Unravelling the impacts of perfluorooctanoic acid on anaerobic sludge digestion process

Perfluorooctanoic acid (PFOA) is a type of persistent organic pollutant that has been detected in wastewater treatment systems, subsequently entering the waste activated sludge (WAS) anaerobic digesters. Nevertheless, how PFOA affects the anaerobic digestion of WAS has never been reported till now. In this study, a series of batch digesters were set up to assess the performance of the anaerobic sludge digestion processes with exposures to different levels of PFOA. Experimental results revealed that the increased PFOA concentration (3-60 μg/g-TS) caused the 11.1-19.2% decrease in methane production than the control. Correspondingly, the relative abundances of several key microbes related to acidification (e.g., Longilinea sp.) and methanation (e.g., Methanosaeta sp.) decreased when exposed to PFOA, as demonstrated by microbial community analysis. Further investigations based on modelling and intermediate metabolites analysis confirmed the inhibition of acidification and methanation caused by PFOA, thus decreasing the methane production potential of WAS in anaerobic digestion.