Insight of the bio-cathode biofilm construction in microbial electrolysis cell dealing with sulfate-containing wastewater

[Display omitted] •Superior viability performance of SRB bio-cathode biofilm than non-C4-HSL addition.•More efficient and quick sulfate reduction was achieved by C4-HSL addition.•Extracellular polymers’ secretion promotes uniform biofilms forming due to C4-HSL.•Acidogenic fermentation bacteria co-metabolized with SRB improve sulfate reduction. Signaling molecules are useful in biofilm formation, but the mechanism for biofilm construction still needs to be explored. In this study, a signaling molecule, N-butyryl-l-Homoserine lactone (C4-HSL), was supplied to enhance the construction of the sulfate-reducing bacteria (SRB) bio-cathode biofilm in microbial electrolysis cell (MEC). The sulfate reduction efficiency was more than 90% in less time under the system with C4-HSL addition. The analysis of SRB bio-cathode biofilms indicated that the activity, distribution, microbial population, and secretion of extracellular polymers prompted by C4-HSL, which accelerate the sulfate reduction, in particular for the assimilatory sulfate reduction pathway. Specifically, the relative abundance of acidogenic fermentation bacteria increased, and Desulfovibrio was co-metabolized with acidogenic fermentation bacteria. This knowledge will help to reveal the potential of signaling molecules to enhance the SRB bio-cathode biofilm MEC construction and improve the performance of treating sulfate-containing wastewater.