Effects of sulfate concentration and external voltage on operation efficiency, sludge characteristics, and microbial community of a bioelectrochemical system

In this study, a coupled anaerobic baffled reactor-microbial electrolysis cell (ABR-MEC) was constructed for treatment sulfate wastewater, with an external power supply. The concentration of sulfate and the external power supply intensity were changed to explore the variations in the operation efficiency and sludge characteristics of the system. When the sulfate concentration was 1000 mg/L, COD/SO42-= 2:1, and the voltage was adjusted to 1 V (the stage Ⅰ), the average sulfate removal rate was 73% and the COD removal rate was above 80%. At the conditions of sulfate concentration of 1300 mg/L, COD/SO42- = 1.5:1, and a voltage of 1 V (the stage Ⅱ), the activities of coenzyme F420 and 6-phosphofructokinase increased by 23.8% and 26%, respectively. However, the sulfate removal rate of the system reduced to 69.3% with voltage adjusted to 2 V (the stage Ⅲ). The dominant microbial community in the system were Proteobacteria, Euryarchaeota, and Thermotogae at sulfate concentration 1000 mg/L. With sulfate concentration in the influent increased to 1300 mg/L, the abundance of Thermodesulfobacteria increased to 10.55%. After increasing the external voltage, the relative abundance of Firmicutes increased by 4.51%. Metagenomic analysis illustrated that with the increase in sulfate concentration and external voltage, the glycolysis and sulfate metabolic pathway modules showed a downward trend, and the conversion efficiency decreased.