Enhancing bioavailability of alkaline-lysed waste activated sludge by using sodium acetate to suppress iron-mediated humification

Alkaline lysis (AL) for waste activated sludge (WAS) resource utilization is often hindered by refractory organic matter formation. This study developed NaAc-coupled AL-WAS (NaAc-AL-WAS) technology to improve bioavailability. Compared to AL-WAS, the five-day biochemical oxygen demand and soluble chemical oxygen demand ratios of 0.5%, 1%, and 5% NaAc-AL-WAS increased by 0.9-, 1.1-, and 1.3-fold. Specifically, 5% NaAc-AL-WAS reduced humic substances (HS) and high-molecular-weight proteins by 10.3% and 61.0%. The denitrification rate and potential increased by 5.1- and 0.4-fold, while methanogenic rate and maximum methane potential increased by 3.4- and 1.2-fold. Mechanistically, NaAc maintained strongly alkaline environment and promoted flocculation for continuous organic release. NaAc-induced iron precipitation (Fe2+/Fe3+ below the detection line in the lysate) and Fe(Ⅲ) reduction (24.5% decrease in the sludge) weakened iron binding and catalytic activity toward humic precursors, inhibiting HS formation to enhance bioavailability. These findings provided a new approach to optimize carbon resource recovery from sludge.