Clean Technologies

24 pages, 9291 KiB

Open AccessArticle

The Efficiency of Chlorella vulgaris in Heavy Metal Removal: A Comparative Study of Mono- and Multi-Component Metal Systems

by Eleni Kyratzopoulou, Nikoletta Kyzaki, Lamprini Malletzidou, Evangelos Nerantzis and Nikolaos A. Kazakis

Clean Technol. 2025, 7(2), 35; https://doi.org/10.3390/cleantechnol7020035 - 18 Apr 2025

Abstract

The occurrence of heavy metals in aquatic ecosystems is a serious environmental hazard, and their effective removal is imperative. In this regard, the feasibility of living microalga Chlorella vulgaris (C. vulgaris) to remove heavy metals (Ni, Pb, Zn, Cd, and Cu) [...] Read more.

The occurrence of heavy metals in aquatic ecosystems is a serious environmental hazard, and their effective removal is imperative. In this regard, the feasibility of living microalga Chlorella vulgaris (C. vulgaris) to remove heavy metals (Ni, Pb, Zn, Cd, and Cu) is investigated by using 1, 5, and 10 ppm concentrations of single- and multiple-metal-treated (MT) cultures. Experiments were performed in controlled laboratory conditions, and metal removal analysis was performed through atomic absorption spectroscopy (AAS). The cultures were also examined by means of optical microscopy, UV-Vis spectrophotometry, and Fourier transform infrared (FTIR) spectroscopy to follow the cultures’ pigment content, cell population, and functional group changes during cultivation. The removal efficiency results of both single and multiple MT cultures were evaluated using the Langmuir isotherm model. The results indicate that C. vulgaris presents potential for heavy metal bioremediation, even towards multi-MT conditions, despite the influence of a competitive uptake in multi-MT cultures. In mono-MT cultures, the removal efficiency of C. vulgaris presents values of 65–99% on Day 3 and 72–99% on Day 7 of cultivation, while the results for the multi-MT cultures are 49–99% and 62–99% for Days 3 and 7 of cultivation, respectively. The research illustrates the potential for C. vulgaris as a promising biosorbent for heavy metal remediation along with its post-treatment use in applications supporting the green circular economy. Full article

(This article belongs to the Special Issue Pollutant Removal from Aqueous Solutions by Adsorptive Biomaterials)

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21 pages, 5728 KiB

Open AccessArticle

Hydroxyapatite-Based Adsorbent Materials from Aquaculture Waste for Remediation of Metal-Contaminated Waters: Investigation of Cadmium Removal

by Mirco Cescon, Francesco Chiefa, Tatiana Chenet, Maura Mancinelli, Claudia Stevanin, Annalisa Martucci and Luisa Pasti

Clean Technol. 2025, 7(2), 34; https://doi.org/10.3390/cleantechnol7020034 - 14 Apr 2025

Abstract

Adsorption represents an effective strategy for water remediation applications, particularly when utilising eco-friendly materials in a circular economy framework. This approach offers significant advantages, including low cost, material availability, ease of operation, and high efficiency. Herein, the performance of cadmium ion adsorption onto [...] Read more.

Adsorption represents an effective strategy for water remediation applications, particularly when utilising eco-friendly materials in a circular economy framework. This approach offers significant advantages, including low cost, material availability, ease of operation, and high efficiency. Herein, the performance of cadmium ion adsorption onto hydroxyapatites, derived through a calcination-free process from shells of two mollusc species, Queen Scallop (Aequipecten opercularis) and Pacific Oyster (Magallana gigas), is examined. The phase and morphology of the synthesised adsorbents were investigated. The results showed that hydroxyapatites obtained from mollusc shells are characterised by high efficiency regarding cadmium removal from water, exhibiting rapid kinetics with equilibrium achieved within 5 min and high adsorption capacities up to 334.9 mg g⁻¹, much higher than many waste-based adsorbents reported in literature. Structural investigation revealed the presence of Cadmium Hydrogen Phosphate Hydrate in the hydroxyapatite derived from oyster shells loaded with Cd, indicating the formation of a solid solution. This finding suggests that the material not only has the capability to decontaminate but also to immobilise and store Cd. Overall, the results indicate that hydroxyapatites prepared via a synthetic route in mild conditions from waste shells are an economical and efficient sorbent for heavy metals encountered in wastewater. Full article

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15 pages, 1916 KiB

Open AccessArticle

Member Size Effect in Seebeck Coefficient of Cement Composites Incorporating Silicon Carbide

by Byeong-Hun Woo, Kyu-Tae Park, Kyung-Suk Yoo and Jee-Sang Kim

Clean Technol. 2025, 7(2), 33; https://doi.org/10.3390/cleantechnol7020033 - 11 Apr 2025

Abstract

This study investigates the size effect on the Seebeck coefficient (SC) in cement composites incorporating silicon carbide (SiC). Two specimen shapes, cubic (50 × 50 × 50 mm³) and beam (40 × 40 × 160 mm³), were analyzed with [...] Read more.

This study investigates the size effect on the Seebeck coefficient (SC) in cement composites incorporating silicon carbide (SiC). Two specimen shapes, cubic (50 × 50 × 50 mm³) and beam (40 × 40 × 160 mm³), were analyzed with varying SiC substitution ratios (0%, 50%, and 100%) for fine aggregates. Thermal and electrical conductivities were measured to assess their influence on the SC. The results showed that a higher SiC content increased porosity, which reduced mechanical strength but significantly improved thermal and electrical conductivities. Thermal conductivity increased from 1.88 W/mK (0% substitution) to 11.89 W/mK (100% substitution), while electrical conductivity showed an improvement from 0.0056 S/m to 0.065 S/m. Cubic specimens exhibited higher SC values compared to beam specimens, with a maximum SC of 1374 μV/K at 100% SiC substitution, attributed to shorter thermal diffusion distances. The findings suggest that optimizing member size and SiC content can significantly improve the thermoelectric performance of cement composites, potentially enhancing energy efficiency in construction applications. Full article

(This article belongs to the Special Issue Latest Advances in Renewable Energy Technologies)

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15 pages, 1903 KiB

Open AccessArticle

Physicochemical Composition and Features of Skeleton Fractions Obtained from Fish Hydrolysate Production: Exploring Valuable Ca/P Sources

by Miriam López-Álvarez, Sara Pérez-Davila, José Antonio Vázquez, Jesús Valcarcel, Julia Serra and Pío González

Clean Technol. 2025, 7(2), 32; https://doi.org/10.3390/cleantechnol7020032 - 11 Apr 2025

Abstract

The expansion of fisheries and aquaculture in recent decades has led to a substantial increase in fish by-products. This study investigates the extraction and characterization of calcium phosphates from the by-products of representative species in these industries, aiming to identify potential sources for [...] Read more.

The expansion of fisheries and aquaculture in recent decades has led to a substantial increase in fish by-products. This study investigates the extraction and characterization of calcium phosphates from the by-products of representative species in these industries, aiming to identify potential sources for biotechnological and pharmaceutical applications. Clean bones obtained by enzyme hydrolysis from the heads, central skeletons, and/or tails of Atlantic horse mackerel, blue whiting, hake, mackerel, and farmed turbot were subjected to calcination to obtain calcium phosphates. The clean bone content in terms of nitrogen, lipids, organic matter, total protein, and amino acids was evaluated together with the chemical bonds, structures, and elemental composition of calcium phosphates. Results indicated a significantly higher yield of wet bone recovery (23%, p < 0.05) for the central skeleton of Atlantic horse mackerel and the highest mineral fraction for the heads of Atlantic horse mackerel (73.2%), followed by that of blue whiting (72.6%). Hake and turbot presented the lowest mineral fractions and, therefore, the highest protein content (27–31%, p < 0.05), with significant levels of collagen-related amino acids (p < 0.05). X-ray diffraction (XRD) and Fourier-transform Raman spectroscopy (FT-Raman) confirmed the biphasic calcium phosphate composition for most samples based on hydroxyapatite with contributions of whitlockite/β-tricalcium phosphate. The highest contribution to the non-apatite phase was made by the central skeletons of both mackerel and Atlantic horse mackerel. Full article

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16 pages, 7109 KiB

Open AccessArticle

The Variability of Textural Properties and Drying Characteristics of Dehydrated Sewage Sludge

by Sergio Luis Parra-Angarita, Mohamad Wael Al Sayed and Angélique Léonard

Clean Technol. 2025, 7(2), 31; https://doi.org/10.3390/cleantechnol7020031 - 7 Apr 2025

Abstract

This study investigates the drying behavior and rheological properties of dehydrated sewage sludge from various wastewater treatment plants in the Liege region (Belgium). Emphasizing the characterization of key parameters to enhance sludge management strategies, a series of experiments were conducted, including total solid [...] Read more.

This study investigates the drying behavior and rheological properties of dehydrated sewage sludge from various wastewater treatment plants in the Liege region (Belgium). Emphasizing the characterization of key parameters to enhance sludge management strategies, a series of experiments were conducted, including total solid content (TSC) determination, volatile solid content (VSC) analysis, texture profile analysis (TPA), penetrometry, and oscillatory rheology tests. Results showed no significant trends between specific evaporation capacity and the analyzed variables, cohesiveness, TSC, VSC, hardness, yield, and flow point. However, a clear trend indicated that higher G′ values are associated with improved drying rates. This aligns with the existing literature, suggesting that the viscoelastic properties of sludge, represented by G′, could potentially predict drying performance. A strong correlation between G′ and cohesiveness was also observed, recommending the use of G′ as the primary parameter due to the standardization and reliability of rheological tests. Despite the limited sample size, the study provides a valuable starting point for future research. Further investigations with larger sample sizes and controlled laboratory conditions are recommended to validate these findings and establish ranges within which the studied properties can be useful for future calculations and analyses. These efforts will contribute to optimizing sludge drying processes and promoting sustainable wastewater treatment practices. Full article

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24 pages, 2151 KiB

Open AccessArticle

The Potential to Produce Bio-Based Ammonia Adsorbents from Lignin-Rich Residues

by Daniel Chernick, Valerie Dupont and Andrew B. Ross

Clean Technol. 2025, 7(2), 30; https://doi.org/10.3390/cleantechnol7020030 - 5 Apr 2025

Abstract

The ammonia adsorption capacity of lignin-rich biomass solids was tested for the first time at low partial pressures (<1.5 kPa) and 20 °C. The biomass samples included untreated tree barks, husks, and peats, as well as the biochars produced by their slow pyrolysis. [...] Read more.

The ammonia adsorption capacity of lignin-rich biomass solids was tested for the first time at low partial pressures (<1.5 kPa) and 20 °C. The biomass samples included untreated tree barks, husks, and peats, as well as the biochars produced by their slow pyrolysis. Proximate and ultimate analyses, lignin content, and metal content are also presented. The untreated biosolids had higher VM/FC ratios, molar H/C, and O/C than the treated biosolids (biochars and treated biochars). A novel methodology is described for the safe generation of gaseous ammonia at predictable low partial pressures from tabletop-scale batch reaction experiments of NaOH with (NH₄)₂SO₄ in aqueous solution, leading to the determination of ammonia adsorption capacities from low-cost experiments. Statistically significantly larger NH₃ adsorption capacities were obtained for the untreated biosolids than for their biochars (p < 0.001). In contrast, the biochars were found to be poor NH₃ adsorbers without further treatment. The NH₃ adsorption capacities from this study’s biosolids were compared with those of common adsorbent types in the same conditions using the existing literature through equilibrium model interpolation (Dubinin–Astakhov, Toth, and Freundlich) or cubic spline fit from graphical isotherms. Controls consisting of commercially sourced activated carbons (AC) had low adsorption capacities, close to those derived from the literature in the same conditions for similar materials, confirming the methodology’s robustness. The untreated biosolids’ NH₃ adsorption capacities were in the same range as those reported for silica, gamma-alumina, and some of the treated or doped ACs. They also performed better than the undoped, untreated ACs. The work suggests lignin-rich untreated biosolids such as barks and peats are competent low-cost ammonia adsorbents. Full article

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20 pages, 6520 KiB

Open AccessArticle

Effect of Gravel Size, Microwave Irradiation (1 to 2.5 min), Moisture, and Quenching on Aggregate Properties of Chert Gravel: Valorizing a “Waste” Byproduct of Sand Quarrying

by Mark Tzibulsky and Vladimir Frid

Clean Technol. 2025, 7(2), 29; https://doi.org/10.3390/cleantechnol7020029 - 3 Apr 2025

Abstract

Chert gravel, a byproduct of sand quarrying, remains an underutilized material in construction due to its low microwave (MW) absorption and high mechanical strength. The present study deals with the potential of MW irradiation as a novel, energy-efficient method for processing chert gravel [...] Read more.

Chert gravel, a byproduct of sand quarrying, remains an underutilized material in construction due to its low microwave (MW) absorption and high mechanical strength. The present study deals with the potential of MW irradiation as a novel, energy-efficient method for processing chert gravel into high-quality aggregates, reducing reliance on virgin materials. The research systematically examines MW exposure duration (1–2.5 min), rock size (150–800 g), moisture conditions, and cooling methods (air vs. water quenching) to optimize fragmentation. Experimental results indicate that larger rock sizes (600–800 g) yield coarser, less uniform aggregates, while prolonged MW exposure (>2 min) induces extensive micro-fracturing, producing finer, well-graded particles. Water quenching significantly intensifies fragmentation, generating irregular but highly fragmented aggregates, whereas pre-wetted samples exhibit finer and more uniform breakage than dry samples. The findings introduce a novel approach for optimizing chert gravel fragmentation, a material previously considered unsuitable for MW treatment. The study proposed a customizable methodology for tailoring aggregate properties through precise control of MW parameters, offering a sustainable alternative to conventional crushing. The results contribute to resource conservation, reduced energy consumption, and climate change mitigation, paving the way for more sustainable construction practices. Full article

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21 pages, 3520 KiB

Open AccessArticle

Carbon Credit Earned by Rooftop PV Systems: Assessing Opportunities for Carbon Market Adoption in the Ecuadorian Context

by Ruben Hidalgo-Leon, Jose Campoverde-Gil, Jaqueline Litardo, Miguel Torres, Maria Luisa Granda, Viviana Villavicencio, Scarleth Vasconcelos, Cristian A. Hernandez, Juan Solano-Aguirre, Pritpal Singh and Guillermo Soriano

Clean Technol. 2025, 7(2), 28; https://doi.org/10.3390/cleantechnol7020028 - 1 Apr 2025

Abstract

This study assessed the techno-economic and environmental feasibility of a grid-connected PV system on a university building, with a focus on potential revenue from carbon credit sales. The analysis assumes a regulated CO₂ emissions market in Ecuador and references carbon credit prices [...] Read more.

This study assessed the techno-economic and environmental feasibility of a grid-connected PV system on a university building, with a focus on potential revenue from carbon credit sales. The analysis assumes a regulated CO₂ emissions market in Ecuador and references carbon credit prices from the European Union, New Zealand, China, and the Republic of Korea. Seven PV system configurations, varying in size and capacity, were modeled using Homer Pro and assessed for their techno-economic feasibility and environmental performance. The results indicated that the 166 kWp system was the most promising, supplying approximately 74% of the building’s electricity demand. Thus, this system was selected as the baseline for evaluating potential revenues from carbon credit sales in international markets, based on average carbon prices in 2022. The selected markets generated annual revenues of USD 4410.68, USD 2587.55, USD 446.34, and USD 958.37, respectively. While these additional revenues improved the Net Present Value (NPV) of the 166 kWp system, the overall NPV remained negative due to the high initial investment costs. Full article

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18 pages, 3782 KiB

Open AccessArticle

Thermal Performance and Cost Assessment Analysis of a Double-Pass V-Trough Solar Air Heater

by Eduardo Venegas-Reyes, Naghelli Ortega-Avila, Yuridiana Rocio Galindo-Luna, Jonathan Ibarra-Bahena, Erick Cesar López-Vidaña and Ulises Dehesa-Carrasco

Clean Technol. 2025, 7(1), 27; https://doi.org/10.3390/cleantechnol7010027 - 18 Mar 2025

Abstract

Solar air heating systems offer an effective alternative for reducing greenhouse gas emissions at a profitable cost. This work details the design, construction, and experimental evaluation of a novel double-pass V-trough solar air heater with semicircular receivers, which was built with low-cost materials [...] Read more.

Solar air heating systems offer an effective alternative for reducing greenhouse gas emissions at a profitable cost. This work details the design, construction, and experimental evaluation of a novel double-pass V-trough solar air heater with semicircular receivers, which was built with low-cost materials readily available in the Mexican market. Thermal performance tests were conducted in accordance with the ANSI-ASHRAE 93-2010 standard. The results indicated a peak collector efficiency of 0.4461 and total heat losses of 8.8793 W/(m² °C), with an air mass flow rate of 0.0174 kg/s. The instantaneous thermal efficiency varied between 0.2603 and 0.5633 with different air flow rates and an inlet air temperature close to the ambient temperature. The outlet air temperature reached 70 °C, making it suitable for dehydrating fruits or vegetables at competitive operating costs. Additionally, a second-law analysis was carried out, and the exergy efficiency was between 0.0037 and 0.0407. Finally, a Levelized Cost of Energy analysis was performed, and the result was USD 0.079/kWh, which was 31% lower than that of a conventional electric air heater system. Full article

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14 pages, 5290 KiB

Open AccessArticle

Recycling-Oriented Characterization of Space Waste Through Clean Hyperspectral Imaging Technology in a Circular Economy Context

by Giuseppe Bonifazi, Idiano D’Adamo, Roberta Palmieri and Silvia Serranti

Clean Technol. 2025, 7(1), 26; https://doi.org/10.3390/cleantechnol7010026 - 14 Mar 2025

Abstract

Waste management is one of the key areas where circular models should be promoted, as it plays a crucial role in minimizing environmental impact and conserving resources. Effective material identification and classification are essential for optimizing recycling processes and selecting the appropriate production [...] Read more.

Waste management is one of the key areas where circular models should be promoted, as it plays a crucial role in minimizing environmental impact and conserving resources. Effective material identification and classification are essential for optimizing recycling processes and selecting the appropriate production equipment. Proper sorting of materials enhances both the efficiency and sustainability of recycling systems. The proposed study explores the potential of using a cost-effective strategy based on hyperspectral imaging (HSI) to classify space waste products, an emerging challenge in waste management. Specifically, it investigates the use of HSI sensors operating in the near-infrared range to detect and identify materials for sorting and classification. Analyses are focused on textile and plastic materials. The results show promising potential for further research, suggesting that the HSI approach is capable of effectively identifying and classifying various categories of materials. The predicted images achieve exceptional sensitivity and specificity, ranging from 0.989 to 1.000 and 0.995 to 1.000, respectively. Using cost-effective, non-invasive HSI technology could offer a significant improvement over traditional methods of waste classification, particularly in the challenging context of space operations. The implications of this work identify how technology enables the development of circular models geared toward sustainable development hence proper classification and distinction of materials as they allow for better material recovery and end-of-life management, ultimately contributing to more efficient recycling, waste valorization, and sustainable development practices. Full article

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21 pages, 2981 KiB

Open AccessArticle

Nitrogen-Doped Porous Waste Biomass as a Sustainable Adsorbent for CO₂ Capture: The Influence of Preparation Conditions

by Christiano B. Peres, Leandro C. Morais and Pedro R. Resende

Clean Technol. 2025, 7(1), 25; https://doi.org/10.3390/cleantechnol7010025 - 12 Mar 2025

Abstract

In the context of global warming, technologies and studies aimed at mitigating carbon dioxide (CO₂) have become increasingly relevant. One such technology is CO₂ capture by activated and functionalized N-doped carbon from biomasses. This paper explores the ways to find [...] Read more.

In the context of global warming, technologies and studies aimed at mitigating carbon dioxide (CO₂) have become increasingly relevant. One such technology is CO₂ capture by activated and functionalized N-doped carbon from biomasses. This paper explores the ways to find the optimal CO₂ adsorption conditions, based on the carbonization temperature, impregnation rate, and preparation method, considering four different preparation routes in activated and functionalized carbon-N (PCs) of banana peel biomass residues. PCs were produced and chemically activated by K₂C₂O₄ and H₂O and functionalized by ethylenediamine (EDA). Carbon dioxide capture was investigated using functional density theory (DFT). Nitrogen (N) doping was confirmed by X-ray photoelectron spectroscopy (XPS), while the thermal characteristics were examined by thermogravimetric analysis (TGA). Surface morphology was examined by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) detection, and surface functional groups were characterized using Fourier-transform infrared (FTIR) spectroscopy. In addition, the inorganic components were characterized by X-ray diffraction (XRD). The best performance of CO₂ adsorption of 1.69 mmol/g was achieved at 0 °C and 1 bar over the adsorbent synthesized at 600 °C with 60 min residence time, a 1:1 degree of impregnation, and a dry preparation method (single-stage preparation). This work presents as a great innovation the use of biomass as a raw material in the adsorption of the main greenhouse gases, using easy and accessible products. Full article

(This article belongs to the Special Issue Green Solvents and Materials for CO₂ Capture)

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26 pages, 858 KiB

Open AccessArticle

Environmental Implications of Drone-Based Delivery Systems: A Structured Literature Review

by Abhijeet Kumar, Victor Prybutok and Vikas Kumar Reddy Sangana

Clean Technol. 2025, 7(1), 24; https://doi.org/10.3390/cleantechnol7010024 - 12 Mar 2025

Abstract

This study presents a structured review of 59 academic articles, identified through an extensive literature survey, focused on the environmental implications of drone-based delivery systems within the broader fields of transportation, logistics, and sustainability. The reviewed journals cover a multidisciplinary range of topics, [...] Read more.

This study presents a structured review of 59 academic articles, identified through an extensive literature survey, focused on the environmental implications of drone-based delivery systems within the broader fields of transportation, logistics, and sustainability. The reviewed journals cover a multidisciplinary range of topics, reflecting the intersection of drone technology with environmental science, logistics management, and operational research. Key journals, such as Transportation Research Part C: Emerging Technologies, Computers and Industrial Engineering, and Applied Mathematical Modelling, offer critical insights into how drone technology can reshape logistics systems, reduce environmental impacts, and contribute to intelligent transportation solutions. In addition, niche publications in areas like artificial intelligence, disaster risk reduction, and sustainable transportation further enhance the breadth of this review. By identifying and categorizing these publications, this review provides a valuable resource for researchers and practitioners aiming to explore the environmental and operational challenges of drone-based delivery systems, while also offering a foundation for future research on their sustainability and integration into existing logistics frameworks. Full article

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31 pages, 9587 KiB

Open AccessArticle

Multi-Criteria Optimization of a Hybrid Renewable Energy System Using Particle Swarm Optimization for Optimal Sizing and Performance Evaluation

by Shree Om Bade, Olusegun Stanley Tomomewo, Ajan Meenakshisundaram, Maharshi Dey, Moones Alamooti and Nabil Halwany

Clean Technol. 2025, 7(1), 23; https://doi.org/10.3390/cleantechnol7010023 - 7 Mar 2025

Abstract

The major challenges in designing a Hybrid Renewable Energy System (HRES) include selecting appropriate renewable energy sources and storage systems, accurately sizing each component, and defining suitable optimization criteria. This study addresses these challenges by employing Particle Swarm Optimization (PSO) within a multi-criteria [...] Read more.

The major challenges in designing a Hybrid Renewable Energy System (HRES) include selecting appropriate renewable energy sources and storage systems, accurately sizing each component, and defining suitable optimization criteria. This study addresses these challenges by employing Particle Swarm Optimization (PSO) within a multi-criteria optimization framework to design an HRES in Kern County, USA. The proposed system integrates wind turbines (WTS), photovoltaic (PV) panels, Biomass Gasifiers (BMGs), batteries, electrolyzers (ELs), and fuel cells (FCs), aiming to minimize Annual System Cost (ASC), minimize Loss of Power Supply Probability (LPSP), and maximize renewable energy fraction (REF). Results demonstrate that the PSO-optimized system achieves an ASC of USD6,336,303, an LPSP of 0.01%, and a REF of 90.01%, all of which are reached after 25 iterations. When compared to the Genetic Algorithm (GA) and hybrid GA-PSO, PSO improved cost-effectiveness by 3.4% over GA and reduced ASC by 1.09% compared to GAPSO. In terms of REF, PSO outperformed GA by 1.22% and GAPSO by 0.99%. The PSO-optimized configuration includes WT (4669 kW), solar PV (10,623 kW), BMG (2174 kW), battery (8000 kWh), FC (2305 kW), and EL (6806 kW). Sensitivity analysis highlights the flexibility of the optimization framework under varying weight distributions. These results highlight the dependability, cost-effectiveness, and sustainability for the proposed system, offering valuable insights for policymakers and practitioners transitioning to renewable energy systems. Full article

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23 pages, 6146 KiB

Open AccessArticle

Design and Implementation of a Low-Pressure Briquetting Machine for the Use of Pinus spp. Wood Residues: An Approach to Appropriate Rural Technology

by Mario Morales-Máximo, Víctor Manuel Ruíz-García, José Guadalupe Rutiaga-Quiñones and Luis Bernado López-Sosa

Clean Technol. 2025, 7(1), 22; https://doi.org/10.3390/cleantechnol7010022 - 6 Mar 2025

Abstract

This research analyzes the technical feasibility and implementation of an appropriate technology for the production of briquettes from Pinus spp. waste (sawdust and shavings) in a rural community in Michoacán, Mexico. The results indicate that local small-scale briquette production in the Pichátaro community [...] Read more.

This research analyzes the technical feasibility and implementation of an appropriate technology for the production of briquettes from Pinus spp. waste (sawdust and shavings) in a rural community in Michoacán, Mexico. The results indicate that local small-scale briquette production in the Pichátaro community has the potential to boost a local economy based on the manufacturing and marketing of densified solid biofuels. The design of the manual briquetting machine was developed through a participatory approach with community users. Structural simplicity and locally accessible maintenance were prioritized, the aspects that were addressed little in previous studies. The machine allows for the production of briquettes using a low-cost mixture composed of sawdust and Pinus spp. shavings, corn starch, and water. Based on local conditions and production needs, parameters such as reduced processing times and simplified manufacturing methods were identified as essential to establishing an efficient regional production and supply chain. Furthermore, the valorization of solid waste through the production of alternative biofuels contributes to the diversification of the energy matrix in rural residential sectors and small industries in communities in Mexico. The estimated cost of the machine is USD 75.44, and most of its components are easily replaceable, which favors its sustainability and prolonged use. This study demonstrates that the implementation of a low-pressure briquette system based on appropriate rural technologies represents a viable strategy for the use of wood waste and the promotion of sustainable energy solutions in rural communities. Full article

(This article belongs to the Special Issue Sustainable Biofuel and Biochemical Production from Lignocellulosic Biomass)

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16 pages, 15608 KiB

Open AccessArticle

Financial Feasibility of Bioenergy Products Based on Forest Residues: Case of Costa Rica Northern

by Juan Carlos Valverde, Dagoberto Arias-Aguilar and Rooel Campos-Rodríguez

Clean Technol. 2025, 7(1), 21; https://doi.org/10.3390/cleantechnol7010021 - 6 Mar 2025

Abstract

This research identified the optimal scenarios to produce three bioenergy outputs: dual generation (electricity and heat), electricity, and heat in two regions located in the northern part of Costa Rica. Two biomass conversion technologies—boilers and gasification—with 2, 5, and 10 MW production capacities [...] Read more.

This research identified the optimal scenarios to produce three bioenergy outputs: dual generation (electricity and heat), electricity, and heat in two regions located in the northern part of Costa Rica. Two biomass conversion technologies—boilers and gasification—with 2, 5, and 10 MW production capacities were assessed to ascertain the most suitable technology-capacity pairing for each bioproduct. To this end, a comprehensive financial model was developed to maximize the net present value. Following this, the equilibrium point for biomass supply and demand was ascertained, alongside estimations of the associated costs and energy utility. The findings indicated that the three bioenergy products could be completed within the local energy market at prices below 0.14 USD/kWh, with maximum supply distances of 90 km. The boiler and turbine technology proved most suitable for dual and electricity generation, with capacities ranging between 2 MW and 5 MW, where differentiation was influenced by biomass transportation. Furthermore, heat generation demonstrated financial viability at a capacity of 2 MW. In the evaluation of supply-demand break-even points, a maximum benefit of 26% was observed, with dual production yielding the highest benefits and heat production being the least favorable option due to the costs linked to biomass transportation and the low efficiency of energy transformation. Full article

(This article belongs to the Collection Bioenergy Technologies)

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41 pages, 2447 KiB

Open AccessReview

Addressing Plastic Waste Challenges in Africa: The Potential of Pyrolysis for Waste-to-Energy Conversion

by Milon Selvam Dennison, Sathish Kumar Paramasivam, Titus Wanazusi, Kirubanidhi Jebabalan Sundarrajan, Bubu Pius Erheyovwe and Abisha Meji Marshal Williams

Clean Technol. 2025, 7(1), 20; https://doi.org/10.3390/cleantechnol7010020 - 5 Mar 2025

Abstract

Plastic waste poses a significant challenge in Africa and around the world, with its volume continuing to increase at an alarming rate. In Africa, an estimated 25–33% of daily waste is made up of plastic, posing a threat to the environment, marine life, [...] Read more.

Plastic waste poses a significant challenge in Africa and around the world, with its volume continuing to increase at an alarming rate. In Africa, an estimated 25–33% of daily waste is made up of plastic, posing a threat to the environment, marine life, and human health. One potential solution to this problem is waste-to-energy recycling, such as pyrolysis, which involves the conversion of waste materials into oil, char, and non-condensable gasses through a thermochemical process in the absence of oxygen. Given the abundance of waste in Africa and the continent’s energy challenges, pyrolysis offers a sustainable solution. This review delves into the concept of pyrolysis, its products, thermodynamics, and endothermic kinetics, presenting it as a promising way to address the plastic waste problem in Africa. Despite the African Union’s goal to recycle plastic waste, the continent faces significant barriers in achieving this target, including infrastructural, economic, and social difficulties. It is crucial to implement sustainable strategies for managing plastic waste in Africa to mitigate environmental degradation and promote a cleaner and healthier living environment. Pyrolysis technology is highlighted as a viable solution for plastic waste management, as it can convert plastic waste into valuable byproducts such as oil, char, and syngas. Case studies from countries like South Africa and Nigeria demonstrate the potential for scaling up pyrolysis to address waste management issues while generating energy and job opportunities. This review underscores the need for investment, regulatory support, and public awareness to overcome the challenges and unlock the full potential of pyrolysis in Africa. Embracing pyrolysis as a method for managing plastic waste could lead to significant environmental and economic benefits for the continent. Full article

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17 pages, 3519 KiB

Open AccessArticle

Application of Plasma Treatment on Coliform Inactivation, Dehydration Kinetics and Quality Attributes of Powder-Form Nutraceuticals

by Majid Soleimani and Oon-Doo Baik

Clean Technol. 2025, 7(1), 19; https://doi.org/10.3390/cleantechnol7010019 - 3 Mar 2025

Abstract

This study was conducted to determine the performance of atmospheric cold plasma (ACP) on powder-form biological materials including wheat flour (WF) and whey protein isolate (WP). Coliform bacteria inactivation and optimization were performed based on a central composite design with two variables, namely [...] Read more.

This study was conducted to determine the performance of atmospheric cold plasma (ACP) on powder-form biological materials including wheat flour (WF) and whey protein isolate (WP). Coliform bacteria inactivation and optimization were performed based on a central composite design with two variables, namely residence time and mass of the sample. The results indicated that both variables had a significant effect on bacterial inactivation with more importance of residence time compared to mass of the substrate. The drying process was conducted for selected conditions including mild, moderate, and extreme conditions. The results indicated that plasma can even be used as a fast and effective tool for drying biological materials. Among all models used in this study, the Henderson–Pabis model was more suitable in predicting the dehydration kinetics of both materials. Drying rate constants obtained using this model indicated that the ratios of residence time over mass of the material did not have a significant impact on this parameter. Analysis of the functional properties revealed that water absorption can be highly (≈70%) enhanced in WF. However, properties such as oil absorption (in WF and WP), protein solubility and emulsifying activity index (EAI), and stability (in WP) were slightly changed by the plasma treatment. Full article

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19 pages, 2154 KiB

Open AccessArticle

Modeling of CO₂ Capture by Electro-Swing Reactive Adsorption from Low-Concentration Streams

by Célisse Chevrel, Paul de Joannis, Christophe Castel and Olivier Authier

Clean Technol. 2025, 7(1), 18; https://doi.org/10.3390/cleantechnol7010018 - 21 Feb 2025

Abstract

This article investigates the performance of Faradaic electro-swing reactive adsorption (ESA) for CO₂ capture using simulations. Traditional methods such as amine scrubbing face energy efficiency challenges, particularly at low CO₂ concentrations. ESA, which uses electricity for CO₂ regeneration, offers a [...] Read more.

This article investigates the performance of Faradaic electro-swing reactive adsorption (ESA) for CO₂ capture using simulations. Traditional methods such as amine scrubbing face energy efficiency challenges, particularly at low CO₂ concentrations. ESA, which uses electricity for CO₂ regeneration, offers a promising alternative due to its isothermal operation and scalability. The study models ESA using quinone-based redox-active CO₂ carriers in an electrochemical cell with an ionic liquid electrolyte, allowing reversible adsorption and release through voltage control. The model estimates system productivity and energy consumption, considering transport and chemical kinetics. Key findings show that operating parameters, such as applied potential and gas flow rate, have a significant effect on efficiency. Applying a potential of −1.3 V improved the adsorption capacity, reducing CO₂ capture time compared to −1.1 V. At a 1% CO₂ concentration and a low flow rate, effective capture resulted in a productivity of 1.6 kg/(m³·day) with an energy consumption of 0.6 MWh/tCO₂. However, higher gas flow rates reduced capture efficiency due to CO₂ transport limitations in the ionic liquid. Optimization of electrode design is essential to improve ESA efficiency. Full article

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26 pages, 7119 KiB

Open AccessArticle

High-Temperature Steam- and CO₂-Assisted Gasification of Oil Sludge and Petcoke

by Sergey M. Frolov, Viktor A. Smetanyuk, Ilyas A. Sadykov, Anton S. Silantiev, Fedor S. Frolov, Vera Ya. Popkova, Jaroslav K. Hasiak, Anastasiya G. Buyanovskaya, Rina U. Takazova, Tatiana V. Dudareva, Valentin G. Bekeshev, Alexey B. Vorobyov, Alexey V. Inozemtsev and Jaroslav O. Inozemtsev

Clean Technol. 2025, 7(1), 17; https://doi.org/10.3390/cleantechnol7010017 - 14 Feb 2025

Abstract

A new high-temperature allothermal gasification technology is used to process three types of oil waste: ground oil sludge (GOS), tank oil sludge (TOS), and petcoke. The gasifying agent (GA), mainly composed of H₂O and CO₂ at a temperature above 2300 [...] Read more.

A new high-temperature allothermal gasification technology is used to process three types of oil waste: ground oil sludge (GOS), tank oil sludge (TOS), and petcoke. The gasifying agent (GA), mainly composed of H₂O and CO₂ at a temperature above 2300 K and atmospheric pressure, is produced by pulsed detonations of a near-stochiometric methane-oxygen mixture. The gasification experiments show that the dry off-gas contains 80–90 vol.% combustible gas composed of 40–45 vol.% CO, 28–33 vol.% H₂, 5–10 vol.% CH₄, and 4–7 vol.% noncondensable C₂–C₃ hydrocarbons. The gasification process is accompanied by the removal of mass from a flow gasifier in the form of fine solid ash particles with a size of about 1 μm. The ash particles have a mesoporous structure with a specific surface area ranging from 3.3 to 15.2 m²/g and pore sizes ranging from 3 to 50 nm. The measured wall temperatures of the gasifier are in reasonable agreement with the calculated value of the thermodynamic equilibrium temperature of the off-gas. The measured CO content in the off-gas is in good agreement with the thermodynamic calculations. The reduced H₂ content and elevated contents of CH₄, CO₂, and C_xH_y are apparently associated with the nonuniform distribution of the waste/GA mass ratio in the gasifier. To increase the H₂ yield, it is necessary to improve the mixing of waste with the GA. It is proposed to mix crushed petcoke with oil sludge to form a paste and feed the combined waste into the gasifier using a specially designed feeder. Full article

(This article belongs to the Special Issue Gasification and Pyrolysis of Biomass and Waste)

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