Dual-stage pretreatment strategy: Coupling sodium disilicate with thermal hydrolysis to optimize methane yield from sludge digestion.

Anaerobic digestion of waste activated sludge is inherently limited by the recalcitrance of extracellular polymeric substances (EPS) and microbial cell envelopes. This study developed an innovative dual pretreatment method integrating sodium disilicate (SD) with thermal hydrolysis (TH) to overcome barriers to biomass degradation. The synergistic effect of SD and TH significantly increased methane yield by 93.3 % (203 vs 105 mL/g volatile solids) compared to untreated sludge, providing a practical approach for efficient bioenergy recovery. Mechanistically, SD disrupts sludge flocs through chelation of metal ion (e.g., Ca/Fe) in EPS and pH-induced structural changes, while subsequent TH lyses the exposed microbial cells, releasing intracellular substrates. This sequential action enriched key microbial communities (e.g., Bacillota, Halobacteriota) and enhanced enzymatic activities, with protease increasing by 3.7 times and coenzyme F420 by 6 times, confirming the strategy's effectiveness in improving biodegradability while avoiding Maillard reactions at lower temperatures. This approach offers an economically and environmentally advantageous pathway for sludge valorization, reducing energy input by 38 % and net treatment cost to $41.7 per metric ton of sludge.