Effects of bioelectricity generation processes on methane emission and bacterial community in wetland and carbon fate analysis

Wetlands are an important carbon sink for greenhouse gases (GHGs), and embedding microbial fuel cell (MFC) into constructed wetland (CW) has become a new technology to control methane (CH₄) emission. Rhizosphere anode CW–MFC was constructed by selecting rhizome-type wetland plants with strong hypoxia tolerance, which could provide photosynthetic organics as alternative fuel. Compared with non-planted system, CH₄ emission flux and power output from the planted CW–MFC increased by approximately 0.48 ± 0.02 mg/(m²·h) and 1.07 W/m³, respectively. The CH₄ emission flux of the CW–MFC operated under open-circuit condition was approximately 0.46 ± 0.02 mg/(m²·h) higher than that under closed-circuit condition. The results indicated that plants contributed to the CH₄ emission from the CW–MFC, especially under open-circuit mode conditions. The CH₄ emission from the CW–MFC was proportional to external resistance, and it increased by 0.67 ± 0.01 mg/(m²·h) when the external resistance was adjusted from 100 to 1000 Ω. High throughput sequencing further showed that there was a competitive relationship between electrogenic bacteria and methanogens. The flora abundance of electrogenic bacteria was high, while methanogens mainly consisted of Methanothrix, Methanobacterium and Methanolinea. The form and content of element C were analysed from solid phase, liquid phase and gas phase. It was found that a large amount of carbon source (TC = 254.70 mg/L) was consumed mostly through microbial migration and conversion, and carbon storage and GHGs emission accounted for 60.38% and 35.80%, respectively. In conclusion, carbon transformation in the CW–MFC can be properly regulated via competition of microorganisms driven by environmental factors, which provides a new direction and idea for the control of CH₄ emission from wetlands. Graphical Abstract: [Figure not available: see fulltext.].