting, followed by selective water leaching, provides a rapid and effective route for high-efficiency lithium recovery from NMC- and NCA-based battery materials.

Recycling doi: 10.3390/recycling11070113

Authors: Wenpeng Liu Junbiao He Qingyun Xu Zhijie Pi Nan Zhang Di Wang

Tailings are solid waste generated during mining and mineral processing. Their tremendous accumulation not only encroaches on arable land but also pollutes the environment. Currently, tailings are considered a viable alternative to natural fine aggregates in concrete because of their suitable physicochemical properties. However, existing studies remain highly fragmented and often report inconsistent conclusions owing to the considerable variability in tailings mineralogy, particle morphology, and physicochemical characteristics. To date, a comprehensive synthesis linking these intrinsic properties to the fresh, mechanical, durable, microstructural, environmental, and economic performance of tailings concrete remains lacking. Therefore, this review provides a systematic and critical assessment of tailings as aggregate in concrete and proposes an integrated framework connecting tailings characteristics, microstructural evolution, engineering performance, and sustainability outcomes. It systematically examines the physico-mechanical properties, durability, microstructure, hydration characteristics, environmental impact, and economic benefits of the resulting tailings concrete. The results showed that although tailings varied considerably in particle size, chemical composition, and mineralogy, they typically exhibited a rough surface texture and high water absorption. Furthermore, partial substitution of fine aggregates with tailings was found to improve the physical–mechanical properties and durability. However, to prevent performance decline, the substitution ratio should not exceed 50%. These benefits originated primarily from the filling effect and optimized particle packing, which increased matrix density. Microstructural analyses indicated that moderate tailings contents refined the pore structure, strengthened the interfacial transition zone (ITZ), and promoted hydration. In contrast, excessive substitution ratios weakened bonding and increased porosity. From an environmental perspective, the use of tailings generally reduced carbon emissions (by up to ~28%) and production costs (by up to ~50%) by lowering natural resource consumption and enabling large-scale waste valorization. Overall, tailings represent a sustainable aggregate alternative, provided that substitution levels are carefully controlled to balance workability, performance, and durability.

Recycling doi: 10.3390/recycling11070112

Authors: Eduardo Guevara Hernández Alba Jocelyne Aldabalde Hernández Fernando Andrés Rojas Aguilar Efraín Martínez Prior Luis A. Godínez Víctor A. Ramírez Francisco J. Rodríguez-Valadez

Floating wetlands have emerged as a sustainable alternative for improving water quality, and although some studies have investigated their performance, there is still much to be understood regarding their integration with energy-generating technologies. This study evaluated a combined system of floating wetlands and microbial fuel cells (MFCs) for treating real wastewater and generating bioelectricity. Experiments were conducted in batch mode to simulate application in natural water bodies, using real wastewater collected on different dates. As a result of the natural variability of the influent, initial chemical oxygen demand (COD) concentrations of 405 and 289 mg/L were observed. Performance was assessed in terms of organic matter and nitrogen removal, as well as voltage generation. COD removal efficiencies reached 50% and 69% for the higher and lower organic loads, respectively, indicating improved treatment at reduced concentrations. Maximum removals of 56% for ammoniacal nitrogen (NH3-N) and 40% for total nitrogen (TN) were achieved, reflecting moderate nutrient removal capacity. Voltage generation was sustained for approximately 21 days, confirming stable bioelectrochemical activity, and power output was found to depend on the organic load serving as substrate for electrogenic microorganisms. Overall, the system represents a viable approach for wastewater treatment with the added benefit of energy recovery, although its performance is influenced by influent characteristics and operation conditions.

Recycling doi: 10.3390/recycling11060111

Authors: Farjallah Alassaad Houssam Affan Abdelrahman Mohamad Amro Yaghi Bechara Haddad

This study investigates the feasibility of recycling scallop shells as a partial substitute for natural coarse aggregates in concrete at replacement rates of 20%, 30%, and 40% by mass. The originality of the work lies in combining conventional mechanical and durability tests with a six-month environmental monitoring protocol under simulated rainfall and an end-of-life regulatory interpretation of chemical release. Processed shells were used as a 2/20 mm coarse fraction and characterized by a density of 2713 kg/m3, a water absorption of 2.93%, and a Los Angeles coefficient of 15.1. At 28 days, compressive strength decreased from 33.7 MPa for the reference concrete to 27.9 MPa, 28.1 MPa, and 26.7 MPa for SS20, SS30, and SS40, respectively. Water-accessible porosity increased from 7.8% to 9.9%, and carbonation depth after 70 days increased from 6.2 mm to 12.8 mm at 40% shell replacement. In contrast, chloride ion migration decreased from 19.0 × 10−12 m2/s for the reference concrete to 17.4, 16.3, and 12.1 × 10−12 m2/s at 90 days for SS20, SS30, and SS40, respectively. Environmental monitoring showed low runoff concentrations for anions and trace metals, all below the French regulatory thresholds considered in this work. Under the conditions of this study, shell replacement up to 30% appears technically feasible for non-structural or lightly loaded applications, while the environmental behavior remained compatible with an inert end-of-life classification.

Recycling doi: 10.3390/recycling11060110

Authors: Raman Rao Aditya Sarker Rakshit Kumar Mariangeles Salas Luis Pena Naimul Haque Summia Rahman Vaishnavi Srinivasan Raghul Thiyagarajan Lokendra Pal

Municipal solid waste (MSW) management is a critical challenge to advancing recycling and circular economy approaches. This review provides a comprehensive overview of MSW management, encompassing sourcing, policy frameworks, characterization techniques, separation technologies, preprocessing strategies, and utilization pathways. First, generation patterns and sourcing mechanisms are discussed in both U.S. and global contexts, with emphasis on the influence of policy frameworks on waste reduction and diversion. Second, characterization techniques are evaluated, focusing on physical and chemical analysis for material recyclability. Third, sorting technologies are critically reviewed, covering conventional methods and emerging sensor-based approaches. Preprocessing techniques are then evaluated for their role in improving downstream conversion efficiency. Finally, valorization pathways such as waste-to-syngas, waste-to-biochar, and waste-to-sustainable aviation fuel (SAF) are assessed in terms of their role in climate mitigation and the circular economy. It is anticipated that this review will provide a foundational reference for researchers, policymakers, and industry stakeholders aiming to strengthen the recyclability infrastructure and maximize the efficiency of MSW management systems in the framework of the circular economy.

Recycling doi: 10.3390/recycling11060109

Authors: Mariyam Hussain Fatima Alsenaani Afnan Khalil AlRayyan Albazi Fatemeh Bahaeddin Noura Al-Mazrouei Ameera F. Mohammad

The rapid growth in the use of carbon fiber-reinforced polymers (CFRPs) and fused-deposition-modeled (FDM) polylactic acid (PLA) has generated substantial non-biodegradable and thermoplastic waste streams, creating urgent needs for scalable recycling and valorization strategies. This study develops and evaluates an integrated route that chemically recovers carbon fibers (CFs) from CFRP waste and converts them into high-performance reinforcements for recycled PLA matrices. CFRP fragments were pre-swollen in acetic acid (120 °C, 1 h), then depolymerized by means of oxidation with 1 M KMnO4 (100 °C, 2 h), washed, dried (100 °C, 24 h), and size-reduced by means of cryogenic milling. Recycled CFs (treated) and untreated CFRP fragments were blended with 3D-printing PLA waste at 10, 20 and 30 wt.% via melt mixing (175 °C, 5 min, 70 rpm) and molded into ASTM D638 dog-bone specimens. Materials were characterized via XRD, FTIR, Raman, SEM and mechanical testing. XRD and Raman confirmed retention of the graphitic backbone after treatment; FTIR and Raman revealed oxygen-containing surface functionalization consistent with oxidation, while SEM showed effective removal of epoxy and improved fiber surface cleanliness. Compared with neat PLA (tensile strength 45.4 MPa; modulus 2.6 GPa; elongation 6.3%), composites reinforced with chemically recycled CFs exhibited marked mechanical enhancement: at 30 wt.% treated CF, the tensile strength increased to 102.6 MPa (+126%), elastic modulus to 11.7 GPa (+350%), and toughness to 250.3 MPa, while ductility decreased to 2.9%. Equivalent composites with untreated CFRP exhibited smaller gains (30 wt.%: tensile 87.3 MPa; modulus 10.3 GPa), highlighting the benefit of epoxy removal and surface activation for fiber–matrix adhesion. The proposed chemical recycling pathway is operationally simple and cost-effective, produces reusable CFs with preserved graphitic structure and enhanced surface chemistry, and enables the fabrication of high-performance, waste-derived PLA composites suitable for structural and engineering applications. This work demonstrates a viable waste-to-value approach that advances circularity for both CFRP and 3D-printing polymer waste streams.

Recycling doi: 10.3390/recycling11060108

Authors: Valentin Kamburov Mihail Zagorski Dimitar Arnaudov Valentin Mateev Antonio Nikolov Konstantin Dimitrov Rayna Dimitrova Evgeniy Tongov Krum Petrov Yana Stoyanova

The present study investigates the application of electric resistive heating to photovoltaic (PV) panels, aimed at enabling their subsequent thermo-mechanical delamination. The key process parameters—namely current magnitude and applied voltage—required for direct electro-resistive heating are identified, and the process is experimentally demonstrated under laboratory conditions. The electric resistive heating of a composite photovoltaic panel, consisting of a solar cell layer (crystalline silicon, c-Si, with a metallic grid), a backsheet, and a glass layer, is analyzed in detail using a virtual model of a single-crystal silicon solar cell implemented as coupled electric-thermal analysis. The temperature dependence of the electrical resistance of the solar cell layer is experimentally measured, and exponential relationships are derived and subsequently incorporated into the numerical model. The virtual model results are validated, demonstrating that, for a given geometry and configuration of the conductive metallic grid (busbars and fingers), the electrical resistance of the semiconductor layer containing the p–n junction governs the temperature achieved during electro-resistive heating as a function of the applied current. Furthermore, results for the terminal current and voltage, current density in the busbars and fingers, electric field intensity, and the resulting temperature within the semiconductor layer of the single-crystal silicon solar cell are presented and analyzed.

Recycling doi: 10.3390/recycling11060107

Authors: Joana C. Vieira Pedro Videira António de O. Mendes Paula Pinto Belinda Soares Mariana P. Costa Paulo T. Fiadeiro Joana M. R. Curto Maria E. Amaral Ana P. Costa Vera L. D. Costa

Harmonized laboratory methodologies, notably the CEPI recyclability laboratory test method (latest version 3, released February 2025) and the 4evergreen protocol (latest revision 1, released January 2025), are widely used to assess the recyclability of paper-based materials. However, the extent to which laboratory-scale results reflect pilot-scale behavior remains insufficiently documented. In this work, the recyclability of brown packaging paper was evaluated at both laboratory and pilot scales. Disintegration was performed under identical consistency, temperature, and duration, followed by screening, filtrate analysis, macro-stickies quantification, and paper sheet adhesion evaluation according to the CEPI methodology. In parallel, recycled paper prototypes were produced in a pilot paper machine and were mechanically characterized. The material was classified as technically recyclable in a conventional recycling mill at both scales, with closely aligned recyclability scores. Nevertheless, pilot-scale testing revealed higher dissolved and colloidal substances, increased macro-stickies content, and sheet adhesion phenomena not fully apparent at laboratory scale. These results demonstrate that while laboratory tests are robust for recyclability classification, pilot-scale trials provide essential insights into runnability and operational risks relevant for industrial implementation.

Recycling doi: 10.3390/recycling11060106

Authors: Jihene Nouairi Slávka Andrejkovičová Oumaima Karoui Tiago Pinho Rafael Rebelo Gil Gonçalves Angelo Camerlenghi Mounir Ghribi Fernando Rocha

The increasing accumulation of mine waste and the associated release of toxic elements represent a major environmental challenge, particularly in regions impacted by Pb–Zn mining activities. In this context, this study aims to investigate the valorization of mine waste from Lakhouat, an abandoned Pb–Zn site in Northern Tunisia, as a sustainable additive in metakaolin-based geopolymers. This approach contributes to circular economy strategies by transforming hazardous waste into value-added materials for environmental and construction applications. Geopolymer formulations were synthesized by incorporating mine waste at different proportions (0, 5, 10, 20, and 30 wt.%) with metakaolin, while maintaining constant SiO2/Al2O3 and Na2O/Al2O3 molar ratios. The materials were prepared through alkali activation using sodium silicate and sodium hydroxide, followed by curing. Comprehensive characterization was carried out using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). In addition, adsorption experiments using methylene blue (MB) were conducted to evaluate the environmental performance of the synthesized geopolymers. The results revealed that the mine waste contains high concentrations of potentially toxic elements (up to 2.23 wt.% Pb and 8.2 wt.% Zn), highlighting the need for effective stabilization. Microstructural analysis confirmed the formation of predominantly amorphous geopolymer matrices with varying degrees of reaction depending on MW content. The highest compressive strengths (25–30 MPa) were achieved for formulations containing 5–10 wt.% MW after 28 days of curing. Furthermore, the geopolymers demonstrated efficient methylene blue removal, following pseudo-second-order kinetics and fitting the Langmuir isotherm model, with enhanced adsorption performance observed at higher MW contents. These findings indicate that MW-based geopolymers are promising materials for mine waste valorization and methylene blue removal. However, standardized leaching tests are required to confirm the long-term immobilization of Pb, Zn, Cd, As, and other potentially toxic elements within the geopolymer matrix. The study highlights their potential as sustainable, low-impact materials, supporting waste valorization and contributing to the development of environmentally resilient systems within a circular economy framework.

Recycling doi: 10.3390/recycling11060105

Authors: Ruslan Sapinov Natalya A. Kulenova Marzhan A. Sadenova Nikolay Charykov Olga V. Rudenko Zhanserik Shoshay Yegor Rakov

This study addresses the pressing issue of utilising plastic from electronic waste as a filler to replace mineral sand. Currently, the use of plastic in construction concrete is limited due to a significant deterioration in the mechanical properties of modified concrete when plastic filler is added at levels exceeding 15–20%. As a result of the research, it was established that the addition of a nano-preparation—fullerene—in amounts as low as 0.001% significantly improves the mechanical properties of concrete with plastic aggregate. Replacing 50% of the mineral aggregate with plastic aggregate, combined with the addition of fullerene at a concentration of 0.01% of the mixing water mass, more than doubles the mechanical properties of the concrete compared to concrete without the nano-additive, with compressive strength increasing by 65.2%, from 16.33 MPa to 26.97 MPa. The impact strength and freeze–thaw resistance of the concrete were also significantly increased. This makes it possible to use concrete with a high plastic aggregate content of up to 50% without a significant reduction in mechanical properties. The use of machine learning and AI data processing methods such as AdaBoost and Random Forest allows for highly accurate prediction of the characteristics of the resulting materials, with a coefficient of determination (R2) for the resulting models close to 1.

Recycling doi: 10.3390/recycling11060104

Authors: Zhongli Jiang Qinggang Wang Yinnan Cao Pengfei Chen Hongyu Chen Zhi Li Chengjie Yin

The massive generation of coal-based solid wastes (CBSWs) poses severe environmental challenges globally, while widespread soil degradation threatens food security and ecosystem stability. This review critically evaluates the technical feasibility and agro-ecological benefits of valorizing CBSWs—including coal gangue, fly ash, gasification slag, and desulfurization gypsum—as soil amendments within a circular economy framework. We systematically examine the physicochemical characteristics of major CBSW types, analyze modification methods that enhance their performance and safety, and assess their multifaceted effects on soil physical structure, chemical properties, nutrient dynamics, heavy metal immobilization, and microbial communities. A dedicated section addresses environmental risks, particularly toxic element leaching, and outlines integrated control strategies from source selection to post-application monitoring. Critical knowledge gaps persist regarding long-term contaminant stability under climate change scenarios, molecular-scale immobilization mechanisms, and economic scalability. Future research must prioritize advanced low-energy modification technologies, robust long-term field studies, and harmonized international regulations. We conclude that with scientifically guided modification and stringent risk management, CBSWs can be transformed into safe, multifunctional soil conditioners, simultaneously addressing industrial waste management and contributing to global restoration of degraded soil health.

Recycling doi: 10.3390/recycling11060103

Authors: Andrey Medvedev Gevorg Tepanosyan Grigor Ayvazyan Shushanik Asmaryan

The research aims to develop methodologies for the detailed characterization and spatial zoning of landfills as a means of assessing their environmental impact. The principal objective is to establish an integrated framework for evaluating landfill conditions through multisource data analysis, encompassing remote sensing, field investigations, and geochemical analyses. The proposed framework incorporates several critical components: satellite and UAV-based remote sensing, multispectral vegetation assessment, geochemical soil profiling, temporal and functional zoning, and morphodynamic evaluation. Research findings indicate substantial environmental pollution in the vicinity of landfill sites, at levels that exceed the natural self-purification capacity of surrounding ecosystems. This encompasses the contamination of all principal environmental components, including groundwater, surface water, soil, vegetation, and atmosphere. The key findings demonstrate that only a comprehensive environmental impact analysis, conducted in conjunction with detailed landfill zoning, yields a thorough understanding of the associated adverse effects. Remote sensing methodologies are shown to play a pivotal role in data acquisition and ongoing monitoring. The practical contribution of this study lies in the development of methodological frameworks for detailed landfill zoning, environmental impact assessment, monitoring, damage mitigation measures, and waste management optimisation. The results obtained have the potential to improve waste management systems, inform the development of effective monitoring protocols, and underpin strategies aimed at reducing the environmental footprint of landfills. Overall, this research advances scientific and technical knowledge in the field of waste management and contributes towards efforts to mitigate environmental impact—a matter of persistent concern given rising rates of waste generation and the increasingly constrained availability of suitable landfill capacity.

Recycling doi: 10.3390/recycling11060102

Authors: Soranosuke Shimizu Takuma Kariyada Mizuki Toda Keisuke Tomita Kazuya Watanabe

Anaerobic digesters (ADs) are widely used for the recovery of energy from biomass waste, while performance deterioration of ADs sometimes occurs under high organic loads. Microbial electrolysis cells (MECs) have been examined for incorporation into ADs to improve methane production, while responses of MEC-assisted ADs (MEC-ADs) to changes in operational conditions have yet to be sufficiently examined. Here we operated laboratory ADs and MEC-ADs with food waste as a feed, and organic loading rates (OLRs) were varied by changing hydraulic residence times (HRTs). Analyses of AD performances, including methane production and chemical oxygen demand (COD) removal, show that MEC-ADs exhibit higher performances than ADs at OLRs of 7 g COD L−1 D−1 or higher (HRT of 10 days or less). In addition, pH was stably maintained in MEC-ADs at high OLRs. Metabarcoding of rRNA gene amplicons showed that Desulfuromonadaceae bacteria were enriched at the anodes in MEC-ADs, while Methanobacteriaceae archaea were increased at the cathodes. It is suggested that the MEC system is useful for stably operating ADs at high OLRs and/or short HRTs.

Recycling doi: 10.3390/recycling11060101

Authors: Lieve Göbbels Karoline Raulf Setenay Orbatu Kathrin Greiff

In this work, the development and validation of an AI- and sensor-based inline quality monitoring system for the analysis of particle size distributions (PSDs) of comminuted construction and demolition waste (CDW) material flows are described. In this, a custom-developed multitask CNN (CDW-MT-CNN) was developed using manually sieve analyzed particles. This model is able to rapidly and simultaneously predict the particle class and weight, essential for the determination of the PSD. The single particle data are then aggregated per raw image, usually consisting of around 1000 particles for full-scale experiments, to acquire a per-image PSD. The inline mounted RGB line scan sensor records high-resolution images in subsecond frequencies. With an inference time of around 54 ms for a single image, this model would be able to provide a PSD every minute in a full-scale plant. For the purpose of inline monitoring of CDW material flows in a comminution process, such intervals are sufficient according to experts and solve existing gaps regarding the upscaling of laboratory-developed systems. Together with the high predictive performance of the model, especially in terms of classification (82% accuracy), it is shown that this technology has potential for monitoring in full-scale plants, for instance by offering operators new insights to improve operation efficiency. Further research should focus on increasing the precision for weight prediction, for instance by increasing the labeled data set with a larger number of unique particles and on methods to verify the performance of the model on pilot or full-scale plants during live operation.

Recycling doi: 10.3390/recycling11060100

Authors: Pablo Kählig Wolfgang Ipsmiller Andreas Bartl Jakob Lederer

Recycling cotton–PET textile blends using alkaline solutions has gained increasing attention, with studies showing promising treatment pathways with diverse process setups. However, these separation processes use various input materials and focus on a small number of treatment parameter values which render the comparison of results over a large parameter range difficult. This study presents the feasibility of recovering cotton or PET at fabric level from cotton–PET blends across a wide range of temperatures (from −30 °C to 95 °C) and alkaline concentrations (from 0 to 40% (w/w)). The focus of this study is centered on the share of separation and recoverable fiber mass after hydrolyzing one component using alkaline hydrolysis or alkaline pre-treatment followed by enzymatic hydrolysis. A comparison of purity and material loss of the recovered polymers for all parameter sets is given. Experiments were performed on two distinct textiles while process parameters were selected in a straightforward manner, excluding catalysts, co-solvents and defibration. The results map temperature and alkaline concentration areas where these cotton–PET separation processes are feasible regarding recoverable fiber mass. Based on these results, separation efficiency could be optimized to design economic and environmentally friendlier process conditions.

Recycling doi: 10.3390/recycling11060099

Authors: Abhishek N. Srivastava Arun Krishna Vuppaladadiyam Rakhi Punnadan Koroth Christoph Pfeifer Ajay Kumar Kaviti Jafar Fathi Alan Maslani Praveen Barmavatu Maksym Buryi Michael Pohorely Vineet Singh Sikarwar

Landfilling remains the dominant waste disposal method worldwide, particularly in developing countries, posing serious environmental, health, and climate challenges. Inefficient practices, weak regulations, and un-engineered sites contribute to massive greenhouse gas (GHG) emissions and resource loss. Transitioning to a circular economy (CE) offers a transformative path for sustainable waste management. By closing material loops, recovering energy, urban mining, controlling emissions and CE strategies can convert traditional landfills into eco-efficient systems. The integration of artificial intelligence (AI) further enhances this transition, enabling real-time monitoring, predictive management, and optimized resource recovery, thereby maximizing environmental and economic benefits. This review presents a three-level CE framework at micro (individual organizations), meso (industrial networks), and macro (national and international) levels designed to extract maximum value from waste streams and mitigate climate impacts. The proposed strategies demonstrate the potential to drastically reduce GHG emissions, promote clean energy via waste-to-energy routes, and contribute to SDGs 7, 11, 12, 13 and 15. By combining technology, innovation, and strategic management, this work highlights how AI-driven CE approaches can transform landfills from environmental liabilities into engines of sustainability and climate action. In implementing CE strategies at various levels, various challenges including technological, socio-economic, ethical, policy-based, and unintended consequences are encountered which impact sustainability initiatives. This review comprehensively discusses challenges associated with CE implementation and identifies technological advancement, social awareness and data-driven AI/ML-based modeling which could ensure success in circularity and ultimately curb climate change impacts in the long term.

Recycling doi: 10.3390/recycling11060098

Authors: Bo Su Jie Chi Siqi Zhang Jia Li Keqing Li Xingyang Xu Wen Ni

A quaternary solid-waste-based binder was prepared from low-titanium slag, municipal solid waste incineration (MSWI) fly ash, steel slag, and flue-gas desulfurization gypsum (FGDG) to clarify the activating effect of MSWI fly ash on low-titanium slag and its influence on hydrate evolution. Unlike conventional solid-waste-based binders in which MSWI fly ash is mainly regarded as a hazardous residue requiring stabilization, this study demonstrates its specific role as a Ca-rich alkaline activator for promoting low-titanium slag depolymerization and coordinated hydrate formation. The results showed that the compressive strength first increased and then decreased with increasing MSWI fly ash content. Considering both strength development and MSWI fly ash utilization, the optimum mixture was identified as low-titanium slag:MSWI fly ash:steel slag:FGDG = 43.0:17.2:25.8:14.0, with compressive strengths of 9.51 and 46.32 MPa at 3 and 90 d, respectively. These values corresponded to 5.66 and 1.04 times those of the reference mixture without MSWI fly ash, respectively. Ettringite and C-(A)-S-H gel were the main strength-contributing hydration products, while Friedel’s salt was identified as a chloride-bearing AFm phase. Moderate MSWI fly ash addition promoted alkaline activation and low-titanium slag depolymerization, leading to increased formation of ettringite, C-(A)-S-H gel, and Friedel’s salt, which contributed to improved compressive strength. In contrast, excessive MSWI fly ash disturbed the Ca-Si-Al balance and inhibited effective hydrate formation. These results demonstrate that MSWI fly ash can serve as an effective Ca-rich activator for low-titanium-slag-based low-carbon cementitious materials and provide a feasible route for the synergistic utilization of multiple solid wastes.

Recycling doi: 10.3390/recycling11060097

Authors: Thanaporn Chandransu Krishmanust Sunankingphet Somyote Kongkarat

This study evaluates the feasibility of using waste Bakelite thermoset as a slag foaming and iron oxide reduction agent in electric arc furnace (EAF) steelmaking. Bakelite was blended with metallurgical coke at three ratios (10–30 wt% Bakelite), designated as Blend#1 to Blend#3. All carbon samples were heat-treated at 1000 °C under an argon atmosphere to produce char and were subsequently assessed for carbon–slag interactions at 1550 °C, with emphasis on slag foaming behavior and FeO reduction. The incorporation of Bakelite increased the total carbon content and significantly altered coke ash chemistry, marked by reduced SiO2 and Al2O3 and increased CaO contents. Structural analysis revealed enhanced carbon graphitization with increasing Bakelite proportion. Among all samples, Blend#3 exhibited the most stable and pronounced slag foaming, achieving a maximum volume ratio of approximately 1.7 and forming uniformly distributed, multi-sized gas bubbles within the slag. FeO reduction improved with Bakelite addition, with metallization degrees of 77.30, 81.65, 80.56, and 84.41% for coke, Blend#1, Blend#2, and Blend#3, respectively. Blend#3 produced the lowest total gas emission (186,000 ppm), approximately 30% lower than that of pure coke. These findings demonstrate that waste Bakelite thermoset is an effective low-carbon alternative carbon source for EAF steelmaking, enhancing FeO reduction, slag foaming stability, and overall environmental performance.

Recycling doi: 10.3390/recycling11060096

Authors: Yerlan Doszhanov Adilkhan Orazbayev Murat Zhumabayev Saule Kaldybayeva Aigerim Kerimkulova Aliya Alimbetova Nariman Pravin Arman Zhumazhanov Aitugan Sabitov Ospan Doszhanov Dauren Baiseitov

This study explores the possibility of making cardboard and molded egg carton packaging from corn residues and common reed as alternatives to wood-based pulp. Six formulations were made: corn husks (CHs), corn leaves (CLs), corn leaves (35%) plus corn husks (30%) and a corn blend (15%) of wollastonite (CaSiO3) (CH + CL + W), a corn blend (CH + CL: husks 60%, leaves 40%), mixed corn waste (MCW) and shredded common reed (SR). Optical microscopy was used to evaluate the fiber morphology, including the calculation of the flexibility coefficient, the cell wall rigidity and the Runkel ratio, for raw materials and fiber after alkaline hydrolysis and casting of egg cartons in silicone molds. The grammage, burst strength and index, folding endurance, thickness and moisture content were measured in the cardboard samples, while warping, compressive deformation, moisture and ink absorption were measured in the egg cartons. The flexibility coefficient of the common reed fibers (64.5%) was better than that of the corn fibers (23.6%), and so was the Runkel ratio (0.86 vs. 1.2). In the case of cardboard formulations, the maximum burst strength (462.4 kPa) and the maximum burst index (3.0 kPa·g/m2) values were obtained with the MCW formulation, and the highest folding endurance (42 and 38 double folds) was obtained with the CH and SR formulations, respectively. The addition of wollastonite improved folding endurance to 28 double folds and reduced moisture content to 4.1%, whereas the moisture content was reduced but burst strength decreased to 250.5 kPa. Egg cartons made from corn were found to satisfy all the requirements tested for good packaging, while the reed-based cartons were found to have inadequate ink absorbency time (20 min), making them less printable. Overall, mixed corn residues seem to be the most promising raw materials for sustainable packaging, and wollastonite can be used to adjust the flexibility–strength balance.

Recycling doi: 10.3390/recycling11050095

Authors: Letizia Caroscio Cristian Chiavetta Adrian I. Yoris-Nobile Eva Cuesta-Astorga Alessandra Bonoli Elena Blanco-Fernandez

This study investigates the reuse of mussel shell waste as a secondary raw material in bio-cement mortars designed for the additive manufacturing of artificial reefs for marine habitat restoration. The novelty of the research lies in combining a high recycled shell content (60 wt.%), low-clinker cement, and two 3D-printing techniques: Extruded Material Systems (EMS) and Powder-Based Systems (PBS). Mechanical performance was evaluated through flexural and compressive tests after 7, 28, and 91 days under both air and freshwater curing conditions, while environmental impacts were assessed through Life Cycle Assessment (LCA). The LCA evaluated both the environmental performance of shell-based mixtures compared with conventional materials and the impacts associated with the investigated fabrication techniques. The best-performing bio-mixtures achieved compressive strengths up to 46.01 MPa and flexural strengths up to 9.91 MPa after freshwater curing, demonstrating the suitability of shell-based mortars for submerged applications. LCA results showed reduced impacts in land use and mineral resource depletion compared with conventional mixtures, despite slightly higher energy and water demands associated with shell pre-treatment. The results demonstrate the technical and environmental feasibility of integrating aquaculture waste into sustainable 3D-printed marine restoration solutions.

Recycling doi: 10.3390/recycling11050094

Authors: Igor Cleyton Ferreira de Sousa Cláudio Henrique de Almeida Feitosa Pereira Yuri Sotero Bomfim Fraga

The excessive generation and improper disposal of Construction and Demolition Waste (CDW) represent one of the main environmental challenges in the sector. However, its potential for reuse and recycling enables the mitigation of these impacts through sustainable practices. In this context, the present study aimed to estimate reference values for the Federal District, Brazil, regarding the environmental impacts associated both with the transportation stage of CDW—from its point of origin to the processing facility—and with the operations involved in its conversion into recycled aggregates, through the application of a simplified Life Cycle Assessment approach. The analysis focused on quantifying the consumption of electricity, water, and fossil fuels, as well as carbon dioxide emissions and the generation of contaminant residues throughout the analyzed process. The system boundary adopted corresponds to a “cradle-to-gate” scope, with a declared unit of 1 tonne of recycled aggregate. Additionally, a survey of scientific studies providing life cycle inventory data related to aggregate production was conducted, enabling a consistency analysis with the data obtained in this study. Primary data related to the recycled aggregate production process were collected through direct field observations, in situ measurements, and the analysis of operational records from the studied facility. For the year 2024, the environmental indicators obtained showed that the production of 1 tonne of recycled aggregate required 1.23 kWh of electricity, 5.65 L of water, and 2.14 L of diesel, in addition to resulting in emissions of 6.64 kg CO2 eq and the generation of 2.3 kg of contaminant waste.

Recycling doi: 10.3390/recycling11050093

Authors: Jiani Tian Daohong Zhang Ning Jiang Chengze Yu Jiaqi Hou Chunming Hu Panpan Wang Chaocan Li

Effective management of organic wastes is essential for green and low-carbon development. Conventional technologies, including incineration, pyrolysis, hydrothermal carbonization (HTC), gasification, anaerobic digestion (AD), and composting, have supported waste reduction and basic resource recovery, but they remain limited in high-efficiency conversion and high-value utilization. This review comparatively evaluates these conventional routes together with advanced and intensified technologies, including microwave-assisted pyrolysis (MAP), plasma treatment, supercritical water gasification (SCWG), and flash joule heating (FJH), with emphasis on suitable feedstocks, performance characteristics, application boundaries, and integration potential. In general, wastes with high moisture content are more suitable for HTC, AD, and SCWG, whereas relatively dry wastes and wastes with high carbon content are more suitable for pyrolysis, gasification, plasma treatment, and FJH upgrading. The review also discusses representative integrated pathways, such as HTC-SCWG, pyrolysis and plasma coupling, AD and gasification coupling, and pyrolysis and FJH coupling, which may improve carbon conversion, broaden product portfolios, and reduce residual pollutants. However, large-scale implementation is still constrained by feedstock heterogeneity, heat and mass transfer limitations, catalyst deactivation, reactor corrosion, and system cost. Overall, no single technology is universally optimal; technology selection should depend on feedstock properties, moisture content, and target products.

Recycling doi: 10.3390/recycling11050092

Authors: Maria del Carmen Aragón-Duarte Hilda Esperanza Esparza-Ponce Lillian Vianey Tapia-Lopez Antonia Luna-Velasco Luis Fernando Jiménez-Tinoco Javier Servando Castro-Carmona

This study proposes the development of a recycling process for the reintegration of dental zirconia waste into CAD/CAM systems for rapid prototyping, with the objective of demonstrating the feasibility of manufacturing functional products from recycled zirconia obtained from a commercial dental laboratory. The proposed methodology aims to explore a simple and economically viable process, which involves the purification and processing of a heterogeneous zirconia powder, followed by the fabrication of pre-sintered blocks suitable for CAD/CAM applications. The recycled bulk ceramic was characterized and compared with commercial zirconia through density measurements, X-ray diffraction, scanning electron microscopy, Vickers hardness, flexural strength testing, and sintering shrinkage analysis. The results indicated that, although recycled zirconia exhibits lower property values than the commercial reference material, it retains adequate characteristics for specific practical applications. Consequently, to demonstrate industrial feasibility, four components were designed using CAD and machined using CAM from the recycled blocks, simulating a rapid prototyping process. The fabricated components exhibited a smooth and flawless surface, were mechanically robust and solid to the touch, and showed well-defined contours with sharp edges. Dimensional analysis demonstrated high accuracy, with an average percentage error of 0.53% ± 0.14. These findings demonstrate that high-value ceramic waste can be reintegrated into the production chain as functional industrial components through a process that is closely aligned with the real conditions of industrial recycling, while also mitigating environmental contamination from hazardous industrial waste.

Recycling doi: 10.3390/recycling11050091

Authors: Ivan Gaytán Aguilar María del Consuelo Hernández Berriel Federico del Razo López Everardo Efrén Granda Gutiérrez María del Consuelo Mañón Salas Roberto Alejo Eleuterio

Municipal solid waste management (MSWM) systems in Latin America are constrained by limited access to high-resolution operational data, compelling local authorities to depend on aggregated national statistics that are inadequate for behaviorally informed intervention design. This limitation is particularly evident in the State of Mexico, which generates about 16,187 tons of waste every day but only recycles only 11%. In this context, this study introduces a diagnostic data science framework to identify behaviorally grounded citizen segments and their defining attributes, supporting evidence-based decision-making in MSWM. Primary survey data from 560 households across three municipalities were used, and a three-stage analytical pipeline was implemented to account for contextual heterogeneity. First, k-means clustering was applied to identify behavioral segments. Second, random forest classifiers were used to validate cluster coherence and quantify feature importance. Third, the Apriori algorithm was used to extract association rules that capture recurrent material-mixing behaviors. The results revealed municipality-specific segmentation structures (Tequixquiac: K = 6; Tlalpujahua: K = 3; Xalatlaco: K = 2), with material-specific disposal behaviors emerging as stronger segmentation drivers. Random forest classifiers validated cluster coherence with 100% accuracy, confirming that segments represent behaviorally distinct archetypes. The proposed framework converts raw behavioral data into actionable municipal visions. This approach focuses on finding diagnostic patterns instead of making predictions by utilizing machine-learning-driven MSWM research.

Recycling doi: 10.3390/recycling11050090

Authors: Anayansi Estrada-Monje Sergio Alonso-Romero Anayansi Zaragoza-Estrada María Cristina Kantún-Uicab Claudia Ivone Piñón-Balderrama Claudia Alejandra Hernández-Escobar Erasto Armando Zaragoza-Contreras

The increasing use of biodegradable polymers, especially poly (lactic acid) (PLA), has raised concern about their entry into conventional post-consumer recycling streams. This review examines the technical and systemic consequences of PLA contamination in the high-density polyethylene (HDPE) circular economy through the “drop-in delusion,” defined here as the mistaken assumption that a sustainability-marketed polymer can enter an established recycling stream without compromising system compatibility. Focusing on contamination-sensitive conditions in which segregation, sorting, or stream purity are insufficient to prevent cross-contamination, the review discusses the immiscibility of HDPE/PLA blends and the resulting changes in stiffness, ductility, toughness, and aging behavior. It also analyzes mitigation routes such as improved sorting, compatibilization, and policy measures, while emphasizing that the practical severity of contamination depends on local infrastructure and contamination levels. In addition, it considers the risk that contaminated materials diverted into lower-value applications may become more vulnerable to interfacial damage, weathering, and secondary fragmentation. Overall, the review argues that circular-plastics strategies must distinguish biodegradability from recycling-system compatibility to protect the quality and value of HDPE recyclates.

Recycling doi: 10.3390/recycling11050089

Authors: Md Kaviul Islam Anirudha Karati Ikenna C. Nlebedim Pranav Shrotriya

The printed circuit board (PCB), a central component of most electronic devices, represents a significant fraction of the electronic product waste stream. The complex composition of PCBs, consisting of metals, polymers, and fiberglass, requires specialized recovery steps to reclaim valuable and critical materials and the safe disposal of brominated compounds. In this review paper, we describe the current state of critical material recovery and traditional recycling technologies and identify key obstacles to large-scale implementation. Metals present at high concentrations, such as copper, lead, and iron, are conventionally recovered from PCBs using hydrometallurgical, pyrometallurgical, or electrometallurgical processes. Hydrometallurgical methods achieve high selectivity through chemical leaching but pose significant challenges for effluent and reagent recovery. Pyrometallurgical methods facilitate rapid metal separation through smelting but require substantial energy and may release harmful gases. Electrometallurgical techniques produce high-purity metals but are constrained by pretreatment requirements and the consumption of energy. The non-metallic fraction of PCB waste is recycled using thermochemical conversion, microwave-aided heating, and direct recycling of epoxy–fiberglass composites, enabling material or energy recovery. The recovered polymer from direct recycling may have reduced mechanical strength and poor compatibility with new polymer matrices, and the resulting products from the thermal conversion suffer from incomplete conversion, degradation of quality, and residual contamination, as compared to synthetic polymers. Recent process developments have focused on extracting rare earth and supply-critical materials present at lower concentrations in the waste stream. The literature on existing and emerging approaches for recycling PCB wastes is reviewed to identify sustainable, economically viable, and environmentally responsible strategies for the recovery and reuse of critical materials from waste streams.

Recycling doi: 10.3390/recycling11050088

Authors: Wojciech Szymański Sonia Boczkal Dawid Kapinos Joanna Hrabia-Wiśnios Elżbieta Szymańska Lutz Stobbe Thomas Mager Marek Kościelski

Aluminum multifunctional housings can enhance circularity in electronics by replacing polymer enclosures while integrating heat sinking and electronic functions via laser direct structuring (LDS). Within the ALU4CED concept, we applied an IR-compatible LDS lacquer on aluminum, formed conductive tracks by electroless Cu/Ni/Au metallization, assembled components, and assessed end-of-life recyclability. Controlled remelting trials compared three disassembly levels: complete housings with PCBs and components, housings without PCBs, and housings with only integrated tracks. Metal yield rose from 81.4% for complete assemblies to 93.2% after PCB removal, while leaving integrated LDS tracks did not measurably penalize recovery. Only the complete electronics variant showed critical contamination (Cu = 1.64 wt.% vs. 0.25 wt.% limit for EN AC 4343); after PCB removal, composition remained close to the reference and major elements (Si, Mg, Fe) stayed within specification. Prefil testing indicated very low total inclusion content (0.006/0.001/0.002 mm2·kg−1), confirming high melt cleanliness despite coatings. Following remelting → billet casting → extrusion, tensile properties (Rm ≈ 120–123 MPa, Rp0.2 ≈ 59–61 MPa, A ≈ 29–33%) were comparable to the reference profile. These results demonstrate the technological feasibility of closed-loop recycling for LDS functionalized aluminum housings and inform clear Design-for-Recycling guidance: design for rapid PCB removal, allow LDS layers to remain during melting, and maintain compatibility with the 4343 family to enable efficient internal recycling.

Recycling doi: 10.3390/recycling11050087

Authors: Gavin E. Collis Renée L. Webster Aaron Seeber Chris Sheedy Sherman Wong Thomas J. Raeber Yanyan Zhao

Using strategies employed in synthetic chemistry, we investigated the chemicals found in lithium iron phosphate (LFP) spent battery via an initial dichloromethane (DCM) extraction of the individual cathode and anode. The pre- and post-treated electrodes and DCM extracts were examined using a range of analytical techniques. A total of 26 compounds were identified, which included the following: (1) some of the benchmark materials, LFP, lithium hexafluorophosphate (LIPF6), polyvinylidene fluoride (PVDF), graphite and carbon black; (2) NMR spectroscopy of DCM extract revealed five main chemicals, which were ethylene and propylene carbonate solvents, LiPF6, lithium tetrafluoroborate (LiBF4), and an unknown fluorochemical; (3) analysis of the water-treated DCM extract revealed 21 chemicals by GCMS, several fluorochemicals; (4) 12 chemicals were found in both cathode and anode and three only in the anode; (5) only 13 of the 21 chemicals could be properly named, whilst four had some notable functionality and three could not be identified; and (6) ICP analysis revealed high levels of Al, Cu, Fe, V, and Zn in both electrodes and spent electrolyte. The high number of chemicals present in the spent electrolyte and electrodes suggest battery manufacturers use many proprietary chemicals to enhance battery properties. This procedure allows insight and identification of chemicals present in waste LIBs which will require advanced chemical techniques to recover high yields and purity of recycled materials and the need to dispose of hazardous waste.

Recycling doi: 10.3390/recycling11050086

Authors: Wilfrido Campos Francisco Jonathan Villanueva Tavira Jonathan Jesús Carranza Vega Blanca Dina Valenzuela Robles Erik Rosado Tamariz Andrés Blanco Ortega

Municipal Solid Waste (MSW) is a common problem in all cities worldwide; it is expected to increase to 3400 billion tons by 2050. In Mexico, an average of 108,146 tons of MSW are generated daily. Artificial Intelligence (AI) is a computer tool that allows the development of systems that facilitate the recycling process. However, most AI programs focus on classifying paper, plastic, glass and metal; therefore, wood and textile waste have received little attention. Using texture techniques such as Local Binary Pattern (LBP), Gray-Level Co-occurrence Matrix (GLCM), Histogram of Oriented Gradients (HOG), Canny/Sobel edge detection, Fractal Dimension (FD), feature values were extracted and integrated from 4396 images belonging to wood and textile categories. Using the Random Forest Importance method, the most significant features were selected to train three Machine Learning (ML) algorithms. Multilayer Perceptron (MLP) achieved the best performance in accuracy with 96.70%, followed by Random Forest (RF) at 95.45% and Support Vector Machine (SVM) with 95.22%. The implementation of these comparisons will serve as a basis for the development of new technological tools with low computational cost that carry out a proper waste separation.

Recycling doi: 10.3390/recycling11050085

Authors: Samuel Alcoceba-Pascual Nicolás I. Villanueva-Martínez Abel Ortego Ricardo Magdalena Sofia Russo Marta Iglesias-Émbil Alicia Valero

The automotive sector is the third-largest consumer of plastics in Europe, after packaging and construction, and its demand is expected to grow. Plastic recycling at the end of vehicle life remains low, with 80% of plastics ending up in energy recovery or landfills. Three vehicle models (SEAT Ibiza Gen. IV and SEAT Leon Gen. II and III) with two trim versions (Reference and Formula Racing) were examined to identify the most critical plastic components from an exergy perspective. Ecodesign measures were defined by considering both the disassemblability of vehicle components and their recyclability potential as key criteria to evaluate end-of-life recovery pathways and guide material and design optimization strategies. The proposed methodology classified the measures into three types: (1) substitution of high-exergy plastics with lower-impact alternatives; (2) use of recycled plastics instead of primary materials, with substitution rates depending on the material; and (3) reuse of components in new models, evaluated by disassemblability and end-of-life condition. Results show that Type 1 measures achieved savings up to 70 MJ, mainly in the floor covering and engine compartment insulator, while Type 2 measures provided larger reductions, up to 1.7 GJ, mainly in bumpers and carpets. Type 3 measures showed reuse potential for paddings and insulators but faced limitations in carpets and dashboards. Findings highlight the importance of material selection and implementing disassembly and recycling strategies to reduce the exergy of vehicle plastics.

Recycling doi: 10.3390/recycling11050084

Authors: Nutcha Taneepanichskul

Urban plastic waste management in large metropolitan regions remains constrained by low recovery rates despite growing policy attention. This study adopts a sustainability-oriented innovation (SOI) perspective to examine how policy–technology integration reshapes system-level performance in urban plastic waste systems. Using Bangkok as a representative case, a system-level model integrates plastic waste generation growth, time-dependent behavioural adoption of separation at source, contamination-sensitive sorting efficiency, and mass-balance material flows. Three scenarios are assessed: Business-as-Usual, separation-at-source policy only, and an integrated policy–technology system with advanced sorting. Results show that the baseline system remains stagnant at approximately 3.1% recovery. Policy intervention alone increases recovery gradually, reaching around 20% by 2045 despite participation approaching an 85% ceiling. In contrast, integrating policy with advanced sorting generates non-linear gains, surpassing 20% recovery within two years and reaching approximately 47% by 2045, driven by substantial contamination reduction. A Monte Carlo sensitivity analysis extends the integrated pathway to 2060. The median recovery trajectory stabilises at 68%, while the probability of achieving more than 70% recovery rises to 28% by 2040 and plateaus at 33% thereafter. The findings demonstrate that circular economy performance is probabilistic and depends on system-level alignment between behavioural participation, material quality, and technological capability.

Recycling doi: 10.3390/recycling11050083

Authors: Thobile Zikhathile Harrison Atagana Joseph Bwapwa Taurai Mutanda

Healthcare waste management is a growing environmental and economic challenge due to increasing waste volumes, hazardous materials, and continued reliance on linear disposal methods such as incineration and landfilling. This review aims to examine how circular economy and zero-waste approaches can be applied to healthcare waste management to improve sustainability, resource efficiency, and system performance. A structured narrative review was conducted using peer-reviewed literature obtained from prominent scientific databases, concentrating on circular strategies, zero-waste initiatives, digital technologies, and policy frameworks relevant to healthcare waste systems. The reviewed studies indicate that practices such as improved waste segregation, recycling and material recovery, reusable product design, digital waste tracking, and Extended Producer Responsibility can significantly reduce waste generation, lower environmental impacts, and achieve cost savings, while maintaining infection control and patient safety. However, the review also identifies key barriers to implementation, including regulatory complexity, limited infrastructure, financial constraints, and weak coordination among stakeholders. The novelty of this review lies in its integrated analysis of circular economy and zero-waste strategies through the lens of digital enablement, offering a systems-based framework for transforming healthcare waste management beyond incremental improvements. The findings highlight that successful circular healthcare waste management requires strong institutional leadership, supportive policies, and the integration of digital technologies to enable monitoring, traceability, and decision-making. This review enhances the comprehension of how circular economy principles can facilitate the transition from linear to sustainable healthcare waste systems and provides guidance for policymakers, healthcare managers, and researchers. Future research should focus on evaluating real-world implementation, advancing recyclable and reusable medical materials, and developing standardised indicators to measure circular performance in healthcare settings.

Recycling doi: 10.3390/recycling11050082

Authors: Andrea Margheri Matteo Cordara Andrea Ballarino Carlo Brondi

Variability in life cycle assessment (LCA) results for metal recycling technologies arises from multiple sources, including allocation methods, recycling route, regionality of impacts, and type of waste treated. Among these factors, waste composition is particularly critical, as it directly influences process performance by affecting auxiliary material consumption and emissions. This work investigates four waste categories: metals from incineration bottom ash (MBA), waste-printed circuit boards (WPCBs), industrial waste from gold refining (GRA), and spent automotive and industrial catalysts (SCs). The Climate Change (CC) for 1000 kg of waste was estimated at 3251 × 103 kg CO2eq for WPCBs, 3923 × 103 kg CO2eq for MBA, 1569 × 103 kg CO2eq for GRA, and 2101 × 103 kg CO2eq for SCs. A sensitivity analysis was performed to assess the influence of allocation methods on results for 1 kg of recycled metal. The highest variability in CC across waste categories was observed for gold (up to 8477%) with the black-box economic allocation method, while different allocation methods reached 21,700% for WPCBs. These results highlight the strong influence of methodological choices and waste characteristics, emphasizing the need for transparent and consistent LCA reporting.

Recycling doi: 10.3390/recycling11050081

Authors: Inês Costa Bruna Machado Bruno Silva Catarina Dias Luís Silva Isabel Carvalho Vera Sá Alexandre Pereira Catarina Basto-Silva

The European woodworking and furniture sector faces increasing sustainability challenges, including dependence on virgin raw materials and low recycling rates of furniture waste, highlighting the need for integrated environmental and economic assessments to support circular solutions. The purpose of this study is to evaluate and compare the environmental and economic performance of boards produced with different proportions of Polyethylene Recycling Waste (PRW) sourced from a Portuguese plastic recycling company, using an integrated Life Cycle Assessment and Life Cycle Costing approach. The environmental performance was assessed following ISO standards using the ReCiPe 2016 Midpoint (H) method, while the economic analysis included internal and external costs. First, the environmental and economic performance of PRW was assessed per 1 kg of material. Subsequently, four board formulations produced at pre-industrial scale, in a Portuguese company, were compared per 1 m3 of board: 100PRW; 80PRW20FW (with 20% furniture waste, FW); 80PRW20PE (with 20% virgin polyethylene, PE); and 80PRW20PU (with 20% virgin polyurethane, PU). Results show that waste-based boards (100PRW and 80PRW20FW) consistently present lower environmental impacts and improved cost-efficiency compared to formulations incorporating virgin polymers, particularly PU. Global warming and terrestrial ozone formation were the main contributing impact categories, largely driven by energy consumption. The dominant impact stage varied by formulation, with pressing prevailing in waste-based options and raw material production in virgin-polymer-based boards. These findings demonstrate that increasing the share of waste materials can significantly improve both environmental and economic performance, supporting the transition towards circular material solutions in the furniture sector. This study provides a novel contribution by integrating LCA and LCC in the assessment of pre-industrial PRW boards, offering practical insights for industry decision-making and sustainable material design.

Recycling doi: 10.3390/recycling11050080

Authors: Chin Mei Chan Amal Asheeba Romzi Linda Lim Biaw Leng Muhammad Raziq Rahimi Kooh

Developing practical low-cost adsorbents for dye-contaminated wastewater remains a critical challenge, especially for persistent cationic dyes such as crystal violet (CV). Here, raw rockmelon skin (RMS), an abundant fruit-processing residue, and its NaOH-modified derivative (NaOH-RMS) were investigated as adsorbents for CV adsorption. Alkaline treatment altered the biomass’s characteristics and affected its adsorption behaviour. Equilibrium was reached within 120 min, and the kinetic data were best fit by the pseudo-second-order model. Equilibrium analysis showed that the Freundlich model best described RMS. In contrast, NaOH-RMS was better represented by the Langmuir model, indicating that alkaline treatment altered the adsorption behaviour of the biomass surface. The Langmuir-derived maximum adsorption capacities were 343.7 mg g−1 for RMS and 295.2 mg g−1 for NaOH-RMS, indicating that NaOH modification did not increase the maximum adsorption capacity. Adsorption was spontaneous across 298–343 K, and both materials retained satisfactory removal performance over five regeneration cycles, particularly under basic desorption conditions. Overall, NaOH treatment altered the adsorption behaviour from heterogeneous adsorption on RMS to a more Langmuir-type adsorption pattern on NaOH-RMS, despite not increasing the maximum adsorption capacity. These findings support the valorisation of fruit-processing residues as practical adsorbents for dye-contaminated wastewater.

Recycling doi: 10.3390/recycling11040079

Authors: Inês Silva Graça Martinho Mário Ramos

The progression towards a circular economy in the construction sector has gained attention as a response to rising resource consumption and construction and demolition waste generation, with material reuse playing a central role. In this context, this study analyses the literature on reuse in the construction sector, examining its investigation over time and its relation to European regulatory frameworks and policy strategies. A systematic literature review was conducted using a structured search across the B-on, Scopus, and Web of Science databases. The search targeted peer-reviewed journal articles in English, published between 2008 and 2023, focusing on titles, abstracts, and keywords with predefined terms. A total of 78 articles met the inclusion criteria and were analysed. Research activity has increased in recent years, reflecting growing European policy attention, particularly the Waste Framework Directive, its 2018 amendment, and the Circular Economy Action Plan. Most studies address strategies to promote the circular economy, waste management practices, life cycle assessments, and the identification of barriers and opportunities to reuse. Despite the expanding literature, reuse remains insufficiently addressed. These findings underline the need for more targeted research and stronger integration between policy and practice to support effective reuse in the construction sector.

Recycling doi: 10.3390/recycling11040078

Authors: Dheeraja Winter Svea Ziegner Simone Krafft Markus Grömping Silvio Beier

The paper sector is characterised by high freshwater consumption and a strong need for improved resource efficiency. In this context, industrial digestates derived from short-fibre residues in paper recycling mills represent a promising substrate for water recovery within a circular economy framework. This study investigated the dewatering of short-fibre digestates as a pre-treatment for downstream membrane processes, aiming to maximise the liquid fraction (LF) recovery while minimising dry matter (DM) content. Seven scenarios were studied: sedimentation (S0); pre-sedimentation with chemical addition using iron(III) chloride (FeCl3) + polydiallyldimethylammonium chloride (polyDADMAC) (S1), FeCl3 + starch (S2), Nanofloc® (S3), and polyDADMAC (S4); and direct dewatering without pre-sedimentation using polyDADMAC with cloth filtration (S5) and centrifugation (S6). With reference to the sedimentation supernatant, S4 achieved the highest DM separation efficiency of 76%, followed by S1 (64%), whereas S2 and S3 were below 40%. However, LF recovery relative to the initial digestate was limited in scenarios S1–S4 to 17% (170 g/kgdigestate), with DM concentrations of 2.0–4.8 g/kgLF. In contrast, direct dewatering increased LF recovery substantially, with centrifugation (S6) achieving up to 690 gLF/kgdigestate and cloth filtration (S5) 420 g/kgdigestate, while maintaining a low DM (1.7 g/kgLF). Chemical oxygen demand (COD) and phosphorus (Ptot) were largely separated from the liquid fractions in all the scenarios. Nitrogen (Ntot) and ammonium (NH4-N) in the LF remained more variable, ranging from 22 to 153 and 5 to 22 mg/kgdigestate, respectively. These results indicate that centrifugation with polyDADMAC is the most effective approach, suggesting that mechanical force with a chemical additive can be used for the efficient dewatering of short-fibre digestates.

Recycling doi: 10.3390/recycling11040077

Authors: Noemi García-Gomez Roifer Pérez-Vásquez José Luis Pasquel-Reátegui Manuel Fernando Coronado-Jorge Enrique Navarro-Ramírez Karen Gabriela Documet-Petrlik Pierre Vidaurre-Rojas Keller Sánchez-Dávila Ángel Cárdenas-García

Orange waste, generally discarded, is a source of many bioactive compounds that could be used for the development of high-value-added products in the food, cosmetic, and pharmaceutical industries. The objective of this study was to evaluate the influence of extraction method (automated Soxhlet extraction and temperature-controlled maceration), solvent system, and extraction time on the recovery of bioactive compounds from Valencia orange (Citrus sinensis) by-products. Proximate characterization of the dried orange residue (DOR) was performed prior to extraction. The type of solvent (ethanol and methanol), solvent:water ratio (50, 75, and 100%), and extraction time (60 and 120 min) were evaluated in terms of total extraction yield (TEY), total phenolic content (TPC), and antioxidant capacity determined by ABTS and DPPH assays, for each extraction method. ASE generally provided higher extraction yield and total phenolic content, particularly with 75:25 ethanol:water at 120 min, whereas TCM combined with methanol produced the highest antioxidant capacity. Extracts with up to 46.32% TEY, 5.57 mg GAE/g dm, and antioxidant capacities of 66.49 and 11.10 µmol TE/g dm determined by ABTS and DPPH assays, respectively, were obtained. The results demonstrated that Valencia orange by-products are a source of phenolic compounds and antioxidants with potential for product development across different industrial sectors.

Recycling doi: 10.3390/recycling11040075

Authors: Pauls P. Argalis Kristers Gelzis Ralfs K. Valdovskis Laura Vitola

This preliminary study investigates the viability of substituting high-performance Aalborg white Portland cement (CEM I 52.5 R) with five diverse industrial byproducts: wood ash, silica waste, clay brick, glass fibre, and calcined sewage sludge ash. Sewage sludge ash was produced in a laboratory from two different sludges from wastewater treatment plants in the Latvian cities of Jelgava and Liepaja. The research evaluates the influence of substitution levels ranging from 5% to 20% on the rheology of fresh material and its early-age mechanical performance (day 7). Results indicate that particle morphology largely dictates workability; porous and angular materials, such as wood ash, clay brick, and sewage sludge ash, reduce flowability, whereas non-absorbent milled glass fibres unexpectedly improve spread diameter. Regarding mechanical performance, glass fibre and clay brick waste demonstrated the highest potential, exceeding the 48–62 MPa reference compressive strengths by achieving up to 69 MPa at a 10% substitution level. Conversely, wood ash and silica waste exhibited significant strength degradation at higher substitution levels, due to agglomeration and high water demand. This approach not only identifies viable waste streams for cement substitution but also diverts significant industrial waste from landfills, thereby reducing CO2e emissions and advancing more sustainable construction practices.

Recycling doi: 10.3390/recycling11040076

Authors: Rhudson Fellipy de Oliveira Almeida Ivaldo Itabaiana Maria Alice Zarur Coelho

Proteases are key biocatalysts widely applied in the food, pharmaceutical, detergent, and environmental industries. One of the most costly steps in large-scale enzyme production is the preparation of the culture medium, making agro-industrial wastes attractive as low-cost nutrient sources and potential inducers. The non-conventional yeast Yarrowia lipolytica stands out in bioprocess engineering due to its high secretion capacity, GRAS status, and ability to metabolize diverse industrial residues. In this study, Brazilian agro-industrial by-products, namely Corn steep liquor (CSL), brewer’s yeast residue (BYR), and okara, were evaluated as alternative nitrogen sources for protease production by Y. lipolytica IMUFRJ 50678. Enzyme activity was quantified by the azocasein method at optimized conditions (40 °C, 40 min, pH 5 and 8). After an initial exploratory screening (n = 1), brewer’s yeast residue (BYR) and okara were identified as promising candidates for protease production. These preliminary findings guided subsequent experiments performed in biological triplicate (n = 3), which confirmed the reproducibility and comparative performance of these substrates, showing higher acid protease (AXP) activity in the BYR medium ((5.4 ± 0.3) U/mL), whereas alkaline protease (AEP) activities were comparable between the BYR ((8.4 ± 0.6) U/mL) and okara ((7.5 ± 0.9) U/mL) media. CSL was associated with higher lipase activity ((11.7 ± 0.9) × 103 U/L), while esterase activity was higher in the BYR medium. These findings indicate that agro-industrial residues, particularly BYR and okara, can serve as effective nitrogen sources for protease production by Y. lipolytica IMUFRJ 50678, supporting their use in waste valorization and sustainable bioprocesses.

Recycling doi: 10.3390/recycling11040074

Authors: Daví Matos Lopes Monica Luci Oliveira de Brito Josiel Isaac Domingues de Almeida Danilo Corado de Melo Jhon Adno de Almeida Santana Manoel Ferreira Lima Neto Maico Chiarelotto

This study aimed to evaluate the effects of adding sludge generated in water treatment plants on the composting of sewage sludge, urban organic waste, and agroindustrial waste. Four treatments were conducted with different proportions of water treatment plant sludge (WTS). Four treatments were conducted with 0%, 10%, 20%, and 30% proportions of WTS. The different proportions allowed for the evaluation of the effects of WTS addition on composting. The study was carried out in composting reactors. Kinetic models were applied to study the degradation of organic matter. Physicochemical and microbiological parameters were analyzed. During the process, temperature variation and basal respiration exhibited similar patterns. Principal component analysis showed that the 30WTS (32.2% water treatment sludge) treatment presented higher values of cation exchange capacity (CEC)/total organic carbon (TOC) ratio (3.83), and germination index (94.35%), and lower values of TOC (23.67%) and C/N (carbon/nitrogen) ratio (14.45). The composts produced in all treatments complied with Brazilian regulations for the environmental and agronomic quality of organic composts. It was concluded that the inclusion of up to 30% of WTS in composting did not negatively affect the composting process and did not compromise the environmental or agronomic quality of the final organic composts.

Recycling doi: 10.3390/recycling11040073

Authors: Linda Y. Pérez-Morales Adriana Guzmán-López Rita Miranda-López Micael Gerardo Bravo-Sánchez José E. Botello-Álvarez

Latin America faces growing challenges in the management of municipal solid waste (MSW). This is particularly evident in medium-sized and metropolitan cities where rapid urbanization, limited infrastructure, and high proportions of organic waste (40–70%) converge. This review synthesizes the most recent advances in organic waste management, valorization strategies, environmental performance, and policy frameworks in Mexico and Latin America. To provide a comprehensive overview, evidence from studies on informal recycling systems, route optimization, sustainable landfill siting, food waste valorization, life cycle assessments (LCAs), and biogas production is integrated. Techno-economic analyses of energy recovery from organic fractions are specifically reviewed. This review highlights that valorization of organic waste through composting, anaerobic digestion, food supplementation, and bioproduct generation can reduce greenhouse gas emissions by 40–70% compared to landfilling, with AD–composting hybrids achieving the highest reductions of 60–70%. Community composting achieved moderate reductions, 30–50%, but at significantly lower cost and with greater social co-benefits. These alternatives for valorizing the organic fraction extend the lifespan of both confined and open landfills. It also contributes to mitigating the public health impacts related to open dumping, disease vectors, and contaminated leachate. In short, this review also highlights shortcomings in policy coherence, financial mechanisms, source separation, and technology adoption. A strategic framework is proposed that prioritizes decentralized treatment systems, the integration of informal recyclers, tax incentives, community-based waste separation, and planning based on Life Cycle Assessment (LCA). The findings point to a viable strategy for transitioning from landfill dependency to circular waste management systems that improve the quality of life for the population of Latin America and the Caribbean.

Recycling doi: 10.3390/recycling11040072

Authors: Denis Miroshnichenko Yurii Parkhomov Yurii Lypko Vladislav Reivi Yurii Rohovyi Mariia Shved Bohdan Korchak Serhiy Pyshyev

The effective utilization and effective valorization of various organic industrial wastes have become increasingly important issues. One significant area for enhancing the circular economy is the processing of waste generated from vegetable oils and animal fats. This article focuses on the processing and use of soapstocks, which result from the chemical reaction between fatty acids and alkali. These soapstocks represent the most significant portion (approximately 70–90 wt% by weight) of waste produced by the oil and fat industry. The raw material for this study was soapstock obtained from the neutralization of sunflower oil at the PJSC “Zaporizhzhya Oil and Fat Plant,” designed by the Belgian company “De Smet.” The soapstock yield was found to be 9.95 wt% based on 100 wt% oil. Through a series of treatments involving water, acid, and multiple washes, a low-sulfur fuel component was produced that nearly meets the standards for boiler fuels as outlined in DSTU 4058-2001 and PN-C-96024:2020, except for the heat of combustion. It fully complies with the requirements specified in ISO 8217:2024. The sulfur content of the final product was determined to be 0.12 wt%. Additionally, the fuels produced contained 75.33 wt% carbon, 11.64 wt% hydrogen, and 12.00 wt% oxygen. Due to the relatively low oxygen content, the resulting product exhibits approximately twice the heat of combustion of similar fuels derived from other waste streams in the oil and fat industry.

Recycling doi: 10.3390/recycling11040071

Authors: Placide Uwizeyimana Tania Lopes Rodolphe Sonnier Anthony Burlet Mohammed Rakkane Wissal Bouamri Marc Potin

The building sector is a major source of CO2 emissions and construction waste, motivating the development of sustainable materials and end-of-life recycling strategies. Bio-concretes, combining mineral binders with plant-based aggregates, offer low density and favorable hygrothermal performance but remain insufficiently studied with respect to recyclability, particularly for gypsum-based materials. This study experimentally investigates the thermal recycling of gypsum–hemp bio-concrete, in which gypsum acts as the binder and hemp shiv as the aggregate. Thermogravimetric analysis of individual constituents and the bio-concrete was conducted to identify a temperature range enabling gypsum dehydration without hemp degradation. Controlled oven treatments at selected temperature–time couples were then applied to determine optimal recycling conditions, followed by the bio-concrete remanufacturing using 100% recycled constituents. Physical, thermal, and mechanical properties were evaluated before and after recycling under controlled conditions. Results show that a treatment at 180 °C for 60 min enables effective gypsum dehydration (18–20% mass loss) while preserving hemp integrity. Recycled gypsum–hemp bio-concrete exhibits increased density (368 to 587 kg·m−3) and compressive strength (0.05 to 0.52 MPa), accompanied by a moderate increase in thermal conductivity (0.081 to 0.096 W·m−1·K−1). These findings demonstrate the feasibility of 100% thermal recycling of gypsum–hemp bio-concrete without constituent separation.

Recycling doi: 10.3390/recycling11040070

Authors: Zunaida Zakaria Arif Rochman Paul Refalo

In recent years, plastic recycling has emerged as a critical concern in environmental protection and waste management. Among the various techniques for repurposing plastic waste into valuable products, extrusion of filaments for 3D printing has proven to be a highly effective method. A thorough understanding of the crystallization behavior of recycled plastics used in 3D printing is essential, as it significantly influences their final performance. This review provides an in-depth analysis of the crystallization behavior and crystallinity of recycled semi-crystalline polymers, with particular emphasis on recycled commodity plastics such as recycled polyethylene terephthalate (rPET), recycled polypropylene (rPP), and recycled high-density polyethylene (rHDPE). Recent research published between 2015 and 2025 was systematically synthesized and provides information on sources of plastic waste, additives employed, and recycling processes involved, with the findings summarized in a table that highlights their effects on polymer crystallinity. Furthermore, the key factors impacting the crystallinity of 3D-printed recycled plastics were examined, including the influence of additives, multiple processing cycles, printing parameters, and thermal treatments. Research gaps and the challenges faced during the printing process were also identified and discussed. By consolidating recent findings, this review provides a comprehensive understanding of the crystallization behavior of recycled plastics in 3D printing, thereby providing guidance for future research and developing strategies to optimize the performance of these materials.

Recycling doi: 10.3390/recycling11040069

Authors: Diana Meza-Rojas James Holliman David Penney Anthony R. Lewis Peter J. Holliman

A method has been developed to delaminate the organic components (paint, foam) from the steel skins of composite polyisocyanurate (PIR) steel insulation panels at ambient temperature and in 20 min using selected solvents combined with ultrasonication. Using this method, polyisocyanurate foam can be selectively delaminated from polymer-based paint (PVC plastisol) and, in turn, the polymer paint can be selectively delaminated from the galvanised steel. Both the foam and paint are removed as intact layers, leaving the galvanised steel intact for the next steps of recycling, enabling the subsequent individualised recycling of each sub-component or layer. Several solvents have been tested, and the data show that H-bonding solvents (e.g., H2O, alcohols) are less effective at delaminating these polymers. Whilst high polarity, medium H-bonding acetonitrile and DMSO remove PVC paint and some PIR foam, the most effective solvent for both PIR foam and PVC paint removal is medium polarity, medium H-bonding acetone.

Recycling doi: 10.3390/recycling11040068

Authors: Megan Wagaman Brendan Derrick Taff Jeremy Shellhorn Haven Everhart Jennifer Carrigan Melissa Jung Elizabeth A. Himschoot

The Grand Canyon National Park (GRCA) attracts roughly five million visitors annually, creating immense pressure on the waste stream managed in the park. To reduce environmental impacts, the National Park Service, collaborating organizations and concessionaires are in the process of implementing large-scale reusable foodware systems, replacing single-use plastics. This pilot study aimed to engage visitors in the design process to inform preferences and attitudes to further support management decision-making regarding the design and implementation of reusable foodware systems in the park. During September 2025, park visitors were intercepted at key concessionaire food vending locations and asked to complete a brief survey. The survey contained attitudinal questions, persuasive phrases, and potential logos and graphic designs that could be used with program implementation, which were evaluated via Likert scales by n = 164 respondents. Results suggest that respondents have overwhelmingly positive attitudes and norms towards reusing foodware at the park. Results highlight phrases and graphic designs that will be most effective as the program launches and can be used to inform future research.

Recycling doi: 10.3390/recycling11040067

Authors: Dimitrios-Aristotelis Koumpakis Dimitrios Christoforidis Vasileios Diamantis Alexandra V. Michailidou Christos Vlachokostas

The lack of centralized waste management infrastructure in certain regions makes plastic waste an escalating environmental and economic problem. This research investigates how modular portable pyrolysis systems function as sustainable decentralized solutions. A standard shipping container houses a custom-designed pyrolysis unit which demonstrates flexibility and adaptability. The system contains a batch rotary kiln reactor with a processing capacity of 750 kg per batch which is fed with urban plastic waste, to produce pyrolytic oil, syngas and char. The produced pyrolytic oil exhibits an energy content comparable to that of conventional diesel fuel. Additionally, the integration of biomass briquettes and recycled pyrolytic gas can reduce to a big extent the external energy requirements, improving the system’s overall energy autonomy. Therefore, the system becomes economically reliable due to its low operational expenses and the short cycle of approximately 7-h operation. The unit’s mobility enables on-site treatment operations which reduces both transportation emissions and expenses. The analysis includes technical design elements together with performance metrics for different plastics. This conceptual study demonstrates the feasibility of containerized pyrolysis as a practical method to enhance plastic waste chemical recycling rates while presenting a scalable framework for industrial symbiosis and local waste-to-energy conversion.

Recycling doi: 10.3390/recycling11040066

Authors: Aleksandr B. Stefaniak Lauren N. Bowers Callee M. Walsh Sonette Du Preez Elizabeth D. Brusak Jason E. Ham Ryan F. LeBouf M. Abbas Virji Johan L. Du Plessis

Distributed recycling of high-density polyethylene (HDPE) into filament for use in material extrusion 3D printing has been proposed as part of a circular economy. There is a gap in the understanding of the potential for HDPE to release contaminants that are potentially hazardous to human health during reuse. Herein, HDPE from post-consumer packaging waste was sorted into food and non-food (NF) streams and virgin HDPE was taken as a benchmark material. All materials were extruded into filaments and recycled multiple times while monitoring emissions. In general, particle and organic chemical emissions decreased by 93 to 99% and 73 to 99%, respectively, with increased reprocessing cycle without appreciable decline in mechanical (Young’s modulus decreased by 5 to 16%), processability (melt flow index stable from 0.2 to 0.7 g/10 min for waste plastics), and thermal properties (crystallinity ranged from a 6% decrease to a 9% increase) of plastics. An exception was a sub-stream of NF plastic that had increased particle emissions (up to 3100%) with reprocessing cycle. Reductions in emissions during filament extrusion appeared to be more influenced by reprocessing cycle than by any specific process step (grinding, etc.). The progressive decline in emissions without appreciable loss of polymer integrity could be exploited to pre-condition HDPE to reduce potential hazardous emissions prior to extruding into filament. This work helps fill the knowledge gap on approaches to recycling plastics in distributed settings such as home-based businesses, which is critical for developing effective recommendations for controls to enable safe work practices such as the use of ventilation to minimize exposures.

Recycling doi: 10.3390/recycling11040065

Authors: Luca Taglieri Pietro Romano Francesco Vegliò Alberto Gallifuoco Luciano Fratocchi

Rare earth elements (REEs) are essential to many low-carbon and digital technologies, yet the primary supply is geographically concentrated; waste electrical and electronic equipment (WEEE) could act as an “urban mine”, but recovery pathways remain fragmented. We synthesize the evidence through a structured literature review of Scopus and Web of Science indexed studies focusing on WEEE-derived feedstocks for REE recovery: 148 records were screened and 51 papers met the inclusion criteria. Reporting of the search and study selection process follows PRISMA 2020. We coded each study by WEEE source/fraction, core technology family, and process configuration, target REEs, performance reporting, environmental proxies, and maturity, and discussed gaps against circularity goals. Results show an intense concentration on a few feedstocks, permanent magnets (22 studies), fluorescent lamps (16), and batteries (6), with only limited attention to multi-source streams. Hydrometallurgical routes dominate, while biometallurgical options are less explored. Recovery is more frequently reported than selectivity and environmental indicators, and most solutions remain at proof-of-concept maturity. Due to the heterogeneity of feedstocks, process configurations, and reported metrics, the findings were synthesized qualitatively (no meta-analysis). This review highlights priorities for future work: multi-source and heavy rare earth elements focused feedstocks, more selective and intensified flowsheets, harmonized performance reporting, and scale-up supported by life-cycle and cost assessments.

Recycling doi: 10.3390/recycling11040064

Authors: Pauls P. Argalis Laura Vitola

The escalating production of sewage sludge presents a significant environmental challenge, while the construction industry simultaneously seeks sustainable raw materials to improve its circularity. This review analyses the technical and regulatory landscape for valorizing SS within the Latvian construction sector, set against the divergent strategies of its Baltic neighbours. While global research confirms the technical viability of using SS in fired-clay bricks and as a supplementary cementitious material (SCM), national management approaches differ starkly. Lithuania has adopted widespread incineration, and Estonia has focused on advanced composting. In contrast, Latvia’s national strategy is failing, with 51% of its 2024 sludge production diverted to “temporary storage”. This review identifies this crisis as a unique opportunity, arguing that incorporating dewatered digestate into fired-clay bricks is the most logical and economically viable pathway for Latvia, as it leverages existing industrial infrastructure. The primary obstacle to this circular solution is not technical but legal, specifically the lack of a national “End-of-Waste” (EoW) criterion for sludge-derived construction materials. Therefore, this article proposes a strategic roadmap for Latvia, centred on developing this essential legal framework, creating a national sludge characterization map, and initiating a pilot project to bridge the research-to-industry gap. Although Latvia is the primary focus of this review, the regulatory, infrastructural and material constraints analysed here are common in many small and mid-sized countries, making the insights applicable beyond the Latvian context.

Recycling doi: 10.3390/recycling11030063

Authors: Abderrazzak El Hafiane Abdelali En-nadi Mohamed Ramadany

Integrating Lean Construction (LC), the Circular Economy (CE), and Construction 5.0 (C5.0) remains challenging in emerging delivery contexts. This difficulty increases when procurement routines determine which practices become enforceable across tendering, contracting, and site execution. This study prioritized barriers to LCCE5.0 implementation in Morocco and translated expert judgments into actionable recommendations. A structured literature review informed the barrier inventory and conceptual framing. The study proposed a three-layer, life-cycle LCCE5.0 framework that links governance, operational routines, and digital enablers. It operationalized 40 critical barrier factors across six dimensions and five life-cycle macro-phases. A two-round Delphi study was conducted with 22 Moroccan experts using a 7-point Likert scale. Barriers were ranked using Round 2 (T2) medians with ties resolved using the interquartile range. Top-box agreement (ratings of 6–7) and consensus tiers were reported. The ranking showed strong stability across rounds, with 92.5% of barrier factors remaining stable. Kendall’s W at T2 equaled 0.817 (p < 0.001), indicating high panel consensus. Results indicated that constraints clustered in upstream governance. Three procurement-centered regulatory and contractual barriers topped the ranking (Mdn_T2 = 7). These barriers reflected missing CE procurement guidelines, limited weighting of environmental criteria, and the absence of circularity and digital requirements in tenders. Six additional barriers reinforced this procurement bottleneck. They included limited owner commitment, weak enforcement authority, limited top-management commitment, and regulatory instability. They also included low interorganizational trust, limited risk-sharing contracts, and tool-centered deployment of LCCE5.0 practices. These findings support procurement-focused recommendations to institutionalize auditable circular requirements and data-enabled verification in tendering and contracting routines. The proposed LCCE5.0 mechanism and the resulting recommendations require empirical validation beyond this Delphi-based prioritization.

Recycling doi: 10.3390/recycling11030062

Authors: Siti Nurkomariyah Dodik Ridho Nurrochmat Dikky Indrawan Harianto

Indonesia, as a major global textile exporter, faces substantial sustainability challenges due to its linear production model, which generates massive volumes of post-industrial polyester waste (PIPW). However, reliable data and recycling pathways remain critically lacking. This study quantifies the volume, composition, and textile-to-textile (T2T) recyclability potential of PIPW across Indonesia’s national textile and clothing production chain, employing a mixed-methods approach that integrates material flow analysis (MFA), site visits, and stakeholder interviews. The results indicate that 572 kilotonnes of PIPW were generated in 2023, with garment manufacturing identified as the most waste-intensive. Nineteen waste types were identified; 61% comprise fibre blends, which significantly constrain closed-loop recycling. A novel five-tier waste typology was developed to classify waste streams based on material characteristics, technological availability, and economic feasibility. The circularity map reveals that Indonesia is trapped in pseudo-circularity. Scenario analysis suggests that up to 184 kilotonnes of PIPW could be feasibly redirected towards higher-value chemical recycling. The research recommends mandatory source segregation, fiscal incentives, investment in chemical recycling infrastructure, and the integration of circular design into national standards. The study provides the first national-level MFA of PIPW in Indonesia and establishes an empirical baseline to advance T2T recycling in emerging economies.

Recycling doi: 10.3390/recycling11030061

Authors: Gidalti García Cabrera José Aurelio Sosa Olivier Guadalupe Hernández Gerónimo José Ramón Laines Canepa Alejandro Padilla Rivera Gabriel Núñez-Nogueira María del Carmen Cuevas Díaz

Greenhouse gas (GHG) emissions from sanitary waste (SW) are not usually quantified in institutional inventories, which limits the ability to assess its management and associated carbon footprint. This study establishes emission factors (EF) for SW generated in a higher education institution (HEI), focusing on toilet paper. In 2022, 19 sanitary waste sources were monitored, obtaining a per capita generation of 3.02 g person−1 day−1 and an annual total of 356.87 kg of SW. Samples were characterized through proximate and elemental analyses, applying stoichiometric calculations for two disposal-site degradation pathways: Aerobic: 841.95 kg (total climate indicator) t−1 SW, and Anaerobic: 7041.97 kg (total climate indicator) t−1. The arithmetic mean of the aerobic and anaerobic EFs was 3941.96 kg (total climate indicator) t−1 SW. Based on an estimated annual mass of 1.12 t yr−1, emissions ranged from 0.35 to 6.71 t yr−1 (total climate indicator: CO2 + CH4-derived CO2e) depending on the scenario. Emissions could be reduced by over 90% when aerobic degradation or controlled methane capture predominates. The results suggest that separating SW at its point of generation and ensuring that it undergoes aerobic or energy-recovery treatment processes can limit its contribution to institutional GHG inventories. Having material-specific EF enables quantitative comparison among management strategies and guides continuous-improvement decisions.

Recycling doi: 10.3390/recycling11030060

Authors: Tendai Tawonezvi Anele Sinto Mihle N. Qhina Dorcas Zide Emihle Mlotha Bernard J. Bladergroen

The strong adhesion between cathode materials and aluminium (Al) foil substrates presents a significant challenge in the recycling of spent lithium-ion batteries (LiBs). Conventionally, high temperatures and high concentrations of costly organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) are used to enhance ultrasonication-based delamination. In this study, a novel, eco-efficient approach was demonstrated for delaminating cathode materials from Al foil using a low-concentration organic citric-acid-assisted low-power ultrasonic treatment coupled with a gentle, low-power-per-volume mechanical mixing system at room temperature. The separation mechanism was attributed to the structure disruption, possibly swelling, of the polyvinylidene fluoride (PVDF) binder using low-concentration citric acid and the cavitation effects induced by ultrasound. Key parameters influencing the delamination efficiency included the solvent type, temperature, ultrasonic power, and treatment duration. Under optimised conditions, citric acid was used as the sonication reagent, with a process temperature of 20 °C, 60 W ultrasonic power, and 80 min of ultrasonication; a delamination efficiency of approximately 92% was achieved. The recovered cathode materials exhibited low agglomeration, favouring subsequent leaching processes. This work proposes an environmentally friendly and effective method for cathode and Al foil recovery from spent LiBs, integrating manual dismantling, ultrasonic treatment, and material separation.

Recycling doi: 10.3390/recycling11030059

Authors: Ruijiao Zhai Kui Huang Shanjin Mao Rugui Li Haili Dong Xi Zhai

Amid growing environmental pressure and increasing demand for resource sustainability, the efficient recovery of valuable metals from spent lithium-ion batteries (LIBs) has become a critical challenge in the field of resource recycling. Therefore, a novel approach is presented for selective lithium (Li) and manganese (Mn) separation from LiNixCoyMn1−x−yO2 by combining carbothermic reduction roasting and selective leaching. Low-cost glucose (C6H12O6) was selected as the reduction roasting reductant, which converts the cathode materials into water-soluble lithium carbonate (Li2CO3), water-insoluble cobalt (Co), nickel (Ni), and manganese oxide (MnO). Wet magnetic separation was employed to preferentially extract Li while simultaneously removing excess carbon from Ni, Co, and MnO. Under optimal roasting conditions at 600 °C for 90 min followed by wet magnetic separation with a liquid–solid ratio of 30 mL/g for 30 min, 95.42% of Li was preferentially extracted. Subsequently, at a formic acid (HCOOH) concentration of 1.6 mol/L, liquid–solid ratio of 6 mL/g, and leaching time of 30 min, 94.29% of Mn was selectively extracted from the wet magnetic separation products, whereas Ni and Co were leached at 6.13% and 7.22%, respectively. The acid-leaching residue can be recycled as a Ni-Co alloy.

Recycling doi: 10.3390/recycling11030058

Authors: Zhiji Gao Jin’an Xu Hanjie Qiu Maoxin Shi Siyao Li Rusheng Qian Jingchen Luo Fanli Wu Haibo Nie Tengfei Ma

Granite sawdust is a by-product in the process of stone processing, which is usually piled up, thus easily causing environmental pollution. To achieve resource utilization, granite sawdust was used as a partial substitution of cement in this work. The effects of different sawdust contents (10–50%) were systematically studied on the pore structure and the mechanical properties of its dry powder mortar. Combined with the grey correlation theory, the correlation between pore size distribution and compressive strength was analyzed. The results showed that the consistency and mechanical properties of the mortar gradually decreased along with the increasing sawdust content, while its critical pore-diameter decreased. The mortar performance was the best when its sawdust content is 10%, which meets the M25 technical requirements. When content reaches up to 30%, the mortar still met the strength standard of M20. Compared to fly ash, the mortar with 30% sawdust as the substitution has a higher water retention rate but lower mechanical strength. The grey correlation analysis indicated that the pores with diameters less than 10 nm and greater than 1000 nm had the most significant impact on the compressive strength.

Recycling doi: 10.3390/recycling11030056

Authors: Harrison Appiah Paul Asamoah Armando Gabriel McDonald

Rising global municipal solid waste (MSW) generation poses severe environmental and resource challenges, necessitating sustainable management strategies beyond landfilling. This review critically synthesizes thermochemical waste-to-energy (WtE) technologies, including incineration, pyrolysis, gasification, and hydrothermal carbonization, as viable pathways for converting heterogeneous MSW into energy (electricity, heat, syngas, bio-oil) and valuable materials (biochar, ash for construction). Drawing on recent literature, it highlights their superior greenhouse gas reductions, energy recovery efficiencies, and residue valorization potential compared to traditional disposal, while addressing persistent limitations such as feedstock variability, tar formation, high capital costs, and stringent emission controls. Advanced variants and integration with circular economy principles enhance feasibility, particularly in diverse regional contexts. Despite technical and economic barriers, thermochemical WtE offers a transformative approach to resource-efficient waste management, supporting zero-waste goals and renewable energy transitions when combined with optimized pre-treatment, policy incentives, and ongoing innovation in process efficiency and pollutant mitigation.

Recycling doi: 10.3390/recycling11030057

Authors: Ma. Guadalupe Plaza Maria Luisa Mendoza López José de Jesús Pérez Bueno Edain Belén Pérez Mendoza Martha Elva Pérez Ramos

Injection-molding purges are heterogeneous, bulky residues whose uncertain composition and irregular geometry hinder direct reinsertion, making cold shredding costly and maintenance-intensive. This work develops a low-infrastructure solar-assisted pre-processing route using a PMMA Fresnel lens to induce controlled sub-onset softening and enable clean shear cutting without destructive thermal histories. The sub-onset softening is here defined into a viscoelastically active range (at or above Tg for the amorphous phase) while remaining below the melting onset (Tm, onset) and below the onset of thermal degradation (Td, onset). The station was engineered via QFD and risk-oriented design tools, while a weighted Pugh matrix selected shear cutting over saw-based alternatives. A screening factorial DOE showed that lens height, angle, and their interaction significantly govern focal-spot diameter and receiver temperature, yielding linear relations for conservative set-point selection. Receiver benchmarking further indicated that copper reaches substantially higher temperatures than graphite under identical exposure conditions, supporting copper as the simplest, rapid-heating receiver. Under DOE-calibrated operation, tear-free shear cutting was achieved across representative purge families (PP–ABS, PC–ABS–PP, PA66, PA66-filler, and POM) without forced convection. From a recycling and waste-management perspective, the approach converts bulky purge scrap into mill-compatible feedstock with reduced mechanical resistance, lowering tool wear and fines generation, accelerating downsizing, and limiting stockpiling that elevates combustible-inventory fire risk. Overall, the proposed DOE-calibrated, operator-friendly framework improves recycling feasibility by enabling safer handling, more stable preprocessing throughput, and reduced reliance on disposal or long-term storage for heterogeneous industrial purges.

Recycling doi: 10.3390/recycling11030055

Authors: Jinzhao Li Xin Zuo Changchun Xin

The large-scale dredging activities in port areas generate substantial quantities of dredged soil, leading to land occupation and disposal challenges, while industrial wastes such as fly ash and desulfurization gypsum remain underutilized. In this study, industrial wastes were employed as a curing agent to stabilize dredged soil, aiming to achieve both mechanical performance improvement and cost-effective recycling. In total, 100 g of curing agent was added to 1 kg of sludge. The optimal strength-maximizing formulation comprised 4.5% activator 1 #, 4.5% fly ash, 4.5% mineral powder, and 0.5% desulfurization gypsum. It achieved an unconfined compressive strength of 0.794 MPa. For enhanced cost-effectiveness, a modified binder blend (1.88% activator 1 #, 4.5% fly ash, 4.5% mineral powder, and 0.5% desulfurization gypsum) delivered 0.63 MPa at 28 days, satisfying mechanical construction specifications. Results demonstrate that unconfined compressive strength increases with solid wastes; however, with the extension of solidification time, the unconfined compressive strength of dredged soil gradually slows down.

Recycling doi: 10.3390/recycling11030054

Authors: Javier Rodrigo Nahuat-Sansores Karla del Carmen García-Uitz Julio César Cruz-Argüello Carlos Andrés Ramírez-Pinto Ricardo Enrique Vega-Azamar Danna Lizeth Trejo-Arroyo Yazmin Vidal Valdez

Sugarcane bagasse ash (SCBA) has been widely studied as a partial supplementary cementitious material; nonetheless, its hydration behavior and performance when combined with nanoscale modifiers remain insufficiently understood. The aim of this study is to assess the pozzolanic potential of SCBA, the hydration behavior of binary SCBA–cement composites and the mechanical performance of ternary mortars with silica nanoparticles (Si-NPs). SCBA reactivity was confirmed by a Chapelle index of ~300 mg Ca(OH)2/g, while hydration development in binary pastes (5–20 wt% SCBA) was quantified using TG/dTG and semi-quantitative XRD. Low SCBA replacement levels (5–10 wt%) enhanced the hydration degree by up to ~12% at 28 days compared with the reference paste. Ternary mortars incorporating 5 wt% SCBA and Si-NPs exhibited significant strength gains, with the optimal blend (2.5 wt% Si-NPs) achieving a 42% increase in 28-day compressive strength relative to the reference mortar. A sustainability assessment showed concurrent reductions in clinker intensity and CO2 intensity of approximately 33% and 32%, respectively. These findings support the sustainable and technical viability of combining agro-industrial waste and nanotechnology as complementary strategies for reducing clinker content while enhancing eco-efficiency in alternative cementitious composites.