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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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

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 (16,607mL, 51.81%) than those at pH 6.0 (6916mL, 42.9%) and 8.0 (9739mL, 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., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

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]

[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]