Influence of perfluorooctanoic acid on alkaline anaerobic fermentation of waste activated sludge: Perspective from volatile fatty acids production and sludge reduction.

Alkaline anaerobic fermentation is an effective approach for resource utilization and reduction of waste activated sludge (WAS). Perfluorooctanoic acid (PFOA) is widespread in WAS, however, its potential impact on alkaline anaerobic fermentation of WAS remains largely unknown. Hence, this study focused on investigating the influence of PFOA on volatile fatty acids (VFAs) production and sludge reduction during alkaline anaerobic fermentation (pH = 10 ± 0.1), as well as the critical mechanisms. Results demonstrated that low PFOA concentration (5 mg/kg-TS) raised VFAs yield to 109.37%, while high levels of PFOA (25 and 50 mg/kg-TS) remarkably decreased VFAs production to 89.55% and 80.44% of the control. Mechanism exploration revealed that PFOA facilitated the solubilization process, and low PFOA level enhanced the accumulation of VFAs via increased bioavailable substrates and the activities of enzymes and microorganisms. On the contrary, high levels of PFOA were substantial biotoxicity, inducing excessive ROS production, causing oxidative damage, and reducing enzyme activity and functional microbial abundance, thereby decreasing VFAs production. Additionally, further analysis of sludge physicochemical properties confirmed that the effect of PFOA on WAS reduction exhibited the same trend as VFAs production. This work provides a basis for PFOA environmental risk assessment and WAS resource utilization.