Gene

Anaerobic digestion

Methane

Engineering

Ecology

Methanogenesis

Bacteria

Biology

Euryarchaeota

Archaea

Biochemistry

Methanosaeta

Food science

Aeration

Firmicutes

16S ribosomal RNA

Genetics

Organic chemistry

Methanobacterium

Environmental chemistry

Microbial population biology

Chemistry

Pulp and paper industry

Fuel

Micro-aeration has been shown to be favorable for anaerobic digestion (AD) process. However, the underlying mechanisms are not fully revealed. In this study, the effects of micro-aeration on AD process were investigated, the underlying mechanisms were also explored by comprehensively analysis of the substrate degradation, intermediate products, electron-transfer capacity, key enzymes and microbial communities. Results showed micro-aeration could benefit the AD process, and the beneficial effects were oxygen intensity-dependent. Maximum methane yield (262.0 ± 6.0 mL/(g·VS)) was achieved at micro-aeration of 0.2 mL/(g·VS·day), which was 7.8% higher than that of the control (without micro-aeration). The volatile fatty acids concentration, cellulase activity, soluble humic acids (SHAs) concentration and substrate degradation rate were all enhanced under micro-aeration condition. Moreover, micro-aeration could regulate the bacterial and archaeal communities: bacterial diversities and relative abundances of facultative and acetate-oxidizing bacteria (e.g., Firmicutes, Synergistota and Spirochaetota) increased, leading to higher substrate utilization rate; archaeal diversities decreased while oxygen-tolerating methanogens (e.g., Methanobacterium) became dominant to promote the methanogenesis. AD system with micro-aeration showed higher electron-transfer capacity and better conductive environment due to the increased SHAs concentration. The increased relative abundance of direct-interspecies-electron-transfer (DIET)-associated microbes could be favorable to DIET-based syntrophic methanogenesis which promotes AD under micro-aeration.

Understanding the mechanisms behind micro-aeration to enhance anaerobic digestion of corn straw