Enhanced Ethanol-Type Fermentation from Sulfate-Laden Organic Wastewater through Yeast Supplementation and Increased Organic Loading Rate

Establishing a direct interspecies electron transfer methanogenic pathway via ethanol-type fermentation offers an efficient strategy for energy recovery from sulfate-rich organic wastewater. This study rapidly constructed ethanol-type fermentation by integrating yeast addition and elevated organic loading rate (OLR), thereby achieving a self-sufficient ethanol substrate to enhance sludge conductivity. The results demonstrate that with an OLR of 7.5 kg COD/m3/d, yeast addition enabled rapid establishment of ethanol-type fermentation. In addition, hydraulic retention time (HRT) significantly influenced ethanol production, which peaked at 1882.8 mg COD/L in the yeast group under an HRT of 12 hours and OLR of 16 kg COD/m3/d. Crucially, yeast supplementation increased the abundance of cysteine synthase (cysC) and sulfite reductase (cysJ, cysI), boosting sulfate reduction efficiency from 34% to 88% under acidic conditions. Overall, the addition of yeast can rapidly establish ethanol fermentation and enhance the sulfate reduction efficiency, especially at lower pH values.