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Bioelectrochemistry system (BES) provides a new strategy for the improvement of low temperature anaerobic digestion (AD) for methane production. In this study, the BES with carbon brushes as electrodes was operated at 15 °C to analyze the changes of microbial abundance and functional genes. The microbial community structure showed that the application of voltage had no effect to type and relative abundance of bacteria based on 16S-rRNA sequencing. Metatranscriptomic analyses revealed that significantly enhanced the abundance of fermentation bacteria in the fluid activated sludge, and the relative abundance of biosynthesis of other secondary metabolites (61.56%) was also highly expressed. More than that, the abundance of electricigens (Pseudomonas , Syntrophomonas) was also enriched in the BES system. These electricigens could interact with methanogens to promote electron transfer by direct interspecies electron transfer (DIET). The expression level of functional enzyme related to electron transport was increased at the anode (30.60%), but decreased at the cathode (−33.84%). Analysis of methanogens found that the application of voltage decreased the relative abundance of Methanosarcina and promoted the enrichment of Methanothrix. At 15 ℃, acetoclastic was the mainly methanogenic pathway. What's more, the application of voltage could enhance the acetoclastic and inhibited the hydrogenotrophic and the methylotrophic pathway. Further, the acetoclastic pathway was changed from acetate kinase (EC: 2.7.2.1) and phosphate acetyltransferase (EC: 2.3.1.8) to acetate-CoA ligase (EC: 6.2.1.1) by applied voltage. These results are conducive to the further development of low-temperature AD treatment technology. [Display omitted] • Methahnosarcina and Methanothrix were dominated in DNC and SC reactor, respectively. • The applied voltage increased the abundance of electroactive microorganisms. • The application of voltage promoted the acetoclastic pathway at low temperature. • The SC reactor achieved acetate to acetyl-CoA by acetate-CoA ligase. • The DNC reactor was through acetate kinase and phosphate acetyltransferase. [ABSTRACT FROM AUTHOR]

[Display omitted] • The methanogenic performance was better when the applied voltage was 0.8 V. • Clostrodium and Methanosaeta were the most dominant microbial populations. • MES-Cathode was more tolerant to the effects of higher NH 4 +-N concentration. • CH 4 was produced mainly via hydrogenotrophic methanogenic pathway in MES-Cathode. • MES produced CH 4 via SOAB, hydrogenotrophic archaea if acetoclastic pathway curbed. Microbial electrosynthesis (MES) has great potential for energy and resource recovery in wastewater treatment and has therefore gradually become a popular research topic. In this study, MES with an applied voltage (0.6 V, 0.8 V and 1.0 V) significantly improved biogas production (36.0 %, 52.3 %, and 59.1 %, respectively) compared with the control (without electrodes). Analysis of microbial community structure revealed that Clostridium and Methanosaeta had the highest relative abundance in all reactors. The abundances of Acetivibrio and Geobacter dominated the bioanode, and methane production was mainly mediated by the acetoclastic methanogenic pathway. On the biocathode, the abundances of Methanolinea and Methanothermobacter were higher than those of other microbes, and methane was produced primarily through the hydrogenotrophic methanogenic pathway. When the acetoclastic methanogenic pathway in the biocathode was inhibited, MES could efficiently produce methane through other pathways. In addition, MES was more tolerant to the effects of high NH 4 +-N concentrations than anaerobic digestion (AD). These results suggest that applying voltage to the bioanode and biocathode could better improve the efficiency of methane production. [ABSTRACT FROM AUTHOR]

To strengthen mass heat transfer in dry fermentation and avoid the high shear forces breaking microbial flora. A reactor is designed to rotate itself instead of mechanical stirring. Its performance was verified by comparing it with the common stirring of dry digestion and wet digestion. The results showed that the designed reactor could effectively overcome the existing problems of stirring dry digestion. The total solids removal rate was up to 68.74%, which was 18% higher than that of wet digestion. Acetic acid and propionic acid were the main volatile fatty acids in dry digestion, and acetic acid and butyric acid were higher in wet digestion. The high diversity of fermentation bacteria integrated with hydrotrophic methanogens in the designed dry reactor resulted in its better performance. The information provided will be useful to research the anaerobic treatment of solid municipal waste. • A reactor used rotating instead of stirring was designed for dry fermentation. • The designed reactor performed well in the dry fermentation of kitchen waste. • More functional bacteria and hydrotrophic methanogens lead to good fermentation. • Methahnosarcina dominated in both designed dry reactor and common wet reactor. • Proteiniphilum and Enterococcus dominated in the designed reactor. [ABSTRACT FROM AUTHOR]