System performance and microbial community in ethanol-fed anaerobic reactors acclimated with different organic carbon to sulfate ratios.

Graphical abstract Highlights • Sulfate removal percentages were 99–49% at COD/SO 4 2− ratios from 2 to 0.67. • Acetate was accumulated and propionate was rapidly utilized by SRB. • Propionate was degraded through pyruvate & propanoate metabolism pathway. • Incomplete oxidizing SRB were superior to complete oxidizing SRB. • Pseudomonas and Desulfobulbu s could potentially participate in DIET. Abstract Sulfate influences the organics removal and methanogenic performance during anaerobic wastewater treatment. System performance, microbial community and metabolic pathways in ethanol-fed anaerobic reactors were investigated under different COD/SO 4 2− ratios (2, 1 and 0.67) and control without sulfate addition. The sulfate removal percentages declined (99%, 60% and 49%) with decreasing COD/SO 4 2− ratios, and methanogenesis was completely inhibited. Acetate accumulated to 903–734 mg/L, though propionate was constantly lower than 30 mg/L. Without sulfate, acetate and propionate did not accumulate, despite the extended time for propionate degradation. Incomplete oxidizing sulfate reducing bacteria (Desulfobulbus and Desulfomicrobium) and hydrolysis-acidification genera (Treponema and Bacteroidales) predominated but could not degrade acetate. Desulfobulbus was the key genus for propionate degradation through the pyruvate & propanoate metabolism pathway. Pseudomonas and Desulfobulbu s, possessing genes encoding Type IV pili and cytochrome c6 OmcF, respectively, potentially participated in the direct interspecies electron transfer in sulfate-rich conditions. [ABSTRACT FROM AUTHOR]