Synergistic Enhancement of Anaerobic Digestion and Resource Recovery via Extraction of Gelatinous Extracellular Polymeric Substances from Waste Activated Sludge: Performance and Underlying Mechanism

This study systematically evaluated the effects of nongelatinous and gelatinous extracellular polymeric substances (ngEPS and gEPS) on the anaerobic digestion performance of waste activated sludge (WAS). Extraction of ngEPS and gEPS enhanced methane production by 10.6 and 51.6%, respectively. Additionally, the process enabled the recovery of high-value resources such as alginate-like exopolysaccharides (ALE, a key polysaccharide component of gEPS) at concentrations in the range of 14.0–57.20 mg·gVSEPS–1 and phosphorus (P) accounting for approximately 40.0–61.2% of the total P content in WAS. Mechanistic analyses revealed that hydrophobic EPS components hindered WAS hydrolysis, whereas EPS extraction improved fluidity, reduced viscoelasticity, and promoted mass transfer efficiency. Metagenomic results further demonstrated that EPS extraction alleviated hydrolysis limitations, enriched acidogenic bacteria, and restructured microbial communities toward enhanced carbon metabolism. These findings provide both theoretical insights and practical guidance for advancing anaerobic digestion efficiency and resource recovery from WAS. The study highlights the potential of EPS-targeted strategies to optimize WAS management practices, contributing to the development of more sustainable and circular resource recovery systems.