Boron-doped diamond electrodes degrade short- and long-chain per- and polyfluorinated alkyl substances in real industrial wastewaters

Abstract

Electrochemical oxidation (ECO) with boron-doped diamond (BDD) electrode of six legacy perfluoroalkyl substances (PFAS) present in semiconductor fabrication wastewaters was investigated in single-solutes, multi-solutes, and real wastewater matrices. ECO degradation kinetics decreased as carbon length decreased in single-solute systems. Because heterogeneous catalysis involves PFAS interacting at the electrode surface, the impact of PFAS in solution on altering the potential affinity for PFAS itself on the surface was quantified. The BDD electrode surface wettability, defined by the surface contact angle, increased with longer chain length and diminished with increasing PFAS concentration. PFASs with a sulfonated head group degraded 2–3x faster than their carboxylic counterparts. Industrial wastewaters can have high background organic concentrations and have a large pH range prior to discharge, offering different opportunities to treat for PFAS near the semiconductor manufacturing tool or prior to pH adjustment and discharge to sanitary sewers. Increasing pH (up to 12) decreased the evolution of reactive oxygen species on the electrode surface and therefore decreased removal kinetics compared to pH 3 and 7. The presence of surfactants (tetramethylammonium hydroxide [TMAH] and sodium dodecyl sulfonate [SDS]) in the wastewater significantly reduced the degradation efficiency of ECO. However, compared to single-solute PFAS systems, multi-solute solutions (mixture of 6 PFASs) had higher degradation rates during ECO. In a real wastewater (originated from RO concentrate), PFASs were efficiently removed in ~320 min reaction time. These results demonstrated the promise for ECO to treat PFAS contained in industrial manufacturing processes at both tool level and blended wastewater.