Deep eutectic solvents pretreatment enhances methane production from anaerobic digestion of waste activated sludge: Effectiveness evaluation and mechanism elucidation

Abstract

Anaerobic digestion (AD) is a prevalent waste activated sludge (WAS) treatment, and optimizing methane production is a core focus of AD. Two DESs were developed in this study and significantly increased methane production, including choline chloride-urea (ChCl-Urea) 390% and chloride-ethylene glycol (ChCl-EG) 540%. Results showed that ChCl-Urea mainly disrupted extracellular polymeric substances (EPS) structures, aiding in initial sludge solubilization during pretreatment. ChCl-EG, instead, induced sludge self-driven organic solubilization and enhanced hydrolysis and acidification processes during AD process. Based on the extent to which the two DESs promoted AD for methane production, the AD process can be divided into stage Ⅰ and stage Ⅱ. In stage Ⅰ, ChCl-EG promoted methanogenesis more significantly, microbiological analysis showed both DESs enriched aceticlastic methanogens-Methanosarcina. Notably, ChCl-Urea particularly influenced polysaccharide-related metabolism, whereas ChCl-EG targeted protein-related metabolism. In stage Ⅱ, ChCl-Urea was more dominant than ChCl-EG, ChCl-Urea bolstered metabolism and ChCl-EG promoted genetic information processing in this stage. In essence, this study investigated the microbial mechanism of DES-enhanced sludge methanogenesis and provided a reference for future research.