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The aim of this work was to investigate the mesophilic methane fermentation of rice straw at different organic loading rates (OLRs) in a 300 m 3 bioreactor. It was found that biogas production increased when the OLR was below 2.00 kg VS substrate /(m 3 ·d). The average volumetric biogas production reached 0.86 m 3 /(m 3 ·d) at an OLR of 2.00 kg VS substrate /(m 3 ·d). Biogas production rate was 323 m 3 /t dry rice straw over the whole process. The pH, chemical oxygen demand, volatile fatty acid, and NH 4 + -N concentrations were all in optimal range at different OLRs. High-throughput sequencing analysis indicated that Firmicutes , Fibrobacteres , and Spirochaetes predominated in straw samples. Chloroflexi , Proteobacteria , and Planctomycetes were more abundant in the slurry. The hydrogenotrophic pathway was the main biochemical pathway of methanogenesis in the reactor. This study provides new information regarding the OLR and the differences in the spatial distribution of specific microbiota in a rice straw biogas plant. [ABSTRACT FROM AUTHOR]

Laboratory-scale reactors, in which the pH could be auto-adjusted, were employed to investigate the mesophilic methane fermentation with pig manure (7.8% total solids) at pH 6.0, 7.0, and 8.0. Results showed that the performance of anaerobic digestion was strongly dependent on pH value. Biogas production and methane content at neutral pH 7.0 were significantly higher (16,607 mL, 51.81%) than those at pH 6.0 (6916 mL, 42.9%) and 8.0 (9739 mL, 35.6%). Denaturing gradient gel electrophoresis fingerprinting and Shannon’s index indicated that the samples contained highly diverse microbial communities. The major genus at pH 7.0 was Methanocorpusculum , compared with that was Methanosarcina at both pH 6.0 and 8.0. Our research revealed that cultures maintained at pH 7.0 could support increased biogas production, which has significant implications for the scale-up biogas engineering. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion is considered to be an efficient way to improve the biogas production. The abundance, dynamic and interactional networks of prokaryotic community were investigated between co-digestion and mono-digestions of corn stalk and pig manure in mesophilic batch test. Co-digestion showed higher methane production, and contributed to suitable microenvironment as well as stable prokaryotic community structure. The highest methane production was achieved with the highest relative abundance of Methanosaeta. Prokaryotic community in mono-digestions might inhibited by FA or FVFA. The functional modules in co-digestion and mono-digestion of pig manure clustered together with bigger size and higher degree, and the connections of metabolic functions were better-organized, which means high-efficient utilization of substrate and prevention of the two digestion systems crash. The partial mantel tests showed the functional modules were significantly affected by environmental factors. These results further explained that why co-digestion was more efficient than mono-digestion owing to suitable microenvironment. [ABSTRACT FROM AUTHOR]

[Display omitted] • The feasibility of DLC pretreatment in anaerobic digestion (DLC-AD) was proved. • Lower scum, higher substrate utilization and organic biodegradability promoted CH 4. • DLC pretreatment enriched Ruminofilibacter and Methanobacterium in AD. • More positive interspecies relationships were detected in co-network of DLC-AD. • Comamonas and Methanobacterium , etc. as the hub microbes were constructed in DLC-AD. The recalcitrant characteristics of lignocellulosic waste and difficulties in biomass transportation and storage severely limit bioenergy production through anaerobic digestion (AD). In this study, Densifying Lignocellulosic biomass with Chemicals (DLC) pretreatment was developed to address these issues. The results showed that DLC treated corn stover (CS) reached a cumulative methane yield of as high as 224.30 mL/g VS (Volatile Solids), which was 59.27 % higher than that of un-treated. The reduced scum formation in the reactor, increased components consumption of solid phase, and higher organic biodegradability of liquid phase in AD of DLC treated CS enhanced methane yield. Microbial analysis indicated that DLC pretreatment affected the bacterial and methanogenic community structure, and a co-network with Comamonas and Methanobacterium , etc. as hub microbes was constructed. This study proposed a promising technology that could be potentially applied to industrial AD of lignocellulosic biomass. [ABSTRACT FROM AUTHOR]

This study investigated the performance of anaerobic digestion systems using four types of fibrous biofilm carriers, a polypropylene, a polyester, a polyamide, and a polyurethane fiber material. The biogas and methane production, pH, chemical oxygen demand, total solids content, volatile solids content, residual coenzyme F 420 , and microbial community compositions were determined during the experimental runs. Furthermore, scanning electron microscopy was employed to identify the microbial consortium and examine their attachment onto the surface of the four fibrous biofilm carriers. The polypropylene fiber system maintained the highest biogas and methane production in the reactor, which was 44.80% and 49.84% higher than that noted in the control, respectively, during the entire anaerobic fermentation cycle. Meanwhile, the polypropylene fiber system exhibited the highest TS, VS, and COD removal efficiency. The results of high-throughput sequencing indicated that the dominant species in the polypropylene fiber system were Methanoregula and Methanobacterium . [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of specific inoculation and acetate supplement in LBR-UASB was studied. • Exogenous additives improved FW hydrolysis and lactate–butyrate conversion in LBR. • The increase in methane yield relied on the enhancement of butyrate fermentation. • Carbon conversion efficiency in this two-phase AD increased by 33% with additives. In this study, exogenous Megasphaera elsdenii inoculum and acetate supplementation were introduced at the acidogenic phase to regulate the acidogenic fermentation pathway and assess their effects on food waste (FW) carbon conversion in two-phase anaerobic digestion (AD) system. These two additives significantly accelerated organic removal efficiency and subsequently increased FW hydrolysis and acidogenesis by 16% and 35%, respectively. As expected, two exogenous additives promoted butyrate fermentation during FW acidogenesis. With regard to the role of exogenous additives, both hydrogen and butyrate yields increased by over 60%. This desired increment resulted in a 25% increase in methane production. The overall carbon conversion from FW in the integrated two-phase AD system was enhanced by biochemical additives, which was 1.3-fold higher than that in control without any additives. Collectively, findings demonstrate the feasibility of regulating acidogenic fermentation via exogenous biochemical additives and its benefits on FW carbon conversion during AD process. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of water replacement with/without gas diversion in LBR-UASB was studied. • Water replacement improved solubilization and hydrolysis of solid waste. • Leach bed reactor with 15% TS presented the highest carbon conversion efficiency. • The novel integrated AD system at TS 15% had a 36% increase in energy recovery. • Acidogenic off-gas diversion alone increased 11.2% of energy recovery. An integrated two-phase AD with acidogenic off-gas diversion from a leach bed reactor to an upflow anaerobic sludge blanket was developed for improving methane production. However, this system had its own technical limitation such as mass transfer efficiency for solid-state treatment. In order to optimize the mass transfer in this two phase AD system, leachate recirculation with various water replacement rates regulating the total solids contents (TS) at 12.5%, 15%, and 17.5% was aim to investigate its effect on methane generation. The solubilization of food waste was increased with decreasing TS content, while the enzymatic hydrolysis showed the opposite trend. A TS contents of 15% presented the best acidogenic performance with the highest hydrogen yield of 30.3 L H 2 /kg VS added , which subsequently resulted in the highest methane production. The present study provides an easy approach to enhance food waste degradation in acidogenic phase and energy conversion in methanogenic phase simultaneously. [ABSTRACT FROM AUTHOR]

[Display omitted] • GAC-mediation and temperature rise decreased viscosity of fermentation broth. • Methane yield in the GAC-H system was 214.42 m3/t dry corn straw. • The λ was shorten and R m was increased by GAC-mediation and temperature rise. • Euryarchaeota and Thermotogae were dominant microorganism in GAC-H system. Anaerobic digestion (AD) systems with high substrate concentrations are characterized by high viscosity, which affects material and energy transfer efficiencies, thereby influencing methane production efficiency. In this study, adding granular activated carbon (GAC) and increasing the temperature decreased the viscosity by 4.56–10.19% and 27.13–28.85%, respectively, and improved AD efficiency. Adding GAC and increasing the temperature enhanced the methane yields by 34.37–38.15% and 25.60–28.31%, respectively. Distance-based redundancy analysis showed that the viscosity, temperature, and GAC had the greatest effects on the composition of the microbial community. The dominant bacteria in the medium-temperature AD system at the phylum level belonged to Firmicutes , Bacteroidetes , and Euryarchaeota. In addition to the dominant bacteria in the medium-temperature AD system, the thermophilic phylum Thermotogae was abundant in the high-temperature AD system. Moreover, the relative abundance of Euryarchaeota , which contained most of the methanogens, was higher in the high-temperature AD system than in the medium-temperature AD system. [ABSTRACT FROM AUTHOR]

• Mixed inorganic/organic Cu had positive effects on AD performance and ARGs removal. • These positive effects might be due to the low bioavailability of mixed Cu salts. • The highest Clostridia _MBA03 and Methanobacterium abundances were in mixed Cu group. • Microbial community induced by environmental factors mainly determined ARGs profiles. • Mixed Cu could be an alternative to replace inorganic Cu in animal feed additives. This study investigated methane production and ARGs reduction during thermophilic AD of swine manure with the addition of different Cu salts (cupric sulfate, cupric glycinate, and the 1:1 mixture of these two salts). Results showed methane production was increased by 28.78% through adding mixed Cu salts. The mixed Cu group effectively reduced total ARGs abundance by 26.94%, suggesting mixed Cu salts did not promote the potential ARGs risk. The positive effects of mixed Cu salts on AD performance and ARGs removal might be ascribed to the low bioavailability. Microbial community analysis indicated the highest abundances of Clostridia _MBA03 and Methanobacterium in the mixed Cu group might cause the increased methane production. Spearman's rank correlation analysis elucidated the succession in microbial community induced by environmental factors was the main driver for shaping ARGs profiles. Thus, mixed Cu salts could be an alternative to replace the inorganic Cu salt in animal feed additives. [ABSTRACT FROM AUTHOR]