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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)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The increasing concentration of livestock farms results in large amounts of waste production and the need for their management. The study of anaerobic digestion (AD) technology, under mesophilic conditions, applied to pig slurry is of the upmost importance for biogas recovery and sanitised digestate, contributing to a circular economy. The assessment of the effects of a feast/famine regime on biogas and biomethane (bio-CH 4 ) yield with different feeding frequencies was performed. The evaluation was made in regards to three scenarios: the first is based on daily feeding (FR1); in the second, the feeding occurs once every two days (FR2); and in the third, the feeding happens once every three days (FR3). The results demonstrate that the biogas and methane yield increased by 34% and 37% between FR1 and FR3. The stability inside the reactor was maintained since specific loading energetic rate values did not exceed the recommended limit (0.4 d -1 ). It was also possible to conclude that the AD technology was efficient to sanitise the pig slurry, with the count of Escherichia coli going from 1 × 10 5  colony-forming units (CFU) g -1 to less than 100 CFU g -1 , meeting the legal requirements for agricultural valorisation. The total anaerobic mesophile plate counts were significantly ( p  < 0.1) reduced from feeding to digestate, and the plate counts of Clostridia were significantly ( p  < 0.05) increased, reflecting the changes in the composition of the microbiota. The increasing yield in bio-CH 4 in accordance with Clostridium counts suggests this genus as a positive microbiological key indicator of the AD performance.

Straws as lignocellulosic agricultural biomass have a huge amount and are widely used for biomethane production by anaerobic digestion (AD). However, the mechanism of impacts of straw composition and surface properties on biomethane production remain unclear. Here, a lab-scale AD incubation experiment was conducted and the characterization of four types of straws (corn straw, wheat straw, sweet sorghum straw, and rice straw) were also determined. The straw compositions and net cumulative methane production showed significant difference. Although the relative contents of key organic components and carbon had no significant correlation to the biomethane production (r = -0.36, P > 0.05), there existed differences of non-polar characteristics, steric hindrance effect and special surface morphology in four types of straws, indicating that the surface characteristics affected anaerobic biomethane production process. In addition, the straw matrix associating with silicon might hinder the biotransformation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobic digestion (AD) of organics is a challenging task under high-strength sulfate (SO 4 2- -reducing bacteria (SRB) causes low methane (CH 4 2- -reducing bacteria (SRB) causes low methane (CH 4 ) production. This study investigated the feasibility of alleviating sulfide inhibition and enhancing CH 4 production by using an anaerobic reactor with built-in microbial electrolysis cell (MEC), namely ME-AD reactor. Compared to AD reactor, unionized H 2 S in the ME-AD reactor was sufficiently converted into ionized HS - due to the weak alkaline condition created via cathodic H 2 production, which relieved the toxicity of unionized H 2 S to methanogenesis. Correspondingly, the CH 4 production in the ME-AD system was 1.56 times higher than that in the AD reactor with alkaline-pH control and 3.03 times higher than that in the AD reactors (no external voltage and no electrodes) without alkaline-pH control. MEC increased the amount of substrates available for CH 4 -producing bacteria (MPB) to generate more CH 4 . Microbial community analysis indicated that hydrogentrophic MPB (e.g. Methanosphaera) and acetotrophic MPB (e.g. Methanosaeta) participated in the two major pathways of CH 4 formation were successfully enriched in the cathode biofilm and suspended sludge of the ME-AD system. Economic revenue from increased CH 4 production totally covered the cost of input electricity. Integration of MEC with AD could be an attractive technology to alleviate sulfide inhibition and enhance CH 4 production from AD of organics under SO 4 2- -rich condition., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

This study investigates the distribution of microbiome in microbial electrosynthesis systems at different applied voltages (0.5, 1.0, and 1.5 V) for methane production. Results revealed that more favorable conditions for methane production were observed with 1.0 V applied voltage. In Venn plots, the bioelectrodes at 1.0 V had higher numbers of unique operational taxonomic units compared to those at 0.5 and 1.5 V. Hierarchical cluster, non-metric multidimensional scaling, and principal component ordinate analyses revealed that the biocathode at 1.0 V clustered separately from the rest of the biofilms mainly because of the quantitative differences in the microbial distribution. Taxonomically, exoelectrogens (Geobacter spp.) dominated the bioanode at 1.0 V, while the syntrophic assemblages of hydrogen-producing bacteria (i.e., Bacteroidetes and Firmicutes) and hydrogen-consuming methanogens (i.e., Methanobacterium sp.) existed in the biocathode. These results suggest that the optimum applied voltage enriched specific microbial communities on the anode and cathode for enhanced methane production., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Anaerobic digestion (AD) is an effective strategy combined advantages of maintaining the global carbon flux and efficient energy conversion. Various conductive materials (CMs) have been applied in anaerobic digesters to improve the performance of anaerobic fermentation and methanogenesis, including carbon-based CMs and metal-based CMs. Generally, CMs facilitated the AD thermodynamically and kinetically because they triggered more efficient syntrophic metabolism to increase electron capture capability and accelerate reaction rate as well as enhance the performance of AD stages (hydrolysis-acidification, methanogenesis). Besides, adding CMs into anaerobic digester is benefit to dealing with the deteriorating AD, which induced from temperature variation, acidified working condition, higher H 2 partial pressure, etc. However, few CMs exhibited inhibition on AD, including ferrihydrite, magnesium oxide, silver nanoparticles and carbon black. Inhibition comes from a series of complex factors, such as substrate competition, direct inhibition from Fe(III), Fe(III) reduction of methanogens, toxic effects to microorganisms and mass transfer limitation., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Weak magnetic field (WMF) provided by a magnet was proposed to enhance CH 4 production from a swine manure-fed digester supplemented with micron-sized zero valent iron (ZVI). Compared to the control without ZVI addition and WMF application (R Control ), treatments that included ZVI only (R ZVI ) and coupled WMF with ZVI (R ZVI/WMF ) increased the CH 4 production by 77.0% and 124.5%, respectively. As evidenced by the elevated levels of total soluble iron, WMF apparently promoted the corrosion of ZVI, providing extra H 2 for hydrogenotrophic methanogenesis and creating a more reductive environment to reduce propionic-type fermentation. Microbial analysis results revealed that the relative abundance of Methanothrix (capable of accepting electrons) in R ZVI/WMF were 75.1% higher than that in R ZVI . Essentially, WMF application promoted the direct interspecies electron transfer-based methanogenesis by (1) providing more electrons as the direct substrate, and (2) inducing Lorentz force to facilitate the mass transfer between the released electrons and the methanogens., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

To optimize the energy yield (EY) of food waste (FW) via hydrothermal carbonization (HTC), a response surface method was applied. Hydrochars and spent liquor were further conducted to evaluate their characterization and anaerobic digestion potential. Results found that optimal parameters for HTC of FW were suggested as temperature of 260 °C, reaction time of 4 h and moisture of 80%, with higher EY of 66.1%. Higher heating value, good combustion quality, lower H/C and O/C ratios indicated that hydrochar could be utilized as a safe solid fuel. Biochemical methane potential (BMP) experiment showed that spent liquor and hydrochars could be used as feedstocks for anaerobic digestion. Interestingly, hydrochars added in the spent liquor could promote the specific methane yield, which was 2.53 times higher than no addition of hydrochars. The finding of this study could provide useful information for HTC of FW and the utilization of hydrochars and spent liquor., (Copyright © 2018. Published by Elsevier Ltd.)

The exploration of the energetics of anaerobic digestion systems can reveal how microorganisms cooperate efficiently for cell growth and methane production, especially under low-substrate conditions. The establishment of a thermodynamically interdependent partnership, called anaerobic syntrophy, allows unfavorable reactions to proceed. Interspecies electron transfer and the concentrations of electron carriers are crucial for maintaining this mutualistic activity. This critical review summarizes the functional microorganisms and syntroph partners, particularly in the metabolic pathways and energy conservation of syntrophs. The kinetics and thermodynamics of propionate degradation to methane, reversibility of the acetate oxidation process, and estimation of microbial growth are summarized. The various routes of interspecies electron transfer, reverse electron transfer, and Poly-β-hydroxyalkanoate formation in the syntrophic community are also reviewed. Finally, promising and critical directions of future research are proposed. Fundamental insight in the activities and interactions involved in AD systems could serve as a guidance for engineered systems optimization and upgrade., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In this research the inhibitory effects of ammonia on the AD of synthetic OFMSW were examined under different total ammonia nitrogen (TAN) concentrations of 2,500, 5,000, 7,500, and 10,000mg/L and at pH levels of 7.5, 8.0 and 8.5 using a factorial experimental design and statistical analysis. Reduction in Cumulative Biogas Production (CBP) at a TAN concentration of 2,500mg/L was close to 10% for all 3 pH levels. For a TAN concentration of 10,000mg/L the percent reduction in CBP was over 80% for all 3 pH levels showing significant inhibition due to ammonia with neglible influence due to change in pH. However, pH played a more significant role for TAN concentrations between the above two levels, as at a TAN concentartion of 7,500mg/L, the percent reduction in CBP increased from 42.2% at a pH of 7.5 to 76.5% at a pH of 8.5. Regression analysis was used to estimate CBP and % reduction (%R) in CBP using a quadratic equation with pH and TAN as independant variables (R 2 =0.95 and 0.94). Methane produciton per g of COD removed was obsereved to vary from 264mL CH 4 /g COD d for control reactors at pH 7.5 down to 1mL CH 4 /g COD d for the reactor at pH of 8.5 which contained 10,000mg/L TAN. Results of gradual ammonia loading also showed that mesophilic bacteria could be adapted to a TAN concentration of up to 5,000mg/L at pH 7.5 through gradual TAN loading. At 10,000mg/L TAN CBP in reactors with gradual TAN loading was more than 1.9-3 times the CBP in reactors with abrupt TAN addition., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Magnetic biochar is a potential economical anaerobic digestion (AD) additive. To better understand the possible role of magnetic biochar for the improvement of biomethanization performance and the retention of methanogens, magnetic biochar fabricated under different precursor concentrations were introduced into organic fraction of municipal solid waste (OFMSW) slurry AD system. Results showed that methane production in AD treatment with magnetic biochar fabricated under 3.2g FeCl 3 :100g rice-straw ratio increased by 11.69% compared with control treatment without biochar addition, due to selective enrichment of microorganisms participating in anaerobic digestion on magnetic biochar. AD treatment with magnetic biochar fabricated under 32g FeCl 3 :100g rice-straw ratio resulted in 38.34% decreasement of methane production because of the competition of iron oxide for electron. Furthermore, 25% of total methanogens were absorbed on magnetic biochar and can be harvested with magnet, which can offer a potential solution for preventing the methanogens loss in the anaerobic digesters., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Conductive materials have been widely investigated to accelerate and stabilize the conversion of organic wastes to methane. However, the potential mechanisms involved with different types of conductive materials are still unclear. In this study, magnetite (Fe 3 O 4 ) and granular activated carbon (GAC), as the two typical conductive materials, were respectively supplemented to acidogenesis and methanogenesis of a two-phase anaerobic digestion (AD) system in an attempt to explore their different mechanisms. The results showed that, magnetite supplemented to the acidogenic phase could enhance the decomposition of complex organics into simples, but significantly raise the hydrogen partial pressure as well as enrich the hydrogen-utilizing methanogens, which were not expected for aceticlastic methanogenesis known as a mainstream of methanogenesis in most of traditional digesters. GAC supplemented to the methanogenic phase had less influences on syntrophic metabolism of alcohols and fatty acids when acidogenesis was ineffective or out of work. Microbial community analysis suggested that direct interspecies electron transfer (DIET) had been established on the GAC, though the insignificant improvement of performances. Once magnetite was supplemented to the acidogenesis to improve the acidification efficiency, the syntrophic conversion of alcohols and fatty acids to methane in the GAC-supplemented methanogenic phase was significantly improved. These results suggested that, DIET was unlikely to participate in the direct decomposition of complex organics, even in the presence of GAC, but it could work effectively once acidogenesis functioned well., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Biochemical reactions occurring during anaerobic digestion have been modelled using reaction kinetic equations such as first-order, Contois and Monod which are then combined to form mechanistic models. This work considers models which include between one and three biochemical reactions to investigate if the choice of the reaction rate equation, complexity of the model structure as well as the inclusion of inhibition plays a key role in the ability of the model to describe the methane production from the semi-continuous anaerobic digestion of green waste (GW) and food waste (FW). A parameter estimation method was used to investigate the most important phenomena influencing the biogas production process. Experimental data were used to numerically estimate the model parameters and the quality of fit was quantified. Results obtained reveal that the model structure (i.e. number of reactions, inhibition) has a much stronger influence on the quality of fit compared with the choice of kinetic rate equations. In the case of GW there was only a marginal improvement when moving from a one to two reaction model, and none with inclusion of inhibition or three reactions. However, the behaviour of FW digestion was more complex and required either a two or three reaction model with inhibition functions for both ammonia and volatile fatty acids. Parameter values for the best fitting models are given for use by other authors.

A lot of lignocellulosic matters are usually present in excess sludge, which are hardly degraded in anaerobic digestion (AD) and thus remains mostly in digested sludge. This is a reason why the conversion rate of sludge organics into energy (CH4) is often low. Obviously, the hydrolysis of AD cannot destruct the structure of lignocellulosic matters. Structural destruction of lignocellulosic matters has to be performed in AD. In this study, pretreatments with the same principles as cell disintegration of sludge were applied to destruct lignocellulosic matters so that these materials could be converted to CH4 via AD. Acid, alkali, thermal treatment and ultrasonic were used in the experiments to observe the destructed/degraded efficiency of lignocellulosic matters. Thermal treatment was found to be the most effective pretreatment. Under optimized conditions (T = 150 °C and t = 30  min), pretreated sludge had a degraded rate of 52.6% in AD, due to easy destruction and/or degradation of hemicelluloses and celluloses in pretreatment. The sludge pretreated by thermal treatment could enhance the CH4 yield (mL CH4 g(-1) VSS) by 53.6% compared to raw sludge. Economically, the thermal treatment can balance the input energy with the produced energy (steam and electricity).

This study discussed the effects of different concentrations (0.625, 1.875 and 3.125 mM) of copper (Cu) in the form of CuSO4 on biomethane production and on the dynamics of microbial communities during the mesophilic anaerobic digestion (AD) of cow manure. The effects on biomethane production were found to depend on CuSO4 concentrations. After 50 days of AD, treatment A3 (3.125 mM) had lower cumulative biomethane production than the no-Cu control. The maximum value of cumulative biomethane production was detected under treatment A2 (1.875 mM). These results suggested that the stimulation or inhibition to biomethane production might be related to the concentration and chemical forms of Cu. Moreover, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was used to discuss the dynamics of microbial communities. Results revealed that different concentrations of CuSO4 had effects on the richness and diversity of bacterial and archaeal communities. The predominance of Bacteroidetes bacterium (GU339485.1) was verified through the sequencing of the dominant DGGE bands. Furthermore, Bacteroidetes bacterium could be detected during the whole AD process and is adaptable to a certain concentration range of CuSO4., (© The Author(s) 2014.)

Mixture models are introduced as a new and stronger methodology for statistical prediction of biomethane potentials (BPM) from lignocellulosic biomass compared to the linear regression models previously used. A large dataset from literature combined with our own data were analysed using canonical linear and quadratic mixture models. The full model to predict BMP (R(2)>0.96), including the four biomass components cellulose (xC), hemicellulose (xH), lignin (xL) and residuals (xR=1-xC-xH-xL) had highly significant regression coefficients. It was possible to reduce the model without substantially affecting the quality of the prediction, as the regression coefficients for xC, xH and xR were not significantly different based on the dataset. The model was extended with an effect of different methods of analysing the biomass constituents content (DA) which had a significant impact. In conclusion, the best prediction of BMP is pBMP=347xC+H+R-438xL+63DA., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

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) 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]

Abstract A submersible microbial fuel cell (SMFC) was coupled with anaerobic digestion (AD) system to establish synergy for enhancing the electricity and methane production at different glucose concentration of 2, 4 and 10 g/l. High amount of stable current generation of 0.35 mA was obtained at 4 g/l, which was about 1.5 times higher than the SMFC-AD operated at 10 g/l glucose. Methane production and yield were enhanced by 69% and 28%, respectively in SMFC-AD in comparison with AD operation at 2 g/l. Maximum methane yield of 0.32 l-CH 4 /g COD was observed in SMFC-AD operation at 2 g/l, followed by 4 g/l (0.28 l-CH 4 /g COD) and 10 g/l (0.18 l-CH 4 /g COD). Furthermore, the SMFC-AD process increased COD removal and maintained proper pH of around 6.8–7.3 for efficient methane production. This study suggests that the SMFC-AD can achieve enhanced methane production compared to stand-alone AD with additional electricity generation. Highlights • Integration of SMFC and AD enhanced the methane generation. • Highest electrical and CH 4 production was observed at 4 g/l glucose in SMFC-AD. • More SCOD removal was obtained in SMFC-AD compared to the control. • VFA accumulation inhibited methane generation at 10 g/l glucose. [ABSTRACT FROM AUTHOR]

Abstract Microbial electrochemical system (MES) was integrated into anaerobic digestion (AD) to improve the overall process efficiency by enhancing methane (CH 4) production. CH 4 fermentation at various glucose concentrations (2, 4, 8 and 10 g/l) was evaluated along with corresponding control (without electrodes) operations. The maximum CH 4 yield of 0.34 l- CH 4 /g COD was obtained with both 2 and 4 g/l glucose concentrations (MES), which was about 1.4 and 2.4 times, respectively, higher than the values obtained with corresponding control operations. However, at 10 g/l, similar performance (∼0.07 l- CH 4 /g COD) was observed with both control and MES operations, which might be due to pH drop occurred by volatile fatty acids (VFAs) buildup in the process. Substrate removal was amplified in the presence of MES with faster degradation of VFAs at all substrate concentrations except 10 g/l. This enhanced utilization of VFAs in the MES process is an important aspect to recover from initial pH drops, especially at higher substrate concentration to maintain the optimum pH for methane fermentation. The current generation and cyclic voltammetric profiles suggest that the enhanced CH 4 production in MES was attributed to the bioelectrochemical reactions on the electrodes. Graphical abstract Image 1 Highlights • Enhancement of overall performance was achieved in MES integration with AD. • The COD loading up to 8 g/l showed enhanced methane generation compared to control. • Maximum enhancement of CH 4 production was observed at 4 g/l glucose concentration. • MES delayed VFAs accumulation and facilitated optimum pH and redox microenvironment. [ABSTRACT FROM AUTHOR]

Kinetic models which can express the behaviors of hydrolysis and biogas generation more precisely than the conventional models were developed. The developed models were evaluated based on the experimental data of six batch reactors. Anaerobic digestion test was co-digestion of food and vegetable waste with inoculating horse dung by 15% of the total wet weight, at the temperature of 37oC. For hydrolysis, the modified model was developed from an original first-order kinetic model. The modified first-order kinetic model was proved to be better than the original one with the hydrolysis rate constant in the range of 0.22- 0.34/day and hydrolyzable rate of 0.80 to 0.84. Kinetics of carbon dioxide and methane were developed from a current potential model. The comparison between experimental data and modeling values had the high correlation of determination (0.9918-0.9998) and low root mean square errors (0.08-4.51) indicating the feasibility of the developed model. In which, the evolution of methane showed the rate constant in the range of 0.031-0.039/day. The carbon dioxide from fermentation accounted for 12-44% of the total observed carbon dioxide. Thus, separation of fermentation and methanogenesis by various reactors may reduce the price of methane enrichment significantly. There was a lag time between methanogenesis and fermentation in reactors (λ = 7-11 days). Also, the biogas yield was in the range of 431.6-596.9 Nml/g-VS with the CH4 concentration of 56.2-67.5%. The best methane yield (393.7 Nml/g-VS) was in a reactor with food waste to the vegetable waste ratio by 1.8:1 (wet basis) and C/N ratio by 25.4. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is an important technology for the treatment of livestock and poultry manure. The optimal experimental conditions were studied, with deer manure as a fermentation material and mushroom residue as an inoculum. At the same time, methane production was increased by adding zeolite and changing the magnetic field conditions. The results showed that a 6% solid content was the best condition for producing methane. The optimal conditions for methane production were obtained by adding 35 g of mushroom residue to 80 g of deer manure at 35 °C. The addition of organic wastewater (OW) improved methane production. The result of improving the methane production factor showed that adding zeolite during the reaction process could increase the methane production rate. When the amount of zeolite was over 8% total solids (TSes), methane production could improve, but the rate decreased. Setting a different magnetic field strength in the AD environment showed that when the distance between the magnetic field and the reactor was 50 mm and the magnetic field strength was 10–50 mT, the methane production increment and the content of methane in the mixed gases increased.

Anaerobic digestion (AD) of chemically enhanced primary treatment (CEPT) sludge and non-CEPT (conventional sedimentation) sludge were comparatively operated under mesophilic and thermophilic conditions. The highest methane yield (692.46 ± 0.46 mL CH 4 /g VS removed in CEPT sludge) was observed in mesophilic AD of CEPT sludge. Meanwhile, thermophilic conditions were more favorable for the removal of total antibiotic resistance genes (ARGs). In this study, no measurable difference in the fates and removal of ARGs and class 1 integrin-integrase gene ( intI 1) was observed between treated non-CEPT and CEPT sludge. However, redundancy analysis indicated that shifts in bacterial community were primarily accountable for the variations in ARGs and intI 1. Network analysis further revealed potential host bacteria for ARGs and intI 1. [ABSTRACT FROM AUTHOR]

• Prepared novel conductive polypyrrole to improve the anaerobic sludge digestion performance. • The accumulative methane production was increased by 27.83% by adding Ppy. • Metatranscriptomic analysis illustrated Ppy promoted acidogenesis and methanogenesis. • Ppy enhances the utilization of acids and electrons by methanogens through DIET. Anaerobic digestion (AD) is a promising method for treating waste activated sludge (WAS), but the low methane yield limits its large-scale application. The addition of conductive nanomaterials has been demonstrated to enhance the activity of AD via promoting the direct interspecies electron transfer (DIET). In this study, novel conductive polypyrrole (Ppy) was prepared to effectively improve the AD performance of WAS. The results showed that the accumulative methane production was enhanced by 27.83% by Ppy, with both acidogenesis and methanogenesis being efficiently accelerated. The microbial community analysis indicated that the abundance of bacteria associated with acidogenesis process was significantly elevated by Ppy. Further investigation by metatranscriptomics revealed that fadE and fadN genes (to express the key enzymes in fatty acid metabolism) were highly expressed in the Ppy-driven AD, suggesting that Ppy promoted electron generation during acid production. For methanogenesis metabolism, genes related to acetate utilization and CO 2 utilization methanogenesis were also up-regulated by Ppy, illustrating that Ppy facilitates the utilization of acetate and electrons by methanogenic archaea, thus potentially promoting the methanogenesis through DIET. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] We compared seven annual and multi-annual biomass crops in view of methane production. [•] Potential CH4 yield in batch incubation assay ranged between 216 and 316mlg−1 VS. [•] Maize prevailed in net energy yield (248 vs. 171GJha−1 average six alternative crops). [•] Arundo, Switchgrass and biomass sorghum prevailed over maize in energy efficiency. [•] Enhanced biodegradability is needed to improve alternative crops competitiveness. [Copyright &y& Elsevier]

Highlights: [•] Blue algae storage led to cell death, microcystins release and VS reduction. [•] Short-time storage as pretreatment was beneficial to blue algae methanation for AD. [•] AD of blue algae stored for 15d led to the highest CH4 yield of 287.6mLg−1 VS. [•] VS removal, VFA and enzymes variation proved higher efficiencies of stored algae AD. [•] AD presented significant biodegradation potential for microcystins from blue algae. [ABSTRACT FROM AUTHOR]

Highlights: [•] Giant reed was pretreated by hydrothermal methods with and without H2SO4 catalyst. [•] Cumulative CH4 yield of untreated Giant reed was archived at 273mlg−1 VS. [•] Highest increase in methane yield (23%) after pre-treatment at 180°C for 10min. [•] Pre-treatments with H2SO4 catalyst exhibited a strong methanogenic inhibition. [ABSTRACT FROM AUTHOR]

Abstract: Over 9million dairy cows generate an estimated 226billionkg of wet manure annually in the US. The purpose of this study was to demonstrate the viability of a novel two-stage anaerobic digestion (AD) process for producing methane-rich biogas on pre-fermented dairy manure. In summary, it was observed that AD of thickened pre-fermented manure can generate comparable biogas quantities to AD using raw manure, with enhanced methane content. Despite receiving a lower quality (i.e., partially biodegraded) substrate, biogas stoichiometry and overall process stability in the two-stage system was also comparable to AD receiving raw manure. Finally, the two-stage AD was more enriched with the acetoclastic methanogen Methanosarcinaceae (Msc; compared to AD of raw manure) and biogas production appeared closely linked with the Msc fraction. In fact, the enhanced enrichment of Msc likely contributed to the successful and stable operations. [Copyright &y& Elsevier]

Abstract: Selection and evaluation of biofilm carrier represent the two significant ways for improving the anaerobic digesters. This study investigated the performances of the AD (anaerobic digestion) reactors using three types of fibrous biofilm carriers, including the ACF (activated carbon fiber), the PVAF (polyvinyl alcohol fiber) and the GF (glass fiber). The biogas and methane production, pH, COD (chemical oxygen demand), TS (total solids), VS (volatile solids), residual coenzyme F420 as well as the residual amount of methanogen were measured periodically during the experimental run. Also, the SEM (scanning electron microscopy) was used to identify the microbial consortium and their attachments onto the surface of ACF carrier. The ACF carrier performed better than the other two types of carriers in achieving higher amount of biogas and methane production and pollutants’ removal. The experimental results also demonstrated that the ACF carrier could make the reactor keep higher biogas and methane productions than the control blank reactor during the long run. [Copyright &y& Elsevier]

Performance of a hydrolysis reactor in which the solids and liquid retention times were uncoupled to give enhanced solids retention and removal of hydrolysis products was evaluated for a feedstock of biodegradable municipal waste (BMW). The reactor was operated both alone and as part of a two-stage process in series with an anaerobic filter. Operating with a hydraulic flush to give hydraulic retention times (HRT) between 1.6 and 5.3 days, and a solids retention time (SRT) of 20 days increased hydrolysis in comparison with a control reactor where HRT and SRT were equal. Overall biodegradability was low; however, with an effluent chemical oxygen demand (COD) equivalent to ∼30% of the substrate biochemical methane potential (BMP). When operated as part of a two-stage process using effluent from the anaerobic filter as the flush liquor the characteristics of the system changed substantially with an increase in performance to an overall methane production of 0.22–0.24 L g−1 volatile solids (VS) added. This was achieved even when the maximum loading of 7.5 gVS L−1day−1 was applied. During acclimatization the first-stage hydrolytic reactor became methanogenic despite the short HRT, and was responsible for as much as 70% of the overall methane production. The system could not revert to single-stage operation after acclimatization, showing the continuing importance of the anaerobic filter. The combined system was robust, and could recover from major disturbances and step increases in loading without reduction in continuous methane production, indicating some potential for larger scale application in BMW disposal. [ABSTRACT FROM AUTHOR]

Anaerobic treatment of high-fat content wastewater could produce significant methane yields, making anaerobic treatment a promising alternative to energy-consuming aerobic treatment. However, accumulated intermediate LCFA may inhibit the conversions of both SCFA to acetate and of acetate further to methane. The effect of feed-to-inoculum ratio was evaluated in biochemical methane potential (BMP) tests for anaerobic digestibility of animal rendering wastewater (RW). Results showed that more than 90% of RW COD was converted during BMP tests with volumetric feed-to-inoculum ratio of 1. Higher feed-to-inoculum ratios led to RW COD conversion efficiencies below 64% and caused lag periods of >6 days in methane production. Degradation of acetate at different time points in relation to conversion of LCFA suggested that LCFA accumulation partially hindered acetate utilization. The methanogenic community shifted from hydrogenotrophic to acetoclastic methanogenesis in moderately-loaded BMPs. At highest feed-to-inoculum ratio of 9, acetoclastic methanogens were severely inhibited. The bacterial genus Syntrophomonas was present in increasing relative abundance with increasing feed-to-inoculum ratio. Increased relative abundance of the genus Desulfovibrio with increasing feed-to-inoculum ratio was likely a response to the high sulfate concentration in RW. • Anaerobic digestibility of rendering wastewater was evaluated in BMP tests. • Higher feed-to-inoculum ratios reduced methane production rate. • LCFA accumulated in highest feed-to-inoculum ratio tested. • Syntrophomonas relative abundance increased with increasing feed-to-inoculum ratios. • Acetoclastic methanogens were inhibited at higher feed-to-inoculum ratios. [ABSTRACT FROM AUTHOR]

A combined two-levels control method has been developed and tested on a long term operation of a two-phases pilot-scale anaerobic process for the concurrent production of volatile fatty acids, hydrogen and methane. The latter was designed for the treatment of food waste of urban origin (namely, the organic fraction of municipal solid waste). The optimized control method was set on the base of the inputs of three online probes: a pH-meter in the fermentation reactor, a pH-meter and a conductivity probe in the digestion reactor. The first control level managed the pH in the fermentation reactor while the second control level managed the ammonia concentration in the digestion reactor. This combination established the volume of the digestate to be recycled from the digestion to the fermentation reactor, optimizing the yield of volatile fatty acid (0.31–0.32 kg COD VFA /kg COD fed) and the specific hydrogen production (SHP; 0.070–0.074 m3 H 2 /kg TVS fed) in the fermentation reactor and the specific methane production (SMP; 0.48–0.55 m3 CH 4 /kg TVS fed) in the digestion reactor. A new process configuration was also proposed and applied over the course of the long operation period. This configuration allowed to remove part of the volatile fatty acid-rich liquid stream from the fermenter effluent, maintaining the corresponding solid-rich effluent in the whole system (as feed for the digestion reactor) by using a solid/liquid separation unit. In this way, the concentration of volatile fatty acids in the digester was kept at a low level, even with high loading rates, so maintaining a satisfying efficiency of methane production and utilizing the excess volatile fatty acids (out of the system) as building blocks for other purposes. The optimized two-levels control method for the anaerobic treatment of food waste provides new perspectives for the valorisation of such waste stream; the production of building blocks namely volatile fatty acids supports new innovative bio-refinery platforms for the production of bio-products. Image 1 • It is possible to automatically control an anaerobic process to valorise food waste. • New perspectives for constant production of volatile fatty acids from organic waste. • A mathematical model prediction of the ammonia level in anaerobic digestion. • The system supports innovative bio-refineries for the production of bio-products. [ABSTRACT FROM AUTHOR]

In this study the environmental impact of the anaerobic digestion (AD) of sewage sludge within an activated sludge wastewater treatment plant (WWTP) was investigated. Three alternative AD systems (mesophilic, thermophilic, and temperature-phased anaerobic digestion (TPAD)) were compared to determine which system may have the best environmental performance. Two life cycle assessments (LCA) were performed considering: (i) the whole WWTP (for a functional unit (FU) of 1 m3 of treated wastewater), and (ii) the sludge line (SL) alone (for FU of 1 m3 of produced methane). The data for the LCA were obtained from previous laboratory experimental work in combination with full-scale WWTP and literature. According to the results, the WWTP with TPAD outperforms those with mesophilic and thermophilic AD in most analyzed impact categories (i.e., Human toxicity, Ionizing radiation, Metal and Fossil depletion, Agricultural land occupation, Terrestrial acidification, Freshwater eutrophication, and Ozone depletion), except for Climate change where the WWTP with mesophilic AD performed better than with TPAD by 7%. In the case of the SL alone, the production of heat and electricity (here accounted for as avoided environmental impacts) led to credits in most of the analyzed impact categories except for Human toxicity where credits did not balance out the impacts caused by the wastewater treatment system. The best AD alternative was thermophilic concerning all environmental impact categories, besides Climate change and Human toxicity. Differences between both LCA results may be attributed to the FU. [ABSTRACT FROM AUTHOR]

• Corn stover was treated with and without ammonia at the different HP conditions. • AD performance of corn stover was investigated at low pretreatment severity levels. • The highest VFAs concentration (4616.23 mg/L) was achieved at a HP severity of 4.56. • The highest removal rate of cellulose and lignin was 19.6% and 32.9%, respectively. • The maximum methane yield was 31.35% higher than that of the untreated group. The anaerobic digestion (AD) performance of corn stover was investigated under low hydrothermal pretreatment (HP) severity. Pretreated corn stover, with and without ammonia was examined at the three temperatures (50, 70, and 90 °C) coupled with different pretreatment time (24–72 h). The results showed that the pH value decreased with increasing pretreatment time for the same temperature. The highest volatile fatty acids (VFAs) concentration (4616.23 mg/L) was achieved at a HP severity of 4.56. The highest removal rate of cellulose, hemicellulose, and lignin were 19.62%, 25.53%, and 32.91% for HP with ammonia (HPA) severities of 3.34, 3.34, and HP severity of 4.35, respectively. The maximum methane yield of corn stover was 148.19 mL/g∙VS under 50 °C held for 24 h (HPA severity of 2.59), which was 31.35% higher than that of the untreated corn stover. The research results suggest that properly pretreatment severity can play an important role in promoting methane production. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is an important technology for the treatment of livestock and poultry manure. The optimal experimental conditions were studied, with deer manure as a fermentation material and mushroom residue as an inoculum. At the same time, methane production was increased by adding zeolite and changing the magnetic field conditions. The results showed that a 6% solid content was the best condition for producing methane. The optimal conditions for methane production were obtained by adding 35 g of mushroom residue to 80 g of deer manure at 35 °C. The addition of organic wastewater (OW) improved methane production. The result of improving the methane production factor showed that adding zeolite during the reaction process could increase the methane production rate. When the amount of zeolite was over 8% total solids (TSes), methane production could improve, but the rate decreased. Setting a different magnetic field strength in the AD environment showed that when the distance between the magnetic field and the reactor was 50 mm and the magnetic field strength was 10–50 mT, the methane production increment and the content of methane in the mixed gases increased. [ABSTRACT FROM AUTHOR]