Poly and perfluoroalkyl substances (PFAS) have been used extensively in different industries and products due to their unique chemical and thermal stability. Recent studies have shown that the consumption of PFAS poses health risks, and the ineffectiveness of conventional biological treatment processes has resulted in the bioaccumulation of PFAS in the environment. Their extensive use has caused wastewater streams to be contaminated with these compounds. In wastewater treatment plants, the activated sludge is a significant sink for PFAS. Therefore, the liquid extracted from the sludge (centrate) also contains high PFAS concentrations. In this study, the effect of the wastewater components on PFAS removal was investigated. Centrate was chosen as a critical wastewater side stream to target PFAS removal and it was concentrated using nanofiltration by a volume factor of 10 before electrochemical treatment. The feasibility of electrooxidation was examined by applying 30 mA/cm2 to a tubular Ti4O7 reactive electrochemical membrane (REM) to treat the preconcentrated centrate. Total chemical oxygen demand (COD) was removed by 87%, and total PFAS removal was 82% at the conclusion of the electrochemical oxidation experiment after 24 hours of oxidation (233 seconds of electrolysis time). However, it was observed short-chain PFAS accumulated during electrolysis. For example, perfluorohexanoic acid (PFHxA) was only removed by 38%, and perfluoropentanoic acid (PFPeA) concentration increased by ~4.2-fold. To study the effects of solution conditions on PFAS removal, electrochemical oxidation experiments with synthetic solutions containing perfluorooctanoic acid (PFOA) and select non-target water constituents (e.g., major ions, organics, other PFAS) were systematically studied. It was observed that the addition of other PFAS did not significantly affect PFOA oxidation kinetics. However, the addition of select ions was shown to negatively impact oxidation kinetics. The results of this study were used to propose treatment train approaches for PFAS removal from domestic wastewater centrate solutions.

Effect of wastewater elements on the PFAS oxidation with tubular Ti4O7 Membranes

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