Sulfite altered permanganate pretreatment effects on the volatile fatty acid production during sludge anaerobic fermentation

Anaerobic fermentation is a low-carbon strategy for waste activated sludge (WAS) treatment with resource re-covery. This study compared the effects of potassium permanganate (PM) and calcium sulfite-assisted PM (PM/ CS) pretreatment on volatile fatty acids (VFAs) production during WAS fermentation. The effects of combined PM/CS on the total VFAs production were observed to be inferior to sole PM (2689 versus 3507 mg COD/L), but PM/CS pretreatment resulted in acetate-enriched VFAs (88.2% ratio) with improved sludge dewatering. The scavenging effects of interfering compounds on free radicals, which are previously speculated for extracellular polymeric substances (EPS) disruption, and the EPS-binding effects of Ca2+ in PM/CS reactors might both restrain the effective WAS solubilization and hydrolysis efficiencies in comparison with that of PM, and thus resulted in the reduced VFAs production. Moreover, both PM and PM/CS pretreatment altered the microbial community structure and metabolic traits, which were beneficial to the VFAs generation. However, the PM/CS pretreatment was more conducive to the enrichment of acetate-producing bacteria (e.g., Proteiniclasticum and Christensenellaceae_R_7_group) and acetate-forming metabolic functions (e.g., pyruvate metabolism and prop-anoate and butanoate degradation). Also, methanogenesis, which is an acetate-consumption process, was remarkably inhibited in PM/CS reactor, thereby promoting acetic acid accumulation effectively. This study demonstrated the distinct effects of different PM-based pretreatment on WAS fermentation and provided guid-ance on the appropriate pretreatment selection for WAS disposal.

Automated summary

This study compared the effects of potassium permanganate (PM) and calcium sulfite-assisted PM (PM/ CS) pretreatment on volatile fatty acids (VFAs) production during waste activated sludge (WAS) fermentation. PM/ CS pretreatment resulted in acetate-enriched VFAs with improved sludge dewatering. The scavenging effects of interfering compounds and the EPS-binding effects of Ca2+ in PM/CS reactors might both restrain the effective WAS solubilization and hydrolysis efficiencies, thus resulting in reduced VFAs production. Moreover, both PM and PM/CS pretreatment promoted the enrichment of acetate-producing bacteria and acetate-forming metabolic functions, but PM/CS pretreatment was more conducive to this process.