Search Results (1,560)

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. Full article

This study presents a comprehensive multi-objective optimization of sewage wastewater treatment using bio-based coagulants, guided by the Grey Wolf Optimizer (GWO) and its multi-objective variant (MOGWO). Experimental coagulation data, employing Citrullus lanatus and Cucumis melo as natural coagulants, were modeled using multivariate regression techniques, yielding high coefficients of determination (R² > 0.95) across key water quality parameters. The optimization process targeted maximal reductions in turbidity, total suspended solids (TSS), biochemical oxygen demand (BOD), and chemical oxygen demand (COD) through strategic manipulation of pH and coagulant dosage. The single-objective GWO achieved significant outcomes, including a 96.68% turbidity reduction at pH 5 and 50 mg/L dosage. The MOGWO algorithm identified Pareto-optimal solutions, such as a 94.2% turbidity reduction at pH 5 and 72 mg/L dosage, and a balanced BOD reduction of 52.7% at pH 7. The predictive models indicated that optimal treatment conditions could reduce chemical usage by up to 90% compared to conventional coagulants, resulting in potential cost savings of up to 30%. Moreover, the algorithms demonstrated rapid convergence, averaging 200 iterations, highlighting their computational efficiency and robustness. These findings illustrate that integrating bio-based coagulants with advanced optimization techniques can achieve high treatment efficiency while reducing chemical inputs, thus directly supporting environmental sustainability by minimizing sludge and secondary pollution. In this situation, the wastewater treatment plant will focus on resource-recovery systems with less or no waste at the end of the treatment process. This approach aligns with circular economy principles by promoting eco-friendly, cost-effective wastewater treatment solutions suitable for resource-limited settings. The study offers a forward-looking pathway for environmentally responsible wastewater management practices that significantly reduce chemical dependency and contribute to pollution mitigation efforts. Full article

In municipal wastewater treatment plants (WWTPs), anaerobic digestion of municipal mixed sludge (MMS) often yields low energy recovery and operational instability due to imbalances between primary and secondary sludges. Anaerobic co-digestion (AcoD) with readily biodegradable wastes, such as fruit and vegetable waste (FVW), can enhance process stability and biogas production. Life cycle assessment (LCA) methodology is used in this study to evaluate the environmental performance of implementing AcoD of MMS and FVW in a municipal WWTP, compared with a business-as-usual scenario combining mono-digestion of MMS and incineration of FVW. The LCA was modelled in openLCA 2.5 using the ecoinvent 3.9.1 database (cut-off allocation approach), and impacts were assessed with the ReCiPe 2016 Midpoint (H) method, focusing on climate change, terrestrial acidification, fossil fuel depletion, and marine eutrophication. Results indicate that AcoD reduces impacts across all environmental categories, mainly due to higher biogas yields that increase on-site electricity generation and decrease reliance on grid electricity. Improved total solids removal also lowers digestate production and composting-related burdens. Electricity consumption remains the main hotspot in both scenarios, highlighting the importance of energy efficiency and electricity mix. Sensitivity analysis on methane content (61–65% v/v) confirms the robustness of AcoD’s environmental benefits. Full article

Sewage sludge management remains a critical challenge in Greece, where increasing regulatory pressure, environmental constraints, and limited stakeholder participation complicate regional decision-making. In particular, the revision of regional Waste Management Plans requires decision-support approaches that are both technically robust and socially legitimate. This study develops and applies a participatory, data-driven multi-criteria decision analysis framework to evaluate sustainable sewage sludge management strategies in the Region of Eastern Macedonia and Thrace. The framework combines structured stakeholder participation with quantitative performance assessment, enabling transparent, reproducible, and systematic comparison of alternative sewage sludge management options. Four realistic sludge management alternatives—composting fr agriculture, forestry use, land restoration, and thermal drying with energy recovery were assessed against fifteen economic, environmental, and social sub-criteria. Data were collected through structured questionnaires administered to forty-four representatives from five stakeholder groups: utilities (water and sewerage service providers), local authorities, scientists/experts, end-users, and citizens. Group preferences were aggregated using equal group weighting to ensure balanced representation. The results show that environmental and economic criteria outweigh social aspects. The highest mean weights were assigned to compliance with environmental requirements for products derived from the disposal method (0.105) and compliance with stricter national environmental legislation (0.104), followed by energy intensity (0.097), installation cost (0.065), and operation and maintenance (O&M) cost (0.061). Overall rankings identified composting and thermal drying as the most preferred options, followed by land restoration and forestry use; sensitivity analysis (±10% variation in sub-criterion weights) confirmed ranking stability. The proposed framework enhances decision transparency by embedding measurable criteria and stakeholder inputs within a structured analytical process. From a policy perspective, it addresses participation gaps in Greek waste planning and offers a transferable decision-support tool for future regional planning. Further extensions may include integration with life cycle assessment and cost–benefit analysis to support adaptive updates under circular economy objectives. Full article

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. Full article

Energy recovery from sewage sludge represents a sustainable and technically feasible alternative to promote integration between environmental sanitation and renewable energy generation. This study presents a case analysis of the municipality of Ribeirão Preto, São Paulo, focusing on comparisons between two wastewater treatment systems: an Upflow Anaerobic Sludge Blanket (UASB) reactor and a continuous-flow activated sludge system. Using the UASB configuration, we prepared a preliminary design of a treatment plant based on population and effluent generation projections over a 20-year horizon. The estimated sludge and biogas production allowed us to simulate electricity generation then. The comparative economic assessment, which employed Net Present Value (NPV) and Internal Rate of Return (IRR) indicators in accordance with ANEEL Resolution No. 482/2012, showed that the UASB system yields hard superior methane (up to 3235.6 m³/day) and higher electricity generation potential (1839.7 MWh/year) than the activated sludge system (1990 m³/day and 1654.3 MWh/year, respectively). Both systems were economically viable, with a positive NPV, an IRR of up to 16.83%, and payback periods starting in the first cycle. Furthermore, we estimated the cost per cubic meter of generated biomethane, conducted a sensitivity analysis, and assessed the impact on the most important economic indicators, all to identify the advantages and disadvantages of the proposed project and the best use of the generated biogas. This analysis showed that it is possible to recover energy from sewage treatment systems while also reusing sewage sludge for agricultural applications, thereby highlighting additional environmental and economic benefits, particularly in regions with a strong presence of agribusiness, e.g., Ribeirão Preto. Full article

Municipal sewage sludge is an environmental liability but also an energy-rich biomass that can support circular economy resource recovery. Here, we benchmark thin-layer drying of dewatered municipal sewage sludge (sludge cake) (40 g; layer thickness ≤ 5 mm) under open-air, convective hot air (40–150 °C), and microwave (70–1200 W) conditions to quantify drying kinetics, hygienisation indicators, and a screening-level energy-use proxy. High-power microwave drying reduced the time to constant mass from 32 h (open air) and 25 h 05 min (40 °C convection) to 20 min (900 W) and 14 min 05 s (1200 W). Faecal indicators (total/thermotolerant coliforms and presumptive Escherichia coli) were below detection after ≥100 °C convection or ≥300 W microwave treatment, while mesophilic aerobes and sulfite-reducing Clostridium spp. decreased by ~3–4 log10 with increasing exposure. A dragonfly-optimised ε-support vector regression model (DA–SVR) predicted drying trajectories across modes (overall RMSE ≈ 0.79 percentage points; held-out RMSE ≈ 1.47; R² ≥ 0.99). Overall, microwave thin-layer drying coupled with DA–SVR decision support enables constraint-based screening of sewage–sludge conditioning windows for logistics and thermal valorisation pathways; the framework can be extended to incorporate additional analytical endpoints where available. Full article

The sustainable management of olive wastes represents an important environmental challenge. Biochars and hydrochars derived from biomass are promising adsorbents for removing emerging pollutants from water. In the present work, olive stone wastes were converted into biochar and hydrochar by using pyrolysis (500 °C for 30 min) and hydrothermal carbonization (HTC) processes (220 °C for 10 h). Then, the obtained materials were physically activated by using CO₂ gas (750 °C for 30, 60 and 180 min). Various analytical techniques were applied for the chemical, textural and structural characterization of these carbonaceous materials (i.e., ultimate and proximate analysis, scanning electron microscopy (SEM), BET surface area, Raman spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy). Afterwards, the selected activated biochar and hydrochar were applied for the removal of amoxicillin from aqueous solutions. The experimental results show that the generated hydrochar has many microspheres on its surface and inside, while the produced biochar exhibits a porous structure with irregular forms. CO₂ physical activation has induced an important improvement of the biochar and hydrochar’s structural, textural, and surface chemistry properties. For instance, the activated biochar samples show a highly porous structure, with large specific surface areas that increase with the burn-off, reaching 1349.3 m² g⁻¹ following 3 h of activation. Regarding the activated hydrochar samples, they exhibit a spherical morphological structure with an important specific surface area, which increased to 846.7 m² g⁻¹ after 3 h of activation. Moreover, both activated materials have an amorphous structure with low oxygen surface groups. The selected novel CO₂-activated biochar and hydrochar efficiently remove amoxicillin from aqueous solutions under wide experimental conditions, with adsorption capacities of 386.4 and 215.9 mg g⁻¹, respectively. These efficiencies are higher than those reported for various activated biochars derived from lignocellulosic biomass, from sewage sludge, and from animal manure. Future research works are required to assess these materials’ effectiveness in treating real pharmaceutical effluents, to optimize the regeneration of the amoxicillin-loaded materials, and to design full-scale devices for a real application. Full article

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. Full article

This study assessed the feasibility of cultivating Lavandula dentata in Technosols produced from fine and coarse coal mining waste, focusing on plant development, substrate functionality, essential oil production, and post-mining ecosystem restoration. The Technosols were formulated using coal waste from the Moatize Coal Mine, Mozambique, combined or not in different configurations with agricultural soil and amended with sewage sludge (3% organic matter) and chemical fertilizer to ensure adequate nutrient availability. The experiments were conducted in 30 L containers, performed in triplicate for each experimental group. All settings allowed good plant growth, although the treatment that used only fine waste presented the closest performance to agricultural soil in terms of the production of aerial biomass. In this case, the dried biomass production of the shoots reached an average of 165 g per pot over 8 months (with a standard deviation of 20.3). The study showed a positive correlation between plant development and the available water capacity of the substrates. The plant tissue of L. dentata, in all the Technosols configurations studied, presented a similar composition to the control, with a biomass composition within the standard range established by the literature. The essential oil production ranged from 0.3 to 0.7% (m/m), averaging 0.5% (m/m), with chemical characteristics also alike the control trial. Technosols composed of coal waste from Moatize appear to be an alternative, both to provide a suitable destination for mining waste and to provide conditions for the revegetation and recovery of degraded areas by coal mining. This avoids the commissioning of nearby areas to supply soil for the restoration process. L. dentata, in addition to its various medical, ornamental, and aromatic uses, has potential as an “ecological trigger” in the restoration process with environmental and socioeconomic benefits. Full article

Petroleum hydrocarbons remain major environmental contaminants, and understanding the mechanisms governing their biodegradation is essential for designing effective remediation plans. The strategy in this article is slightly different from other cases in the literature. Such literature models require, for their elaboration, a significant number of experiments; the number of experimental determinations is at least proportional to the square of the number of constants introduced in the mathematical expressions. For this reason, the strategy followed in this article is different—starting from a set of experiments carried out and presented in a coherent and published manner, a simple methodology for building specific and minimal models, which will allow solving specific problems, was effectively developed. This study develops a nonlinear mathematical structure, expressed as a system of coupled differential equations, that simultaneously describes the degradation of petroleum hydrocarbons and the dynamics of hydrocarbon-degrading bacteria and fungi in soil–sludge mixtures. The model was calibrated using experimental data obtained from biopiles prepared with different volumetric ratios of contaminated soil and sewage sludge. Approximate analytical solutions were derived and the distributed constants were evaluated. For a consistent discussion, the analytical solutions were assessed against numerical desk simulations performed with a classical fourth-order Runge–Kutta method, which accurately reproduced the nonlinear behavior of the specific system. This numerical approach was chosen in order to overcome the proper difficulties encountered in this strategy implementation. The results show that the soil–sludge ratio strongly influences biodegradation efficiency, while kinetic parameters determine whether microbial communities evolve toward a stationary regime or accelerated contaminant removal. The combined analytical–numerical framework provides a robust predictive tool for optimizing mixture composition and improving the design of bioremediation treatments for petroleum-contaminated soils. Full article

Wastewater treatment plants (WWTPs) are among the most energy-intensive components of urban infrastructure. In light of the revised EU directive on municipal wastewater treatment, which targets energy neutrality by 2045, effective energy management in this sector is becoming essential. This article reviews the current knowledge regarding energy consumption in WWTPs and analyses opportunities to increase their energy self-sufficiency by reducing energy demand and recovering energy. Key factors influencing energy consumption are discussed, including facility size, the range of technological processes used, automation level, and equipment condition. Attention is given to aeration systems, which account for the largest share of electricity consumption, and the possibilities for their modernization and optimization using energy-efficient diffusers and advanced process control systems. The potential for recovering chemical energy from sewage sludge is analyzed, with emphasis on anaerobic digestion and co-digestion with other organic wastes. Alternative sludge conversion methods, such as incineration, pyrolysis, gasification, and hydrothermal carbonization, are also presented. The analysis is complemented by technologies for recovering physical energy from wastewater, including the use of thermal energy via heat pumps and hydraulic energy from wastewater flow. The findings indicate that achieving energy self-sufficiency in WWTPs requires site-specific, hybrid solutions combining energy savings with selective energy recovery, considering technical and economic conditions. Full article

This article presents the results of investigations into washed mineral waste (WMW) from grit chambers, fly ash generated during the thermal treatment of municipal sewage sludge (SSA), and their mixtures prepared in varying proportions. Their general physicochemical characteristics and heavy metal concentrations were presented. An experiment was conducted to assess the mobility of metals in the analyzed samples during extraction with distilled water and groundwater. The feasibility and safety of using the recovered materials in the ground environment, as soil backfills, and as materials for the construction of roads and flood embankments, were assessed. The feasibility of safely using materials in the indicated construction solutions was demonstrated for WMW and mixtures with a dominant WMW content. These results will be helpful in further research on solid waste applications. To the best of the authors’ knowledge, this study is the first to confirm the ecological safety of the analyzed wastes, as evidenced by assessments of heavy metal content and mobility. Furthermore, taking into account the laboratory and field costs associated with waste verification to obtain appropriate values for other physical and mechanical parameters (e.g., compaction index or shear strength), and the need to determine the level of waste contamination before practical application, the physicochemical tests carried out are economically justified. Full article

Ultra-high-performance concrete exhibits excellent mechanical performance but relies on a high binder content, resulting in substantial carbon emissions. This study investigates sustainable ultra-high-performance concrete incorporating sewage sludge ash, aiming to balance mechanical performance, environmental safety, and life-cycle impacts within an integrated material system. High volumes of sewage sludge ash were incorporated into ultra-high-performance concrete under autoclave curing, with mixture proportions designed based on particle packing theory. Fresh properties, mechanical performance, shrinkage behavior, microstructural characteristics, heavy-metal leaching, as well as life-cycle environmental and economic impacts were systematically evaluated. The incorporation of porous sewage sludge ash modified the pore structure of ultra-high-performance concrete, thereby enabling a substantial reduction in cement content. At a sewage sludge ash replacement level of 60%, life-cycle assessment results indicate a 42.7% reduction in carbon emissions while maintaining a compressive strength of approximately 147 MPa under autoclave curing, remaining within a practically viable range for ultra-high-performance concrete. This confirms that sewage sludge ash can be safely incorporated into ultra-high-performance concrete, delivering a favorable sustainability–performance trade-off alongside significant environmental and economic benefits. Full article

The growing demand for sustainable soil management strategies has intensified interest in hydrochar (HC), a waste-derived amendment produced via hydrothermal carbonization (HTC). This review synthesizes recent advances in HC production, characterization, and agri-environmental applications within a waste-to-resource framework. It covers studies conducted mainly over the last decade, encompassing a wide range of feedstocks, including agricultural residues, sewage sludge, animal manures, and food waste. HTC is typically performed at 130–280 °C under autogenous pressure (2–15 MPa), generating HCs with low intrinsic surface area (<50 m²g⁻¹) and oxygen-containing functional groups that govern nutrient dynamics and soil interactions. Reported application rates vary broadly between 10 and 60 t ha⁻¹, with most experiments conducted under greenhouse conditions. Positive effects on soil pH, cation exchange capacity, water retention, and phosphorus availability are frequently observed. However, plant responses vary according to the type of stimulation promoted by HC, as well as its processing conditions, application rates, and the soil characteristics in which it is applied. Advanced molecular-level analyses (e.g., FT-ICR-MS, GC-MS, and ¹³C-NMR) have provided mechanistic insights into carbon stability, nutrient release, and interaction with soil organic matter. Reusing HTC process water offers an additional pathway for nutrient recovery, although concerns about phytotoxic compounds remain. Despite promising short-term results, long-term field evaluations and standardized assessment protocols are still limited. This review integrates structural, functional and agri-environmental perspectives to identify critical knowledge gaps and guide the optimized and context specific use of hydrochar in sustainable agricultural systems. At the same time, it emphasizes its role in advancing carbon sequestration and in operationalizing resource-circular strategies, thereby underscoring its broader practical and strategic relevance. Full article