Understanding of the effect of COD/SO42− ratios and hydraulic retention times on an MFC-EGSB coupling system for treatment sulfate wastewater: Performance and potential mechanisms

Abstract

In this study, the microbial fuel cell-expanded granular sludge bed (MFC-EGSB) coupling system was constructed to investigate the removal of chemical oxygen demand (COD) and sulfate (SO₄²⁻), electrochemical performance, and the changes of microbial community structure under different COD/SO₄²⁻ ratios and hydraulic retention time (HRT) operating conditions. As the COD/SO₄²⁻ ratios decreased from 1 to 0.67, 0.44 (stages I, stage II, and stage III), the COD removal efficiency in the MFC-EGSB coupling system decreased and the average removal rate decreased from 48.91 % to 45.47 % and 37.49 %. At the same time, the output voltage of the MFC-EGSB coupling system reduced. Proteobacteria and Euryarchaeota were the dominant phylum in the first three stages of the MFC-EGSB coupling system and EGSB system. When HRT was extended to 48 h (stage IV), the COD removal efficiency of the MFC-EGSB coupling system and the EGSB system increased to 58.88 % and 72.24 %, respectively. Meanwhile, the relative abundance of Bacillota responsible for power generation increased, and the expression of the dissimilatory sulfate reduction pathway module (MD: M00596) was up-regulated, with high sulfate reduction potential. The increase in HRT was beneficial to the conversion between sulfite and sulfide. These results could be used as a reference for choosing the operation parameters reasonably for sulphate wastewater treatment.