Search Results (634)

This study evaluates the potential use of reclaimed sand from municipal wastewater treatment plants (WWTP), categorized as waste under code 19 08 02, as a full substitute for natural sand in cement mortars. The sand was subjected to alkaline pretreatment using sodium hydroxide (NaOH) at concentrations of 0.5%, 1% and 2% to reduce organic impurities and improve surface cleanliness. All mortar mixes were prepared using CEM I 42.5 R as the binder, maintaining a constant water-to-cement ratio of 0.5. Mechanical testing revealed that mortars produced with 100% WWTP-derived sand, pretreated with 0.5% NaOH, achieved a mean compressive strength of 51.9 MPa and flexural strength of 5.63 MPa after 28 days, nearly equivalent to reference mortars with standardized construction sand (52.7 MPa and 6.64 MPa, respectively). In contrast, untreated WWTP sand resulted in a significant performance reduction, with compressive strength averaging 30.0 MPa and flexural strength ranging from 2.55 to 2.93 MPa. The results demonstrate that low-alkaline pretreatment—particularly with 0.5% NaOH—allows for the effective reuse of WWTP waste sand (code 19 08 02) in cement mortars based on CEM I 42.5 R, achieving performance comparable to conventional materials. Although higher concentrations, such as 2% NaOH, are commonly recommended or required by standards for the removal of organic matter from fine aggregates, the results suggest that lower concentrations (e.g., 0.5%) may offer a better balance between cleaning effectiveness and mechanical performance. Nevertheless, 2% NaOH remains the obligatory reference level in some standard testing protocols for fine aggregate purification. Full article

Societies are aiming to have a higher ecological consciousness in wastewater treatment operations and achieve a more sustainable future. With this said, global demands for larger quantities of resources and the consequent waste generated will inevitably lead to the exhaustion of current municipal wastewater treatment works. The utilization of biosolids (particularly microbial proteins) from wastewater treatment operations could generate a sustainable bio-adhesive for the wood industry, reduce carbon footprint, mitigate health concerns related to the use of carcinogenic components, and support a more circular economic option for wastewater treatment. A techno-economic analysis for three 10 MGD wastewater treatment operations producing roughly 11,300 dry pounds of biosolids per day, in conjunction with co-feedstock defatted soy flour protein at varying ratios (i.e., 0%, 15%, and 50% wet weight), was conducted. Aspen Capital Cost Estimator V12 was used to design and estimate installed equipment additions for wastewater treatment plant integration into an urban biorefinery process. Due to the mechanical attributes and market competition, the chosen selling prices of each adhesive per pound were set for analysis as USD 0.75 for Plant Option P1, USD 0.85 for Plant Option P2, and USD 1.00 for Plant Option P3. Over a 20-year life, each plant option demonstrated economic viability with high NPVs of USD 107.9M, USD 178.7M, and USD 502.2M and internal rates of return (IRRs) of 24.0%, 29.0%, and 44.2% respectively. The options examined have low production costs of USD 0.14 and USD 0.19 per pound, minimum selling prices of USD 0.42–USD 0.51 per pound, resulting in between 2- and 4-year payback periods. Sensitivity analysis shows the effects biosolid production fluctuations, raw material market price, and adhesive selling price have on economics. The results proved profitable even with large variations in the feedstock and raw material prices, requiring low market selling prices to reach the hurdle rate of examination. This technology is economically enticing, and the positive environmental impact of waste utilization encourages further development and analysis of the bio-adhesive process. Full article

Biodrying and composting are aerobic processes to treat and stabilize organic solid waste, but biodrying involves a shorter process time and does not require the addition of water. The resulting biodried material (BM) is mainly used as an energy source in cement production or in municipal solid waste incineration with energy recovery, but when obtained from agricultural or agroindustrial organic waste, it could also be used as a soil amendment, such as compost (CO). In this study, the phytotoxicity of BM compared to CO, both made from organic wastes (orange peel, mulch and grass), was evaluated on seed germination and growth (for 90 days) of lettuce (Lactuca sativa L.) seedlings on treatments prepared from mixtures of BM and soil, soil (100%) and a mixture of CO and soil. The germination index (GI%) was higher for BM extracts (200 g/L) than for CO extracts (68% vs. 53%, respectively). According to their dry weight, lettuce grew more on the CO mixture (16.5 g) than on the BM (5.4–7.4 g), but both materials far exceeded the soil values (0.15 g). The absence of phytotoxicity suggests that BM acts as a soil amendment, improving soil structure and providing nutrients to the soil. Therefore, biodrying is a quick and low-cost bioprocess to obtain a soil improver. Full article

A three-year optimization study was conducted at a mechanical biological treatment plant with the aim of enhancing organic fractions recovery from mechanically separated fine fractions (MSFF) of residual waste using a screw press. The study aimed to optimize key operating parameters for the employed screw press, such as pressure, liquid-to-MSFF, feeding quantity per hour, and press basket mesh size, to enhance volatile solids and biogas recovery in the generated press water for anaerobic digestion. Experiments were performed at the full-scale facility to evaluate the efficiency of screw press extraction with other pretreatment methods, like press extrusion, wet pulping, and hydrothermal treatment. The results indicated that hydrolysis of the organic fractions in MSFF was the most important factor for improving organic extraction from the MSFF to press water for fermentation. Optimal hydrolysis efficiency was achieved with a digestate and process water-to-MSFF of approximately 1000 L/ton, with a feeding rate between 8.8 and 14 tons per hour. Increasing pressure from 2.5 to 4.0 bar had minimal impact on press water properties or biogas production, regardless of the press basket size. The highest volatile solids (29%) and biogas (50%) recovery occurred at 4.0 bar pressure with a 1000 L/ton liquid-to-MSFF. Further improvements could be achieved with longer mixing times before pressing. These findings demonstrate the technical feasibility of the pressing system for preparing an appropriate substrate for the fermentation process, underscoring the potential for optimizing the system. However, further research is required to assess the cost–benefit balance. Full article

The co-disposal of municipal solid waste incineration fly ash (MSWI-FA) in cement kilns is an effective method for managing incineration by-products in China. However, the presence of heavy metals in MSWI-FA raises environmental concerns. This study analyzed the Cu, Zn, Cd, Pb, Cr, and Ni concentrations in MSWI-FA from 11 representative facilities across China and assessed the efficacy of a three-stage water washing process for Cl and heavy metal removal. The results revealed significant regional variations in heavy metal content that were strongly correlated with surface soil levels, with Zn, Pb, and Cu exhibiting the highest concentrations. Elemental correlations, such as Cu-Pb and Zn-Cd synergies and Cd-Ni antagonism, suggest common waste sources and temperature-dependent volatilization during incineration. The washing process (solid–liquid ratio = 1:10) achieved 97.1 ± 2.0% Cl removal, reducing residual Cl to 0.45 ± 0.32%, but demonstrated limited heavy metal elimination (10.28–19.38% efficiency), resulting in elevated concentrations (32.5–60.8% increase) due to 43.4 ± 9.2% mass loss. Notably, the washing effluents exceeded municipal wastewater discharge limits by up to 52-fold for Pb and 38-fold for Cd, underscoring the need for advanced effluent treatment. To mitigate environmental risks, the addition of washed MSWI-FA in cement kilns should be restricted to ≤0.5%, with Cd content prioritized in pre-disposal assessments. This study provides actionable insights for optimizing MSWI-FA co-processing while ensuring compliance with ecological safety standards. Full article

Adequate treatment of the organic fraction of municipal solid waste (OFMSW) in co-digestion with sewage sludge (SS) through dark fermentation (DF) technologies has been widely studied and recognized. However, there is little experience with a high-solids approach, where practical and scalable conditions are established to lay the groundwork for further development of feasible industrial-scale projects. In this study, the biochemical hydrogen potential of OFMSW using a 7 L batch reactor at mesophilic conditions was evaluated. Parameters such as pH, redox potential, temperature, alkalinity, total solids, and substrate/inoculum ratio were adjusted and monitored. Biogas composition was analyzed by gas chromatography. The microbial characterization of SS and post-reaction percolate liquids was determined through metagenomics analyses. Results show a biohydrogen yield of 38.4 NmLH₂/gVS OFMSW, which forms ~60% of the produced biogas. Aeration was proven to be an efficient inoculum pretreatment method, mainly to decrease the levels of methanogenic archaea and metabolic competition, and at the same time maintain the required total solid (TS) contents for high-solids conditions. The microbial community analysis reveals that biohydrogen production was carried out by specific anaerobic and aerobic bacteria, predominantly dominated by the phylum Firmicutes, including the genus Bacillus (44.63% of the total microbial community), Clostridium, Romboutsia, and the phylum Proteobacteria, with the genus Proteus. Full article

Mechanical–biological treatment plants face challenges in effectively separating organic fractions from residual municipal solid waste for biological treatment. This study investigates the optimization measures carried out at the Erbenschwang MBT facility, which transitioned from solely aerobic treatment to integrated anaerobic digestion using a screw press. This study focused on evaluating the efficiency of each mechanical pretreatment step by investigating the composition of the residual waste, organic fraction recovery rate, and screw press performance in recovering organic material and biogas to press water. The results showed that 92% of the organic material from the residual waste was recovered into fine fractions after shredding and trommel screening. The pressing experiments produced high-quality press water with less than 3% inert material (0.063–4 mm size). Mass balance analysis revealed that 47% of the input fresh mass was separated into press water, corresponding to 24% of the volatile solids recovered. Biogas yield tests showed that the press water had a biogas potential of 416 m³/ton VS, recovering 38% of the total biogas potential. In simple terms, the screw press produced 32 m³ of biogas per ton of mechanically separated fine fractions and 20 m³ per ton of input residual waste. This low-pressure, single-step screw press efficiently and cost-effectively prepares anaerobic digestion feedstock, making it a promising optimization for both existing and new facilities. The operational configuration of the screw press remains an underexplored area in current research. Therefore, further studies are needed to systematically evaluate key parameters such as screw press pressure (bar), liquid-to-waste (L/ton), and feed rate (ton/h). Full article

The use of pharmaceuticals and personal care products (PPCPs) is steadily growing as the world’s population both increases and ages. Many of these products are released into the environment via municipal wastewater treatment plants and onsite wastewater treatment systems (septic tanks). Consequently, it is essential to ascertain whether these contaminants pose any risk to aquatic organisms who live in the water bodies receiving this waste. Risk quotients (RQ) are a commonly used method to do so. For our pilot study, we undertook such analysis for three trophic levels: algae, crustaceans, and fish from two small lakes, one fed by septic tanks and the other not. This research was conducted in 2021 from the end of the dry season and through most of the wet season in west central Florida, USA. Of the 14 PPCPs measured, six had RQs that posed a risk to all three trophic levels. This risk increased during the wet season. Both lakes, regardless of whether they directly received PPCPs from septic tanks or not, had some level of risk. However, the lake without septic tanks had a smaller risk, both in elevated RQs and the occurrence to the various species. Of the PPCPs measured, DEET, caffeine, and theophylline posed the greatest risk. Full article

Implementing efficient strategies for the circular recovery and reuse of nutrients from wastewaters is mandatory to meet the Green Deal objectives and Sustainable Development Goals. In this context we investigated the use of zeolitic tuff (containing chabazite and phillipsite) in the selective recovery and reuse of N from various anaerobic liquid digestates in view of their implementation in farm-scale treatment plants. We tested the method on three livestock digestates and two municipal organic solid waste digestates. Adsorption isotherms and kinetics were assessed on each digestate, and a large set of parameters, including (i) contact time, (ii) initial NH₄⁺ concentration, (iii) presence of competing ions, (iv) total solids content, and (vi) separation methods (microfiltration and clarification), were considered in the experimental design. Our results showed that the adsorption mechanism can be explained by the Freundlich model (R² up to 0.97), indicating a multilayer and heterogeneous adsorption, while the kinetic of adsorption can be explained by the pseudo-second-order model, indicating chemical adsorption and ion exchange. The efficiency in the removal of NH₄⁺ was indirectly related to the K⁺ and total solids content of the digestate. Maximum NH₄⁺ removal exceeded 90% in MSW-derived digestates and 80% within 60 min in livestock-derived digestates at a 5% solid/liquid ratio. Thermodynamic parameters confirmed favorable and spontaneous adsorption (ΔG up to −7 kJ⋅mol⁻¹). Farm-scale projections estimate a nitrogen recovery potential of 1.2 to 16 kg N⋅day⁻¹, depending on digestate type and process conditions. These findings support the application of natural zeolitic tuffs as a low-cost, chemical-free solution for ammonium recovery, contributing to sustainable agriculture and circular economy objectives. Full article

The integration of different agroecological practices could significantly mitigate the impact of climate change. Therefore, a 2-year field experiment on organic zucchini was carried out to study the effects of clover (Trifolium alexandrinum L.) cover crop management (green manure, GM vs. flattening using a roller crimper, RC), compared to a control without cover (CT). This agroecological practice was tested in combination with the following different fertilizer treatments: T1. compost produced by co-composting coal mining wastes with municipal organic wastes compost plus urea; T2. compost produced with the same matrices as T1, replacing urea with lawn mowing residues; T3. non-composted mixture of the industrial matrices; T4. on-farm compost obtained from crop residues. The GM management showed the highest marketable yield and aboveground biomass of zucchini, with both values higher by approximately 38% than those recorded in CT. The T1, T2, and T3 treatments showed higher SOC values compared to T4 in both years, with a gradual increase in SOC over time. The residual effect of fertilization on SOC showed a smaller reduction in T3 and T4 than in T1 and T2, in comparison with the levels recorded during the fertilization years, indicating a higher persistence of the applied organic matter in these treatments. The findings of this study pointed out that combining organic fertilization and cover cropping is an effective agroecological practice to maintain adequate zucchini yields and enhance SOC levels in the Mediterranean environment. Full article

The treatment of wastewater and the utilization of the by-products of these processes are an important part of the circular economy. The sewage sludge, a result of wastewater treatment, could be used as a material for plant nutrient supply and/or soil-improving products. The city of Nyíregyháza, Hungary, with 120,000 citizens, has a well-planned water treatment plant operated by Nyírségvíz Ltd., which, in cooperation with the Research Institute of Nyíregyháza, developed a municipal sewage sludge compost (SSC). The closed loop of sewage water treatment and the agricultural utilization of its by-product has been developed and managed. The compost product called Nyírkomposzt was planned for acidic sandy soils. Beyond the agronomic benefits, the sustainable and environmentally sound utilization of SSC reduces sewage sludge disposal. This active involvement of a water utility company demonstrates the potential of cross-sectoral cooperation in solving environmental problems. The quality of the compost fits the Hungarian legislation. To study the effects of 0, 9, 18, and 27 t ha⁻¹ doses of compost on acidic sandy soil, a long-term small plot experiment was started in 2003. The cumulative effects of the regular (every third year, last treatment before sampling in 2021) application of the SSC showed positive changes in basic soil properties, depending on the doses used. Increasing values were found in the case of pH from 4.5 to 6, plant available P₂O₅ from 240 to 690 ppm, and plant available K₂O from 180 to 200 ppm. The plant-available zinc and copper content also increased. Soil organic matter and total N content stabilized at around 0.9% and 0.08%, respectively. The grain yields of winter rye also increased in both investigated years. The yields of 18 t ha⁻¹ treatment were about two times higher compared to the control, but only in 2022 was the difference significant. Our findings underscore the potential of well-planned SSC applications to improve the fertility of ploughed, acidic sandy soil, taking into account the theory of the circular economy by utilizing wastes and decreasing landfilling. Full article

The integration of renewable energy with circular economy strategies offers effective pathways to reduce greenhouse gas emissions while enhancing local energy independence. This study analyses three real-world projects implemented in Spain that exemplify this synergy. LIFE Smart Agromobility converts pig manure into biomethane to power farm vehicles, using anaerobic digestion and microalgae-based upgrading systems. Smart Met Value refines biogas from a wastewater treatment plant in Guadalajara to produce high-purity biomethane for the municipal fleet, demonstrating the viability of energy recovery from sewage sludge. The UNDERGY project addresses green hydrogen storage by repurposing a depleted natural gas reservoir, showing geochemical and geomechanical feasibility for seasonal underground hydrogen storage. Each project utilises regionally available resources to produce clean fuels—biomethane or hydrogen—while mitigating methane and CO₂ emissions. Results show significant energy recovery potential: biomethane production can replace a substantial portion of fossil fuel use in rural and urban settings, while hydrogen storage provides a scalable solution for surplus renewable energy. These applied cases demonstrate not only the technical feasibility but also the socio-economic benefits of integrating waste valorisation and energy transition technologies. Together, they represent replicable models for sustainable development and energy resilience across Europe and beyond. Full article

Municipal sewage sludge, a by-product of urban wastewater treatment, is increasingly recognized to be a strategic resource rather than a disposal burden. Traditional management practices, such as landfilling, incineration, and land application, are facing growing limitations due to environmental risks, regulatory pressures, and the underuse of the sludge’s energy and nutrient potential. This review examines the evolution of sludge management, focusing on technologies that enable energy recovery and resource valorization. The transition from linear treatment systems toward integrated biorefineries is underway, combining biological, thermal, and chemical processes. Anaerobic digestion remains the most widely used energy-positive method, but it is significantly improved by processes such as thermal hydrolysis, hydrothermal carbonization, and wet oxidation. Among these, hydrothermal carbonization stands out for its scalability, energy efficiency, and phosphorus-rich hydrochar production, although implementation barriers remain. Economic feasibility is highly context-dependent, being shaped by capital costs, energy prices, product markets, and policy incentives. This review identifies key gaps, including the need for standardized treatment models, decentralized processing hubs, and safe residual management. Supportive regulation and economic instruments will be essential to facilitate widespread adoption. In conclusion, sustainable sludge management depends on modular, integrated systems that recover energy and nutrients while meeting environmental standards. A coordinated approach across technology, policy, and economics is vital to unlock the full value of this critical waste stream. Full article

Circular economy in the context of municipal organic waste management has boosted the emergence of novel composting scenarios, such as community composting and decentralized urban composting in small installations, which favors localized management and valorization of organic waste streams. However, there is little information about the agronomic use of the composts obtained from these new organic waste management systems as an alternative for inorganic fertilization in crop production. In this work, municipal solid waste-derived composts from two decentralized composting scenarios (CM1 and CM2 from community composting, and CM3 and CM4 from decentralized urban small-scale composting plants) were applied and mixed in the top layer of a calcareous clayey-loam soil to assess their effects as alternative substitutes for conventional soil inorganic fertilization (IN) during two successive cultivation cycles of lettuce (Lactuca sativa L.) grown in pots with the amended soils. These treatments were also compared with an organic waste (goat–rabbit manure, E) and a control treatment without fertilization (B). The effects of the fertilizing treatments on the crop yield and quality, as well as on the properties of the soil considered were studied. In general, the application of the different composts did not produce negative effects on lettuce yield and quality. The compost-derived fertilization showed similar lettuce yields compared to the inorganic and manure-derived fertilizations (IN and E, respectively), and higher yields than the soil without amendment (B), with increases in the initial yield values of B, for the first cycle from 34.2% for CM1 to 53.8% for CM3, and from 20.3% for CM3 to 92.4% for CM1 in the second cycle. Furthermore, the organically amended soils showed a better crop development, obtaining higher values than the control treatment in the parameters studied. In addition, the incorporation of the organic treatments improved the soil characteristics, leading to 1.3 and 1.2 times higher organic matter contents in the soils with CM2 and in the soils with CM1, CM3, and E, respectively, compared to the control soil without fertilizing treatment (B), and 2.0 and 1.8 times greater organic matter contents, respectively, compared to soil with inorganic fertilization (IN). Therefore, the use of municipal solid waste-derived composts from these new organic waste management systems, such as the decentralized composting scenarios studied (community composting and urban decentralized small-scale composting plants), is presented, not only as a sustainable valorization method, but also as an alternative for the use of inorganic fertilizers in lettuce cultivation, while enhancing soil properties, contributing to increasing the circularity of agriculture. Full article

Volatile fatty acids (VFA) are valuable intermediates with growing demand in chemical, pharmaceutical, and environmental applications. Their sustainable production from organic waste is increasingly explored in the context of circular economy and biorefinery models. This study investigates the co-fermentation of waste-activated sludge (WAS) and the organic fraction of municipal solid waste (OFMSW) as a strategy for integrated VFA and biogas production. Semi-continuous experiments were carried out to assess the effect of the substrates ratio (WAS:OFMSW = 90:10 and 30:70), hydraulic retention time (HRT), and pH control (5, 9, no control) on VFA yield and composition. Results showed that higher OFMSW content and alkaline conditions favoured VFA production, with a maximum yield of 144.9 mgHAc·gVS⁻¹ at pH 9 and 70:30 ratio. Acetate dominated, while butyrate production peaked at 114.1 mgHBu·gVS⁻¹ under high sludge conditions. However, the addition of alkali required for pH control may lead to excessive accumulation of alkaline-earth metal ions, which can disrupt biological processes due to their potential toxicity. Anaerobic digestion of fermentation residues enhanced biomethane yields significantly (0.27 NL·gVS⁻¹ vs. 0.05 NL·gVS⁻¹ from raw sludge). The proposed process demonstrates potential for converting wastewater treatment plants into biorefineries, maximising resource recovery while reducing environmental impact. Full article