Effects of adding different carbon sources on the microbial behavior of sulfate-reducing bacteria in sulfate-containing wastewater

Excessive sulfate levels pose a threat to the environment and human health. To address the problem of sulfate pollution and provide a basis for sulfate removal and sulfur recovery, this study searched for organics readily available to sulfate-reducing bacteria (SRB). To investigate the utilization characteristics of different organic matter by SRB, this study investigated microbial sulfate reduction under different carbon sources, including alcohols, small organic acids and sugars, and at different carbon-sulfur (C/S) ratios. Differences in the conversion pathways of different carbon sources were the main factors affecting the sulfate reduction process. Due to the presence of incompletely oxidizing SRB (incomplete oxidizers), the rapid incomplete oxidation of sugars and alcohols that produced acetic acid inhibited the activity of SRB by lowering the solution pH. In contrast, the conversion of small organic acids with stable pH produced more sulfides. Among all the tested carbon sources, faster sulfate reduction was observed using propionate, lactate, ethanol and formate, and the optimal C/S ratio was three times higher than the stoichiometric ratio. The type of carbon source also influenced sulfate reduction by shaping the microbial community. The presence of ethanol and propionate favored the vigorous proliferation of the incomplete oxidizers Desulfomicrobiaceae and Desulfovibrionaceae, while the completely oxidizing SRB Desulfuromonadaceae and Desulfococcaceae dominated formate-containing cultures. Incomplete oxidizers generally grow faster and tend to have higher electron transport system activity but lower carbon source utilization efficiency.