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Background: In this study, individual methanogenic (anaerobic), granular biofilms were used as true community replicates to assess whole-microbial-community responses to environmental cues. The aggregates were sourced from a lab-scale, engineered, biological wastewater treatment system, were size-separated, and the largest granules were individually subjected to controlled environmental cues in micro-batch reactors (μBRs). Results: Individual granules were identical with respect to the structure of the active community based on cDNA analysis. Additionally, it was observed that the active microbial community of individual granules, at the depth of 16S rRNA gene sequencing, produced reproducible responses to environmental changes in pH, temperature, substrate, and trace-metal supplementation. We identified resilient and susceptible taxa associated with each environmental condition tested, as well as selected specialists, whose niche preferences span the entire trophic chain required for the complete anaerobic degradation of organic matter. Conclusions: We found that single anaerobic granules can be considered highly-replicated whole-ecosystems with potential usefulness for the field of microbial ecology. Additionally, they act as the smallest whole-community unit within the meta-community of an engineered bioreactor. When subjected to various environmental cues, anaerobic granules responded reproducibly allowing for rare or unique opportunities for high-throughput studies testing whole-community responses to a wide range of environmental conditions. [ABSTRACT FROM AUTHOR]

Wastewater treatment plants (WWTPs) contribute to the release of microplastics into the environment. While the removal efficiency of MPs in WWTPs can reach up to 99.9 %, the highest amount of microplastics is retained in the sludge. Anaerobic digestion, one of the most promising and common processes, can help reduce sludge volume and odour, and due to the formation of biogas, mainly consisting of methane (CH4) and carbon dioxide (CO2), can help decrease the operating costs of WWTPs. A test measuring the inhibition of biogas production using the OxiTop® measuring system was employed to determine the effect of added microfibres (MFs) on biogas production. Particles less than 1 mm in size of polyester, polyamide, and polyacrylic, were added to anaerobic sludge at concentrations ranging from 0.05 to 0.10 g l–1 to simulate their effect on biogas production. The yields of CH4 and CO2 produced during anaerobic digestion of the MFs-contaminated sludge were determined. The addition of MFs to sewage sludge affects methane production. The results indicated that the lowest added concentrations of 0.05 g l–1 of MFs promoted methane production, while the presence of 0.1 g l–1 decreased methane production for all types of MFs used. Polyacrylic at 0.1 g l–1 had the most negative effect on methane production (up to 27 %), while polyamide at 0.05 g l–1 reached the highest methane production (up to 25 %). [ABSTRACT FROM AUTHOR]

The production of value‐added products from sewage sludge is considered to be one of the solutions for the sustainable management of sludge in wastewater treatment plants (WWTPs). The presence of carbon, nitrogen, and phosphorus sources has made the sewage sludge of WWTPs a valuable and low‐cost substrate for the production of fermentative products. In the current study, a process was developed for microbial lipid production from two types of sewage sludge from a WWTP in northern Isfahan: anaerobic digester inlet sludge (DIS) and anaerobic digester outlet sludge (DOS). This process was based on the release of volatile fatty acids (VFAs) from the sludge by combinations of γ‐ray irradiation, anaerobic digestion, and acidogenic fermentation followed by utilization of VFAs in a microbial process by the oleaginous yeast Cryptococcus aureus UIMC65. After γ‐ray irradiation, the acidogenic fermentation of the treated sludge released 72% of the organic matter content of the sludge with acidification efficiency of 12% leading to 0.516 g L−1 VFAs. The oleaginous fermentation of the released VFAs for 7 days was accompanied by production of 1.58 g L−1 dry cell biomass with 40% lipid content. The results of this study indicate that the sewage sludge from urban WWTP has the potential to be used for the production of microbial lipids. [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]

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]

Anaerobic digestion (AD) relies on the cooperation of specific microbial communities, making it susceptible to process disruptions that could impact biogas production. In this regard, this study presents a technological solution based on the Arduino platform, in the form of a simple online monitoring system that can track the produced biogas profile, named as biogas analyzer module (BAM). The applicability of the BAM focused on monitoring the biogas produced from sugarcane vinasse inoculated with sewage sludge biodigestion processed in mesophilic conditions (38 oC), in a pH range of 6.5–7.5, and following a three-stage operational model: (i) an adaptation (168 h), (ii) complete mixing (168 h), and (iii) bio-stimulation with glycerol (192 h). Then, the lab-made BAM was used to trace the produced biogas profile, which registered a total biogas volume of 8,719.86 cm3 and biomethane concentration of 95.79% (vol.), removing 90.8% (vol) of carbon dioxide (CO2) and 65.2% (vol) of hydrogen sulfide (H2S). In conclusion, the results ensured good accuracy and efficiency to the device created by comparisons with established standards (chromatographic and colorimetric methods), as well as the cost reduction. The developed device would likely be six times cheaper than what is available in the market. [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]

To meet global food demands sustainably, it is necessary to safeguard finite natural resources and reduce harmful emissions to the environment. Nutrients in biowastes are often not managed appropriately. Instead, they can be recovered, recycled into bio-based fertilizers (BBFs) and reincorporated into food production systems. This review addresses three critical issues for developing and adopting new BBFs, focusing on the European context: (1) BBFs should match the agronomic efficiency of mineral fertilizers. We propose that the agronomic efficiency of BBFs can be increased through pre-treating the inputs in biowaste transformation processes (e.g., anaerobic digestion), chemical treatments of existing BBFs, organo-mineral combinations, and soil placement strategies. (2) Production and use of new BBFs is not free of environmental impacts, and these are influenced by regional conditions. (3) Public perception and end-user preferences play a significant role in the adoption of BBFs. Therefore, it is vital to address the requirements of end-users of BBFs. Our findings indicate that for widespread adoption, BBFs need sufficient and reliable nutrient amounts and crop-adequate ratios, as well as competitive pricing. A key advantage of BBFs over mineral fertilizers is their ability to improve soil fertility. However, farmers also require fertilizers that can be handled and applied with existing machinery and offer the practicality of commercial products. Another important aspect is the willingness of consumers to buy products fertilized with BBFs. Designing and promoting BBFs requires a careful assessment of environmental impacts and regional conditions, as the sustainability of BBFs depends on factors like energy sources and biowaste transport distances. Ultimately, the goal is to promote a circular economy and not just to substitute mineral fertilizers with new products. This review aims to guide researchers, policymakers, and stakeholders by highlighting key innovations and addressing critical barriers. [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]

This work assessed the performance of a pilot‐scale cascade anaerobic digestion (AD) system when treating mixed municipal wastewater treatment sludges. The cascade system was compared with a conventional continuous stirred tank reactor (CSTR) digester (control) in terms of process performance, stability, and digestate quality. The results showed that the cascade system achieved higher volatile solids removal (VSR) efficiencies (28–48%) than that of the reference (25–41%) when operated at the same solids residence time (SRT) in the range of 11–15 days. When the SRT of the cascade system was reduced to 8 days the VSR (32–36%) was only slightly less than that of the reference digester that was operated at a 15‐day SRT (39–43%). Specific hydrolysis rates in the first stage of the cascade system were 66–152% higher than those of the reference. Additionally, the cascade system exhibited relatively stable effluent concentrations of volatile fatty acids (VFAs: 100–120 mg/l), while the corresponding concentrations in the control effluent demonstrated greater fluctuations (100–160 mg/l). The cascade system's effluent pH and VFA/alkalinity ratios were consistently maintained within the optimal range. During a dynamic test when the feed total solids concentration was doubled, total VFA concentrations (85–120 mg/l) in the cascade system were noticeably less than those (100–170 mg/l) of the control, while the pH and VFA/alkalinity levels remained in a stable range. The cascade system achieved higher total solids (TS) content in the dewatered digestate (19.4–26.8%) than the control (17.4–22.1%), and E. coli log reductions (2.0–4.1 log MPN/g TS) were considerably higher (p < 0.05) than those in the control (1.3–2.9 log MPN/g TS). Overall, operating multiple CSTRs in cascade mode at typical SRTs and mixed sludge ratios enhanced the performance, stability digesters, and digestate quality of AD. Practitioner Points: Enhanced digestion of mixed sludge digestion with cascade system.Increased hydrolysis rates in the cascade system compared to a reference CSTR.More stable conditions for methanogen growth at both steady and dynamic states.Improved dewaterability and E. coli reduction of digestate from the cascade system. [ABSTRACT FROM AUTHOR]

Sewage sludge (SS) is a potential source of bioenergy, yet its management is a global concern. Anaerobic digestion (AD) is applied to effectively valorize SS by reclaiming energy in the form of methane. However, the complex floc structure of SS hinders hydrolysis during AD process, thus resulting in lower process efficiency. To overcome the rate-limiting hydrolysis, various pre-treatment methods have been developed to enhance AD efficiency. This review aims to provide insights into recent advancements in pre-treatment technologies, including mechanical, chemical, thermal, and biological methods. Each technology was critically evaluated and compared, and its relative worth was summarized based on full-scale applicability, along with economic benefits, AD performance improvements, and impact on digested sludge. The paper illuminates the readers about existing research gaps, and the future research needed for successful implementation of these approaches at full scale. HIGHLIGHTS AD offers sustainable sludge management by harnessing energy recovery.; Pre-treatment approaches for enhanced hydrolysis during AD.; Challenges and recent advances during sludge pre-treatments are discussed.; Further research on detailed characterization after pre-treatment is required.; The future outlook for pre-treated sewage sludge digestion has been discussed.;

Today, the transition to renewable energy from conventional energy practices is more important than ever to establish energy security and mitigate climate change. The wastewater treatment plants (WWTP) consume a remarkable amount of energy and cause significant greenhouse gas emissions. The energy balance of WWTP can be improved by implementing energy-efficient applications such as anaerobic digestion. However, most of the existing WWTPs utilize only sewage sludge in conventional anaerobic digesters (CAD) which results in low biogas generation. Generally, co-digestion is indicated as an effective solution for the low biogas generation faced in mono-digestion. Moreover, recently, anaerobic membrane bioreactors (AnMBR) have been promoted as a prominent alternative to CADs. This paper overviews the current situation of co-digestion applications by AnMBRs for municipal WWTPs. Furthermore, the environmental and economic aspects of these applications were reviewed. Lastly, challenges and future perspectives related to the co-digestion applications by AnMBR were thoroughly discussed. [ABSTRACT FROM AUTHOR]

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]

Conventional pretreatment technologies have been assessed to resolve the slow hydrolysis of sewage sludge, but high operating costs have prevented their wide use. This study investigated non-thermal plasma (NTP) technologies as an alternative to promote anaerobic digestion (AD). Various contact time (CT) and temperature (T) conditions were used to assess how NTP pretreatment improves the methane conversion of organics in sewage sludge. A multi-response surface model (RSM) using a central composite design (CCD) identified the optimal CT (4.6 h) and T (45 °C). This statistical optimization of NTP pretreatment led to an enhanced biochemical methane potential of 297 ± 46 mL CH4 g–1 COD by reducing operating cost as power consumption as low as 0.08 USD L–1. The result was comparable to those of other advanced oxidation processes (0.14 – 0.60 USD L–1) demonstrating that accelerated hydrolysis of sewage sludge using NTP pretreatment show potential for improving renewable energy recovery from sewage sludge. [ABSTRACT FROM AUTHOR]

This manuscript presents a scientometric review of recent advances in microwave pretreatment processes for sewage sludge, systematically identifying existing gaps and prospects. For this purpose, 1763 papers on the application of microwave technology to sludge pretreatment were retrieved from the Web of Science (WoS) using relevant keywords. These publications were then analyzed using diverse scientometric indices. The results show that research in this field encompasses applications based on the non-thermal effects of microwaves, enhanced effectiveness of anaerobic digestion (AD), and the energy balance of this pretreatment system. Overcoming existing technical challenges, such as the cleavage of extracellular polymers, reducing microwave energy consumption, understanding the non-thermal effects of microwaves, promoting AD of sludge in combination with other chemical and physical methods, and expanding the application of the technology, are the main scientific focuses. Additionally, this paper thoroughly examines both the constraints and potential of microwave pretreatment technology for wastewater treatment. [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]

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BACKGROUND: To our best knowledge, no experimental study has previously investigated the simultaneous effects of adding Fe powder for the decrease of hydrogen sulfide (H2S) in biogas and the removal of phosphate (PO4‐P) in continuous anaerobic digestion (AD). This study investigated the effects of iron (Fe) powder (5 g L−1) in AD to remove H2S and PO4‐P. A comparative experiment was conducted using two semi‐continuous‐flow anaerobic digesters treating primary sludge at decreasing hydraulic retention times (HRTs) of 20 to 10 days. RESULTS: The addition of Fe powder to AD removed > 98% of H2S at all HRTs, and removed 64–72% of PO4‐P, with the highest removal efficiency at HRT = 10 d. The addition of Fe powder to AD had no noticeable effect on biogas production or pH, but it increased the CH4 content (62.7–66.0% in Fe‐treated vs 58.2–60.4% in the Control) partly due to the greater presence of Methanoregulaceae. The relative abundance of the microbial groups was more affected by HRT than by the addition of Fe powder. The presence of Fe powder notably increased the abundance of Spirochaetaceae and Syntrophaceae. CONCLUSION: As shown, the addition of Fe powder can improve the management of both H2S in the biogas and PO4‐P in the digested sludge in the AD system. © 2024 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Antimicrobial resistance (AMR) is recognized as a global threat. AMR bacteria accumulate in sewage sludge however, knowledge on the persistence of human pathogens and AMR in the sludge line of the wastewater treatment is limited. Sludge can be used, with or without additional treatment, as fertilizer in agricultural fields. The aim of this study is to obtain knowledge about presence of human pathogens and AMR in the sewage sludge, before and after the anaerobic digestion (AD) applying innovative combinations of methods. Fifty sludge samples were collected. Cultivation methods combined with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and Antibiotic Susceptibility Test (AST) were used obtaining knowledge about the microbial community, pathogens, and antibiotic resistant bacteria while the droplet digital Polymerase Chain Reaction (ddPCR) was performed to detect most common AMR genes. In total, 231 different bacterial species were identified in the samples. The most abundant species were spore-forming facultative anaerobic bacteria belonging to Bacillus and Clostridium genera. The AD causes a shift in the microbial composition of the sludge (p = 0.04). Seven pathogenic bacterial species constituting 188 colonies were isolated and tested for susceptibility to Clindamycin, Meropenem, Norfloxacin, Penicillin G, and Tigecycline. Of the Clostridium perfringens and Bacillus cereus isolates 67 and 50 %, respectively, were resistant to Clindamycin. Two B. cereus and two C. perfringens isolates were also resistant to other antibiotics showing multidrug resistance. ARGs (blaOXA, blaTEM, ermB, qnrB, tet(A)-(W), sulI-II) were present at 7–8 Log gene copies/kg of sludge. AD is the main driver of a reduction of some ARGs (1 Log) but resistant bacteria were still present. The results showed the usefulness of the integration of the proposed analytical methods and suggest a decrease in the risk of presence of cultivable pathogens including resistant isolates after AD but a persistent risk of ARGs’ horizontal transmission.

Background: Massive amounts of sewage sludge are generated during biological sewage treatment and are commonly subjected to anaerobic digestion, land application, and landfill disposal. Concurrently, persistent organic pollutants (POPs) are frequently found in sludge treatment and disposal systems, posing significant risks to both human health and wildlife. Metabolically versatile microorganisms originating from sewage sludge are inevitably introduced to sludge treatment and disposal systems, potentially affecting the fate of POPs. However, there is currently a dearth of comprehensive assessments regarding the capability of sewage sludge microbiota from geographically disparate regions to attenuate POPs and the underpinning microbiomes. Results: Here we report the global prevalence of organohalide-respiring bacteria (OHRB) known for their capacity to attenuate POPs in sewage sludge, with an occurrence frequency of ~50% in the investigated samples (605 of 1186). Subsequent laboratory tests revealed microbial reductive dechlorination of polychlorinated biphenyls (PCBs), one of the most notorious categories of POPs, in 80 out of 84 sludge microcosms via various pathways. Most chlorines were removed from the para- and meta-positions of PCBs; nevertheless, ortho-dechlorination of PCBs also occurred widely, although to lower extents. Abundances of several well-characterized OHRB genera (Dehalococcoides, Dehalogenimonas, and Dehalobacter) and uncultivated Dehalococcoidia lineages increased during incubation and were positively correlated with PCB dechlorination, suggesting their involvement in dechlorinating PCBs. The previously identified PCB reductive dehalogenase (RDase) genes pcbA4 and pcbA5 tended to coexist in most sludge microcosms, but the low ratios of these RDase genes to OHRB abundance also indicated the existence of currently undescribed RDases in sewage sludge. Microbial community analyses revealed a positive correlation between biodiversity and PCB dechlorination activity although there was an apparent threshold of community co-occurrence network complexity beyond which dechlorination activity decreased. Conclusions: Our findings that sludge microbiota exhibited nearly ubiquitous dechlorination of PCBs indicate widespread and nonnegligible impacts of sludge microbiota on the fate of POPs in sludge treatment and disposal systems. The existence of diverse OHRB also suggests sewage sludge as an alternative source to obtain POP-attenuating consortia and calls for further exploration of OHRB populations in sewage sludge. 7vWBgxzBnCPA6QWxMbshMg Video Abstract [ABSTRACT FROM AUTHOR]

The widespread use of bisphenol A (BPA) has resulted in the emergence of new pollutants in various environments, particularly concentrated in sewage sludge. This study investigated the effects of BPA on sludge anaerobic digestion, focusing specifically on the interaction of microbial communities and their metabolic responses. While the influence of BPA on methane accumulation is not significant, BPA still enhanced the conversion of soluble COD, protein, and polysaccharides. BPA also positively influenced the hydrolysis-acidogenesis process, leading to 17% higher concentrations of volatile fatty acids (VFAs). Lower BPA levels (0.2–0.5 mg/kg dw) led to decreased hydrolysis and acidogenesis gene abundance, indicating metabolic inhibition; conversely, higher concentrations (1–5 mg/kg dw) increased gene abundance, signifying metabolic enhancement. Diverse methane metabolism was observed and exhibited alterations under BPA exposure. The presence of BPA impacted both the diversity and composition of microbial populations. Bacteroidetes, Proteobacteria, Firmicutes, and Chloroflexi dominated in BPA-treated groups and varied in abundance among different treatments. Changes of specific genera Sedimentibacter, Fervikobacterium, Blvii28, and Coprothermobacter in response to BPA, affecting hydrolysis and acetogenesis. Archaeal diversity declined while the hydrogenotrophic methanogen Methanospirillum thrived under BPA exposure. BPA exposure enabled microorganisms to form structured community interaction networks and boost their metabolic activities during anaerobic digestion. The study also observed the enrichment of BPA biodegradation pathways at high BPA concentrations, which could interact and overlap to ensure efficient BPA degradation. The study provides insights into the digestion performance and interactions of microbial communities to BPA stress and sheds light on the potential effect of BPA during anaerobic digestion. [ABSTRACT FROM AUTHOR]

Dewatered sludges from twenty-two sewage treatment facilities were characterized to develop the quality control indices in India. This study used fertilizer index (FI) and clean index (CI) as a tool for categorizing sludge utilization into different classes (A, B, C and limited use classes LU-1, LU-2, LU-3) by their fertilizing potential, toxicity level, pathogen presence, and vector attraction reduction criteria. The findings revealed that total P (as P2O5), total N, and K (as K2O) in the sludge samples ranged from 0.9 to 5.7%, 1.2 to 3.8%, and 0.1 to 1.5%, respectively. Moreover, all sludges belong to Class C and lower category due to the presence of toxic metals and pathogens. The helminth eggs were found in the range of 25–1450 Numbers/4gTS in sludge samples. The highest number of helminth eggs of 1450/4 g of TS was found in the fecal sludge. The specific oxygen uptake rate (SOUR) values in the sludge samples varied from 0.3 to 4.9, with a median value of 1.3 and an RSD of 86% is way too high. It indicates that the sludge samples need further treatment to be less attractive as a food source for vectors and rodents. However, sludge samples have fertilizing potential and FI values ranges from 4.1 to 4.9, and CI value ranges from 2.5 to 5.0. It indicates that compost is best in quality and has high-fertilizer potential and low heavy-metal content, which is suitable for high-value crops such as organic farming. Further sludge treatment using typical composting, aerobic or anaerobic digestion, and solar or thermal drying could bring the sludges into the Class A and B categories. [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]

Many studies have been conducted on the anaerobic digestion of sewage sludge due to its enormous amount to collect and dispose of. Different methods to improve the process of anaerobic digestion of sewage sludge have been investigated, focusing on the increase of biogas production. In this article, attention is focused on the use of two different carbon-rich products to boost the production of methane in the anaerobic digestion of sewage sludge. The investigation aims to underline the different outcomes that biochar and hydrochar show on methane yield. Both are carbon-rich products but there are differences in their properties and the processes from which they are derived. Biochar is a product of the pyrolysis treatment of biomass. This product can be different in composition and properties depending on the process conditions. Hydrothermal Carbonization (HTC) is an important mid-temperature thermochemical process that converts biomass into hydrochar. The solid HTC by-product seems to be a good accelerator of methane production. The tests are performed in batch reactors, with 0.5, 2, and 5 grams of the two products added to 60 grams of inoculum and 100 grams of sludge, based on the total volatile solids. Mesophilic Anaerobic Digestion was adopted, at a temperature of 35°C, for 34 days, until methane production was stopped. pH is an important parameter for the process, its value being maintained in the 6.8-8 range. The results show a significant increase in methane yield compared to the simple anaerobic digestion process. [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]

The greatly rising amounts of sewage sludge from different sources are causing severe concerns around the globe. Disposal of sewage sludge is exceptionally difficult and poses serious environmental problems due to the significant quantity of toxic heavy metals and organic contaminants in its constituents. This review provides an overview of different conversion methods of sewage sludge into energy, that is, pyrolysis, hydrothermal gasification, hydrothermal liquefaction, hydrothermal carbonization, anaerobic digestion, and transesterification. It also focuses on each conversion route's state‐of‐the‐art research advances, features, and drawbacks to ensure financial and ecological responsibility. The detailed descriptions of the methods and respective energy generation could help scholars and industrialists produce energy from sewage sludge to keep the environment harmless. [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]

Anaerobic co-digestion can effectively break the limitations of mono-digestion. However, there are still some problems such as long residence time, unsatisfactory methane yield, and unstable performance for co-digestion of sewage sludge (SS) and food waste (FW). Therefore, the SS in the reactor treating co-digestion of SS and FW is considered to be pretreated by thermal hydrolysis. In this work, the anaerobic co-digestion of SS of thermal hydrolysis pretreatment (THP) and FW significantly improved the stability, methane production of the digestive reactor, and dewaterability of the digested sludge. The R6 obtained the most cumulative methane production (315.76 mL/g VS). In addition, compared to R3, the cumulative methane production and maximum methane production rate of R5 increased by 9.93% and 14.56%, respectively. The dewaterability of R4, R5, and R6 was improved, while the dewatering performance of the R3 decreased to a greater extent. The results of the kinetic model fitting were consistent with the experimental results. Among them, the hydrolysis constants (Kh) of anaerobic co-digestion of THP-SS and FW were 0.121, 0.130, and 0.114 d−1, respectively, which were higher than those of other groups. And the estimated lag time (λ) of co-digestion was also lower than that of mono-digestion groups. Microbial community analysis indicated that the bacterial diversity and richness of anaerobic co-digested groups of THP-SS and FW were enhanced, while the methanogens with acetoclastic pathway became the main methanogenic microorganisms. This work provides essential information on anaerobic co-digestion containing different THP-SS contents. [ABSTRACT FROM AUTHOR]

This study investigated the effect of ultrasonic (US) pretreatment at three different contact times (30, 45, and 60 min) with a power of 240 W and frequency of 40 kHz on the fate of antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and enteric pathogens during anaerobic digestion (AD) of sludge. By using real time-qPCR, three MGEs (int1, int2, and tnpA) and seven ARGs (sul1, sul2, tetW, tetA, tetO, ermF, and aac(6')-lb) were quantified that have serious human health impacts and represent the most widely used antibiotics (tetracycline, sulfonamide, macrolide, and aminoglycoside). Results indicated that US pretreatment under different contact times improved the removal of ARGs and MGEs. Compared to 30 and 45 min of US pretreatment, 60 min of US pretreatment resulted in a higher reduction of ARGs with total ARG reduction of 41.70 ± 1.13%. Furthermore, the relative abundance of ARGs and MGEs after US pretreatment was reduced more effectively in anaerobic reactors than in a control AD without US pretreatment. The total ARGs and MGEs removal efficiency of control AD was 44.07 ± 0.72% and 63.69 ± 1.43%, and if US pretreatment at different times were applied, the total ARGs and MGEs removal efficiency of the whole pretreatment AD process improved to 59.71 ± 2.76–68.54 ± 1.58% and 69.82 ± 2.15–76.84 ± 0.22%. The highest removal of total ARGs (68.54 ± 1.58%) and MGEs (76.84 ± 0.22%) was achieved after AD with US pretreatment at 45 min. However, US pretreatment and AD with US pretreatment were not effective in inactivation of enteric pathogens (total coliforms and E. coli), suggesting that posttreatment is needed prior to land application of sludge to reduce the level of enteric pathogens. There was no detection of the studied ARGs and MGEs in the enteric pathogens after US pretreatment in subsequent AD. According to this study, long contact times of US pretreatment can mitigate ARGs and MGEs in AD processes, offering valuable insight into improving environmental safety and sustainable waste management. Additionally, the study highlights the need to investigate posttreatment techniques for reducing enteric pathogens in AD effluent, a crucial consideration for agricultural use and environmental protection. [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]

Anaerobic digestion (AD) is a prominent treatment method for the sludge produced from sewage treatment plants. Poor solid reduction and longer retention time are the main drawbacks of AD. Thermal hydrolysis (TH) is a potential pretreatment method for solubilization of sewage sludge (SS) solids thereby improving biogas production during AD post-treatment. In this study, the SS sample (total solids = 1.75 wt% and total chemical oxygen demand (COD) = 15,450 mg L−1) was subjected to TH pretreatment (temperature = 140–180°C and reaction time = 60 minutes) in a 0.7-L capacity stainless-steel high-pressure reactor. At a reaction temperature of 180°C, the maximum solid solubilization (total dissolved solids = 4652 mg L−1) and improved dewaterability (time to filter = 4.7 s.L g−1) were observed. The biochemical methane potential test results showed almost doubling of methane generation from 145 to 284 mL gCOD−1 after TH pretreatment at 180°C. The life cycle assessment approach was used to compare various SS treatment and disposal scenarios, two of which included hydrothermal pretreatment. The scenarios involving hydrothermal pretreatments showed the least global warming potential. [ABSTRACT FROM AUTHOR]

Artificial neural networks (ANNs) simulate an anaerobic co-digestion process of Organic Fraction of Municipal Solid Waste (OFMSW) and bio-flocculated sludge for a mesophilic lab-scale semi-continuous feed reactor. The operational, substrate quality and process control parameters such as Organic Loading Rate, Hydraulic Retention Time, pH, VFA/Alkalinity ratio and Total Solids are input variables and methane yield and Volatile Solids removal are outputs for ANN modelling. The lab-scale experimental results are used to develop a prediction model using fitting application for ANN. The network architecture was optimized to achieve accurate predictions, resulting in a 5-19-2 architecture for methane yield and a 5-17-2 architecture for %VSremoval. The training was performed using the Bayesian Regularization (trainbr) algorithm, leading to high coefficients of determination (R2) of 0.953 and 0.978 for methane yield and %VSremoval, respectively. The results demonstrate the effectiveness of neural network-based modelling in capturing complex relationships within the methane yield process, facilitating accurate prediction of crucial output parameters. [ABSTRACT FROM AUTHOR]

After the industrial revolution, rapid population growth and burning fossil fuels led to the achievement of massive amounts of both liquid and solid waste, which can pose numerous threats for all compartments of environment. Anaerobic Digestion (AD) has been one of the most applicable techniques used during the last few decades to overcome the unpleasant presence of both organic fraction of waste and sewage sludge (SS), and as the result of this technique, biogas which is one of the main sources of energy can be produced. Therefore, the application of AD as a solution to overcome sludge and biodegradable fraction of solid waste has been the center of attentions since significant amounts of waste and sludge are being produced every day. In this regard a comprehensive review was conducted to know the advantages, disadvantages, various techniques that can improve methane yield, insights on the pretreatment methods, and operating factors was conducted to elucidate research gaps and future opportunities. Also, in the current study we discussed about operating conditions of single-stage digesters, two-stage digesters, anaerobic co-digestion. Our study is the first comprehensive review worked on the techniques by which we can improve methane yield from AD system.

Gasification residues/chars (GR) and activated carbon (AC) are added to wastewater treatment processes mainly as a fourth purification stage, e.g., to adsorb heavy metals or pharmaceutical residues. However, the effects of GR or AC, which are transferred to the anaerobic digestion (AD) via the sludge, are not yet fully understood. Although, the positive effect of char addition on AD has been demonstrated in several investigations, systematic studies with chemically well described chars are still missing. Therefore, in this study, different chars were characterized in detail, subjected to AD in different concentrations, and their effect on methane production investigated. GR of a gasification plant with a floating fixed bed technology, carbon made by chemical impregnation with ZnCl2 from waste-wood, carbon produced by thermochemical activation with CO2 from GR and commercial powdered AC were used for the experiments. Among others, thermogravimetric analysis, physisorption, pH, and conductivity analysis were used to characterize the chars. Mesophilic AD batch tests with different concentrations (0.025, 0.05, 0.5, 1.0, 7.0, 14.0 gL−1) of all chars (GR and ACs, respectively) were performed with digester sludge from a wastewater treatment plant for a period of 47 d. Volatile fatty acids (VFA) as well as biogas production and CH4 concentrations were monitored. It could be shown, that concentrations below 1.0 g char L−1 did not result in significant effects on CH4 and/or VFA production, whereas high concentrations of GR and AC influenced both, the CH4 yield and kinetics. Depending on the production process and the characteristics of the chars, the effect on AD varied, whereby both, positive and negative effects on biogas yield and methane production were observed. This study provides the first systematic evaluation of char application to AD processes, and therefore allows for better predictions of char applicability and effect.

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.

The Anaerobic Digestion Model No. 1 (ADM1) was employed to simulate methane (CH4) production in an anaerobic reactor (AR), and the associated bench-scale biochemical methane potential (BMP) assay, having sewage sludge (SWS) from a municipal wastewater treatment plant (WWTP) as feedstock. The SWS presented the following physical-chemical characteristics: pH (7.4–7.6), alkalinity (2,382 ± 100 mg CaCO3 L−1), tCOD (21,903 ± 1,000 mg L−1), TOC (895 ± 100 mg L−1), TS, TVS, and VSS (2.0%, 1.1%, and 0.8%, respectively). The BMP assay was conducted in six replicates under anaerobic mesophilic conditions (37 ± 0.1°C) for 11 days with a CH4 yield registered of 137.6 ± 6.39 NmL CH4 or 124 ± 6.72 CH4 g−1 VS−1. When the results obtained with the BMP bench-scale reactors were compared to the output generated with computational data by the ADM1 model having as input data the same initial sewage tCOD, similar cumulative CH4 production curves were obtained, indicating the accuracy of the ADM1 model. This approach allowed the characterization of the sludge and estimation of its biogas production potential. The combination of BMP assays, experimental data, and ADM1 model simulations provided a framework for studying anaerobic digestion (AD) processes.

The global food crisis approach encourages finding new sources of replenishment of the phosphorus deficit in agriculture, making the unconventional sources of phosphorus particularly relevant. Despite numerous studies of phosphorus recovery methods, the need to increase the content of nutrients in the organo-mineral fertilizers obtained via anaerobic digestion of sewage activated sludge from municipal wastewater still exists. The greatest success in this area has been achieved by the biotechnologies which ensure the simultaneous production of biogas and biofertilizers. The present study proposes a sustainable technology for anaerobic digestion with the simultaneous capture of carbon dioxide and sodium carbonate production. It involves pre-comminution of the organo-mineral substrate (vegetal waste, activated sludge, phosphorus-containing component, and cheese whey) facilitating anaerobic digestion, and extraction of CO2 from biogas by absorption with a 10 % NaOH solution. Biomethanation reaction was found to have the first order with the activation energy of 24.8 kJ/mol, whereas the carbon dioxide absorption degree is proportional to the CO2 content in biogas. The results showed good potential for increasing the efficiency of both phosphorus recovery from municipal wastewater and anaerobic digestion to produce valuable products, including high-purity bio-methane (96 vol. % CH4), concentrated (∑NPKCa 53 %) organo-mineral fertilizer from digestate and soda ash. Obtained fertilizer increased potato yield by 35 wt. %. The study demonstrates a novel concept of carbon dioxide cycle looping in biogas production, as well as reducing greenhouse gas emissions by converting up to 98.7 % of CO2 into an additional marketable product – sodium carbonate, which contains 99 % Na2CO3.

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.