Recovery of microbial fuel cells with high COD molasses wastewater and analysis of the microbial community

The microbial fuel cell (MFC) is a green technology that can be used to simultaneously degrade organics and generate energy. In this work, a double-chamber microbial fuel cell (DCMFC) was used to treat molasses wastewater with different concentrations, in batch tests. The results demonstrated that when the COD of the influent wastewater was low (3630 mg/L), the MFC system ran stably for 12 h, the maximum power density reached 3.28 W/m3, the internal resistance was 94 Ω, and a total COD removal efficiency of 88.5% was obtained at the end of the cycle. However, as the influent increased to 9060 mg/L, the performance of the MFC significantly declined due to the accumulation of volatile fatty acids (VFAs) and low pH. Interestingly, 10 days later the MFC system began to recover: output voltage increased from 209 to 535 mV, VFA declined from 2428.25 to 0 mg/L, and pH increased from 4.83 to 6.98. The microbial diversity of the biofilm on the anode was also investigated using high-throughput sequencing technology in order to clarify the effect of microbials on the treatment efficiency. The dominant microbial genera, such as Azospirillum, Sulfuricurvum, Syntrophomonas and Curvibacter, are highly related to the electron transfer and VFA degradation. In addition, Geobacter found on the carbon felt was responsible for electricity generation. These results demonstrate that MFCs could be an efficient way to treat molasses wastewater, because of its great self-recovery capability.