Destroying perfluorooctanoic acid in water by continuous liquid-phase plasma discharge

Water pollution by per- and poly-fluorinated alkyl substances (PFAS) has become a major concern that needs to be dealt with immediately. In this study, a novel, continuous-flow, liquid-phase plasma discharge reactor (CLPD) was evaluated for its effectiveness and efficiency in removing PFOA in water. Argon was used as the carrier gas to evaluate other operating parameters including gas flow rate, water flow rate, water conductivity, and power applied using a two-level partial factorial design. The results showed that gas flow rate was the most significant factor among the four factors affecting the removal efficiency of PFOA by CLPD (p = 0.0029). The best combination of the four operating parameters was obtained (conductivity = 300 µs/cm, water flow rate = 150 mL/min, gas flow rate = 1.5 sL/min, and power = 100 W), under which the CFLPPD could achieve a PFOA removal rate of 93.4%. The breakdown pathway was estimated to be from PFOA to PFHPA, to PFHXA, to PFHeA, to PFBA, and then to H2O, CO2, F, and short-chain organics.