Performances of microbial fuel cells fed with rejected wastewater from BioCH(4) and BioH(2) processes treating molasses wastewater

Abstract

An integrated process involving conventional anaerobic digestion and microbial fuel cells ( MFCs) has attracted attention recently to produce sustainable energy and to treat wastewater efficiently. To evaluate the possibility of CH4- producing process ( BioCH(4))- MFC or H-2- producing process ( BioH(2))- MFC integrating systems, the MFC performances were investigated using rejected wastewater from a BioCH4 reactor ( RWCH4) or BioH2 reactor ( RWH2) treating molasses wastewater. When RWCH4 or RWH2 was fed into a single-chamber MFC reactor ( designated as AC- MFCCH4 and AC- MFCH2, respectively) at different hydraulic retention times ( HRT) of 1-7 d, both MFC systems showed maximum electricity production efficiencies at a HRT of 3 d. In the AC- MFCCH4 reactor, the average current density and average power density were 60.5 mA m(2) and 8.8 mM m2, respectively. The AC- MFCH2 reactor generated an average current density of 71.4 mA 2 and an average power density of 12.0 mW m 2. The COD removal rates were 45.7% in the AC- MFCCH4 reactor and 90.3% in the AC- MFCH2 reactor. There were no significant differences of the eubacterial community structures between the MFC systems, where Proteobacteria was remarkably dominant in both MFC systems. However, the archaeal community structures were significantly different where Methanothrix ( 89.3%) was remarkably dominant in the AC- MFCCH4 system, while Methanothrix ( 52.5%) and Methanosarcina ( 33.5%) were abundant in the AC- MFCH2 system. These findings demonstrate that the utilization of MFCs after the BioCH4 or BioH2 process is advantageous for energy recovery as well as COD removal from molasses wastewater.