A novel combined Enzymatic-Thermal hydrolysis process for mass reduction and resource recovery from waste activated sludge.

As the generation of waste activated sludge (WAS) increases and the problem of resource scarcity worsens, the demand for sustainable sludge disposal and resource recovery technologies is growing rapidly. In this study, a novel combined enzymatic-thermal hydrolysis process was assessed for enhancing mass reduction and resource recovery from WAS. Heating temperature, as the key parameter was optimized. With combined enzymatic-thermal hydrolysis, a maximum SCOD concentration of 48,619 mg/L was achieved in combined hydrolysis liquid (CHL) under an optimum temperature of 165 ℃ (CHL₁₆₅). The concentration of PS and PN in CHL₁₆₅ were 4.4 % and 11.1 % higher than that in thermal hydrolysis liquid (THL) at 165 ℃ (THL₁₆₅). Meanwhile, the contents of heavy metals (Hg, As, Cd, and Cr) in CHL were all below 0.5 mg/L, indicating that the application posed an extremely low risk to the ecological environment and human health. Comparing with raw WAS, the mass reduction rate of up to 28.3 % was achieved. Moreover, the utilization of CHL₁₆₅ as a carbon source to facilitate nitrate nitrogen (NO₃^--N) removal in wastewater treatment resulted in the efficiency reaching 94.0 % of that achieved with commercial sodium acetate. Accordingly, the CHL₁₆₅ played a prominent role as a carbon source with slow-release effect for denitrification in reducing the cost of NO₃^--N removal. The above research will provide a new direction for the advanced resource utilization of WAS.