Improving methane production from waste-activated sludge by coupling thermal hydrolysis with potassium ferrate pretreatment.

Thermal hydrolysis (TH) is effective in improving the solubilization of waste-activated sludge, but opportunities for enhancement remain, particularly in increasing organic matter conversion and reducing the generation of refractory substances. This study proposed a novel pretreatment method combining TH and potassium ferrate (PF) and evaluated its performance in improving sludge methane production. The results indicated that the combined pretreatment increased the methane yield from 118 ± 2 mL/g VS to 215 ± 7 mL/g VS, an increase of 82.2 % compared to the control. Combined pretreatment promoted the exposure of functional groups in the extracellular polymeric substances (EPS) and altered protein secondary structure composition, thereby disrupting EPS. PF improved the biodegradability of TH-treated sludge by degrading humic acids and Maillard reaction products. In addition, Fe(III) produced by PF induces dissimilar iron reduction, which enhances microbial electron transfer activity and facilitates subsequent hydrolysis and acidification processes. Combined pretreatment increased the abundance of hydrolyzing and acidifying bacteria, but reduced hydrogenotrophic methanogens. This article reveals that PF improves the biodegradability of TH-treated sludge and provides new ideas for advanced TH technologies for sludge resource recovery.