Effects of the bioelectrochemical technique on methane emission and energy recovery in constructed wetlands (CWs) and related biological mechanisms

In this study, effects of bioelectrochemical technique on methane emission and energy recovery, and related mechanism underlying microbial competition were investigated. The results showed that running MFC was beneficial in reducing CH4 emissions and promoting COD removal rates, regardless of whether the plant roots were located at the anode or the cathode. CH4 emission was significantly higher in open-circuit reactors (6.2 mg m-2 h-1) than in closed-circuit reactors (3.1 mg m-2 h-1). Plant roots at the cathode had the highest electricity generation and the lowest CH4 emissions. The highest power generation (0.49 V, 0.33 w m-3) and the lowest CH4 emissions (2.3 mg m-2 h-1) were observed in the reactors where Typha orientalis was planted with plant roots at the cathode. The role of plants in strengthening electron acceptor was greater than that of plant rhizodeposits in strengthening electron donors. Real-time quantitative PCR (q-PCR) and correlation analysis indicated that the mcrA genes and CH4 emissions were positively correlated (r = 0.98, p < 0.01), while no significant relationship between CH4 emissions and pmoA genes was observed. Illumina sequencing revealed that more abundant exoelectrogens and denitrifying bacteria were observed when plant roots were located in cathodes. Strictly acetotrophic archae (Methanosaetaceae) were likely the main electron donor competitors with exoelectrogens. The results showed that the location of both plant species and plant roots at the electrode played an important role in CH4 control and electricity generation. Therefore, it is necessary to strengthen plant configuration to reduce CH4 emissions, to promote sustainable development of wastewater treatment.