Search Results (159)

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

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

This study evaluates the potential of spent coffee grounds (SCGs) as a co-substrate to improve anaerobic co-digestion (AcD) performance, with a focus on biogas yield, methane (CH₄) content, and the removal of volatile solids (VS) and total chemical oxygen demand (TCOD). Biochemical methane potential (BMP) tests were conducted in two stages. In Stage I, SCGs were blended with active sludge (AS) and the organic fraction of municipal solid waste (OFMSW) at varying ratios. The addition of 25% SCGs increased biogas production by 24.47% (AS) and 20.95% (OFMSW), while the AS50 mixture yielded the highest methane yield (0.302 Nm³/kg VS, 66.42%). However, SCG concentrations of 75% or higher reduced process stability. In Stage II, we evaluated the impact of mixing. The AS25 configuration maintained stable biogas under varying mixing conditions, showing system resilience, whereas OFMSW25 showed slight improvement. Biogas production kinetics were modeled using modified Gompertz, logistic, and first-order equations, all of which demonstrated high predictive accuracy (R² > 0.97), with the modified Gompertz model offering the best fit. Overall, SCGs show promise as a sustainable co-substrate for the improvement of methane recovery and organic matter degradation in AcD systems when applied at optimized concentrations. Full article

This study evaluates Spain’s biomethane production potential for 2030 and 2050, focusing on agricultural residues, livestock manure, municipal solid waste (MSW), and wastewater treatment plant (WWTP) sludge. The research aims to provide a regional analysis based on historical data on livestock populations, cultivated land, waste availability, and demographic projections. Using utilization coefficients and technological assumptions derived from existing biogas infrastructure, the study estimates that Spain could generate 9.71 TWh of biomethane by 2030, slightly below the national target of 10.41 TWh. By 2050, agricultural and livestock residues are expected to contribute 30.04 TWh, accounting for nearly 80% of total biomethane production, while the relative share of MSW and WWTP sludge will decrease. Andalusia, Castilla-La Mancha, and Castilla y León emerge as key contributors due to their extensive agricultural and livestock sectors. Catalonia and Madrid maintain significant roles driven by urban waste generation. The findings underscore the need for infrastructure expansion, particularly enhancing biomethane injection facilities into the natural gas grid, alongside financial incentives to support industry growth. This study highlights the role of biomethane in Spain’s renewable energy sector, emphasizing its potential to reduce greenhouse gas emissions, optimize organic waste utilization, and contribute to a sustainable energy transition. Full article

Microplastics have emerged as a global environmental concern due to their widespread presence and potential effects on ecosystems. Wastewater treatment plants (WWTPs) play a critical role in mitigating the release of microplastics into the environment. This study aimed to evaluate the abundance and distribution of microplastics in three municipal WWTPs exhibiting different sludge and water treatment technologies. Samples were collected at various stages of the treatment process, including influent, primary and biological sludge, treated water, thickened sludge and dehydrated sludge. Quantification analyses were performed and then coupled with operational data to assess pollution flow rates and the microplastic balance. An important removal rate (>97%) of microplastics along the water line was observed in all three WWTPs. The lower performance of 0.75 mm screening was observed regarding microplastic capture compared to conventional primary settling on the water line. No significant differences in the pollution flow rates between primary and biological sludge were detected. Whatever the thickening and dehydration technologies that were tested, the specific quantities of microplastics along the sludge treatment lines were steady, implying the comparable behaviour of microparticular pollution to total suspended solids. These results underscored the important role of the different concentration stages of sludge treatment lines in sequestrating microplastics within the sludge fraction. Full article

Sequencing batch reactor Grundfos technology (SBR-GT) system efficiently treats municipal and selected industrial wastewater, designed for small and medium-scale facilities. It offers advanced solutions for biodegradable wastewater, including municipal and food industry effluents. Important features include stable sedimentation under fluctuating influent conditions, no need for sludge recirculation, and full process automation. The system uses a static decanter and constant chamber filling for optimal oxygenation efficiency and reduced costs. The system uses a static decanter and constant chamber filling for optimal oxygenation efficiency and reduced costs. It is ideal for small settlements with variable inflow, such as towns, allowing flexible operation and cost-effective maintenance. Implementations showed stable parameters for COD (chemical oxygen demand), BOD5 (biochemical oxygen demand), total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) and up to 99% pollutant reduction, demonstrating high effectiveness in regular and stormwater conditions. Using multivariate multiple linear regression, significant relationships were identified. A multiple regression analysis revealed a strong relationship between water quality parameters. Total suspended solids, Total nitrogen, and Total phosphorus collectively and significantly influenced both chemical oxygen demand and biochemical oxygen demand (p < 0.01 for all). The models explained a high proportion of variance, with R² values of 0.99 for COD and 0.93 for BOD5 (p < 0.001 for both). Specifically, TSS had a strong positive effect on COD (p < 0.001), while TN and TP also significantly affected COD (p < 0.01). Although the overall BOD5 model was highly significant, the individual effects of TSS, TN, and TP on BOD5 were not statistically significant in this model. This method demonstrated high effectiveness in both regular and stormwater conditions, enhancing overall treatment performance. Full article

This work investigates the adsorption of benzo[a]pyrene (BaP) using a charcoal adsorbent derived from sewage treatment plant sludge. BaP is a polycyclic aromatic hydrocarbon (PAH), carcinogenic to humans, which his used by the World Health Organization as a marker for all PAH mixtures. The charcoal was produced by the pyrolysis (500 °C, 4 h) of municipal sewage sludge. The resulting biochar presented mesoporous and oxygenated functional groups that are beneficial for the adsorption of benzo[a]pyrene. The material contained graphitic structures, suggesting potential sites for π–π interactions. The adsorption followed the Elovich kinetic model. A maximum adsorbed value of 60.8 µg g⁻¹ was achieved for an initial BaP concentration of 100 µg L⁻¹ of BaP at 298 K after 20 min. Parameters related to mass transfer phenomena, such as the intraparticle diffusion coefficient, were determined using the homogeneous solid diffusion model (HSDM). These experimental data demonstrate the great potential for computational fluid dynamics (CFD) applications. The value reached for the intraparticle diffusion coefficient was 1.63 × 10⁻¹³ m²s⁻¹. Adsorption equilibrium experiments showed that the Langmuir model was most suitable for experimental data, suggesting a monolayer molecular adsorption process. The results showed that charcoal can be employed as an effective material for removing BaP. Full article

The majority of microplastics (MPs) removed from urban wastewater during conventional treatments end up in sewage sludge (around 95%). There are not many studies focused on the retention of MPs in secondary sewage sludge. This study explores the amount and kind of MPs retained in secondary sludge from a municipal wastewater treatment plant (WWTP) and the factors affecting the entrapment of MPs within the sludge flocs. The most abundant MPs in the sludges were fibres (61%), and the majority were within the size range of 250–500 μm. In addition, the effect of solid concentration on MP retention in settled sludge was analysed by carrying out a mixing–settling test. Without the addition of any chemicals, a maximum MP retention efficacy of 63% was obtained for a total suspended solids (TSS) concentration of 5.33 g/L. The effect of adding FeCl₃ and non-ionic polyacrylamide (PAM) was also investigated, and the percentage of retained MPs increased to values of 82% and 70%, respectively (with only 0.63 g TSS/L). This improvement occurred predominantly in the case of fibres. The results suggest the possibility of adding chemicals before the secondary settling stage as a means of reducing MP contamination in treated water. Full article

This paper reviews methods of municipal sewage sludge (MSS) disposal in the Republic of Poland. The MSS amount produced in 2022 in sewage treatment plants is 580.7 thousand tons of total solids. This is related to the increase in the amount of treated sewage and the use of the co-digestion of sewage sludge with waste. MSS generated in municipal sewage treatment plants constitutes waste with code 19 08 05—stabilized MSS. It is subjected to the rules of conduct specified in the Act on Waste. According to data from the Central Statistical Office, in 2022, the most popular disposal method was its use in agriculture (27.1%). Approximately 18% of the MSS from treatment plants was thermally treated. A significant part of MSS is also used for crops, compost production, and reclamation. MSS management requires an individual approach from sewage treatment plant operators and the use of effective disposal methods. Considering the assumption of the circular economy, it is necessary to consider the possibility of recovering valuable raw materials from MSS and producing products for reuse. One of the possibilities of reusing MSS is to generate porous materials. Moreover, MSS can be transformed into multiple types of soil improvers and fertilizers. Full article

The presence of toxic and hazardous chemical species in municipal wastewater poses a significant environmental and public health challenge, necessitating innovative, sustainable, and cost-effective treatment solutions. This study pioneers the recovery and valorisation of polycationic metals from real acid mine drainage (AMD) for municipal wastewater treatment, demonstrating a novel approach that integrates resource recovery with wastewater remediation. A key strength of this study is the use of real municipal wastewater (authentic MWW) in the treatment phase, ensuring that the findings accurately reflect real-world conditions. Advanced analytical techniques were employed to characterise both aqueous and solid samples, and batch experiments were conducted to assess the removal efficiency of polycationic metals for key contaminants: ammonium (NH₄⁺), sulphate (SO₄²⁻), phosphate (PO₄³⁻), and nitrate (NO₃⁻). The optimised conditions are 2 g of polycationic metals per 100 mL, 90 min of contact time, and 35 °C. The yielded exceptional removal efficiencies are PO₄³⁻ (>99.9%), NH₄⁺ (>99.7%), NO₃⁻ (>99%), and SO₄²⁻ (>96%), achieving final concentrations of <0.5 mg/L for PO₄³⁻ and NH₄⁺, 2.1 mg/L for NO₃⁻, and 9.1 mg/L for SO₄²⁻. Adsorption kinetics followed a pseudo-first-order model, indicating physisorption, while the Two-Surface Langmuir model suggested a combination of homogeneous and heterogeneous adsorption mechanisms. FTIR, SEM-EDX mapping, and XRF analyses confirmed the retention of P, S, and N in the product sludge, validating the adsorption process. This study is the first of its kind to recover Al-rich Fe species from real AMD and activate them for municipal wastewater remediation using authentic MWW, bridging the gap between laboratory-scale research and real-world applications. By simultaneously addressing AMD pollution and municipal wastewater treatment, this research advances circular economy principles, promotes sustainable water management, and contributes to national and global efforts toward water security and environmental protection. Full article

The enhancement of the treatment of municipal wastewater treatment plants is limited by poor sludge settling qualities, and the excessive discharge of nitrogen and phosphorus exacerbate water eutrophication. The goal of the current work was to remove phosphorus from fresh sewage-activated sludge by developing a new conditioning and flocculation mechanism that included a coagulant and cationic polyelectrolytes in a dual conditioning system. The coagulant (CaCl₂) and the high molecular weight polyacrylamide (CPAM-10) were chosen to be utilized singly or in pairs as cationic–coagulant combinations. The collected results showed that, in comparison to utilizing the coagulant (CaCl₂), conditioning with the high molecular weight polymer (CPAM-10) produced improved settling and less turbidity. Only sludge with a lower solid content (TSS) exhibited better settling when pure CaCl₂ was used for conditioning. CaCl₂ conditioning enhanced settling by just 3%, while CPAM-10 improved the sludge setting by 60% for higher sludge TSSs. According to the results, conditioning settings using a dual mixture including 20 mL CPAM-10 and 50 mL CaCl₂ improved settling by 80%. The amount of phosphorus in the supernatant was decreased by 15% and 9%, respectively, by using the coagulant (CaCl₂) and 50 mL/L polyacrylamide (CPAM-10). As a result, there was a significant amount of phosphorus in the resultant supernatant. This suggested that the polymer had a significant impact on sludge settling because of its high positive charge, but had less of an impact on attracting phosphorus metal. Despite the lower positive charge of CaCl₂, it has a dual action of settling and removing phosphorus. A considerable amount of phosphorus was removed from the sludge and leached to the supernatant during treatment. This treatment was coupled with less sludge settling. However, 90% phosphorus removal was achieved when mixed conditioning agents (20 mL CPAM-10 and 50 mL CaCl₂) were used. Furthermore, phosphorus was reduced by 33 and 39%, respectively, by adding 20 milliliters of CaCl₂ to 100 milliliters of the pre-conditioned supernatant with pure CPAM-10 and CaCl₂. Using the CPAM-10 agent for sludge conditioning has a major impact on settling, because of the high positive charge, and because when a small amount of Ca++ is added to the polymer solution for conditioning to attract fine sludge particles and accelerate their combination, this results in flocculation and rapid dewatering. This mechanism allows for more phosphorus to be released to the supernatant, which has not been reported previously to the best of our knowledge. Full article

Many volatile fatty acids (VFAs) are produced after wet air oxidation, which could be a potential carbon source. In this study, we investigated the impact of NaOH on the removal of hazardous organics and the changes in the produced carbon source. The total and soluble chemical oxygen demand (SCOD) removal rates decreased to 47.9% and 55.3% with 51.6% NaOH addition. The removal rates of total suspended solids (82–85%) and volatile suspended solids (97–99%) remained stable under all conditions. Additionally, the concentrations of acetic acid and isovaleric acid increased with a high pH value. Fluorescent substances closely related to aromatic protein and fulvic acid-like substances were identified and degraded significantly with the addition of NaOH. Moreover, 41.3% NaOH addition (initial pH 13.0) could yield a VFAs/SCOD ratio of 30.5%, demonstrating the good biocompatibility of the carbon source. The effect of the nitrogen element was also considered, with the ratio of the 5-day biological oxygen demand to the total nitrogen being 7.2, indicating that the oxidation solution could provide an abundant carbon source. Thus, the sludge-derived carbon source is suitable to supply biological treatment units for municipal wastewater. Full article

The mining and processing of coal resources generate substantial coal-based solid wastes, such as coal gangue and slag, which pose environmental challenges, occupy land, and are difficult to manage. However, utilizing these wastes for the stabilization and solidification (S/S) of municipal sludge containing chromium (Cr) and nickel (Ni) offers an effective solution for mitigating environmental and groundwater pollution while enabling sustainable waste treatment and resource utilization. This study applied an alkali-activated coal gangue–S95 granulated blast furnace slag-based binder (CGS) to the S/S treatment of municipal sludge. The effects of the liquid-to-solid ratio, alkali activator dosage, sludge content, and incineration on compressive strength and the leaching of Cr and Ni were analyzed. The results showed that compressive strength decreased with increases in the sludge content and liquid-to-solid ratio, while incinerated sludge (ESA) samples exhibited better strength than raw sludge (ES). Incineration decomposed the calcite (CaCO₃) into CaO, which facilitated the oxidation of Cr(III) to Cr(VI) and increased Cr leaching in the ESA. However, the ESA samples demonstrated superior heavy metal stabilization, as CGS reduced Cr(VI) to Cr(III) and immobilized it through the formation of chromite phases. Using ESA as a binder in CGS provides a safe, efficient approach for resource recovery and heavy metal stabilization, offering a novel solution for the environmental management and utilization of coal-based solid wastes. Full article

Poultry litter waste management poses a significant global challenge, attributed to its characteristics (odorous, organic, pathogenic, attracting flies). Conventional approaches to managing poultry litter involve composting, biogas generation, or direct field application. Recently, there has been a surge of interest in a novel technology that involves the bioconversion of organic waste utilizing insects (known as entomoremediation), particularly focusing on black soldier fly larvae (BSFL), and has demonstrated successful transformation of various organic waste materials into insect meal and frass (referred to as organic frasstilizer). Black soldier flies have the capacity to consume any organic waste material (ranging from livestock litter, food scraps, fruit and vegetable residues, sewage, sludge, municipal solid waste, carcasses, and defatted seed meal) and convert it into valuable BSFL insect meal (suitable for animal feed) and frass (serving as an organic fertilizer). The bioconversion of poultry litter by black soldier flies offers numerous advantages over traditional methods, notably in terms of reduced land and water requirements, lower emissions, cost-effectiveness, swift processing, and the production of both animal feeds and organic fertilizers. This review focuses on the existing knowledge of BSFL, their potential in bioconverting poultry litter into BSFL meal and frass, and the utilization of BSFL in poultry nutrition, emphasizing the necessity for further innovation to enhance this sustainable circular economy approach. Full article

Bacteria quickly acquire the ability to survive or grow in the presence of an antibacterial agent that should be able to inhibit or kill them, leading to increased mortality caused by infective diseases. The digestate from the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) is spread on soil, but the knowledge on the presence and persistence of the antibiotic resistance genes (ARGs) is limited. Thus, this study aims to evaluate the presence of seven ARGs (bla_TEM, bla_OXA, ermB, qnrB, sulI, sulII, tetA, and tetW) in the OFMSW and their persistence after the AD, using the innovative droplet digital Polymerase Chain Reaction (ddPCR), not yet used on this matrix. A total of 31 samples were collected from the influent and effluent of the AD in two plants located in Northern Italy. ARG concentration ranged between 4 and 9 Log gene copies/kg of sludge. A limited reduction in the concentration of antibiotic resistance targets given by AD was observed in the study (<1 Log). The persistence of ARGs after mesophilic digestion of the OFMSW suggests a risk of horizontal transmission when directly spread on soil. Further evaluations are needed for safe and sustainable reuse of such sludges. Full article