Heterogeneous photocatalytic degradation of per-/polyfluoroalkyl substances under mild operating conditions has been previously demonstrated in numerous lab-scale experiments; however, key aspects of practical implementation such as photoreactor design and operation, and scalability, have not been intensively studied. Herein, a 7.5 L pilot-scale hybrid photocatalytic-photolytic unit was constructed to investigate the effect of different operational parameters such as UV input power, mixing rate, catalyst loading, and pH on perfluorocarboxylic acid degradation at ppb-level initial concentrations. The setup comprised a stainless-steel reactor, an overhead mixer, and 4×48 W ozone-generating low-pressure mercury lamps (254/185 nm). Bismuth oxyhydroxy phosphate [Bi3O(OH)(PO4)2; BOHP] semiconductor microparticles were used as the photocatalyst, and have been previously shown to efficiently degrade perfluorooctanoic acid (PFOA) under UVC irradiation. In addition to photocatalytic experiments, catalyst-free experiments were conducted – wherein PFOA was degraded only by VUV (185 nm) photolysis – for comparison. The presence of the BOHP catalyst was found to impede the direct VUV PFOA photolysis mechanism, and a net efficiency benefit was only observed under certain operational conditions. Minimum electrical energy per order PFOA destruction (EE/O) values were 74 and 65 kWh*m-3 *order-1, with and without the catalyst, respectively, and were comparable to previous bench-scale reactor results. Additionally, perfluorobutanoic acid (PFBA) degradation by the reactor was always less effective when BOHP was used. Finally, the performance of the system was tested on actual groundwater samples spiked with both PFOA and PFBA. The results of these experiments offer an insight into the applicability of heterogeneous photocatalysis technology for PFAS remediation on larger scales and provide a benchmark for future photocatalyst development studies.

Degradation of perfluorocarboxylic acids by a pilot-scale UV photo(cata)lytic reactor: Effects of reactor aspects on UVC photocatalysis and VUV photolysis efficiencies

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ACS Fall 2022

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