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Anaerobic co-digestion is an effective method for addressing the issue of a single substrate not being able to achieve optimal conditions for anaerobic digestion. By adjusting the mixture ratio of sewage sludge and food waste to achieve the optimal carbon to nitrogen ratio, the effectiveness of thermophilic–mesophilic temperature phase anaerobic co-digestion (TPAcD) was evaluated in comparison to single phase mesophilic anaerobic co-digestion (MAcD) and thermophilic anaerobic co-digestion (TAcD). The results indicated that TPAcD increased methane yield by 50.3% and 32.7% compared to MAcD and TAcD, respectively. The variation in VFA, pH, and ammonia nitrogen levels demonstrated that TPAcD combines the advantages of both MAcD and TAcD, with a higher hydrolysis rate in the early stage under thermophilic conditions (55 °C) and a suitable environment in the later stage under mesophilic conditions (35 °C). The kinetic parameters of anaerobic co-digestions also demonstrated that TPAcD performs better. Therefore, further research on TPAcD of sewage sludge and food waste is warranted due to its significant improvements in methane production rate, total methane yield, and system stability. Additionally, TPAcD contributes to reducing carbon emissions and supports the realization of "carbon neutrality". [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]

Straw pretreatment enhances the cellulose accessibility and increases the methane yield from anaerobic digestion. This study investigated the effects of alkali pretreatments with different chemical agents (NaOH, KOH, and Na2CO3) on the physicochemical and thermal characteristics of barley straw, as well as methane production from codigestion with sewage sludge. Artificial neural network modeling with a feedforward neural network (FFNN) and slime mold optimization (SMO) techniques were used to predict methane production. NaOH pretreatment was shown to be the best pretreatment for removing hemicellulose and lignin and for increasing the cellulose accessibility. Moreover, there was a 2.57-fold higher level of methane production compared to that from codigestion with untreated straw. The removal ratios for the total solids, volatile solids, and chemical oxygen demand reached 59.3, 67.2, and 73.4%, respectively. The modeling results showed that the FFNN-SMO method can be an effective tool for simulating the methane generation process, since training, validating, and testing produced very high correlation coefficients. The FFNN-SMO accurately predicted the amount of methane produced, with an R² of 0.998 and a 3.1x10-5 root mean square error (RMSE). [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) presents a promising avenue for efficiently reducing sewage sludge and generating renewable energy. The success of AD systems largely relies upon the microbial community composition, which is associated with various process parameters. This review aims to investigate the correlations among the microbiota abundances, digestion performances, and process parameters based on 233 datasets in 69 publications. Statistical analysis of the datasets uncovers significant correlations between process parameters with dominant bacterial phyla and archaeal genera. The evolution of microbial relative abundance (RA) reveals that Chloroflexi are positively correlated with Actinobacteria, Spirochaetes, and Synergistetes, while Firmicutes exhibit negative correlations with Proteobacteria, Chloroflexi, and Spirochaetes. Methanosarcina have negative correlations with Methanothrix, Methanobacterium, and Methanomassiliicoccus. Bacteria and archaea exhibit potential competitive (between syntrophic acetate-oxidizing bacteria and acetoclastic archaea) and syntrophic (between hydrogen-producing bacteria and hydrogenotrophic archaea) relationships. Furthermore, the volatile solids reduction and methane yield are significantly correlated with microbiota RAs and the ratio of Bacteroidetes and Firmicutes. This review sheds light on microbial interactions and thus AD performance by establishing the correlations between process parameters and microbiota composition. Future research directions should emphasize the significance of rare taxa, the necessity for experimental validation, and the potential of advanced modeling approaches to optimize sludge AD systems. [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]

Biohydrogen production is influenced by various parameters such as production formation rate, substrates degradation, and biomass utilization. Therefore, it is crucial to predict the kinetics of proper yield. This study was designed to perform a comprehensive kinetic analysis based on several linear or non-linear models. The experimental data analyzed was different co-culture ratios of microalgae and activated sludge with hexitols (glucose, sorbitol, mannitol) as carbon substrates. Results suggest that modified Gompertz model best predicts biohydrogen potential and acetate production in different co-cultures with high R2 values (>0.977 and > 0.982), respectively. A maximum of 9.8 % energy conversion efficiency is achieved in 10 g/L glucose supplemented co-culture, equivalent to traditional fuels. The linearized Luedeking–Piret model also indicates that biohydrogen production is influenced more by substrate degradation/utilization than microalgal biomass. These tools can be utilized to optimize the operational parameters and access the best fit of experimental data for enhanced yield. [Display omitted] • Excellent data fittings of parameters involved in algal activated sludge co-culture. • Biohydrogen and acetate yield can be best predicted by Modified Gompertz model. • Michaelis–Menten model best described kinetic of substrate degradation/utilization. • Relationship of products, substrate, and biomass predicted by Luedeking–Piret model. • Maximum energy conversion efficiency (9.8 %) was achieved in 1:1.5 co-culture ratio. [ABSTRACT FROM AUTHOR]

The ongoing industrial transformation in developing countries, including Ethiopia, has resulted in a significant increase in harmful pollutants in the environment. Various industrial activities release toxic wastewater sludge and spent yeast into the surrounding ecosystem, posing risks to public health and the environment. However, these waste materials have the potential for energy extraction and recycling. This study aimed to investigate and harness the biogas potential through anaerobic codigestion of distillery wastewater sludge and waste yeast. The researchers employed a response surface approach utilizing Box–Behnken experimental designs (BBD) to assess the three key experimental parameters influencing biogas yield: pH levels (6, 7, and 8), volume ratio (85, 92, and 99%), and temperature (33, 36.5, and 40°C). Before and after the digestion process, the researchers measured the total solids (TS), biological oxygen demand (BOD5), chemical oxygen demand (COD), and pH of all substrates. Additionally, measurements of temperature, total nitrate, and total phosphate were taken before digestion. The methane yield was modeled using a second-order polynomial through the BBD method in Design Expert software, with a p value threshold of ≤5%. The results showed that the maximum methane yield of 61.18% was achieved at a pH of 7, a temperature of 36.5°C, and a volume ratio of 92%. Conversely, the lowest methane yield of 40.13% was obtained at a pH of 6, a temperature of 33°C, and a volume ratio of 92%. The linear and quadratic values of the model (A, B, C, A2, B2, and C2) were determined to be significant terms, with p values ≤5%. Overall, the biogas yields obtained from the anaerobic codigestion of distillery wastewater and waste yeast were promising. This process has the potential to effectively remove BOD5, COD, and TS from distillery spent wash and sludge. The findings suggest that anaerobic codigestion could be a viable approach for both energy production and waste management in the setting of distillery waste. [ABSTRACT FROM AUTHOR]

This study investigated the anaerobic co-digestion (AcoD) of brewery by-products for biomethane and bioenergy recovery, focusing on operational performance evaluation, kinetic analysis, microbial metataxonomic, and metabolic function prediction. The biochemical methane potential was conducted under mesophilic (35 °C) and methanogenic conditions (pH 7.5) by mixing brewery wastewater and sludge from the brewery wastewater treatment plant (1:1, v/v), following the addition (2.5 – 12.5 %, w/v) of brewer's spent grains (BSG). The results demonstrate that the highest methane yield (88.02 mL CH4/g TVS) was obtained with 12.5 % BSG, which was 20.66-fold higher than the control reactor operated with wastewater and sludge (4.26 mL CH4/g TVS). The bioenergy recovery from biomethane could generate electricity (0.348 kWh/kg TVS) and heat (1556 MJ/kg TVS), avoiding greenhouse gas emissions (0.114 kg CO2-eq/kg TVS). The microbial community dynamics revealed a predominance of Halobacterota, Chloroflexi, and Euryarchaeota phylum. The genera Methanosaeta and Methanobacterium, and the Anaerolineaceae family predominated in the AcoD process. The metabolic function prediction showed the presence of genes (K01895, K00193, K00625, and K00925) associated with the direct activation of acetate in the acetoclastic pathway and methane production. Finally, the data obtained provide a perspective on using brewery by-products for bioenergy production in a biorefinery concept, reducing the environmental impacts and contributing to the circular bioeconomy transition of the beer industry. [ABSTRACT FROM AUTHOR]

Enhancing production of methane from cellulose is of utmost importance to improve the fermentation efficiency of lignocellulosic biomass. Antibiotics have demonstrated their ability to stimulate anaerobic digestion (AD) by influencing micro-organism activity. However, there has been limited research on the specific effect of antibiotics on cellulose AD. In this study, we investigated the impact of three antibiotics—tetracycline (TC), cephalexin (CLX), and azithromycin (AZM)—on cellulose AD when inoculated with waste sewage sludge. The results revealed that the presence of AZM and TC led to significantly higher methane yields, with increases of 51.94% and 34.96%, respectively, during a 20-day AD period. In contrast, the presence of CLX resulted in a 23.95% lower methane yield compared to the control. Furthermore, detailed analyses indicated that AZM had a positive influence on cellulose AD at all stages, including methanogenesis, acidogenesis/acetogenesis, and hydrolysis. On the other hand, TC primarily promoted AD during the methanogenesis stage. These findings collectively offer valuable guidance for efficiently transforming the energy potential of lignocellulosic wastes. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is the most prevalent stabilization method used in treating waste activated sludge. However, the digested sludge produced has always been difficult to dehydrate. In this study, mesophilic anaerobic digested sludge and thermophilic anaerobic digested sludge were used to compare the dewatering capacity of two chemical coagulants: high-performance polyaluminum chloride (HPAC) and FeCl3. For mesophilic anaerobic digestion, 5% g/g total suspended solids (TSS) was the optimal dose of FeCl3 and HPAC to improve dewaterability. In addition, HPAC was superior to ferric chloride in the removal of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound extracellular polymeric substances (TB-EPS). For thermophilic anaerobic sludge, HPAC is more effective compared with FeCl3 in improving the dewaterability. FeCl3 could effectively remove TB-EPS, while HPAC had better removal efficiency on soluble extracellular polymeric substances (S-EPS) and LB-EPS. Both chemical coagulants have greater potential to degrade EPS during thermophilic anaerobic digestion sludge treatment. The results of the supernatants characterization after conditioning illustrated that FeCl3 and HPAC have similar removal efficiency on organic matter, but HPAC could remove additional small molecular weight compounds, particularly when conditioning with the thermophilic anaerobic sludge; however, there was no apparent changes when using FeCl3. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strong magnetization promotes the fertilizing potential of sewage sludge digestate. • Magnetization enriched the digestate of slow-release nutrient-based precipitates. • Nutrient precipitation in the digestate increases with increasing magnetic exposure. • In-line oxygenation during digestion promoted precipitation more than pre-oxygenation. • The best treatment conditions for struvite formation were identified. Anaerobic digestion (AD) is a sustainable and well-established option to handle sewage sludge (SS), as it generates a methane-rich biogas and a digestate with potential fertilizing properties. In the past, different strategies have been proposed to enhance the valorization of SS. Among these, the application of a static magnetic field (SMF) has been poorly evaluated. This study aims to determine the effects of a high-intensity SMF (1.5 and 2 T) on the chemical composition of SS anaerobic digestate. Several strategies (i.e., number of magnetization cycles, addition of different sources and quantities of magnesium, and digestate aeration) have been applied to evaluate the possible formation of compounds with valuable fertilizing properties in the digestate. Experimental results showed that by combining different strategies promoting digestate exposure to the magnetic field it is possible to favour the reduction in the liquid phase of NH 4 +, NO 3 −, PO 4 3−, SO 4 2− and Mg2+ concentrations up to 28%, 38%, 34%, 39% and 31%, respectively. The XRD analyses conducted on the solid phase of the same magnetized digestate samples showed an increase in crystalline and amorphous phases of nitrogen and phosphorus compounds with fertilizing value, such as struvite. These results highlight that SMF application can increase the fertilizing potential of sewage sludge digestate and promote its valorization in a sustainable and circular perspective. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is the most undesirable inorganic gas in biogas from anaerobic digestion (AD). However, H2S production in AD is complex and understanding of its processes is still limited. This study performed six controlled batch anaerobic co‐digestion experiments to investigate H2S production. Materials were obtained from four field anaerobic digester systems and co‐digestion feedstocks from agroindustry. An additional precipitation experiment was conducted to further examine H2S production dynamics. Digesters containing highly soluble, carbohydrate‐based wastes had a high H2S final specific production (FSP) value. Additionally, the FSP values were negatively correlated with the initial Fe(II):S ratios in the digester liquid of the batch tests. The precipitation experiment indicated that iron sulfide precipitation was preferred in the presence of an anaerobic community. The H2S production as a time series was successfully modeled using a generalized additive model (R2 > 0.82). This study revealed that sulfate, phosphorus, and iron concentrations are important predictors and potential inhibitors of H2S production in AD. Further examination of real‐time H2S modeling in AD is warranted. [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]

Diverse feedstocks utilized in anaerobic digestion (AD) pose challenges to enzymatic disintegration because of their nature and complex physical structures and thereby limiting biogas generation. To overcome this, the AD process is often combined with pretreatment techniques, which facilitate the breaking of organic feedstock into smaller molecules and eventually result in enhanced biogas production. Among several techniques, ultrasound-assisted pretreatment of AD feedstock remains promising because it is simple to implement, requires no chemicals, and combines physical (or cavitation) and biological phenomena for degrading AD feed. This review is primarily centered on the applications of ultrasound pretreatment for disintegrating various feedstocks and increasing biogas production during AD. Biogas generation is described in relation to the ultrasound-assisted disintegration of dairy industry waste, hybrid food and municipal wastes, olive mill wastewater, rice straw, tannery wastewater, meat processing sludge, hybrid industrial waste municipal sewage sludge, and lignocellulosic biomass. The disintegration schemes of feedstocks under ultrasound are proposed. COD is solubilized, and suspended solids (SS) are reduced upon ultrasonication. The impact of ultrasonic treatment on biogas production might be amplified if paired with alkali. Furthermore, the techno-economic commercial scopes of ultrasound pretreatment-based biogas production are discussed, and recommendations for future studies are suggested. [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]

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]

The current global concern is how to replace polluting fossil fuels with sustainable green fuels. On this basis, in this study, a characterization protocol for sewage sludge in Algeria was carried out. Their objective was to study the process of anaerobic digestion for biogas production by analogy to experiments that have already been made in the literature. The performance of the proposed models has been validated with experimental data from the scientific literature. Biodegradable organic matter levels are high (160–500 mg L−1) giving an acceptable yield for biogas production. The modeling of cumulative biogas production was carried out by Gompertz and models were proposed for different products. It has been observed that there is a better agreement of the models proposed with the experimental data with a maximum value of r2 = 0.9996. The modeling of the degradation of organic matter was carried out by the first order‐model, and dimensionless models were proposed. The latter gave a good agreement with the experimental data better than the model in the literature, with a maximum value of r2 = 0.9985. The proposed models to study the anaerobic digestion process of organic matter, as well as those related to the process of cumulative biogas production, are universal (without units of measurement), which will help producers in this field to improve production, as well as reduce the investment cost through preliminary simulations. [ABSTRACT FROM AUTHOR]

Soil amendments, such as pyrochar (PC) and hydrochar (HC), have the potential to enhance soil properties and crop yields. The objective was to investigate the effects of HC from anaerobic digestion effluent (ADE) of sewage sludge (SS), ADE of manure (M), and PC, as soil amendments. Lettuce seeds were sown and grown in soil amended with chars at rates of 1 to 15 g char/kg soil. Soil properties and plant responses were compared to soil without amendment (control). Soil amended with HC-ADE-SS and HC-ADE-M had higher pH, phosphorus content, and cation exchange capacity than the control. All treatments and the control resulted in 80% + emergence rates. Root dry mass of plants grown on soil with 10 and 15 g/kg was higher than the control. No negative effects were observed in emergence and whole-plant dry biomass, indicating that HC-ADE-SS and HC-ADE-M could be amended without negative impacts on soil properties and plant responses. [ABSTRACT FROM AUTHOR]

The thermophilic anaerobic fermentation of mixed materials for simultaneously producing biohydrogen and methane has become a research hotspot. In this study, thermally treated kitchen waste (KW) and municipal sewage sludge (MSS) were used as substrates for a thermophilic two-stage anaerobic digestion process. The effects on gas production performance were investigated in both the hydrogen-producing stage and methane-producing stage under different organic load rates (OLRs). The production rates, volume, removal rates, and energy yields of volatile solids (VS) were optimal under higher OLRs for both the hydrogen (OLR = 12.5 g VS/L·day) and methane stages (OLR = 5 g VS/L·day). These conditions also provided the optimal average removal rate and total energy yield of VS for the entire anaerobic fermentation system (65.4% and 30.9 kJ/g VS, respectively). Overall, the results demonstrate the superior efficiency of VS removal and hydrogen and methane production in a two-stage thermophilic anaerobic co-digestion of KW and MSS with a high solid content under proper material mix ratio and higher OLRs. This study provides the basis for material mass ratio, mixtures' pretreatment, and operation control for future pilot tests. [ABSTRACT FROM AUTHOR]

• Quantitative analysis of GHGs emission in mainstream sludge treatment was studied. • Incineration and bio-stabilization technologies have high GHGs reduction potential. • The LCA method needs to be improved and unified in GWP of sludge treatment. • Resource recovery coupled with N 2 O and CH 4 reduction are the key points. • Novel anaerobic digestion pathways have considerable GHGs reduction potential. This study aims to comprehensively analyze the Greenhouse Gases (GHGs) emissions from current sewage sludge treatment and disposal technologies (building material, landfill, land spreading, anaerobic digestion, and thermochemical processes) based on the database of Science Citation Index (SCI) and Social Science Citation Index (SSCI) from 1998 to 2020. The general patterns, spatial distribution, and hotspots were provided by bibliometric analysis. A comparative quantitative analysis based on life cycle assessment (LCA) put forward the current emission situation and the key influencing factors of different technologies. The effective GHG emissions reduction methods were proposed to mitigate climate change. Results showed that incineration or building materials manufacturing of highly dewatered sludge, and land spreading after anaerobic digestion have the best GHG emissions reduction benefits. Biological treatment technologies and thermochemical processes have great potential for reducing GHGs. Enhancement of pretreatment effect, co-digestion, and new technologies (e.g., injection of carbon dioxide, directional acidification) are major approaches to facilitate substitution emissions in sludge anaerobic digestion. The relationship between the quality and efficiency of secondary energy in thermochemical process and GHGs emission still needs further study. Solid sludge products generated by bio-stabilization or thermochemical processes are considered to have a certain carbon sequestration value and can improve the soil environment to control GHG emissions. The findings are useful for future development and processes selection of sludge treatment and disposal facing carbon footprint reduction. Graphical Abstract. [Display omitted] [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]

• Sludge-derived humic acid is converted into carbon materials. • Low-cost energy storage materials can be prepared. • The purified humic acid-based carbon material has better performance. • Optimized material exhibits high performance in supercapacitors. As one of the main methods for sludge treatment, recovery of renewable biogas energy by anaerobic digestion (AD) is a promising strategy to deal with the conflict between carbon neutralization and sharply increase of sewage sludge. Humic acid (HA) in sludge is a major inhibitor of biogas yields and needs to be removed or pretreated. However, as the graphene oxide-like material, HA is an ideal precursor for the preparation of energy storage materials with high performance. Based on that, this study i) proposes the extraction and utilization of HA in sludge, ii) discusses the feasibility of HA-based materials after thermal reduction as electrodes for supercapacitor, and iii) investigates the factors with positive influences on the structure and electrochemical performance. It reveals that, with a synergistic effect of purification and activation at a low mass ratio, the HA-based material exhibits superior capacitive performance with the highest specific capacitance of 186.7 F/g (at 0.05 A/g), as well as excellent rate capability and cycling stability. Sludge is verified a cheaper and more abundant precursor resource of HA for energy storage application. The results of this study are expected to provide a new green, energy-efficiency and sustainability way for sludge treatment, which has the double benefits: efficient conversion and capture of bio-energy during AD process, and high value-added utilization of HA for supercapacitor. [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]

• Effect of nitrite on semi-continuous two-phase AD was firstly investigated. • The addition of nitrite promoted an increase in STOC and VFA contents. • The addition of nitrite increased VS reduction and had slightly impact on biogas production. • Microbial community changed significantly after addition of nitrite and Vulcanibacillus and Candidatus Methanofastidiosum become the dominant genera. • Nitrite pretreatment is relatively a cost effective alternative. Previous study found that the pre-treatment of sewage sludge with nitrite improves the biogas production during the mono/two-phase anaerobic digestion (AD) using batch biochemical methane potential tests. In this study, the effects of nitrite on hydrolysis-acidification, biogas production, volatile solids destruction and microbial composition in semi-continuous two-phase AD of sewage sludge were investigated. The addition of nitrite promotes sludge organic matter solubilization (+484%) and VFAs production (+98.9%), and causes an increase in the VS degradation rate during the AD process (+8.7%). The comparison of biogas production from the acidogenic and methanogenic reactors with or without the addition of nitrite implies that the nitrite has no significant effect on the overall biogas production of two-phase sludge AD process. High-throughput sequencing analysis shows that the microbial communities of bacteria and archaea in two-phase AD reactors significantly changes after the addition of nitrite. Vulcanibacillus (bacteria) and Candidatus Methanofastidiosum (archaea) become the dominant genera in the acidogenic and methanogenic reactors with the nitrite respectively. These findings provide new insights about using nitrite to promote the organic matter degradation of sewage sludge in a semi-continuous two-phase AD system. [Display omitted] [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]

[Display omitted] • Aerobic SS had the lowest energy with the lowest Ea to start pyrolysis reaction. • The bio-oil yield of aerobic SS was higher than that of raw and anaerobic SS. • Digested SSs required higher temperatures for higher bio-oil yields than raw SS. • Biochar from aerobic SS was most suitable for soil amendment. Studies on the evaluation of sewage sludge (SS) as a feedstock through thermochemical processes have gained momentum. Due to the complex structure of SS, it is necessary to determine SS treatment stage to which thermochemical processes will be added to the wastewater treatment plants and to configure the optimum process scheme. The pyrolysis process is an important process for resource recovery as bio-oil and biochar. While bio-oil is important source of the value-added products, biochar is widely evaluated as soil improver. With the aim of the designation of the optimum process scheme for pyrolysis of three different sewage sludges (SSs): raw SS (RSS), anaerobically digested SS (ANSS), and aerobically digested SS (AESS); after the investigation of thermal behaviors by thermogravimetric analysis (TGA), the optimum process conditions were investigated to obtain maximum possible bio-oil yield from fast pyrolysis of SSs. By applying the central composite design in the response surface methodology, optimum fast pyrolysis operating conditions were determined for each SS type and the fast pyrolysis products obtained under optimum conditions were characterized. While the highest HHV was achieved for RSS, lowest activation energy (Ea) and maximum bio-oil yield was achieved for AESS. The optimum fast pyrolysis operating conditions for obtaining maximum bio-oil yield as 35.75 % were determined as 485 °C and 100 mL min−1 carrier gas flowrate for AESS. While the bio-oil produced from ANSS was determined as a resource for oleic acid production, the toxicity test results revealed that biochar produced from fast pyrolysis of AESS is suitable for soil amendment. [ABSTRACT FROM AUTHOR]

• Inventory data of biological treatment of sludge address all inputs and outputs. • Biogas production varies considerably in the 64 datasets on anaerobic digestion. • Very few data are available on digestate or energy in anaerobic digestion of sludge. • VS degradation in composting is hard to estimate due to the added bulking materials. • Data on emissions into the air are currently scarce for sludge composting processes. The biological treatment of municipal sewage sludge, including anaerobic digestion and composting, was reviewed with the purpose of establishing inventory data to address all the inputs and outputs related to sludge treatment. We identified 193 scientific papers, resulting in 64 datasets on anaerobic digestion and 35 datasets on composting. For anaerobic digestion, biogas production varied significantly (up to a factor of four) depending on the sludge. A useful correlation was identified between the amount of methane produced and the degradation of volatile solids. According to statistical tests, no significant differences were found in biogas production for mesophilic and thermophilic digesters. In addition, methane content varied significantly, and very few data were available for digestate composition or for energy consumption and recovery. For composting, accurate estimates relating to the degradation of sewage sludge could not be made, since organic bulking materials were part of the final composted product. Data on emissions to air are currently scarce, which points to the need for more published information. The inventory data evaluated herein are useful in the feasibility assessment of the biological treatment of sewage sludge, for comparing technologies, for example in LCA studies and as a basis for evaluating the performance of a specific biological sludge treatment plant. However, a great deal of the reviewed data originated from laboratory and pilot-scale studies, and so there is a need for more complete datasets on the performance of full-scale technologies, in order to establish full inventories and identify differences in technologies and operational conditions. [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]

The rising occurrence of emerging contaminants in sludges both inhibits the anaerobic digestion of sludges and induces health issues when sludges are recycled in agriculture, calling for methods to remove contaminants. Here we review emerging pollutants in wastewater treatment plants, before and after anaerobic digestion. We present their inhibitory effects and remediation methods to alleviate inhibition. Pharmaceuticals have been detected in about 50% of the sludge samples. Sewage sludge contaminants include 19% of diuretics, 16–21% of lipid-modifying agents, hydrochlorothiazide, diclofenac, furosemide, clarithromycin, atorvastatin, and carbamazepine. Levels of antibiotics, azithromycin, ciprofloxacin, and estrone range from 500 to 600 ng/g in sludges from wastewater treatment plants. Remediation methods comprise electrooxidation, ultrasonication, thermal hydrolysis, ozonation, and bioaugmentation. Fermenting the sludges with acidogenic bacteria reduces the level of emerging pollutants in the supernatant. Nonetheless, liquid digestates still contains emerging pollutants such as sunscreen octocrylene at 147 ug/L and acetaminophen at 58.6 ug/L. As a result, pretreatment of sludge containing emerging pollutants is required. [ABSTRACT FROM AUTHOR]

• AWOEx pretreated DSS tested at various temperatures, residence times and O 2 dosages. • Methane yield of DSS is improved by 98% using AWOEx and Anaerobic digestion. • Oxygen addition during pretreatment resulted in significant improvement in methane yield. • First-time demonstration of 84% organics conversion in sewage sludge using AWOEx pretreatment. Anaerobic digestion (AD) of sewage sludge shows low carbon conversion efficiency (CCE) due to the poor biodegradability of sewage sludge. The lack of digestibility is specifically linked to the waste-activated sludge (WAS) making up the majority of sewage sludge along with a smaller portion of primary sludge, depending on the wastewater treatment plant configuration. In this study, we examine the Advanced Wet Oxidation & Steam Explosion process (AWOEx) for improving the CCE of digested sewage sludge (DSS) by thermophilic AD. The effect of the pretreatment temperature in the range between 160 and 185 °C at a fixed residence time of 20 min with and without oxygen added at a dosage of 5 % of the organics present was tested. Methane yield improved by 97.92 % to 183.91 ± 4.93 mL/g vS over the untreated DSS (control), whose methane yield was 92.92 ± 9.07 mL/g vS We have demonstrated for the first time that 84 % of the organics in sewage sludge can successfully be transformed into biogas following AWOEx pretreatment, which can contribute significantly to the circular economy instead of greenhouse gas emissions from landfilling. [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]

The positive impact of the thermal hydrolysis process (THP) of sewage sludge on antibiotic resistance genes (ARGs) removal during anaerobic digestion (AD) has been reported in the literature. However, little information is available on how changes in different extracellular polymeric substances (EPS) due to THP can influence ARG propagation during AD. This study focused on systematically correlating EPS components and ARG abundance in AD of sewage sludge pretreated with THP (80 °C, 110 °C, 140 °C, 170 °C). THP under different conditions improved sludge solubilization followed by improved methane yields in the biochemical methane potential (BMP) test. The highest methane yield of 275 ± 11.5 ml CH4/g COD was observed for THP-140 °C, which was 40.5 ± 2.5% higher than the control. Increasing THP operating temperatures showed a non-linear response of ARG propagation in AD due to the rebound effect. The highest ARGs removal in AD was achieved with THP at 140 °C. The multivariate analysis showed that EPS polysaccharides positively correlated with most ARGs and integrons, except for macrolides resistance genes. In contrast, EPS protein was only strongly correlated with β-lactam resistance genes. These results suggest that manipulating THP operating conditions targeting specific EPS components will be critical to effectively mitigating the dissemination of particular ARG types in AD. [ABSTRACT FROM AUTHOR]

Summary: One of the most important problems of the anaerobic digestion (AD) process and the main obstacle to this complex structural conversion is lignocellulose and the difficulty of its biological conversion. One way to disrupt the lignocellulosic composition is using nanoparticles (NPs) with proper concentration. In this study, biomethane potential tests have been used to maximize the biomethane production from anaerobic co‐digestion of municipal solid waste (MSW) and sewage sludge (SS) under different mixing ratios (MSW:SS: 100:0, 50:50, 60:40, 80:20 and 90:10) and different concentrations of iron (Fe) NPs (50, 70, 90 and 110 ppm) to speed up the AD process of the substrate, which increases biomethane production. Increasing the SS ratio up to 40% dramatically increased the biomethane yield, in a way that after 18 days of hydraulic retention time, 90% of methane (270 NmL/g VS) was obtained. The results showed that the highest biomethane yield (based on the optimal mixing ratio obtained in the first experiment, MSW:SS: 60:40) was obtained by adding 90 ppm Fe NPs using the statistical analysis (Duncan test) compared to the control (P < 0.05). Also, using iron NPs (Fe NPs) led to an increase in cellulose by 83%, a decrease in lignin by 62% and a decrease in hemicellulose by 32%, indicating an increase in the degradability due to the presence of NPs. Most of the biomethane was produced at 90 ppm Fe NPs concentration, showing an increase of 44% compared to control, and the maximum reduction in total solids and volatile solids were 36% and 28%, observed in this reactor, compared to the control sample. [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 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]

In anaerobic digestion (AD) system, the C/N ratio can affect utilization efficiency of organic matter and microbial community structure, thereby influencing methane production. This study investigated that the C/N ratio in AD of sewage sludge (SS) suitably enhanced by adding food waste (FW) to improve methane production efficiency. The effects of different C/N ratios (9, 11, 13, and 15) on dry thermophilic anaerobic co-digestion of SS and FW and the microbial community structure were researched. The cumulative methane production at C/N ratio of 11 reached 165.68 ± 11.88 mL/g VSadded which increased by 1.23 times compared with the mono-digestion of SS; and the cumulative methane production increased by 8.15 – 63.55% at C/N ratios of 9, 13, and 15. The methanogenic pathway changed from acetoclastic methanogenesis process to hydrogenotrophic methanogenesis process with the increasing of C/N ratio. Redundancy analysis explained that the C/N ratio had obvious effects on the variation of the microbial phylum and genus, which contributed 21.63% and 29.27%, respectively. The C/N ratio of 11 enriched the dominant bacterial phyla (Firmicutes and Thermotogae) and increased the methanogens diversity at genus level. This research found an approach that could improve methane production in the lower C/N range. [ABSTRACT FROM AUTHOR]

The purpose of this research is to experimentally evaluate the anaerobic co-digestion in the city of Guaranda of slaughterhouse residues (RM) with straw residues from agriculture, such as amaranth residues (AM), quinoa residues (QU) and residues of wheat (TR), to reduce slaughterhouse discharges and prevent contamination of the city. The study was carried out on a laboratory scale in 311-ml biodigesters under mesophilic conditions of 37 °C. In addition, sewage sludge was used as inoculum with two relationships between substrate and inoculum (SIR 1:1 and SIR 1:2). The design was completed using three relationships between substrate (RM) and co-substrate (AM, QU and TR): 25:75, 50:50 and 75:25. Anaerobic co-digestion resulted in methane yields of 407 ml CH4/g VS, with a methane content in the biogas of 77% for the mixture of RM and QU (RM-QU (25:75)). The increase in inoculum in the mixtures composed of RM and QU increased the biodegradability between 17 and 22%. However, in the mixtures of slaughterhouse waste and amaranth (RM-AM (25:75)), a further increase in inoculum reduced biodegradability by 5%. The results revealed that there is a greater synergy between the RM and QU as the percentage of QU in the mixture is increased. This meant that the co-digestion of the RM with the QU accelerates the biodegradability of the mixture, increasing the production of biogas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Removal of antibiotics and ARGs was highly improved at 30 mg/gSS cellulase or papain. • Combination of biological enzymes further enhanced the removal of qnr S and erm X. • Enzymes integrated with ZVI had synergistic effects on removing antibiotics and ARGs. • Enzymes and ZVI changed removal-related bacteria and archaea community structure. • ARGs removal during in situ ADD was mainly due to partial changes of host bacteria. Antibiotics and antibiotic resistance genes (ARGs) in sewage sludge can cause high ecotoxicological risks in the environment and public health concerns. The aims of this study were to establish enzymatic integrated in-situ advanced anaerobic digestion (AAD) by adding cellulase and papain as well as the two enzymes combined with zero valent iron (ZVI) directly into the anaerobic digesters to explore the removal of antibiotics and ARGs under the mesophilic condition (35 °C). The methane production potential during in-situ AAD was effectively improved. Papain and cellulase at 30 mg/gTSS were most effective in improving antibiotic removal. The removal of sulfamerazine (SMZ) and sulfadiazine (SMR) could reach 89.10 % and 71.75 %. Combined enzymes with ZVI also enhanced the removal of all target antibiotics, especially roxithromycin (ROX), SMZ and SMR most significantly. Except for sul 1, tet A and tet B, the removal of ARGs by papain reached 6.33 %-82.15 %. The addition of cellulase effectively improved tet A removal. The combination of biological enzymes further enhanced the removal of qnr S and erm X. The tet G, tet B, sul 3, erm X, erm T, qnr S, and aac (6′)-IB-CR by combined enzymes with ZVI could even not be detected after digestion. Addition of papain, cellulase, and ZVI caused variations in the dominant bacteria. All target antibiotics presented significant positive correlations with the genera norank_f__ Bacteroidetes _ vadinHA17 , norank_f__norank_o__ SJA-15 , norank_f__norank_o__ Aminicenantales. Redundancy analysis showed archaea Methanosaeta and Candidatus_ Methanoacidiosum genera greatly contributed to antibiotics removal with the combination of enzymes and ZVI. Co-occurrence network analysis indicated the removal of ARGs was mainly based on the changes of existence of host bacteria. [ABSTRACT FROM AUTHOR]

Summary: Anaerobic digestion (AD) is an important technology for the effective conversion of waste and wastewater to methane. Here, syntrophic bacteria transfer molecular hydrogen (H2), formate, or directly supply electrons (direct interspecies electron transfer, DIET) to the methanogens. Evidence is accumulating that the methanation of short‐chain fatty acids can be enhanced by the addition of conductive material to the anaerobic digester, which has often been attributed to the stimulation of DIET. Since little is known about the transcriptional response of a complex AD microbial community to the addition of conductive material, we added magnetite to propionate‐fed laboratory‐scale reactors that were inoculated with wastewater sludge. Compared to the control reactors, the magnetite‐amended reactors showed improved methanation of propionate. A genome‐centric metatranscriptomics approach identified the active SCFA‐oxidizing bacteria that affiliated with Firmicutes, Desulfobacterota and Cloacimonadota. The transcriptional profiles revealed that the syntrophic bacteria transferred acetate, H2 and formate to acetoclastic and hydrogenotrophic methanogens, whereas transcription of potential determinants for DIET such as conductive pili and outer‐membrane cytochromes did not significantly change with magnetite addition. Overall, changes in the transcriptional profiles of syntrophic Bacteria and Archaea in propionate‐fed lab‐scale reactors amended with magnetite refute a major role of DIET in the studied system. [ABSTRACT FROM AUTHOR]

This paper presents the energy potential of biogas obtained from the anaerobic digestion (AD) of sewage sludge (SS) preceded by thermal hydrolysis (THP) using Cambi THP® technology. The presented data are for the Tarnów (Poland) wastewater treatment plant for the year 2020. A detailed energy balance of biogas and its use in the cogeneration process and in the production of heat in the water boiler and the steam boiler is presented. The article contains data on the amount of processed SS and the content of dry matter and dry organic matter at different stages of the technological process. The annual plant operation resulted in the production of 3,276,497 Nm3 of biogas as a result of processing 8684 tonnes of dry solids (tDS) of municipal SS from the Tarnów wastewater treatment plant (WWTP) and regional WWTPs. The energy potential of the produced biogas was 75,347.06 GJ. The average calorific value of biogas was 23,021 kJ/Nm3.. The obtained biogas production allowed us to cover the thermal energy demand of the THP 100%. The annual average specific biogas conversion rate during the study period was 0.761 Nm3/kg of dry organic matter reduced and the average organic matter content reduction in the sludge was 64.60%. [ABSTRACT FROM AUTHOR]

This study provides a comprehensive analysis of the potential impact of hydrothermal pretreatment (HTP) on municipal thickened waste-activated sludge (TWAS) and its integration with anaerobic digestion (AD). The research demonstrates that HTP conditions (170 °C, 3 bars for 30 min) can increase the solubilization of macromolecular organic compounds by 41%, which enhances biodegradability in semicontinuous bioreactors. This treatment also results in a 50% reduction in chemical oxygen demand (COD) and a 63% increase in the destruction of volatile solids (VS). The combination of HTP with AD significantly boosts methane yields by 51%, reaching 176 ml/g COD, and improves the digestate dewaterability, doubling the solid content in the dewatered cake. However, a higher polymer dose is required compared to conventional AD. Microbial community analysis correlates the observed performance and alterations; it indicates that HTP enhances resilience to stress conditions such as ammonia toxicity. This comprehensive study provides valuable insights into the transition from wastewater treatment plants (WWTPs) to resource recovery facilities (RRF) in line with circular economy principles. • HTP before AD boosts solubilization of complex organics by 41%. • HTP followed by AD achieves a 50% reduction in COD and a 63% reduction in volatile solids. • HTP coupled with AD doubles dewaterability, requiring a 13.6% higher polymer dose. • Impacts of viscosity and particle size distribution on dewaterability performance were investigated. • HTP induces significant alterations in the microbial community. [ABSTRACT FROM AUTHOR]

• 45 °C for 48 h and 55 °C for extra 48 h was the optimal sludge pre-treatment method. • Low-temperature thermal hydrolysis was improved with increasing solids content. • The optimal pre-treatment enhanced methane yield by 66.39 %. • Pre-treatment and sludge thickening led to increased abundance of specific microbes. • Foaming was observed at an organic loading rate of 2.00 g VS/(L Reactor ·day). This study investigated the impact of two low-temperature thermal pre-treatments on continuous anaerobic reactors' performance, sequentially fed with sludge of different total solids content (∼3 % and ∼6 %) and subjected to progressively increasing Organic Loading Rates (OLR) from 1.0 to 2.5 g volatile solids/(L Reactor ⋅day). Assessing pre-treatments' influence on influent sludge characteristics revealed enhanced organic matter hydrolysis, facilitating sludge solubilization and methanogenesis; volatile fatty acids concentration also increased, particularly in pre-treated sludge of ∼6 % total solids, indicating improved heating efficiency under increased solids content. The reactor fed with sludge pre-treated at 45 °C for 48 h and 55 °C for an extra 48 h exhibited the highest methane yield under all applied OLRs, peaking at 240 ± 3.0 mL/g volatile solids at the OLR of 2.5 g volatile solids/(L Reactor ⋅day). 16S rRNA gene sequencing demonstrated differences in the reactors' microbiomes as evidence of sludge thickening and the different pre-treatments applied, which promoted the release of organic matter in diverse concentrations and compositions. Finally, the microbial analysis revealed that specific foam-related genera increased in abundance in the foam layer of reactors' effluent bottles, dictating their association with the sludge foaming incidents that occurred inside the reactors during their operation at 2.0 g volatile solids/(L Reactor ⋅day). [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Biogas circulation at 5 L/min could not completely replace mechanical stirring. • Intermittent stripping mode proved applicable for in situ ammonia stripping. • Thermophilic digestion could be promoted to 90% of the methanogenic potential. • Exceeding the loading 4.2 g COD/L/d resulted in failure of the stripping mode. High-solid anaerobic digestion of hydrothermal sewage sludge has been developed. In order to upgrade the process by focusing on ammonia inhibition, a simply-equipped stripping system without additional alkali or heat supply was introduced by in situ biogas self-circulation. As the determined limit of total ammonia nitrogen at 1500 mg/L and 1000 mg/L for the mesophilic (MAD) and thermophilic anaerobic digestion (TAD) respectively and stripping rate at 5 L/min, continuous MAD and TAD was conducted in parallel. The stripping system successfully polished up the ammonia inhibition, and methanogenic capability of the TAD was promoted to approximately 90.0 % of the potential. Intermittent stripping mode proved usable. More frequent stripping was inevitable for the TAD as compared to the MAD. Hydraulic retention time below 20 d resulted in failure of the stripping mode due to rapid ammonia generation. Overall, this technology was practical in upgrading high-solid sludge digestion by effective ammonia control. [ABSTRACT FROM AUTHOR]

The conversion of sludge from sewage treatment plants (STPs) into bioenergy is a promising approach to sustainable energy generation and effective waste management. This process occurs through anaerobic digestion in the biodigesters, resulting in biogas production. However, given that the sludge comes from various STPs in different cities, identifying the ideal locations requires careful selection due to the complexity of sludge management, associated costs, and transportation logistics. In this context, this work aims to formulate a mathematical optimization model to determine the best locations for the installation of sludge processing centers, considering the minimization of the economic, environmental, and social costs. The model is implemented in MATLAB software, and geospatial analysis of the regions of interest is performed using QGIS software. For model validation, three distinct instances are considered. The results obtained demonstrate significant potential in terms of biogas and electricity production, with the highest values for the third instance being 61,997,501 Nm³/year and 149,275 MWh/year, respectively. The proposed methodology represents a crucial step toward sustainability, as it promotes the generation and use of bioenergy from STP sludge and contributes to improved waste management and the prevention of air, soil, and water pollution. • A mixed NLP model is proposed to assist in the process of utilizing sewage sludge. • A genetic algorithm is proposed as a metaheuristic for optimization model solution. • Focus is given to minimizing economic, social, and environmental costs. • Computational experiments with real instances are conducted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anaerobic co-digestion of sewage sludge, vinasse and poultry manure at TPAD. • Optimization of the thermophilic acidogenic stage at different HRTs. • Maximum H 2 yield of 40 mL/gVS at 5 days HRT. • Optimization of the mesophilic methanogenic stage and classification of class A biosolids. • Maximum CH 4 yield of 391 mL/gVS at HRT of 12 days. This study responds to the need to optimise anaerobic digestion to achieve the integral valorisation of waste in a sustainable way, obtaining maximum yields in the production of biofuels and biofertilisers. To achieve the maximum benefits of this technology, anaerobic co-digestion with phase separation by temperature and microorganisms (TPAD) of sewage sludge and waste from the agri-food sector (poultry manure and vinasse) was tested. To this end, each phase was optimised separately by applying different hydraulic retention times (HRT) first in the thermophilic acidogenic phase and then in the mesophilic methanogenic phase, in order to find the optimum conditions in terms of hydrogen and methane yield, volatile solids (VS) removal and pathogen removal in the effluent. The results obtained show a maximum hydrogen yield of 40.41mLH 2 /gVS in the acidogenic phase at 5 days of HRT and a methane yield of 391.0mLCH 4 /gVS in the mesophilic methanogenic phase at 12 days of HRT, respectively. At the end of the process, a total removal of VS of 93 % and of pathogens of more than 96.7 % was achieved, which would allow it to be classified as class A biosolid according to USEPA. Therefore, this technology would allow solving a local environmental problem of organic waste generation, valorising it in the form of biohydrogen, biomethane and biofertiliser, thus contributing to the transfer to a circular economy model. [ABSTRACT FROM AUTHOR]