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The composition of waste-activated sludge (WAS) is complex, containing a large amount of harmful substances, which pose a threat to the environment and human health. The reduction and resource utilization of sludge has become a development demand in sludge treatment and disposal. Based on the technical bottlenecks in the practical application of direct anaerobic digestion technology, this study adopted two different thermal and thermal–alkali hydrolysis technologies to pretreat sludge. A pilot-scale experiment was conducted to investigate the experimental conditions, parameters, and effects of two hydrolysis technologies. This study showed that the optimal hydrolysis temperature was 70 °C, the hydrolysis effect and pH can reach equilibrium with the hydrolysis retention time was 4–8 h, and the optimal alkali concentration range was 0.0125–0.015 kg NaOH/kg dry-sludge. Thermal–alkali combination treatment greatly improved the performance of methane production, the addition of NaOH increased methane yield by 31.2% than that of 70 °C thermal hydrolysis. The average energy consumption is 75 kWh/m3 80% water-content sludge during the experiment. This study provides a better pretreatment strategy for exploring efficient anaerobic digestion treatment technologies suitable for southern characteristic sewage sludge. HIGHLIGHTS Enhanced anaerobic digestion of WAS by thermal–alkali pretreatment was studied at a pilot-scale level.; Optimal thermal temperature and retention time were confirmed for a pilot-scale study.; Energy demand can be basically met based on biogas production.;

Biochar (BC) is often used as an additive in anaerobic digestion (AD) to increase yield and/or to stabilise the process when the manure content is increased. Unfortunately, BC is rarely described in detail in terms of its raw material sources, production processes, and structural, physical and chemical properties to allow correlation with its effects on AD. It is an open question whether microorganisms from AD can penetrate into different biochar pore types, depending on their wood origin. In this paper, we describe the preparation (temperatures, treatment times, yields) and characterisation shrinkage, density, pore sizes, pore size distribution, specific surface area, ash, volatiles, fixed carbon, elemental composition, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), benzene, toluene, ethyl-toluene, xylene (BTEX) and volatile halogenated hydrocarbons (VHH) of BC cubes of Scots pine (Pinus sylvestris) and common beech (Fagus sylvatica) powder made from this BC in addition to commercial charcoal powder. The pore size distribution determined by mercury porosimetry differs from that determined by 3D-reflected light microscopy. After incubating BC cubes in AD, the cubes were mechanically cleaned and cut into two pieces. Microorganisms were detected inside the cubes by fluorescence microscopy. Particle size and wood source determine the influence of BC on AD. [ABSTRACT FROM AUTHOR]

Antibiotic resistance genes (ARGs) have emerged as a significant global health threat, contributing to fatalities worldwide. Wastewater treatment plants (WWTPs) and livestock farms serve as primary reservoirs for these genes due to the limited efficacy of existing treatment methods and microbial adaptation to environmental stressors. Anaerobic digestion (AD) stands as a prevalent biological treatment for managing sewage sludge and manure in these settings. Given the agricultural utility of AD digestate as biofertilizers, understanding ARGs' fate within AD processes is essential to devise effective mitigation strategies. However, understanding the impact of various factors on ARGs occurrence, dissemination, and fate remains limited. This review article explores various AD treatment parameters and correlates to various resistance mechanisms and hotspots of ARGs in the environment. It further evaluates the dissemination and occurrence of ARGs in AD feedstocks and provides a comprehensive understanding of the fate of ARGs in AD systems. This review explores the influence of key AD parameters such as feedstock properties, pretreatments, additives, and operational strategies on ARGs. Results show that properties such as high solid content and optimum co-digestion ratios can enhance ARG removal, while the presence of heavy metals, microplastics, and antibiotics could elevate ARG abundance. Also, operational enhancements, such as employing two-stage digestion, have shown promise in improving ARG removal. However, certain pretreatment methods, like thermal hydrolysis, may exhibit a rebounding effect on ARG levels. Overall, this review systematically addresses current challenges and offers future perspectives associated with the fate of ARGs in AD systems. [ABSTRACT FROM AUTHOR]

Among the various techniques used to reduce hydrogene sulfide in biogaz avoiding harmful effects on engines, the chemical and biological treatment appears particularly promising. The main objective of this article was to develop a new process to reduce the harmful effect of hydrogen sulfide (H2S), contained in the biogas resulting from methanization, on the equipment of the wastewater treatment plant (WWTP) of FES city in particular the two cogeneration units. A multiple regime technique for biogas desulfuration, based on the chemical and biological treatment as well as internal micro-aeration of the digester was developed. Owing to the insights gained from this study, it was identified that reducing the concentration of H2S in biogas and improving methane production (biogas production increased from 3.6 M Nm³ in 2018 to 3.8 M Nm³ in 2019, a saving of about 300,000 MAD); reduction of desulfurization tower downtime from 4 times/year to 1 time/year; increasing operating time of generating sets from 8800 in 2018 to 14 400 h in 2019; electricity production increased from 5.9 GWh in 2018 to 7.2 GWh in 2019. In light of these findings, it can be affirmed that the study successfully achieved its objectives, presenting valuable avenues for future scientific exploration. [ABSTRACT FROM AUTHOR]

Anaerobic Digestion (AD) of organic waste is one of the most promising processes and is the ideal solution for the disposal of organic waste (OW) and at the same time, the production of methane gas which may be used as a sustainable energy resource. An anaerobic biodigester with a volume of (20) liters has been used to digest organic waste and to trace the changes that occur during the AD process. Operating parameters such as temperature, pH, total solids, and volatile solids (TS, VS) have been measured which have a significant impact on the rate and quality of biogas production. Experiments on anaerobic biodegradation of OW-SS were monitored under mesophilic conditions (temperature 37 °C, retention time 30–31 days). The pH value varied between (4.2–5.8) for OW-SS. During 30 days of the detection period, the maximum methane production (corrected) occurred on day 21 which was equal to 254.3-ml. The cumulative volume of the produced methane was recorded as (3409 ml), OW-SS, and these results were corrected to the standard conditions, where after correction, it became (2929 ml). The highest rate of methane concentration was estimated at (52 %) for OW-SS, while the rate of decrease in the TS and VS was (54 %, and 45 %), respectively. It is recommended to examine the changes that occur if a larger digester is used than the one used in the current study, such as 50 L, 100 L …. Etc. To compare the data obtained in this study with the results of larger digestions to allow for the opportunity to build anaerobic digesters at the plant level with the benefit of renewable energy production. It is also recommended to investigate the impact of some types of pretreatments on biogas production such as the use of alkali, enzymatic, ultrasonic treatment or acid ton the solid waste feed.

In this study, a reinforced concrete dome biogas plant processing buffalo dung was functioned to investigate the seasonal variations in biogas production, biogas composition, and loss of volatile solid and methane potential of digestate slurry. These analyses were undertaken from January to May 2019. The biogas quality was assessed using gas chromatography and biogas production was measured through the G4 VuGas diaphragm gas meter while methane potential was examined on biochemical methane potential (BMP) assays under mesophilic conditions. In January, when the average digester temperature was 26.1 °C, the minimum biogas production was 0.23 ± 0.004m3/kg VSadded with 67% CH4 and 32.9% CO2. In May, the average digester temperature rose to 36.1 °C and the maximum biogas yield obtained increased to 0.384 ± 0.006m3/kg VSadded, comprising 71% CH4 and 28.8% CO2. In the cold season during January, the percentage losses of biogas production were recorded to be 41% because of lower slurry temperature and accumulation of fatty acids. The average slurry temperatures within the digester during the cold season were 21.3 ∘ C at 6 A.M. and 21.9 ∘ C at 3 P.M., increasing to 36 ∘ C at 6 A.M. and 36.2 ∘ C at 3 P.M. for the warm season. In addition, the methane potential of 115NmL/g VSloss was observed from the digestate slurry through BMP test. The concrete dome biogas plant is favorable for its low cost and was shown to produce adequate amount of biogas to fulfill the domestic requirements during both warm and cold months in Pakistan. [ABSTRACT FROM AUTHOR]

Worldwide methane production by anaerobic digestion (AD) from organic waste has been expanded for greenhouse gas emission reduction by replacing fossil-fuel needs to facilitate sustainable energy supply. India also launched Sustainable Alternative Towards Affordable Transportation (SATAT) policy to promote compressed biogas (CBG) production through anaerobic digestion of organic waste. However, it is vital to understand productivity, raw material availability, and raw material quality to produce biogas at profit margin lucrative for business. The present work depicts biogas production from 11 organic feedstocks from community, industrial, and agricultural waste through 25 m3 demo-scale biogas plant. All materials were analysed for moisture, total solids, organic matter, carbon, nitrogen, C:N (carbon:nitrogen) ratio, and volatile solids, to optimize process parameters. Average 423 Nm3 biogas yield with 57% methane was obtained with average hydraulic retention time (HRT) of 60 days. The design, operation, and cost–benefit analysis of a 5 tons per day (TPD) CBG plant were carried out by integrating two digesters with pressure swing technology (PSA) for biogas purification, which resulted in 14% IRR and 3.6-year payback period after 10 years of operation. The 1500-tons/year CBG production can replace gasoline demand of 2070 kL/year while reducing CO2 emission of 41,218.6 tons/year through replacing gasoline and synthetic fertilizer (urea) by organic biogas slurry as by-product and preventing open dumping of organic waste. [ABSTRACT FROM AUTHOR]

A cross-flow ultrafiltration harvesting system for a pre-concentrated microalgae culture was tested in an innovative anaerobic-based WRRF. The microalgae culture was cultivated in a membrane photobioreactor fed with effluent from an anaerobic membrane bioreactor treating sewage. These harvested microalgae biomasses were then anaerobically co-digested with primary and secondary sludge from the water line. Depending on the needs of this anaerobic co-digestion, the filtration harvesting process was evaluated intermittently over a period of 212 days for different operating conditions, mainly the total amount of microalgae biomass harvested and the desired final total solids concentration (up to 15.9 g·L−1 with an average of 9.7 g·L−1). Concentration ratios of 15–27 were obtained with average transmembrane fluxes ranging from 5 to 28 L·m−2·h−1. Regarding membrane cleaning, both backflushing and chemical cleaning resulted in transmembrane flux recoveries that were, on average, 21% higher than those achieved with backflushing alone. The carbon footprint assessment shows promising results, as the GHG emissions associated with the cross-flow ultrafiltration harvesting process could be less than the emissions savings associated with the energy recovered from biogas production from the anaerobic valorisation of the harvested microalgae. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion offers a promising approach to enhancing biogas production from surplus by-products of wastewater treatment plants (WWTPs) and agricultural waste while reducing environmental negative impact. This study investigated the co-digestion of anaerobic thickened sewage sludge (ATSS) and rice straw (RS) under mesophilic conditions (35 ± 1 °C). In phase 1 of the experiment, lab-scale reactors with varying MRs of RS (0 %, 4 %, 8 %, and 16 % based on sludge weight) were employed to determine the optimal MR for maximizing biogas quantity and methane content. Phase 2 examined the impact of mechanical mixing (MM) on biogas production, pathogen and trace element reduction, and the calorific value (CV) of the co-digested mixture compared to the digested thickened sludge (DTS) and RS individually to assess the potential energy of co-digestion. Results revealed that the 8 % MR yielded the highest biogas volume, approximately 2.5 times that of the DTS alone, with methane and carbon dioxide contents within the typical ranges. MM in phase 2 further increased biogas volume by 2.8 times compared to DTS. The CV of the co-digested mixture was 24,937 kJ/kg and 21,929 kJ/kg for the DTS. Pathogens were effectively eliminated, and trace elements remained below the permissible limits. The 8 % MR with MM was identified as the optimal MR that produces the highest biogas quantity before reaching the turning point. Moreover, co-digestion at this MR enhanced the CV of ATSS by 14 %.

Biochar (BC) is often used as an additive in anaerobic digestion (AD) to increase yield and/or to stabilise the process when the manure content is increased. Unfortunately, BC is rarely described in detail in terms of its raw material sources, production processes, and structural, physical and chemical properties to allow correlation with its effects on AD. It is an open question whether microorganisms from AD can penetrate into different biochar pore types, depending on their wood origin. In this paper, we describe the preparation (temperatures, treatment times, yields) and characterisation shrinkage, density, pore sizes, pore size distribution, specific surface area, ash, volatiles, fixed carbon, elemental composition, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), benzene, toluene, ethyl-toluene, xylene (BTEX) and volatile halogenated hydrocarbons (VHH) of BC cubes of Scots pine (Pinus sylvestris) and common beech (Fagus sylvatica) powder made from this BC in addition to commercial charcoal powder. The pore size distribution determined by mercury porosimetry differs from that determined by 3D-reflected light microscopy. After incubating BC cubes in AD, the cubes were mechanically cleaned and cut into two pieces. Microorganisms were detected inside the cubes by fluorescence microscopy. Particle size and wood source determine the influence of BC on AD.

Slaughterhouse wastewater (SWW) is one of the most harmful agriculture and food industrial wastewaters because of rich impurities, particularly organic matter, suspended solids, oil, grease, and nitrogen (N) nutrients. This study investigated organics and N nutrients removal performance in the developed upgraded anaerobic-aerobic slaughterhouse wastewater treatment process (U-AASWWTP). The supernatant reflux position, ratio and dissolved oxygen (DO) in the aerobic units play key roles, and the optimized solutions were 300% reflux to the second compartment at DO of 4.64-4.90 mg/L. Under such conditions, chemical oxygen demand (COD) removal efficiency only decreased from 98.14% to 95.94% when the loading rates increased from 500 to 2,000 g·COD/(m³·d) gradually, whereas total nitrogen (TN) showed a different removal trend. Effluent TN was the lowest at 1,500 g·COD/(m³·d) and the corresponding effluent COD, TN and NH4+-N all satisfied with the Chinese upcoming discharge standard. Therefore, U-AASWWTP can effectively remove COD and N from SWW and would become the main direction of traditional treatment processes upgrading to addressing the issue of upcoming stricter effluent standard. This study holds significant importance in ensuring the sustainable development of slaughtering industry in China. Additionally, this study enhances the understanding of the synergy relationship between anaerobic digestion and Anammox microorganisms, thereby promoting the intelligent application in SWW treatment processes. [ABSTRACT FROM AUTHOR]

Wasted tofu rich in protein was subject to hydrothermal pretreatment (HTPT) under different conditions (at 120, 140, 160 and 180 ℃; for 0, 30, 60 and 90 min) followed by biochemical methane potential (BMP) tests, and 140 ℃ and 0 min were found to be respectively the best temperature and duration for HTPT of tofu in terms of its biogas production. Under the under the optimal conditions (140 ℃, 0 min) the accumulative methane yield reached up to 510.9 mL·(gVS)-1, which was 26.98 % higher than that without HTPT (402.3 mL·(gVS)-1). The start-up process of continuous anerobic digestion (AD) of the tofu before and after hydrothermal treated (HT) at the optimal HTPT conditions (140 ℃, 0 min) was examined, to investigate and compare how their consequent AD responded to HTPT. It was found that, for start-up of continuous AD, the HT tofu delivered more balanced nutrients and thus led to more stable AD and quicker biogas production. Unavoidably, HTPT generated products refractory to biodegradation, to slightly decrease the total biogas production. During AD of HT tofu some weak ammonia-tolerant microbes, such as methylotrophic methanogens, survived and played indispensable roles. Analyses of living microbial community structure indicated that, some hydrolytic acidification bacteria intolerant to ammonia nitrogen (such as Proteobacteria) were always active and appeared at high proportion. The viable methylotrophic methanogens, e. g. RumEn M2, took obvious responsibilities in start-up of the AD for HT tofu.

Sugarcane ethanol production generates about 360 billion liters of vinasse, a liquid effluent with an average chemical oxygen demand of 46,000 mg/L. Vinasse still contains about 11% of the original energy from sugarcane juice, but this chemical energy is diluted. This residue, usually discarded or applied in fertigation, is a suitable substrate for anaerobic digestion (AD). Although the technology is not yet widespread—only 3% of bioethanol plants used it in Brazil in the past, most discontinuing the process—the research continues. With a biomethane potential ranging from 215 to 324 L of methane produced by kilogram of organic matter in vinasse, AD could improve the energy output of sugarcane biorefineries. At the same time, the residual digestate could still be used as an agricultural amendment or for microalgal production for further stream valorization. This review presents the current technology for ethanol production from sugarcane and describes the state of the art in vinasse AD, including technological trends, through a recent patent evaluation. It also appraises the integration of vinasse AD in an ideal sugarcane biorefinery approach. It finally discusses bottlenecks and presents possible directions for technology development and widespread adoption of this simple yet powerful approach for bioresource recovery. [ABSTRACT FROM AUTHOR]

The anaerobic digestion (AD) study for the valorization of poultry slaughterhouse waste (PSHW) was assessed at laboratory scale and in mesophilic conditions. Different loads, given gradually from 0.5 g VS/L to 3 g VS/L, were used to evaluate the methane production from PSHW via AD. The highest cumulative methane production (CMP) and methane yield (YCH4) were observed for the 2 g VS/L and 1 g VS/L added loads, with values of 566 Nml and 378 Nml/g VS, respectively, in a HRT of 140 h. The efficiency of the process was examined using a response surface method-central composite design (RSM-CCD) to examine the impact of independent variables such as load and HRT on CMP and YCH4. A statistical analysis of variance (ANOVA) was carried out to evaluate the suitability of the developed model. The YCH4 results showed a probability value (P-value)

Anaerobic digestion (AD) is an efficient and eco-friendly process for the biodegradation of various organic biomass which could potentially produce biomethane and results in no waste accumulation. The palm oil industry concurrently produces three types of possible organic pollutants namely palm oil mill effluent (POME), palm empty fruit bunch fiber (PEFF) and oil palm decanter cake (OPDC). Therefore, this work aimed to study the anaerobic mono- and co-digestion of the substrates from palm industry. Results revealed that the co-digestion of PEFF + POME + OPDC resulted in highest cumulative methane yield of 0.40 L CH4/(g VS added); 0.28 L CH4/(g VS added) from PEFF + POME and 0.27 L CH4/(g VS added) from POME + OPDC. The methane content in biogas and volatile solid (VS) reduction from all the mono- and co-digestion experiments were found to be in the range of 69–71.5% and 40–75%, respectively. These results suggest that the co-digestion of these substrates is superior in biogas yield than mono-digestion. Further, the kinetic parameters were evaluated using the modified Gompertz model equation to determine the lag phase of the process and the maximum biogas generation rate from all the reactors, R2 in all the cases was found to be > 0.95. Next-generation sequencing analysis illustrated wide variety of dominant bacterial species belonging to phylum Firmicutes, Bacteroidetes, Proteobacteria and Chloroflexi. Hydrogenotrophic methanogenesis and acetoclastic methanogenesis were the prevailing methane-generating pathway involved that can be confirmed by the abundance of genus Methanospirillum and Methanothrix, Methanosarcina. [ABSTRACT FROM AUTHOR]

The production of biogas from food waste is a good approach to the minimization of food waste and increase in the production of renewable energy. However, the use of food waste as a feedstock for biogas production currently poses a difficulty due to an ineffective hydrolysis process, which is a pretreatment procedure and the initial step of the biogas conversion process. This restriction results from the food waste polymers' solubilization and breakdown. This has an impact on the volume of biogas produced during the methanogenesis stage. It is essential to increase the biodegradation of organic compounds (OC) during the hydrolysis process to increase biogas generation. This study focuses on the enhancement of biogas production by the anaerobic digestion (AD) of food waste (FW). FW was hydrolyzed by the immobilized biofilm and digested anaerobically in a semi-continuous digester. Four different digesters including the control were prepared. The control digester composed of no hydrolyzed food waste had no immobilized biofilm while the other three digesters had immobilized biofilm-hydrolyzed food waste with inoculum concentrations of 10%, 30%, and 50%. The results showed that the 50% digester had the highest biogas yield of about 2000 mL/500 mL. The 10%, 30%, and control digesters had a biogas yield of 1523 mL, 753 mL, and 502 mL respectively. Thus, the analysis of total volatile solid (TVS) reduction in the digesters with 10%, 30%, and 50% inoculum and the control have increased to 43.4% for the digesters with 30% and 10%, 60% for the digester with 50% inoculum, and only 29% for the control. Total chemical demand (TCOD) removal increased to 29%, 33%, 43%, and 56% for the control, and 10%, 30%, and 50%, respectively for the inoculum-to-feed ratio. From these results, the 50% inoculum-to-feed ratio has shown the highest biogas production and highest degradation based on TVS reduction and TCOD reduction. Based on this study, the biofilm pretreatment method can be considered a promising method for the enhancement of biogas volume and biodegradation. Biogas production was high (2000 mL) for hydraulic retention time (HRT = 20) days but the HRT = 15 days was also able to produce a significant amount (1400 mL) of biogas and the 50% inoculum-to-feed ratio has shown the highest volume of biogas production. [ABSTRACT FROM AUTHOR]

In this study, the effect of hydrothermal treatment (HTT) and the evaluation of its application as a pretreatment (HTP) and inter-treatment (HIT) on anaerobic digestion (AD) and fermentation of thickened waste activated sludge (TWAS) were examined. Two configurations were tested: (1) hydrothermal pretreatment, where the hydrothermal treatment was applied prior to single and two-stage anaerobic digestion; and (2) hydrothermal inter-treatment, where the hydrothermal treatment was applied after the first stage, fermentation, and prior to the second stage, methanogenesis. The results revealed the positive impact of hydrothermal pretreatment in both fermentation and anaerobic digestion processes. The chemical oxygen demand (COD) solubilization was higher through HTP (25.5%) than HIT (13%). Hydrothermal pretreatment increased the volatile fatty acids (VFA) production by 40% compared to the raw sample. The results also revealed no significant differences in the methane yield when hydrothermal treatment was applied as pretreatment or inter-treatment. The methane yield for the hydrothermal pretreatment and hydrothermal inter-treatment scenarios were 230 mLCH4/gTCODadded and 227 mLCH4/gTCODadded , respectively, compared to 158 mLCH4/gTCODadded for the raw sample. [ABSTRACT FROM AUTHOR]

Inadequate methane production and insufficient hydrolysis-acidification activity impede the practical application of anaerobic digestion (AD) of waste activated sludge (WAS). Recently, metal-organic framework (MOF) materials attains promising capability of controlling proton/electron transfer in AD processes. This study used a typical iron-based MOF and MIL-88A(Fe) to improve the methane production via digesting WAS. These materials were prepared via a one-step hydrothermal method. The findings indicated that the addition of 150 mg MIL-88A(Fe)/g WAS VS resulted in a 57.23% increase in accumulated methane production and a 43.84% increase in daily maximum methane production. The methane production rate (R max) also increased from 22.25 to 29.14 mL/g VS/d. The enhanced electron transfer capacity, improved hydrolysis of WAS, boosted acetate generation, and mitigated accumulation of volatile fatty acids (VFAs) collectively contributed to the better methane yield in the MIL-88A(Fe)-added system. The significant enrichment of Methanobacterium and Methanosaeta along with the up-regulation of key methanogenesis enzyme-encoding genes jointly suggested that the CO 2 reduction and methanogenesis were strengthened. Moreover, MIL-88A(Fe) stimulated the production of c-type cytochrome and e-pili, facilitating direct interspecies electron transfer (DIET) between norank-f-SC-I-84 and Methanobacterium. This study provided new solutions for improving methane production and offered insights into the mechanism of enhanced methanogenesis of AD in the presence of MIL-88A(Fe). [Display omitted] • MIL-88A(Fe) is a promising Fe-MOF to enhance methanogenic activities. • MIL-88A(Fe) increased Cyt-C and e-pili levels and facilitated electron transfer. • MIL-88A(Fe) stimulated gene expression for acetate-oxidation and CO 2 -reduction. • MIL-88A(Fe) mediated DIET and optimized the electron transfer metabolic pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • Significant progress in both research and industrial development of PFR systems. • Improvements include innovative design, optimized operation and enhanced mixing. • Technical/economic MCDA of mixed PFR with and without internal moving parts. • Mixing without internal parts has better efficiency and simpler operational needs. Plug Flow Reactors (PFRs) are widely recognized for their cost-effectiveness due to lower initial investments and start-up expenses in comparison to alternative systems. However, PFR face substantial challenges, including inadequate mixing leading to low mass transfer, potential issues related to thermal stratification, and complications arising from solid sedimentation. Furthermore, concerns related to floating, or scum formation highlight their limitations in diverse industrial applications. Recent years have witnessed significant progress in both research and industrial development pertaining to PFRs. This progress primarily focuses on improving PFR performance through innovative reactor design, optimized operating conditions and enhanced mixing. This review provides an extensive overview of these advancements, as identified through bibliometric analysis and literature review. The review delves into various retrofitting approaches for PFRs, exploring their impact on digester stability and methane production. Finally, the authors adopted a multi-criteria decision analysis (MCDA) to compare, from a practical/industrial perspective, mixed PFR systems with internal moving parts to those without. The evaluation relies on two criteria categories: technical and economic. The results revealed that mixing without internal moving parts excels in energy efficiency, reduced maintenance, lower contamination risks, and simpler design. Recommendations for future work are provided accordingly. [ABSTRACT FROM AUTHOR]

The potential of trimetallic nanoparticles (TMNPs) to enhance biogas production through microbe-to-microbe interactions and boost biogas yield is evident. This present study employed the central composite design (CCD) of response surface methods (RSM) to determine the optimal conditions of iron-cobalt-zinc TMNPs influenced anaerobic digestion for higher biogas yield. The impact of initial pH (6.6–7.4), TMNPs concentration (0–30 mg L−1), temperature (25-45 °C), and hydraulic retention time (HRT) (0-4 days) were modelled for improved biogas production. The results indicated that the linear model terms of pH and TMNPs concentration, and quadratic model terms of temperature and HRT, significantly affect the biogas production. Linear model terms of TMNPs, temperature, pH, and HRT have significant interactive effects and the numerical analysis identified the best conditions for the evaluated parameters. Ideal anaerobic process settings generated a maximum cumulative biogas production of 3700 mL−1 POME than blank (2000 mL−1), corresponding to an 85 % yield. Optimizing the initial pH, TMNPs concentration, temperature, and HRT can significantly improve biogas yield and could be helpful for developing more efficient AD processes at large volume and commercial biogas plants. Promoting TMNPs as catalysts positively improves an AD process towards sustainable biogas production. [Display omitted] [ABSTRACT FROM AUTHOR]

Biogas production by anaerobic digestion (AD) has emerged as a prominent bio-renewable energy source in recent years. However, the process also produces undesirable by-products, including H 2 S, thereby negatively impacting the biogas quality. This study focused on mitigating H 2 S in a full-scale AD located at a wastewater treatment plant (WWTP) by controlling the internal operational parameters by using an artificial neural network (ANN) model. Data from 54 days of AD operation were used to train and validate a structured ANN with a 5-3-1 topology. To minimize the H 2 S content, optimum values for dry solid (DS), volatile solid (VS), pH, temperature, and primary sludge fraction (PS) were determined to be 6.2 %, 63 %, 7.7, 35.6 °C, and 67.6 %, respectively, using the particle swarm optimization (PSO) algorithm. This optimization indicated a 49 % reduction in the average H 2 S concentration, from 6117 ppm to 3107 ppm. The analysis of relative importance (RI) showed that the pH (RI = −29.5) and PS (RI = −28.7) were the most critical factors affecting biogas quality. Additionally, several solutions derived from the optimization results were practically implemented in the Qom WWTP to achieve optimal conditions, and the outcomes were discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

This study carried out the anaerobic digestion of recycled paper mill wastewater (RPMW) in a high-rate novel anaerobic baffled reactor. The parametric interaction between influent chemical oxygen demand (CODin) and hydraulic retention time (HRT) was modeled, and process responses were optimized by the response surface methodology (RSM) using a three-level factorial design. The results showed that the optimal condition was determined at CODin of 4,000 mg/L and HRT of 2 days and predicted values for COD removal, biochemical oxygen demand (BOD) removal, lignin removal, CH4 content, and CH4 production were found to be 94%, 98%, 68%, 85%, and 20.8 L CH4/d, respectively. According to the statistical analysis of the RSM, all models were significant with very low probability values (from 0.0045 to

Forty percent of the food generated in Canada is wasted, making it the most significant component of municipal solid waste. Food waste characteristics, such as high moisture and oil content, and variable composition, make it difficult to manage with conventional waste treatment methods. Part of food waste is disposed of in landfills, generating greenhouse gases and significantly increasing the carbon footprint. Various treatment methods such as composting and anaerobic digestion have been employed to treat and manage the remaining waste efficiently. This study provides an overview of the impact of composting as a food waste treatment method in Canada and paves way for the research of the usefulness of composting in addition to other food waste treatment methods such as anaerobic digestion. Average composting data for Canada was used to determine the change in the carbon footprint by the diversion of food waste using CCaLC2 software. It was determined that the overall carbon footprint of 1.38 and 1.33 mega-tons of CO2 was reduced from the composting of food waste in the years 2014 and 2016, which were approximately 18% and 20% of the total footprint of Canada municipal solid waste, respectively. The carbon footprint data collected herein were compared to the data from England, Sweden, and the USA to reveal the high effectiveness of composting in Canada. [ABSTRACT FROM AUTHOR]

The profile of microbial diversity in a NABR digesting RPMW was investigated using phylogeneticanalysis of partial 16S rRNA sequences by a neighbor-joining-tree, supported by microbial morphology analysis by SEM. The results showed that microorganism inside NABR consisted of dominant Bacillus (25 strains) and Bacterium (1 strain) which were isolated from the settled sludge at the bottom of the reactor, whilst Bacillus (2 strains), Pseudomonas (2 strain) and Chryseobacterium (2 strain) were isolated from the biofilm formed on the packing material. It revealed that the microbial community strains, function, and structure changed simultaneously throughout the reactor system. The microscopic results showed rich biofacies, while the dominant microorganisms have various morphologies in every compartment of the system. It consisted of a long rod-shaped and filamentous bacterium composed majorly of bacilli of different sizes. Although the study successfully analyzed the microbial diversity and morphology in the system, the microbial communities reported in this study were different from other similar studies. This may be caused by the application of a culture-based technique that usually provides limited information due to the number of barely cultivated or uncultured strains

Antibiotics resistance genes (ARGs) induced by antibiotic abuse is a new type of environmental pollutants. ARGs which can develop drug resistance for bacteria are spreading widely in the environment. Considering the enormous ecological risk, ARGs must be cut down, and removed from environment. Anaerobic digestion (AD) which has been widely used in organic waste treatment is an important organic waste-recycling technology. Studies showed that the abundance of many ARGs decreased significantly after AD, which proved the removal effect of AD on ARGs. Therefore, AD not only can convert organic waste to clean energy but also can annihilate ARGs, thus controlling ARGs' spread in the environment in certain ways. In this paper, the recent research advances in the removal of antibiotic resistance genes by AD was reviewed, involving the AD materials pretreatment, setting of fermentation condition, and the effects of the additives (accelerator, inhibitor) and so on. Hopefully, the review would lend theoretical references for the high-efficient removal of ARGs in the environment. [ABSTRACT FROM AUTHOR]

Fruit and vegetable marketplace waste (FVMW) is an appealing alternative for energy production and should be utilized as a single substrate in anaerobic digestion (AD)–based biogas plants at an industrial-scale level in subtropical climatic countries. India alone generates 961,000 tons of FVMW annually from the major fruit and vegetable markets (FVMs). Utilization of FVMW to produce useful energy by AD could be helpful in meeting the ever-increasing energy demands of these countries. AD of fruit and vegetable waste (FVW) by two-phase systems has revealed good results in terms of stability, performance, and biogas generation; however, innovative approaches like plug flow tank reactor (PFTR) with passive solar heating with no mixing and no energy heating coupled with heat balance models and resistance network–based heat balance models need to be researched for subtropical climatic conditions in order to optimize the economics and energy balance of an AD system. Food waste and slaughter house wastes could be utilized successfully as co-substrates with FVW. C/N ratio is a critical performance parameter in the AD systems involving co-substrates; however, the synergistic relationship among co-substrates and characteristics, viz., macro- and micronutrients of individual co-substrates, must be investigated to improve the AD process. The optimum proportions of co-substrates could be determined by individual substrate characterization, biomethanation potential (BMP), and biodegradation kinetic models, thereby saving time and money as compared with random experimentation. Thermal, ultrasonic, and electrical pre-treatment in addition to physical pre-treatment could be effectively used for pre-treating FVW; however, synergy between co-substrates and pre-treatment method must be researched in order to justify the increased cost in extra pre-treatment. [ABSTRACT FROM AUTHOR]

Hydrolytic performances of different organic compounds in lignocellulosic biomass (LB) during anaerobic digestion (AD) are worth investigating due to the complex and refractory structure of lignocellulose. This study aimed to clarify the hydrolytic performances of different lignocellulosic components (hemicellulose, cellulose and lignin) and other typical organics (saccharides, protein and lipid) in AD process. Furthermore, an in-depth study of different lignocellulosic components mono-/co-digestive performances, as well as their effects on digestive systems were also designed to explain the mechanism. Kinetic models were specially applied to evaluate the hydrolytic process and make comparison among different lignocellulosic components. Results showed that hemicellulose obtained high degradation ratio (77.2-85.0%) during anaerobic digestion, while cellulose was difficult to hydrolyze without sufficient acidity. And organics (saccharides, protein and lipid) were much easier to be hydrolyzed than lignocellulose. Results also depicted that lignocellulose addition could efficiently enhance the volatile solid (VS) removals of digestive systems, while lignin existing in systems reduced the VS removal. The limited hydrolysis of lignocellulose hindered the degradation of total VS in digester. It is quite important to obtain high bioenergy conversion, pretreatments, which can destroy the lignin wrapping in LBs digestion. This study could provide a reference for the AD of LBs. [ABSTRACT FROM AUTHOR]

Perfluorooctanoic acid (PFOA) that accumulates in wastewater and excess sludge interact with the anaerobes and deteriorate the energy recovery and pollutants removal performance in the anaerobic digestion (AD) system. However, the interaction between PFOA and microbial metabolism in the AD systems remains unclear. This study aimed to clarify the effects and mechanism of PFOA on the AD process as well as the removal pathways of PFOA in an AD system. The results showed that the methane recovery efficiency was inhibited by 7.6–19.7% with the increased PFOA concentration of 0.5–3.0 mg/L, and the specific methanogenesis activity (SMA) was inhibited by 8.6–22.3%. The electron transfer system (ETS) was inhibited by 22.1–37.3% in the PFOA-containing groups. However, extracellular polymeric substance (EPS) gradually increased due to the toxicity of PFOA, and the ratio of protein to polysaccharide shows an upward trend, which led to the formation of sludge aggregates and resistance to the toxic of PFOA. The PFOA mass balance analysis indicated that 64.2–71.6% of PFOA was removed in the AD system, and sludge adsorption was the main removal pathway, accounting for 36.1–61.2% of the removed PFOA. In addition, the anaerobes are proposed to have the potential to reduce PFOA through biochemical degradation since 10.4–28.2% of PFOA was missing in the AD system. This study provides a significant reference for the treatment of high-strength PFOA-containing wastes. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is an essential technology for wastewater management, resource recovery and biogas production, and it is considered as an efficient and reliable treatment method for many wastewaters. Operating parameters have been shown to directly affect the stability and treatment performance of AD, especially temperature. For 180 days, the AD of recycled paper mill wastewater (RPMW) was carried out in a modified anaerobic inclining-baffled (MAIB) reactor under various temperature conditions, i.e. 29 °C (low mesophilic), 37 °C (mesophilic) and 55 °C (thermophilic). It was found that total COD removal of 94, 96 and 76%, and methane yields of 0.125, 0.196 and 0.256 L CH4/g CODremoved were attained at temperatures of 29, 37 and 55 °C, respectively. Throughout the three transition periods, the pH level in the MAIB reactor fluctuated slightly within the range of 5.8–6.5 without affecting the system stability. The results concluded that thermophilic condition strongly influenced the MAIB reactor performance, leading to lower COD removal, higher methane yield and gradually recovered pH level. Highlights Novel modified anaerobic inclining-baffled (MAIB) reactor, which combines the development of attached and settled microorganisms, was operated for the treatment of recycled paper mill wastewater (RPMW).; The operational temperature intensive analysis of MAIB was investigated at thermophilic and mesophilic conditions.; The system compartmental characteristics were also analyzed and discussed.;

[Display omitted] • AD patterns in different CMs-mediated AD systems were evaluated at high pH 2. • Abundant electron-exchanging functional groups in biochar promoted maximum DIET flux. • DIET interaction types between acetate oxidizers and Methanothrix relied on added CMs. • CMs selectively induced metabolic coordination from aspect of energy/electron flux. • Functional characteristics of different CMs-mediated DIET optimized CMs selection. In this study, different carbon/metal-based conductive materials (CMs) were amended in traditional anaerobic digestion (AD) system with high hydrogen partial pressure (pH 2) to verify the operational feasibility of CMs-mediated direct interspecies electron transfer (DIET). Operational performances revealed that SCOD removal efficiencies and CH 4 production of CMs-mediated groups including GS (graphene), CTS (carbon nanotube), BS (biochar), IS (magnetite) and MS (MnO 2) were increased by 34.7 %-157.3 %, 33.0 %-154.4 %, 41.2–169.6 %, 30.7 %-146.7 % and 28.1 %-139.5 % when compared with those of control group (54.5 ± 4.1 % and 184.9 ± 12.5 mL/g·VSS). Additionally, electron transfer capacity measurement showed that the equivalent current of biochar-mediated DIET flux (7 × 10-3 A) was 102 and 109 times higher than those in magnetite-mediated and interspecies H 2 transfer (IHT) conditions due to presence of abundant electron-exchanging functional groups. Furthermore, dynamic microbiome distribution and anaerobic metabolism analysis proved that genes encoding syntrophic enzymes were highly stimulated in GS, CTS and BS while genes encoding acidogenic enzymes were more expressed in IS and MS with acetate oxidizers and Methanothrix as CMs-mediated DIET participants, suggesting that metabolic coordination of fermentative bacteria could be selectively induced to cooperate with DIETers for maintaining stable operation of each CMs-mediated AD systems in high pH 2 condition. Overall, this study could offer better understand on application strategies of carbon-based and metal-based CMs for inducing the distinct CMs-mediated DIET process, which further optimized selection basis of CMs and widened real application of CMs-mediated DIET. [ABSTRACT FROM AUTHOR]

Currently, fossil fuels supply the aviation industry with nearly all of its energy requirements. The dependence on this has rendered an economically sustainable system unsustainable. Some steps have been implemented in response to environmental pressures. Depollution and the utilization of renewable energy sources are two approaches to environmental pollution mitigation. Utilizing the Circular Economy (CE) methodology, this study generates crucial recommendations to mitigate cabin waste. These include facilities for converting waste into energy, food donation centers, and the production of fertilizer and animal feed for airports. A conceptual design and assessment of the viability of an Anaerobic Digestion (AD) facility for cabin waste at Antalya Airport were conducted as part of this research endeavor. Remarkable findings of the research include the production of an estimated 36.7 tons.day−1 of edible food for the donation center, 2.5 tons.day−1 of CH 4 , and 5.4 tons.day−1 of fertilizer. The combined heat and power unit (CHP) has the capacity to produce approximately 340 kWh of thermal energy and 514 kWh of electricity with biogas. [Display omitted] • Addresses 'cabin waste' from a novel perspective within Circular Economy (CE). • Proposes an entirely novel zero waste circularity-assisted airport. • Describes the waste-to-energy principled airport components. • Suggests sustainable, holistic approaches to the airport. • Addresses the research gap in the waste-to-energy strategy for cabin waste. [ABSTRACT FROM AUTHOR]

Sugarcane ethanol production generates about 360 billion liters of vinasse, a liquid effluent with an average chemical oxygen demand of 46,000 mg/L. Vinasse still contains about 11% of the original energy from sugarcane juice, but this chemical energy is diluted. This residue, usually discarded or applied in fertigation, is a suitable substrate for anaerobic digestion (AD). Although the technology is not yet widespread—only 3% of bioethanol plants used it in Brazil in the past, most discontinuing the process—the research continues. With a biomethane potential ranging from 215 to 324 L of methane produced by kilogram of organic matter in vinasse, AD could improve the energy output of sugarcane biorefineries. At the same time, the residual digestate could still be used as an agricultural amendment or for microalgal production for further stream valorization. This review presents the current technology for ethanol production from sugarcane and describes the state of the art in vinasse AD, including technological trends, through a recent patent evaluation. It also appraises the integration of vinasse AD in an ideal sugarcane biorefinery approach. It finally discusses bottlenecks and presents possible directions for technology development and widespread adoption of this simple yet powerful approach for bioresource recovery.

Paunch contents are the recalcitrant, lignocellulose-rich, partially-digested feed present in the rumen of ruminant animals. Cattle forage in Europe is primarily from perennial and Italian ryegrasses and/or white clover, so paunch contents from forage-fed cattle in Europe is enriched in these feedstuffs. Globally, due to its underutilisation, the potential energy in cattle paunch contents annually represents an energy loss of 23,216,548,750–27,804,250,000 Megajoules (MJ) and financial loss of up to ~€800,000,000. Therefore, this review aims to describe progress made to-date in optimising sustainable energy recovery from paunch contents. Furthermore, analyses to determine the economic feasibility/potential of recovering sustainable energy from paunch contents was carried out. The primary method used to recover sustainable energy from paunch contents to-date has involved biomethane production through anaerobic digestion (AD). The major bottleneck in its utilisation through AD is its recalcitrance, resulting in build-up of fibrous material. Pre-treatments partially degrade the lignocellulose in lignocellulose-rich wastes, reducing their recalcitrance. Enzyme systems could be inexpensive and more environmentally compatible than conventional solvent pre-treatments. A potential source of enzyme systems is the rumen microbiome, whose efficiency in lignocellulose degradation is attracting significant research interest. Therefore, the application of rumen fluid (liquid derived from dewatering of paunch contents) to improve biomethane production from AD of lignocellulosic wastes is included in this review. Analysis of a study where rumen fluid was used to pre-treat paper sludge from a paper mill prior to AD for biomethane production suggested economic feasibility for CHP combustion, with potential savings of ~€11,000 annually. Meta-genomic studies of bacterial/archaeal populations have been carried out to understand their ruminal functions. However, despite their importance in degrading lignocellulose in nature, rumen fungi remain comparatively under-investigated. Further investigation of rumen microbes, their cultivation and their enzyme systems, and the role of rumen fluid in degrading lignocellulosic wastes, could provide efficient pre-treatments and co-digestion strategies to maximise biomethane yield from a range of lignocellulosic wastes. This review describes current progress in optimising sustainable energy recovery from paunch contents, and the potential of rumen fluid as a pre-treatment and co-substrate to recover sustainable energy from lignocellulosic wastes using AD.

Application of anaerobic digestion (AD) has become common in treating palm oil mill effluent in Malaysia; however, employing AD in treating the organic fraction of municipal solid waste (OFMSW), especially food waste, is still scarce. This study aims to characterize the commercial Malaysian food waste (CMFW) and determine its potential as sustainable bioenergy feedstock through biogas production. The sample was digested via the biomethane potential (BMP) test with the variation of organic loading rates (OLRs), ranging from 0.38 to 3.83 gCOD/L. day, under mesophilic conditions. The digestion process was further evaluated in continuous operation using a 6-L continuous stirred-tank reactor (CSTR). The kinetic properties of the process were also determined. It was found that the CMFW had a significant amount of chemical oxygen demand of 230 g/L and an acidic pH of 4.5 with the carbon to nitrogen (C/N) ratio at 121:1. A maximum methane composition of 81% was obtained at 1.92 gCOD/L in the BMP test with specific methane production (SMP) at 0.952 L. CH4/L.COD fed. The biogas production was well-fitted with the modified Gompertz model with R2 at 0.9983 and the maximum biogas potential production rate at Rm 0.1573 L/day, whereas in the CSTR operation, a maximum methane composition of 85% was produced at OLR 6 gCOD/L. day with the SMP of 1.13 L. CH4/L.COD fed. The CSTR system was in high stability as the pH was maintained in a range of 6.6–6.7, with an alkalinity ratio of 0.28. This study indicates the CMFW is a sustainable feedstock for biogas production in Malaysia. Toward a circular economy approach, the authorities shall introduce commercial scale CMFW AD as part of managing municipal solid waste issues in Malaysia.

Food waste is one of the important reservoirs of antibiotic resistance genes （ARGs）, and its resource utilization has potential environmental risks. Anaerobic digestion （AD） technology can concurrently achieve resource recovery and ARGs removal, which is one of the popular resource technologies for food waste management. However, the removal efficiency of ARGs during the AD process is limited, and thus the safety of digestate for agricultural use is still questioned. Therefore, how to improve the performance of ARGs removal during the AD process is critical for efficient and environmentally friendly bioconversion of food waste. This study summarized the transmission pathways and mechanisms of ARGs in food waste； discussed the effects of different operation parameters on the transmission of ARGs in food waste during the AD process； described the research progress of exogenous addition of conductive materials, feedstock pretreatment, etc., strategies to enhance the removal of ARGs； and analyzed the migration regularity and removal mechanism of ARGs in food waste during the AD process, which mainly included microbial community structure evolution, mobile genetic element changes, and environmental factor changes. Finally, this study prospected the future improvement of methane yield and ARGs removal in the AD process of food waste based on the existing research.