Bioenergy generation and rhizodegradation as affected by microbial community distribution in a coupled constructed wetland-microbial fuel cell system associated with three macrophytes

Abstract

Rhizodeposits excreted by various macrophytes might lead to the potential discrepancy of microbial community distribution in constructed wetland coupled with microbial fuel cell (CW-MFC), which has been considered as main factors for the variations of bioelectricity generation during wastewater treatment. In this study, CW-MFC has been associated with three macrophytes (J. effuses, T. orientalis and S. validus) for domestic sewage treatment, also unplanted CW-MFC was performed as a control system. Macrophyte T. orientalis and S. validus can significantly strengthen the bioenergy output in CW-MFC. Highest current (94.27mAm−2) and power densities (21.53mWm−2) were obtained in CW-MFC planted with T. orientalis. Removal efficiencies of COD, NO3-N and NH3-N in CW-MFC planted with S. validus was respectively 5.8%, 7.2%, and 23.9% higher than that of unplanted system. Notably, the oxygen depletion in S. validus CW-MFC reactor during the dark cycle was higher that of other reactors. Results of high-throughput sequencing analysis showed that higher biodiversity was observed in rhizosphere than that of anode material, and the relative abundance of Desulfobulbus sp. and Geobacter sp. has been apparently promoted in the samples of rhizosphere. However, a higher relative abundance of electrochemically active bacteria (Proteobacteria) was observed on the surface of anode electrode material. In addition, microbes (Cytophagales, Clostridium sp., and Dechloromonas sp., and so forth) found in rhizosphere show a capability to decompose refractory contaminants. These contaminants and death roots in the upper part of wetland could be oxidized to fat acids, which may be used as the electrons acceptors for promoting the bioelectricity generation during wastewater treatment.