Effective methane production from waste activated sludge in anaerobic digestion via formic acid pretreatment

Abstract

Waste activated sludge pretreatment is indispensable as sludge hydrolysis is limited during anaerobic fermentation. In this study, a new pretreatment method by adding formic acid has been proposed to improve carbon recovery from waste activated sludge. With formic acid addition, carbon was recovered as methane or/and volatile fatty acids and the recovery efficiency was higher than HCl pretreatment at the same concentration. The highest carbon recovery efficiency (almost 40%) was shown in the group of 0.1 mol/L formic acid pretreatment which might be attributed to isoelectric-point pretreatment. That was, the produced methane with the purity of 80% and little volatile fatty acids were detected with 0.1 mol/L formic acid pretreatment. However, the carbon recovery efficiency did not increase with the increasing acids concentration. Thus, 0.1 mol/L formic acid was regarded as the optimum pretreatment approach for anaerobic fermentation of waste activated sludge. The results of microbial communities showed that enrichment of hydrogen-producing bacteria Petrimonas and hydrogenotrophic methanogens was triggered, and then might improve carbon recovery from waste activated sludge.