Novel Insights into the Mechanisms of Periodate-Based Pretreatment in Enhancing Short-Chain Fatty Acids from Waste Activated Sludge

Resource recovery in the form of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) is usually limited due to the quantity and quality of SCFAs. To mitigate these restrictions, this study provides a novel method by using periodate (PI) pretreatment. With an increase in the PI concentration from 0 to 50 mg/g total solids (TS), the SCFA yield increased from 1486 to 3109 mg COD/L and acetic acid production was enhanced by more than twice. Further increase of PI had an adverse effect on SCFA production. Electron spin resonance analysis confirmed that hydroxyl radicals (^•OH) and superoxide radicals (^•O₂^–) might play crucial roles in the pretreatment process. Further mechanism studies revealed that PI pretreatment improved the disintegration of WAS and decomposition of humus as well as lignocellulose, thereby providing more substrates for SCFA production. The model-based synthetic wastewater tests combined with enzymatic analyses revealed that the stronger suppression of SCFA consumers compared to SCFA generators causes SCFA accumulation; specifically, the inhibitory order was methanogenesis > hydrolysis > acetogenesis > acidogenesis. The suppressed gene expression of acetate-dependent (such as cdh [EC: 2.1.1.245]) and CO₂-type methanogenesis (such as fwd [EC: 2.3.1.101] and mch [EC: 1.5.98.1]) further triggered SCFA accumulation with PI addition. Moreover, PI pretreatment caused the microbial community to shift toward the favorable hydrolytic and acidification-associated (e.g., Longilinea, Acinetobacter, and Macellibacteroides) microorganisms. This study is expected to broaden an unknown application of PI and provide an alternative strategy for resource recovery in some specific circumstances.