Enhancing Methane Production from Anaerobic Digestion of Waste Activated Sludge through a Novel Sodium Percarbonate (SPC) Pretreatment: Reaction Kinetics and Mechanisms

Abstract

Sodium percarbonate (SPC), a harmless and economical inorganic peroxide, has recently attracted increasing attention in pollutant degradation and sludge treatment. However, the feasibility and mechanisms of SPC pretreatment on improving the anaerobic digestion of waste activated sludge (WAS) have never been revealed before. Therefore, this study is aimed to fill this research gap. The results showed that with the SPC dosage increasing from 0 to 0.3 g/g total suspended solids, the maximum methane production was enhanced by 37.2%. Model-based analysis indicated that SPC pretreatment concurrently enhanced the hydrolysis rate and biochemical methane potential of WAS. Mechanistic studies were performed from two stages, i.e., sludge disintegration and anaerobic digestion. SPC pretreatment accelerated sludge solubilization through disintegrating extracellular polymeric substances and cell walls of WAS, which provided substantial substrates for subsequent anaerobic digestion. Meanwhile, the active radicals contributing to pretreatment were proven to be OH, •O2–, and CO3•–. The strong oxidizing radicals promoted the conversion of organics from nonbiodegradable to biodegradable substances, thus improving the biodegradability of WAS. Furthermore, SPC pretreatment improved hydrolysis, acidogenesis, and methanogenesis bioprocesses of WAS and enriched key microbes involved in complex organic decomposition (e.g., Exiguobacterium sp.), metabolic intermediate generation (e.g., Clostridioides sp.), and methane conversion (Methanosaeta sp. and Candidatus_Methanofastidiosum sp.).