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Wheat straw (WS) constitutes a considerable biomass resource and can be used to produce the energy carrier methane through anaerobic digestion. Due to the low contents of several nutrient elements and water in harvested WS, the use of sewage sludge (SS), consisting of primary sludge and waste-activated sludge, as a nutrient source in co-digestion with steam-pretreated wheat straw (PWS) was investigated theoretically and practically. WS was steam-pretreated, with acetic acid as the catalyst, at 190 °C for 10 min, ending with a rapid reduction in pressure. Process stability and specific methane production were studied for the mono-digestion and co-digestion of PWS and SS in continuous stirred-tank reactors for 208 days. The HRT was 22 days and the OLR 2.1 gVS L−1 d−1. In co-digestion, the OLR was increased to 2.8 gVS L−1 d−1 for one week. Nutrient elements were added to PWS mono-digestion at two different concentration levels. Co-digestion was stable, with a total concentration of short-chain fatty acids (SCFAs) at a safe level below 0.35 g L−1 at both OLRs. The higher OLR during co-digestion would require an increase in reactor volume of 14%, compared to the mono-digestion of SS, but would increase the annual production of methane by 26%. The specific methane production levels for PWS mono-digestion, SS mono-digestion, and co-digestion were 170, 320, and 260 mL g−1VS, respectively. Co-digestion did not result in a synergistic increase in the methane yield. SCFAs accumulated in the mono-digestion of PWS when using lower levels of nutrient supplements, and the concentrations fluctuated at higher nutrient levels. The main conclusion is that PWS and SS can be co-digested with long-term process stability, without the addition of chemicals other than water and acetic acid. The specific methane production for mono-digestion of PWS was relatively low. The effect of using higher concentrations of micronutrients in PWS mono-digestion should be evaluated in future studies. [ABSTRACT FROM AUTHOR]

The concept of the circular economy represents the most relevant mainstream approach to reducing the negative environmental impact of waste. Anaerobic digestion has proved to be one of the leading and widely adopted techniques for sewage sludge treatment under the principles of the circular economy. The purpose of this study is to forecast environmental and economic indicators through modeling the extensive utilization of biogas technologies with a case study of an administrative territorial unit. The proposed methodological framework involves the use of averaged specific indicators and is based on the relationship between inhabitants, waste generation rates, biogas yield, greenhouse gas emission mitigation and biogas energy potential. The widespread use of anaerobic digestion techniques according to the proposed methodology in the instant scenario will ensure the biogas yield of 10 million Nm3 within the considered administrative territory unit with a population of 4.2 million P.E., which ultimately can be expressed in electricity and thermal generation potential of 20.8 and 24.8 million kWh*y, respectively, annual greenhouse gas elimination of 119.6 thousand tons of CO2 equivalent and capital investment attraction of EUR 65.18 million. Furthermore, all sewage sludge will be subjected to disinfection and stabilization procedures to ensure its safe utilization. The findings of this study offer an opportunity for a wide range of stakeholders to assess the environmental and economic benefits of the widespread adoption of biogas technologies. The developed methodology can be utilized to inform management decisions through the use of the instant and scenario forecasts. [ABSTRACT FROM AUTHOR]

With the increasing production of municipal sewage sludge (MSS) worldwide, the development of efficient and sustainable strategies for its management is crucial. Pyrolysis of MSS offers several benefits, including volume reduction, pathogen elimination, and energy recovery through the production of biochar, syngas, and bio-oil. However, the process can be limited by the composition of the MSS, which can affect the quality of the biochar. Co-pyrolysis has emerged as a promising solution for the sustainable management of MSS, reducing the toxicity of biochar and improving its physical and chemical properties to expand its potential applications. This review discusses the status of MSS as a feedstock for biochar production. It describes the types and properties of various co-substrates grouped according to European biochar certification requirements, including those from forestry and wood processing, agriculture, food processing residues, recycling, anaerobic digestion, and other sources. In addition, the review addresses the optimization of co-pyrolysis conditions, including the type of furnace, mixing ratio of MSS and co-substrate, co-pyrolysis temperature, residence time, heating rate, type of inert gas, and flow rate. This overview shows the potential of different biomass types for the upgrading of MSS biochar and provides a basis for research into new co-substrates. This approach not only mitigates the environmental impact of MSS but also contributes to the wider goal of achieving a circular economy in MSS management. [ABSTRACT FROM AUTHOR]

This study aimed to define the optimal composition of three heterogeneous substrates of the anaerobic digestion process to maximize methane production. The investigated substrates were sewage sludge (SS), the organic fraction of municipal solid waste (OFMSW), and horse waste (HW). The optimal composition of these substrates was defined using the mixture design and, more specifically, the simplex–centroid mixture design. Customized methods and materials were employed to study the complex mixture design of these substrates. The findings revealed that the optimal mixture involved all three substrates with the composition 0.17 HW, 0.66 SS, and 0.17 OFMSW, which demonstrated the highest methane yield at 269 NmL·gVS−1. In addition, a mathematical model was developed to predict methane production based on a specific composition of co-substrates. The results were validated at the small pilot scale. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is a biological process that occurs in the limited presence of oxygen. This process involves various difficulties during the operation, such as acidification and increased concentration of volatile fatty acids, which can inhibit methane production. Therefore, in this work, the impact of biochar on the co-digestion of untreated sludge and residual biomass under mesophilic conditions was studied. For the production of biochar, the gasification process was used at different temperatures: 759 °C (BL), 798 °C (BM), and 888 °C (BH). This biochar was added in concentrations of 0 g/L, 3.33 g/L, and 6.67 g/L at the beginning of the co-digestion process. The results showed that a concentration of 6.67 g/L with BH biochar increased the PBM by 18% compared to the control sample and reduced the chemical oxygen demand (COD) by 88%. In addition, there was a reduction of volatile fatty acids (VFA) of 42.75%. Furthermore, FTIR analysis demonstrated that biochar has appropriate functional groups for this process. These data suggest a good interaction of biochar with the mixture of sludge and municipal waste, indicating that biochar can improve the anaerobic co-digestion of untreated sludge and municipal waste. [ABSTRACT FROM AUTHOR]

The mushroom agroindustry generates a huge amount of waste from mushroom production (WMP). The composition of WMP is not standardized but differs mainly in terms of organic matter (OM) content and OM biodegradability. This makes WMP management, including anaerobic digestion (AD), a significant challenge. A potential solution could be co-digestion of WMP with municipal sewage sludge (SS), especially SS generated in small rural wastewater treatment plants (WWTPs). Therefore, this study investigated mesophilic methane production (MP) from WMP, SS, and mixtures of SS and WMP at ratios of 70:30, 50:50, and 30:70 (w/w OM). Even though the maximum cumulative MP from WMP was relatively low (approx. 60 NL/kg OM), co-digesting WMP with SS increased both MP and the methane content of the biogas: with 30%, 50%, and 70% shares of SS, MP increased almost 2, 2.5, and 3.3 times, and the methane content increased to 61%, 62%, and 64%, respectively. As the SS content was increased, the kinetic coefficients of MP and OM removal decreased (from 0.211 to 0.146 d−1 and from 0.215 to 0.152 d−1), whereas the initial rate of MP and of OM removal increased (from 12.5 to 36.8 NL/(kg OM·d) and from 0.51 kg OM/(m3·d) to 0.59 kg OM/(m3·d), respectively). The effectiveness of OM removal (EOMrem) was lowest with WMP only, at 46.6%. When the SS content of the mixtures was increased to 30%, 50%, and 70%, EOMrem also increased to 55.3%, 60.1%, and 64.9%, respectively. The relationship between maximal MP and the overall OM removed was such that both increased simultaneously. The higher values of EOMrem and, consequently, the lower final contents of OM with more effective MP indicate that the organics were degraded more efficiently. These results suggest that co-digestion may be a profitable solution for simultaneously utilizing both of these waste products, increasing the efficiency of biogas production to such an extent that it would be profitable to conduct AD on mushroom farms. This is a flexible approach that allows varying proportions of WMP and SS to be used, depending on the availability of both substrates and the energy needs of the mushroom farm. However, it should be borne in mind that a higher share of WMP results in lower gas productivity. [ABSTRACT FROM AUTHOR]

The recovery of valuable resources from wastewater treatment plants (WWTPs) has received a great deal of attention as part of the concept of a circular economy. Anaerobic digestion for stabilizing sewage sludge in WWTPs, which produces biogas and stabilized biosolids, is a mature technology used worldwide. However, despite the necessity of achieving safe and reliable organic recycling, studies on the effect of some emerging micropollutants on this process are rare. This knowledge gap is of growing relevance because of the increasing use of some endocrine-disrupting compounds (EDCs), microplastics (MPs), and engineered nanoparticles (NPs) in industry and human life. These compounds are ubiquitous in wastewater streams and, therefore, may have serious effects on the course of the anaerobic digestion of sewage sludge, raising concerns about their effects on the environment. This article provides a comprehensive overview of the mechanisms by which selected EDCs, MPs, and NPs affect the valorization of sewage sludge, with a focus on the production of CH4, H2, and volatile fatty acids. This study takes into consideration the performance during all stages of anaerobic digestion, the shifts in microbial abundance and diversity, and the activity of key enzymes during the treatment process. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is a potential treatment for industrial wastewater that provides valuable end-products, including renewable energy (biogas). However, waste streams may be too variable, too dilute at high volumes, or missing key components for stable digestion; all factors that increase costs and operational difficulty, making optimisation crucial. Anaerobic digestion may benefit from process intensification, particularly the novel combination of high-strength source-separated wastewater to minimise volume, together with the use of biosolids biochar as a chemical and microbial stabiliser. This study investigates the stability, yield, and microbial community dynamics of the anaerobic digestion of source-separated industrial wastewater from a food manufacturer and a logistics company, using biosolids biochar as an additive, focusing on gas and volatile fatty acid (VFA) production, process stability, and the microbial community using bench-scale semi-continuous reactors at 30- and 45-day hydraulic retention time (HRT). While gas yields were lower than expected, stability was possible at high HRT. Methane production reached 0.24 and 0.43 L day−1 per litre reactor working volume at 30- and 45-day HRT, respectively, despite high VFA concentration, and was linked to the relative abundance of Methanosarcina in the microbial community. Interactions between substrate, VFA concentration, and the microbial community were observed. Biochar-assisted anaerobic digestion holds promise for the treatment of source-separated wastewater. [ABSTRACT FROM AUTHOR]

The advanced anaerobic digestion process enhances sludge resource utilization. However, thermal hydrolysis pretreatment of anaerobically digested sludge reduces dewatering efficiency due to excessive organic matter decomposition. This necessitates significant time and effort for sludge conditioning in wastewater treatment plants. Using conditioning agents can achieve high dewatering efficiency. This study investigates how the order of adding coagulants and flocculants impacts the dewatering performance of digested sludge. The results indicate that, compared to the flocculation–coagulation process with the same dosage, the coagulation–flocculation process leads to a 15–20% increase in the average particle size of digested sludge. The content of polysaccharides and proteins in S-EPS decreases by 28.8–30.8% and 10.1–11.3%, respectively. The filter cake solids content increases by 8.5%, and there is an increase in surface water channels within the flocs. This is because initially adding coagulants efficiently adsorbs small particles, forming larger aggregates that settle effectively. This promotes the breakdown of extracellular polymeric substances, releasing more bound water. Adding flocculants later bridges the aggregates, further enhancing settling and filtration performance, thereby improving sludge dewatering efficiency. These research findings contribute to a better understanding of the mechanisms of coagulant and flocculant co-conditioning for digested sludge and provide recommendations for optimizing sludge conditioning steps. [ABSTRACT FROM AUTHOR]

Traditionally, anaerobic digestion has been applied to mixed sludge, combining primary sludge (PS) with secondary sludge. However, recent research has unveiled the advantages of dedicated PS digestion due to its higher energy content. Anaerobic digestion (AD) of primary sewage sludge can offer a sustainable solution for managing sewage sludge while generating renewable energy. The present study provides a comprehensive examination of the current state of knowledge regarding the anaerobic digestion of PS. Co-digestion of PS with organic substrates, including food waste and agro-industrial residues, emerges as a promising approach to boost biogas production. Additionally, the utilization of additives such as glucose and clay minerals has shown potential in improving methane yield. Critical factors affecting AD, such as pretreatment methods, carbon-to-nitrogen (C/N) ratio, temperature, pH, volatile fatty acids (VFAs) levels, organic loading rates (OLR), inoculum-to-substrate ratio (ISR), and the role of additives, have been meticulously studied. Finally, this review consolidates existing knowledge to advance our understanding of primary sewage sludge anaerobic digestion, fostering more efficient and sustainable practices in sludge management and renewable energy generation. [ABSTRACT FROM AUTHOR]

Anaerobic digestion of sewage sludge is limited at the hydrolysis stage of the process. The goal of this study was to assess the effects of sludge retention times and ultrasound pretreatment on the ammonium concentration and organic matter transformation in anaerobic digesters treating sewage sludge. To achieve this, two laboratory-scale semicontinuous anaerobic digesters were operated for a period of over 70 d, including a control reactor and another fed by pretreated sludge. Both anaerobic systems were fed with mixed sludge (50%/50% primary/secondary treatment) in mesophilic conditions (37 °C), with solid retention times (SRT) of 7.5 d (Phase I) and 3 d (Phase II). The performance of the anaerobic digestion process was assessed in terms of the methane yield and the total and soluble chemical organic demand, total solids, and volatile solids removal. The results showed that the ultrasound pretreatment caused an increase of around 22.2% in CODt removal for an SRT of 7.5 d. Meanwhile, an SRT of 3 d resulted in a decrease of up to 92.4% in CODt removal. The performance in terms of biogas production and organic matter removal was significantly affected by the SRT reduction to 3 d, showing that the process is not viable in these conditions. [ABSTRACT FROM AUTHOR]

Egypt faces significant challenges in managing its sewage sludge generated in large quantities from wastewater treatment plants. This study investigates the feasibility of utilizing sewage sludge as a renewable resource for hydrogen production through anaerobic digestion at the 100 L bioreactor level. Hydrogen is considered a promising alternative energy source due to its high energy content and environmental benefits. To optimize the microbial degradation process and maximize hydrogen production from sewage sludge, a specialized pretreatment is necessary. Various pretreatment methods have been applied to the sewage sludge, individually and in combination, to study the bio-hydrogen production from sewage sludge. The four methods of treatment were studied in batch assays as a pilot scale. Thermal pretreatment of sewage sludge significantly increases bio-hydrogen production yield compared to other sewage sludge pretreatment methods, producing the highest H2 yield (6.48 LH2/g VS). In general, the hydrogen yield of any type of pretreated inoculum was significantly higher than the untreated inoculum. At the same time, alkaline pretreatment improved the hydrogen yield (1.04 LH2/g VS) more than acid pretreatment (0.74 LH2/g VS), while the hydrogen yield for the combination of pretreatments (shock alkali pretreatment) was higher than both (1.73 LH2/g VS), On the other hand, untreated sewage sludge (control) had almost no hydrogen yield (0.03 LH2/g VS). The self-fermented anaerobic bioreactor improved sewage sludge utilization, increased bioenergy yields, and seems to be promising for treating complex wastes at this scale. [ABSTRACT FROM AUTHOR]

The use of microalgae as a raw material for biogas production is promising. Macroalgae were mixed with cattle manure, wheat straw, and an inoculant from sewage sludge. Mixing macroalgae with co-substrates increased biogas and methane yield. The research was carried out using a three-stage bioreactor. During biogas production, the dynamics of the composition of the microbiota in the anaerobic chamber of the bioreactor was evaluated. The microbiota composition at different organic load rates (OLRs) of the bioreactor was evaluated. This study also demonstrated that in a three-stage bioreactor, a higher yield of methane in biogas was obtained compared to a single-stage bioreactor. It was found that the most active functional pathway of methane biosynthesis is PWY-6969, which proceeds via the TCA cycle V (2-oxoglutarate synthase). Microbiota composition and methane yield depended on added volatile solids (VSadded). During the research, it was found that after reducing the ORL from 2.44 to 1.09 kg VS/d, the methane yield increased from 175.2 L CH4/kg VSadded to 323.5 L CH4/kg VSadded. [ABSTRACT FROM AUTHOR]

Since a large amount of sewage sludge (WSS) is generated daily, exploring effective methods for utilizing WSS is necessary. Although a photo-fermentation system sometimes alters the characteristics of microbial functions, there have been no attempts to perform photo-fermentation using WSS, which is regularly treated via dark fermentation. In this study, the effect of photo-fermentation (photo-irradiation) on anaerobic digestion using WSS was revealed. Photo-irradiation during the anaerobic digestion of WSS significantly reduced the amount of methane and hydrogen sulfide. Methane production was also reduced 5.6-fold at 13 days under light conditions, whereas hydrogen sulfide was consumed almost completely at 6 days. However, it was shown that the activity of sulfate-reducing bacteria in WSS under light treatment increased. Photo-irradiation also stimulated the growth of green sulfur bacteria and induced anoxygenic photosynthesis, via which process the fermented samples turned green in a manner that was correlated with their consumption of hydrogen sulfide. The production of organic acids was lowered in the samples that were irradiated using light. Finally, dark/light switching fermentation was only able to reduce hydrogen sulfide while methane production remained the same. The amounts of methane and hydrogen sulfide were 35 mmol/g VS, and they were undetected at 58 days in photo-irradiated samples compared to the control samples that produced 37 mmol/g VS of methane and 15 ppm/g VS of hydrogen sulfide. [ABSTRACT FROM AUTHOR]

Our study aimed to investigate the applicability of dielectric measurements across three key stages of plant-based biomass utilization: enzymatic hydrolysis of native and microwave pre-processed corn-cob residues, ethanol fermentation of the hydrolysates, and anaerobic co-digestion with meat-industry wastewater sludge. Our major findings reveal that microwave pre-treatment not only accelerates enzymatic hydrolysis but also improves sugar yield. A strong linear correlation (r = 0.987–0.979; R2 = 0.974–0.978) was observed between the dielectric constant and sugar concentrations, offering a reliable monitoring mechanism. During ethanol fermentation, microwave pre-treated samples resulted in higher yields; however, the overall bioconversion efficiency was lower. Dielectric measurements also exhibited a strong linear correlation (r = 0.989–0.997; R2 = 0.979–0.993) with ethanol concentration. Finally, anaerobic co-digestion could be effectively monitored through the measurement of the dielectric constants (r = 0.981–0.996; R2 = 0.963–0.993), with microwave-treated samples showing higher biogas yields. These results demonstrate that dielectric measurements provide a promising alternative for monitoring and controlling biomass utilization processes. [ABSTRACT FROM AUTHOR]

Restoration potential (RP) and deterioration potential (DP) were formulated to shed light on the kinetic balance between anaerobic biochemical reactions. RP is gauged by the ratio of the methanogenesis rate (MR) to the acidogenesis rate (AR), while the DP is the sum of the accumulation rate (AcR) and dilution rate (DR) of total VFAs, normalized using the AR. In an anaerobic digester for a mixture of pulverized food waste and liquified sewage sludge, an RP above 1.0 signifies a restorative state in the kinetic balance of anaerobic biochemical reactions across various operational phases, including startup and steady state, and shifts in organic loading rate. Conversely, a DP value of 0.0 or higher denotes a deterioration in the kinetic balance. The instability index (ISI), calculated as the DP to RP ratio, serves as an indicator of an anaerobic digestion state. When the standard deviation of ISI surpasses 0.2, it signifies instability in biochemical reactions; however, an average ISI below 0.05 indicates a stable digestion process. The study underscores the efficacy of RP, DP, and ISI as robust indicators for assessing the stability of anaerobic digestion based on the kinetics of biochemical reactions. [ABSTRACT FROM AUTHOR]

The effects of co-digesting sewage sludge (SS) and horse waste (HW), the composition of HW, and the ratio of HW:SS were studied using two semi-continuous digesters of 9.5 L of working volume. These digesters were operated in parallel with the mono-digestion of SS in digester 1 (D1) and the co-digestion of SS and HW in digester 2 (D2). In digester 2, there were two phases of digestion (durations of 40 and 43 weeks, respectively). The composition of HW in the first phase was 85% wheat straw (WS), 14% wood chips (WC), and 1% horse manure (HM), with 99% wheat straw (WS) and 1% horse manure (HM) in the second phase. Variable ratios of HW:SS were studied in the digesters. The co-digestion of sewage sludge (SS) and horse waste (HW) produced more biogas than the mono-digestion of SS alone, with a maximum of 15.8 L·d−1, compared to 9 L·d−1 at the end of the experiment. When comparing the results obtained in both phases, the production of methane in phase 2 was 18 NmL·gVS−1 higher than in phase 1. This slight increase in methane yield could be linked to the absence of wood chips (WC), which is considered to have a diluting effect on methane production. Therefore, this study shows that an organic loading rate (OLR) of 4.8 kgVS·m−3·d−1, a ratio of HW:SS of 3, and a composition of HW (99% WS, 1% HM) should be respected in the actual experimental conditions for a well-functioning anaerobic digestion. [ABSTRACT FROM AUTHOR]

The International Water Association's (IWA) established Anaerobic Digestion Model No. 1 (ADM1) was created to serve as a backup for experimental findings regarding the actual anaerobic digestion process. The previous model idea was adjusted and used to simulate an anaerobic digestion process in this study. Testing procedures, such as benchmark tests and balance checks, were performed in order to verify the accuracy of the implementation. These measures worked in tandem to ensure that the model was implemented flawlessly and without inconsistencies. The primary objective of this article is to construct a method that is based on the ADM1 for evaluating co-digestion and predicting the performance of the digestion process or methane yield based on the analyzed substrates' physicochemical properties. Additional equations and simulations have been added to the standard model to create tools for evaluating the feasibility of anaerobic co-digestion. The study's two most intriguing aspects are the optimal mixture and parameter dependence. The adjusted ADM1 is accurate in predicting the measured values of effluent COD, pH, methane, and produced biogas flows with a reasonable degree of accuracy, according to the validation results. This research shows how to use ADM1 in a wastewater treatment plant and other settings where anaerobic digestion is of interest. [ABSTRACT FROM AUTHOR]

Digesters at water resource recovery facilities (WRRFs) operating at different temperatures within the mesophilic and thermophilic temperature range is a flexibilization concept to contribute to heat management. Four 25 L digesters were fed with sewage sludge from a municipal WRRF and were operated at 37, 43, 47 and 53 °C, respectively, to describe changes in the overall process performance and the microbiota. Specific methane yield and COD degradation rates were the highest at 47 °C, only being up to 7% higher compared with at 37 °C. The increase in pH and concentrations of NH4-N and PO4-P above 43 °C were statistically significant. The effect on the microbial community was strong, indicating both a constant specialization towards thermophilic organisms as well as a change from acetoclastic to hydrogenotrophic/methylotrophic methanogenesis. The influence of temperature on process-engineering and physicochemical aspects was rather small compared with the changes in the microbiota. [ABSTRACT FROM AUTHOR]

Brewery wastewater is characterized by a high organic matter content and low pH, which may cause serious ecological hazards if it is discharged without any treatment. In this study, brewery wastewater treatment was integrated with anaerobic digestion of municipal sewage sludge. Additionally, the effects of temperature and mixing ratio of brewery wastewater were investigated. The results showed that the brewery wastewater mixing ratio (v/v) of 20% could maximize the biogas production during anaerobic digestion at the temperature of 34 °C. Additionally, regulating the appropriate mixing ratio, increasing operating temperature and adjusting pH were effective ways to enhance anaerobic digestion efficiency. Furthermore, the distribution of microbial communities was confirmed to be significantly influenced by the mixing ratio of brewery wastewater using high-throughput DNA sequencing technology. With the increasing mixing ratio of brewery wastewater, Firmicutes gradually dominated instead of Chloroflexi. Meanwhile, Methanolinea and Methanosarcina became the dominant methanogens, while the proportion of Methanothrix was significantly reduced. The results of this study will provide data to support the practical process operation of anaerobic co-digestion of brewery wastewater and municipal sewage sludge. [ABSTRACT FROM AUTHOR]

Supplementation with iron oxide nanoparticles has been suggested as a potential method for improving energy generation through anaerobic digestion, specifically by enhancing the rate of methane production. This investigation examined the effects of iron oxide (Fe3O4) nanoparticles (NPs) on anaerobic co-digestion of cow manure (CM) and sewage sludge (SS) through batch testing conducted under mesophilic conditions (35 °C) using a RESPIROMETRIC Sensor System 6 Maxi—BMP (RSS-BMP). The use of Fe3O4 nanoparticles at doses of 40, 80, 120, and 160 mg/L (batches M1, M2, M3, and M5) was studied. The use of 160 mg/L Fe3O4 nanoparticles in combination with mixtures of different ratios (M4, M5, and M6) was further investigated. The findings indicate that the addition of Fe3O4 nanoparticles at a concentration of 40 mg/L to anaerobic batches did not significantly impact the hydrolysis process and subsequent methane production. Exposing the samples to Fe3O4 NPs at concentrations of 80, 120, and 160 mg/L resulted in a similar positive effect, as evidenced by hydrolysis percentages of approximately 94%, compared to 60% for the control (C2). Furthermore, methane production also increased. The use of Fe3O4 nanoparticles at a concentration of 160 mg/L resulted in biodegradability of 97.3%, compared to 51.4% for the control incubation (C2). Moreover, the findings demonstrate that supplementing anaerobic batches with 160 mg/L Fe3O4 NPs at varying mixture ratios (M4, M5, and M6) had a significant impact on both hydrolysis and methane production. Specifically, hydrolysis percentages of 94.24, 98.74, and 96.78% were achieved for M4, M5, and M6, respectively, whereas the percentages for the control incubation (C1, C2, and C3) were only 56.78, 60.21, and 58.74%. Additionally, the use of 160 mg/L Fe3O4 NPs in mixtures M4, M5, and M6 resulted in biodegradability percentages of 78.4, 97.3, and 88.3%, respectively. In contrast, for the control incubation (C1, C2, and C3) biodegradability was only 44.24, 51.4, and 49.1%. [ABSTRACT FROM AUTHOR]

This study evaluates the potential to synthesize an adsorbent for wastewater remediation applications from an anaerobic digestion by-product synthesized using biomaterials and a less energy-intensive process. The synthesized sludge-based granular activated carbon (GAC) was used to adsorb Cr(VI) and Cd(II) in a batch reactor stirred for 24 h at 25 °C. The surface chemistry of the material was assessed porosity with BET, SEM for morphology, EDS-XRF for elemental analysis, and functional groups on these materials using FTIR and TGA for thermal profile. SBET of the SAC was discovered to be 481.370 m2/g with a VT of 0.337 cm3/g, respectively 9.02 and 2.23 times greater than raw sludge. The modification to SAC shows a dramatic increase in performance from 40% to 98.9% equilibrium adsorption rate. The maximum or equilibrium removal (99.99%) of Cr(VI) and Cd(II) was achieved by 0.8 and 1.4 g SAC dosage, respectively. Thus, it can be concluded that activation of sewage sludge was effective in enhancing the surface area and pore volume which made it suitable for AMD remediation application. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is considered as one of the most feasible waste-to-energy technologies for the valorization of organic wastes. It can be applied to many different substrates but the mono-digestion of a single substrate usually has some important drawbacks due to the physico-chemical characteristics of the substrate. A feasible solution is the simultaneous co-digestion of several substrates with different composition and characteristics, so that synergetic effects may be generated and physico-chemical characteristics may be compensated, thus reaching higher process efficiencies and biogas production rates. In this work, a multi-parametric analysis for the objective comparison of industrial wastes was developed in order to help with decision making about their suitability as a co-substrate in anaerobic co-digestion. Criteria considered for this analysis included sample composition, C/N ratios, theoretical biochemical methane potential (BMP), and other important issues such as production rates, seasonality, and the distance to the WWTP or pre-treatment requirements. Results showed that, among the 13 evaluated wastes, 2 of them showed a higher potential for being used in anaerobic co-digestion: 1. Fried corn from the snack food industry and 2. Wet fatty pomace from the olive oil industry. Both wastes showed high estimated BMP values, high lipid and carbohydrate content, and C/N ratios in a proper range to improve the low C/N ratio of sewage sludge. Other wastes such as olive pomace (dry), skinless corn (not fried), and grape pomace from the winery industry may also be used as co-substrates. As a conclusion, this procedure based on a selection matrix can be considered as a useful tool to help both producers and WWTP operators to make decisions about the potential applicability of specific industrial wastes as co-substrates in anaerobic co-digestion. [ABSTRACT FROM AUTHOR]

Temperature plays a significant role in anaerobic digestion (AD) as it affects the microbial communities and ultimately controls the efficiency of the process. Few studies have looked at temperature-adjusted AD, but it is unclear how the temperature shifts affect biogas production and the dynamics of microorganisms involved in methanogenesis. This study tested two temperature shift scenarios in fed-batch mode using anaerobically digested sewage sludge and glucose-based substrate. The first scenario was acclimatized to upshifting temperatures from 42 °C to 48 °C while the second was acclimatized to downshifting temperatures from 55 °C to 45 °C. Both temperature shift scenarios resulted in a decrease in biogas production, especially at 45 °C. The upshifted scenario experienced a maximum decrease of 83%, and the downshifted scenario experienced a 16–33% decrease in methane production. Next-generation 16S rRNA sequencing revealed the domination of Methanoculleus in the upshifted scenario. However, a low correlation between the number of Methanoculleus and the other hydrogenotrophic methanogens to biogas production indicates inhibition in the hydrogenotrophic pathway. The downshifted scenario showed better biogas production due to the substantial domination of acetoclastic Methanosaeta and the low abundance of sulfate-reducing bacteria. Hence, the temperature shift affects the microbial communities, significantly affecting biogas production performance. [ABSTRACT FROM AUTHOR]

The most common technology for the recovery of energy and valuable materials from sewage sludge is anaerobic digestion (AD). Ensuring thermophilic conditions during AD has been proven to cause process intensification and an improvement in its final outcomes. Nonetheless, the search is underway for other methods to bolster the effectiveness of the AD of aerobic granular sludge (AGS), which is characterized by a compact and complex structure. A prospective AGS pre-treatment technology entails the use of solidified carbon dioxide (SCO2). The present study focused on an evaluation of the AGS pre-treatment with SCO2 on the thermophilic AD technological effects. It evaluated the effect of the SCO2 pre-treatment method on changes in the concentrations of organic and biogenic compounds in the dissolved phase and the yield and kinetics of biogas and methane production in periodical reactors, as well as enabled the development of an empirical organizational model of biogas production. SCO2 introduced to AGS caused an increase in the content of COD, N-NH4+, and P-PO43− in the AGS dissolved phase at SCO2/AGS volumetric ratios ranging from 0 to 0.3. A further increase in the SCO2 dose did not cause any statistically significant differences in this respect. The highest biogas and methane yields were obtained at SCO2/AGS of 0.3 and reached 482 ± 21 cm3/gVS and 337 ± 14 cm3/gVS, respectively. The higher SCO2 doses used led to a significant decrease in the pH value of the AGS, which, in turn, contributed to a decreasing CH4 concentration in the biogas. [ABSTRACT FROM AUTHOR]

Sewage sludge to energy conversion is a sustainable waste management technique and a means of militating against the environmental concerns associated with its disposal. Amongst the various conversion technologies, anaerobic digestion and gasification have been identified as the two most promising. Therefore, this study is focused on a detailed evaluation of the anaerobic digestion and gasification of sewage sludge for energy production. Moreover, the key challenges hindering both technologies are discussed, as well as the practical measures for addressing them. The applicable pretreatment measures for efficient transformation into valuable energy vectors were further evaluated. Specifically, the study evaluated various properties of sewage sludge in relation to gasification and anaerobic digestion. The findings showed that a high ash content in sewage sludge results in sintering and agglomeration, while a high moisture content promotes tar formation, which has been identified as one of the key limitations of sewage sludge gasification. More importantly, the application of pretreatment has been shown to have some beneficial features in promoting organic matter decomposition/degradation, thereby enhancing biogas as well as syngas production. However, this has additional energy requirements and operational costs, particularly for thermal and mechanical methods. [ABSTRACT FROM AUTHOR]

Ultrasound and combined alkaline–ultrasound pretreatment (AUP) strategies were examined for primary sewage sludge (SS) disintegration and were utilized to evaluate the degree of solubilization (DS). Further, the pretreated primary SS was operated in microbial electrolysis cells (MECs) to maximize methane production and thereby improve the reactor performance. The highest DS of 67.2% of primary SS was recorded with the AUP. MEC reactors operated with the AUP showed the highest methane production (240 ± 6.4 mL g VSin−1). VS (61.1%) and COD (72.2%) removal in the MEC ALK-US showed the best organic matter removal efficiency. In the modified Gompertz analysis, the substrate with the highest degree of solubilization (AUP) had the shortest lag phase (0.2 ± 0.1 d). This implies that forced hydrolysis via pretreatment could enhance biodegradability, thereby making it easy for microorganisms to consume and leading to improved MEC performances. Microbial analysis implicitly demonstrated that pretreatment expedited the growth of hydrolytic bacteria (Bacteroidetes and Firmicutes), and a syntrophic interaction with electroactive microorganisms (Smithella) and hydrogenotrophic methanogens (Methanoculleus) was enriched in the MECs with AUP sludge. This suggests that the AUP strategy could be useful to enhance anaerobic digestion performance and provide a new perspective on treating primary SS in an economical way. [ABSTRACT FROM AUTHOR]

A demonstrator plant of a recently patented process for improved sludge degradation has been implemented on a municipal scale. In a 1500 m3 sewage sludge digester, an intermediary stage with aerobic sewage sludge reactivation was implemented. This oxic activation increased the biogas yield by up to 55% with a 25% reduction of the remaining fermentation residue volume. Furthermore, this process allowed an NH4-N removal of over 90%. Additionally, 16S rRNA gene amplicon high-throughput sequencing of the reactivated digestate showed a reduced number of methane-forming archaea compared to the main digester. Multiple ammonium-oxidizing bacteria were detected. This includes multiple genera belonging to the family Chitinophagaceae (the highest values reached 18.8% of the DNA sequences) as well as a small amount of the genus Candidatus nitrosoglobus (<0.3%). In summary, the process described here provides an economically viable method to eliminate nitrogen from sewage sludge while achieving higher biogas yields and fewer potential pathogens in the residuals. [ABSTRACT FROM AUTHOR]

In this paper, the possibility to obtain an alternative source of energy from methane fermentation, catalysed by biomass, has been discussed in detail. As a main substrate, the distillation residue from the distillery industry was taken in the case of mono-fermentation and its co-fermentation with sewage sludge. The results showed that higher biogas and methane production can be obtained in a mono-fermentation process. Fermentation lasted for 23 days, and during this time, 333.14 and 249.64 L/kg VS of the total biogas for mono- and co-fermentation was subsequently obtained, which gives around 63% and 50% of methane in both types of the process, respectively. Additionally, to interpret the experimental data obtained and to predict the trend of the accumulation curves, a simple Gompertz model has been applied. The application of the Gompertz model has enabled us to estimate some important parameters with a strict physical meaning, namely, the maximum production value of the biogas and its components, the production rate of a given gas, as well as the incubation phase time. Finally, an approximate analysis of the potential volume of biogas production was also carried out, based on the mass of distillation residue produced annually in Poland. [ABSTRACT FROM AUTHOR]

One of the most pressing environmental problems worldwide is sewage sludge (SS) management. Every year, wastewater volume increases and thus, the amount of SS produced increases as well. The disposal of SS in landfills, as practiced in many countries, is not a sustainable solution. Instead, SS, rich in organic matter and other nutrients, can be used as an alternative soil additive or fertilizer. The properties of these materials depend on their chemical composition and the method of treatment. Experience from a number of countries, such as the US and Europe, has shown that SS can be transformed from a waste into a valuable resource, provided that the final product fulfils the relevant regulatory standards. This review examines the sustainable conversion of SS to sustainable fertilizers, the impact on waste minimization, and the potential benefits in agriculture. [ABSTRACT FROM AUTHOR]

Sewage sludge is a useful raw material for the production of renewable energy due to its stable annual output. In this study, the enhancement of mesophilic anaerobic digestion of sewage sludge through heat pretreatment at 95 °C for 30 min was tested in an anaerobic moving bed biofilm reactor (hAMBBR). The sludge retention time was set at 20, 15, 10, and 5 days during 300 days of operation and compared to a traditional anaerobic continuous stirred tank reactor (AnCSTR) without pretreatment. Results of this research indicate that the digestion ratio of volatile soluble solids in the hAMBBR process could be improved by 50%, and the average conversion ratio of methane could be increased by 45%. When the sludge retention time (SRT) was shortened to 5 days, the methane production approached twice that of the contrast reactor. The expanded anaerobic digestion model, including activated sludge models, was utilized for operation simulation. The effect of sludge retention time (SRT) shortening on volatile suspended solids (VSS) digestibility and methane production was well reproduced with simulations. The research conclusion reveals the impact of pretreatment and reactor types on anaerobic digestion and provides the scientific basis for improving methane production and process efficiency in anaerobic digestion. [ABSTRACT FROM AUTHOR]

The paper presents research on the impact of adding various forms of sorghum to sewage sludge on the anaerobic digestion process. The use of liquid sewage sludge alone in biogas plants at wastewater treatment plants is inefficient due to the low total solid (dry matter) content of this substrate. The tests revealed that the production of methane in biogas is low and amounted to 17.9% (105.4 Nm3∙Mg−1, VS—volatile solid). Therefore, other substrates should be blended with sewage sludge to increase the total solid of the batch. Sorghum silage, sorghum pomace, and sorghum juice were added to the sewage sludge in various proportions during the research. As a result, the improvement of the biogas process, the stabilization of the biogas production curve, as well as the increase in methane yield were observed. The most biogas and methane were obtained from a mixture of sorghum juice (5%) and sewage sludge (664.8 Nm3∙Mg−1 VS and 53.9%, respectively). Biogas production from other substrates based on sorghum and sewage sludge ranged from 457.4 to 588.8 Nm3∙Mg−1 VS. For a mixture of juice (7%) and sewage sludge, the batch was acidified, and biogas production was only 281.5 Nm3∙Mg−1 VS. Studies have shown that intelligent blending of an alternative raw material (compared to traditional maize silage) with sewage sludge allows for similar biogas yields while maintaining a stable anaerobic digestion process. [ABSTRACT FROM AUTHOR]

The interspecies electron transfer (IET) between microbes and archaea is the key to how the anaerobic digestion process performs. However, renewable energy technology that utilizes the application of a bioelectrochemical system together with anaerobic additives such as magnetite-nanoparticles can promote both direct interspecies electron transfer (DIET) as well as indirect interspecies electron transfer (IIET). This has several advantages, including higher removal of toxic pollutants present in municipal wastewater, higher biomass to renewable energy conversion, and greater electrochemical efficiencies. This review explores the synergistic influence of bioelectrochemical systems and anaerobic additives on the anaerobic digestion of complex substrates such as sewage sludge. The review discussions present the mechanisms and limitations of the conventional anaerobic digestion process. In addition, the applicability of additives in syntrophic, metabolic, catalytic, enzymatic, and cation exchange activities of the anaerobic digestion process are highlighted. The synergistic effect of bio-additives and operational factors of the bioelectrochemical system is explored. It is elucidated that a bioelectrochemical system coupled with nanomaterial additives can increase biogas–methane potential compared to anaerobic digestion. Therefore, the prospects of a bioelectrochemical system for wastewater require research attention. [ABSTRACT FROM AUTHOR]

Studies on harnessing solidified carbon dioxide (SCO2) for municipal sewage sludge (MSS) pre-treatment have been conducted exclusively in batch reactors. This makes it difficult to accurately assess how long-term SCO2 treatment affects anaerobic digestion (AD) conditions and performance. The aim of our study was to evaluate the effect of long-term MSS pre-treatment with SCO2 on AD conditions, anaerobic bacterial community, and biogas composition and yields. The presented experiments are the first studies on the effect of pre-treatment with SCO2 on the efficiency of AD of MSS in continuous reactors. So far, the impact of the organic load rate (OLR) on the efficiency of MSS methane fermentation has not been assessed, which is also a novelty of the conducted research. The AD process was conducted in continuous-stirred, continuous-flow anaerobic with an active volume of 20 dm3. The digestion process was run at 38 ± 1 °C. The experiment was divided into two stages. Raw (non-pretreated) MSS was used in stage 1, whereas the MSS used in stage 2 was pre-treated with SCO2. The SCO2/MSS ratio was 1:3. Each stage was sub-divided into four variants, with different levels of the OLR ranging from 2.0 to 5.0 gCOD/dm3·day. Pre-treatment with SCO2 was found to improve AD performance at an OLR of 3.0–4.0 gVS/dm3·day. The 3.0 gVS/dm3·day variant offered the best biogas production performance—both daily (29 ± 1.3 dm3/day) and per VS added (0.49 ± 0.02 dm3/gVS)—as well as the highest CH4 content in the biogas (70.1 ± 1.0%). In this variant, the highest energy output effect of 187.07 ± 1.5 Wh/day was obtained. The SCO2 pre-treatment was not found to change the pH, FOS/TAC, or the anaerobic bacterial community composition. Instead, these variables were mainly affected by the OLR. Our study shows that MSS pre-treatment with SCO2 at a SCO2/MSS ratio of 0.3 (by volume) significantly improves AD performance in terms of methane production and feedstock mineralization. The pre-treatment was found to have no negative effect on the long-term continuous operation of the reactor. [ABSTRACT FROM AUTHOR]

Rapid population growth and urbanization have resulted in a multi-fold increase in water consumption over the last few decades, resulting in the generation of large amounts of sewage and sewage sludge that impose severe environmental burdens if not handled properly. Sludge management itself accounts for up to 50% of the total operating costs of wastewater treatment plants (WWTPs). Conventional sludge management practices such as incineration, landfilling, and ocean disposal have been deemed difficult in light of today's stringent environmental legislation and compliance standards. As a result, progress has been made toward developing more sustainable approaches for sludge management. This study reviews recent advancements in sewage sludge management techniques that not only ensure the safe disposal of sewage sludge but also focus on utilizing the potential of sewage sludge as feedstock for energy and resource recovery. Energy could be recovered by subjecting the pre-treated sludge to controlled anaerobic digestion (AD) to produce biogas or by utilizing the lipid content of the sewage sludge through esterification or direct sludge pyrolysis to produce biodiesel/bio-oil. Heavy metals such as Ag, Au, Cu, Fe, Ga, Cr, and others, as well as nutrients such as N, P, K, Mg, S, and others, could also be recovered. If energy and resource recovery from sewage sludge is practiced on a global scale, it could significantly contribute to global greenhouse gas (GHG) emission reduction. This review discusses the commercially developed and still-under-research technologies for energy and other resource recovery of sewage sludge. Additionally, techniques, along with their limitations and potential measures to improve their yields, are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, the application of magnetite-nanoparticles and a microbial fuel cell (MFC) was studied on the anaerobic digestion (AD) of sewage sludge. The experimental set-up included six 1 L biochemical methane potential (BMP) tests with different external resistors: (a) 100 Ω, (b) 300 Ω, (c) 500 Ω, (d) 800 Ω, (e) 1000 Ω, and (f) a control with no external resistor. The BMP tests were carried out using digesters with a working volume of 0.8 L fed with 0.5 L substrate, 0.3 L inoculum, and 0.53 g magnetite-nanoparticles. The results suggested that the ultimate biogas generation reached 692.7 mL/g VSfed in the 500 Ω digester, which was substantially greater than the 102.6 mL/g VSfed of the control. The electrochemical efficiency analysis also demonstrated higher coulombic efficiency (81.2%) and maximum power density (30.17 mW/ m2) for the 500 Ω digester. The digester also revealed a higher maximum voltage generation of 0.431 V, which was approximately 12.7 times the 0.034 V of the lowest-performing MFC (100 Ω digester). In terms of contaminants removed, the best-performing digester was the digester with 500 Ω, which reduced contaminants by more than 89% on COD, TS, VS, TSS and color. In terms of cost-benefit analysis, this digester produced the highest annual energy profit (48.22 ZAR/kWh or 3.45 USD/kWh). This infers the application of magnetite-nanoparticles and MFC on the AD of sewage sludge is very promising for biogas production. The digester with an external resistor of 500 Ω showed a high potential for use in bioelectrochemical biogas generation and contaminant removal for sewage sludge. [ABSTRACT FROM AUTHOR]

The anaerobic digestion of sewage sludge is highly sensitive to high zinc concentrations. Although sulfate-reducing bacteria (SRB) activity can negatively affect methanogenesis, SRB-mediated metal sulfide precipitation can alleviate zinc toxicity. A series of mesophilic anaerobic batch experiments was performed for the biomethane potential of three different sewage sludge samples for 74 days using the background sludge zinc content, alone or in combination with the external addition of 200, 300 and 400 mg Zn/L. The highest biomethane production was 165 ± 1 mL CH4/g VS using activated sludge (AS) with a background concentration of 93 mg Zn/L. A slight decrease in the biomethane yield (i.e., 157 ± 1, 158 ± 1 and 159 ± 1 mL CH4/g VS) was obtained in the presence of 293, 393 and 493 mg Zn/L, respectively. The potential reason for the high methanogenic activity at high inlet Zn concentrations could be that the AS used in this study was already acclimated to those conditions. Zinc was likely removed from the system by sulfide precipitation, and a removal efficiency above 99% was achieved under all zinc concentrations. A sulfate reduction efficiency of 99% was also obtained. Overall, this study details the potential utilization of biogenic sulfide as a metal detoxifying agent without detrimental effects on methane production from sewage sludge. [ABSTRACT FROM AUTHOR]

The aim of the presented research was the assessment of phosphorus speciation impact on the precipitation of phosphorus in reject water using Ca(OH)2. To achieve this, phosphorus speciation (organic and inorganic phosphorus in suspension and in dissolved form) in reject water that is produced during sludge dewatering, after methane digestion in wastewater treatment plants (WWTPs), was determined. This study covered the materials from four WWTPs with different compositions of feedstock for anaerobic digestion (AnD). In one, the AnD process of primary and secondary sludge was carried out without co-substrate, while in three others, co-substrate (waste from the agri-food industry and external waste-activated sludge and fats from industrial plants) was examined. The investigation was conducted in batch reactors using doses of Ca(OH)2 ranging from 2500 to 5500 mg Ca/dm3. The percentage of phosphorus forms determined in the raw reject water was similar, with the dominant form being soluble reactive phosphorus (SPR) (percentage from 87 to 96%). The small differences observed were dependent on the composition of the AnD feedstock. The results showed that, in all analysed wastewater, very high (exceeding 99.9%) phosphate phosphorus removal efficiencies were obtained using Ca(OH)2 for short reaction times (t = 1 h). The efficiency of phosphate removal depended on pH but not on the forms of phosphorus in the analysed reject water. [ABSTRACT FROM AUTHOR]

Appropriate management is necessary to mitigate the environmental impacts of wastewater sludge. One lesser-known technology concerns the use of solidified CO2 for dewatering, sanitization, and digestion improvement. Solidified CO2 is a normal byproduct of natural gas treatment processes and can also be produced by dedicated biogas upgrading technologies. The way solidified CO2 is sourced is fully in line with the principles of the circular economy and carbon dioxide mitigation. The aim of this review is to summarize the current state of knowledge on the production and application of solid CO2 in the pretreatment and management of sewage sludge. Using solidified CO2 for sludge conditioning causes effective lysis of microbial cells, which destroys activated sludge flocs, promotes biomass fragmentation, facilitates efficient dispersion of molecular associations, modifies cell morphology, and denatures macromolecules. Solidified CO2 can be used as an attractive tool to sanitize and dewater sludge and as a pretreatment technology to improve methane digestion and fermentative hydrogen production. Furthermore, it can also be incorporated into a closed CO2 cycle of biogas production–biogas upgrading–solidified CO2 production–sludge disintegration–digestion–biogas production. This feature not only bolsters the technology's capacity to improve the performance and cost-effectiveness of digestion processes, but can also help reduce atmospheric CO2 emissions, a crucial advantage in terms of environment protection. This new approach to solidified CO2 generation and application largely counteracts previous limitations, which are mainly related to the low cost-effectiveness of the production process. [ABSTRACT FROM AUTHOR]

Solid waste is one of the largest sources of greenhouse gases (GHGs) today. The carbon footprint of landfills also has a large impact on global warming. Therefore, it is becoming more urgent to study the possibility of better environmentally friendly approaches for solid waste management and its safe disposal. The digestion of solid waste is a biological process that breaks down the organic content of the solid waste and thus stabilizes it. It also allows the recovery of valuable resources (such as biogas) and the utilization of stabilized waste in various industries. In this study, six substrates were studied to determine their biomethane potential (BMP) in anaerobic digestion. The substrates were fermented and digested anaerobically, and the biogas production was measured. The methane yield of food waste substrates had a higher methane yield between 354 and 347 mL/g-TCOD, and a biodegradability of 89–87%. Wastewater sludge substrates yielded between 324 and 288 mL/g-TCOD with a biodegradability of 81–73%. A kinetics analysis using first-order and Gompertz models was performed for biodegradation and methane production. [ABSTRACT FROM AUTHOR]

The present study evaluated different sludge-reduction mechanisms in the oxic-settling-anaerobic (OSA) process in terms of their effects on methane productivity by anaerobic digestion of sewage sludge. Two different layouts were investigated for the sludge return from an anaerobic side-stream reactor (ASSR) to the anoxic (scheme A) or the aerobic (scheme B) reactor of a pre-denitrification plant. Biochemical methane-potential (BMP) assays performed on the excess sludge revealed that scheme A promoted an overall increase of methane production in the OSA (20 mLCH4 gVSS−1d−1, +19%), although compared with a control CAS plant a significant decrease in the excess sludge production (31%) was obtained. Operating conditions in scheme A caused the occurrence of cell lysis and EPS hydrolysis, thereby increasing the biodegradability of sludge. In contrast, scheme B favoured the occurrence of uncoupling and a maintenance metabolism that did not involve sludge hydrolysis. Consequently, despite a higher reduction of excess sludge (82%), a significant decrease in methane productivity in the OSA (4 mLCH4 gVSS−1d−1, −41%) was observed. Based on the results, implementing the OSA process may allow high levels of methane production by anaerobic digestion to be maintained if specific sludge-reduction mechanisms are triggered in the waterline, also raising the possibility of co-digestion with other feedstocks. [ABSTRACT FROM AUTHOR]

The liquid fraction from the dewatering of digested sewage sludge (LF-DSS) represents a major processing complication for wastewater treatment facilities, thus necessitating new and effective methods of LF-DSS neutralization. This pilot-scale study examined the evolution of a Chlorella sp. monoculture into microalgal-bacterial granular sludge (M-BGS) during treatment of LF-DSS in a hybrid photo-bioreactor (H-PBR). The M-BGS reached a stable taxonomic and morphological structure after 60 days of H-PBR operation. The biomass was primarily composed of Chlorella sp., Microthrix parvicella, and type 1851 and 1701 filamentous bacteria. A greater abundance of bacteria led to a faster-growing M-BGS biomass (to a level of 4800 ± 503 mgTS/dm3), as well as improved TOC and COD removal from the LF-DSS (88.2 ± 7.2% and 84.1 ± 5.1%). The efficiency of N/P removal was comparable, since regardless of the composition and concentration of biomass, it ranged from 68.9 ± 3.1% to 71.3 ± 3.1% for N and from 54.2 ± 4.1% to 56, 2 ± 4.6% for P. As the M-BGS taxonomic structure evolved and the C/N ratio improved, so did the anaerobic digestion (AD) performance. Biogas yield from the M-BGS peaked at 531 ± 38 cm3/gVS (methane fraction = 66.2 ± 2.7%). It was found that final effects of AD were also strongly correlated with the N and TOC content in the substrate and pH value. A mature M-BGS significantly improved settleability and separability through filtration. [ABSTRACT FROM AUTHOR]

Recently, due to the abundance of carbon, nitrogen and phosphorus in municipal sewage sludge (MSS), the energy potential of MSS has become increasingly prominent. Economically developed regions possess more financial and policy support advantages for the development of MSS energy recovery technology; hence, the selection of the appropriate sludge treatment and disposal technologies to maximize the energy potential of MSS is of great importance. In this study, the energy recovery potential of MSS was evaluated on the basis of regional economies, sludge analysis, a main sludge energy reuse technology review and legislative profile analysis. As the most commonly adopted technology, incineration had a lower energy potential, which may be ascribed to the high moisture content, high disposal costs and difficulties in in situ energy recovery. In contrast, the energy potential for anaerobic digestion, pyrolysis and gasification was relatively high. By conducting a SWOT-FAHP analysis, management evaluation of these four technologies was carried out from the following four perspectives: problem solving, technology development, ecological environment and laws and regulations. Pyrolysis was evaluated to be the most suitable technology from the technical and environmental perspectives because its products had high energy potential and avoided heavy metal problems. The obstacles and problems that pyrolysis technology might encounter in commercial applications in the future are discussed. With this energy-generating, low energy consumption, low-pollution sludge energy reuse technology, the potential of sludge pyrolysis would be high in the long run. These results revealed the factors affecting the energy recovery potential of sludge, and comprehensively evaluated the technologies from the aspects of problem solving, environmental impact, technology development and law, the optimal solution obtained could provide reference on the management decision of sludge disposal technology for economically developed areas in the future. [ABSTRACT FROM AUTHOR]

The management of waste polylactide (PLA) in various solutions of thermophilic anaerobic digestion (AD) is problematic and often uneconomical. This paper proposes a different approach to the use of PLA in mesophilic AD, used more commonly on the industrial scale, which consists of assigning the function of a microbial carrier to the biopolymer. The study involved the testing of waste wafers and waste wafers and cheese in a co-substrate system, combined with digested sewage sludge. The experiment was conducted on a laboratory scale, in a batch bioreactor mode. They were used as test samples and as samples with the addition of a carrier: WF—control and WFC—control; WF + PLA and WFC + PLA. The main objective of the study was to verify the impact of PLA in the granular (PLAG) and powder (PLAP) forms on the stability and efficiency of the process. The results of the analysis of physicochemical properties of the carriers, including the critical thermal analysis by differential scanning calorimetry (DSC), as well as the amount of cellular biomass of Bacillus amyloliquefaciens obtained in a culture with the addition of the tested PLAG and PLAP, confirmed that PLA can be an effective cell carrier in mesophilic AD. The addition of PLAG produced better results for bacterial proliferation than the addition of powdered PLA. The highest level of dehydrogenase activity was maintained in the WFC + PLAG system. An increase in the volume of the methane produced for the samples digested with the PLA granules carrier was registered in the study. It went up by c.a. 26% for WF, from 356.11 m3 Mg−1 VS (WF—control) to 448.84 m3 Mg−1 VS (WF + PLAG), and for WFC, from 413.46 m3 Mg−1 VS, (WFC—control) to 519.98 m3 Mg−1 VS (WFC + PLAG). [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) can produce renewable energy and reduce carbon emissions, but the energy conversion efficiency is still limited in some waste streams. This study tested the effect of applied voltage removal for microbial electrolysis cells (MECs) treating primary sewage sludge. Two MECs were operated in parallel: a MEC-0.3 V with an applied voltage of 0.3 V and a MEC-OCV with open circuit voltage. Both reactors were inoculated with seed sludge originating from a MEC at 0.3 V applied voltage, and three batch cycles were operated for 36 d. The methane production of the MEC-OCV was 3759 mL/L in the first cycle and 2759 mL/L in the second cycle, which was similar (105% and 103%, respectively) to that of the MEC-0.3 V. However, in the third cycle, the methane production of the MEC-OCV (1762 mL/L) was 38.8% lower than that of the MEC-0.3 V (4545 mL/L). The methane contents in the biogas were 68.6–74.2% from the MEC-OCV, comparable to those from the MEC-0.3 V (66.6–71.1%). These results indicate that not only the MEC-0.3V but also the MEC-OCV outperformed AD in terms of methane yield and productivity, and the promotion using MEC-derived inoculum persisted equally with the MEC-OCV for two batch cycles after removing the applied voltage. Therefore, a MEC operation with cycled power supply may be beneficial in reducing the electric energy usage and improving the biogas production performance, compared to conventional AD. [ABSTRACT FROM AUTHOR]

The agricultural spreading of treated sewage sludge is a valid strategy in terms of circular economy for the management of this nutrient-rich waste. Anaerobic digestion (AD) can be applied to stabilize and hygienize sewage sludge, making it suitable for agricultural reuse, while producing biogas to be utilized as an energy vector. However, the presence of contaminants, including petroleum hydrocarbons, could limit the widespread agricultural utilization of sewage sludge. In this context, the impact of dewatering agents, such as cationic polyelectrolytes, on AD efficiency and hydrocarbon biodegradation has been poorly investigated, although it represents a noteworthy aspect when conditioned sludge is digested for agricultural use in centralized biogas plants. This work aims to elucidate the effect of cationic polyelectrolyte addition on biomethanation as well as the degradation and extractability of C10-C40 hydrocarbons during mesophilic AD of sewage sludge. The addition of 26.7 g/kgTS of cationic polyelectrolyte was observed to extend the AD lag phase, although similar methane yields (573–607 mLCH4 per g of degraded volatile solids) were observed for both conditioned and raw sludge. Furthermore, a significant impact on hydrocarbon degradation was observed due to chemical conditioning. Indeed, this work reveals that cationic polyelectrolytes can affect hydrocarbon extractability and suggests moreover that the presence of natural interferents (e.g., biogenic waxes) in sewage sludge may lead to an overestimation of potentially toxic C10-C40 hydrocarbon concentrations, potentially limiting the application of sludge-derived digestates in agriculture. [ABSTRACT FROM AUTHOR]

The treatment of municipal wastewater is considered a cornerstone for the protection of public health and environment. However, a major issue derived from this process is the large quantities of produced sewage sludge. Although anaerobic digestion is a widely applied method in Wastewater Treatment Plants (WWTPs) aiming to stabilize the sludge and to recover energy in the form of methane, it is usually limited due to the reduced decomposition efficiency and slow biodegradation rate of this recalcitrant substrate. For this reason, various pretreatment methods have been proposed aiming to modify the sludge structure, solubilize the organic matter, and decrease the crystallinity of sludge so as to accelerate hydrolysis and consequently enhance methane production. The current research is a comprehensive collection of recent advances in pretreatment technologies that can be potentially applied in wastewater treatment facilities. The critical review analysis presented herein reveals the several advantages and drawbacks, as well as the technical opportunities of the pretreatment methods and provides an assessment of their feasibility/applicability from an energetic, environmental, and economic point of view. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is one of the technologies that will play a key role in the decarbonization of the economy, due to its capacity to treat organic waste, recover nutrients and simultaneously produce biogas as a renewable biofuel. This feature also makes this technology a relevant partner for approaching a circular economic model. However, the low biogas yield of traditional substrates such as sewage sludge and livestock waste along with high installation costs limit its profitability. Further expansion of this technology encounters several barriers, making it necessary to seek improvements to attain a favorable financial balance. The use of co-substrates benefits the overall digestion performance thanks to the balancing of nutrients, the enhanced conversion of organic matter and stabilization, leading to an increase in biogas production and process economics. This article reviews the main co-substrates used in anaerobic digestion, highlighting their characteristics in terms of methane production, kinetic models commonly used and the synergistic effects described in the literature. The main process parameters and their influence on digestion performance are presented, as well as the current lines of research dedicated to improving biogas yields, focusing on the addition of hydrogen, bioaugmentation, supplementation with carbon compounds and nanoparticles, the introduction of bioelectrodes and adsorbents. These techniques allow a significant increase in waste degradation and reduce inhibitory conditions, thus favoring process outcomes. Future research should focus on global process efficiency, making particular emphasis on the extrapolation of laboratory achievements into large-scale applications, by analyzing logistical issues, global energy demand and economic feasibility. [ABSTRACT FROM AUTHOR]

Antibiotics are widely used in human and veterinary medicine, and they are accumulated in various types of waste, including sewage sludge (SS) and cattle slurry (CS), processed by anaerobic digestion (AD). Anaerobic treatment is a method enabling the stabilization of these substrates before transferring to the environment. The presence of contaminants, such as antimicrobials, in organic substrates processed by AD is not regulated by law. The accumulation of antimicrobials in SS and CS is a crucial issue because it may reduce the effectiveness of their stabilization. This study aimed to evaluate the long-term impact of growing concentrations of a mixture of antibiotics on the AD of SS and CS. Methane (CH4) yield, which is the main indicator of the efficiency of AD, was determined. Antibiotic exposure significantly decreased CH4 production only in SS (by 5–8% relative to control; p < 0.05). The copy numbers of the mcrA gene, a functional marker of methanogenesis, were not reliable indicators of CH4 yields in either substrate. During long-term AD, the average concentrations of the mcrA gene were determined at 108 in 1 g of SS digestate and from 108 to 109 in 1 g of CS digestate samples. At the end of long-term AD, methanogens belonging to the family Methanosarcinaceae were more prevalent than methanogens of the family Methanosaetaceae both in SS and CS samples (107 and 108–109 gene copies in 1 g of digestate, respectively). [ABSTRACT FROM AUTHOR]

The inhibition of volatile fatty acid (VFA) production is an important factor affecting biogas (methane) production in the anaerobic co-digestion systems comprising food waste and sewage sludge. In this study, batch experiments were conducted at medium temperature (36 ± 0.5 °C), during which the biogas production index and material–liquid characteristic parameters of the anaerobic digestion systems containing different concentrations of iron-loaded biochar (Fe-BC) were monitored. The cumulative biogas production data were analyzed using a modified Gompertz kinetic model to determine the effect of the Fe-BC on biogas production in the anaerobic co-digestion system. Studies have shown that addition of Fe-BC does not significantly influence the hydrolysis and acidification stages of anaerobic co-digestion, but does have a significant effect on promoting methanogenesis by alleviating the accumulation of VFAs and improving both the buffer capacity of the system and the efficiency of substrate-to-biogas conversion. When the Fe-BC concentration was 16 g·L−1, the cumulative biogas production reached 329.42 mL·g-VS−1, which was 49.7% higher than the blank group, and the lag period was 3.55 d, which was 42% shorter than the blank group. Mechanistic studies have shown that Fe-BC increased the concentration of coenzyme F420 and the conductivity of the digestate in the co-digestion system, which increased the activity of methanogens in the anaerobic digestion system, thereby promoting methanogenesis. [ABSTRACT FROM AUTHOR]