UC Riverside

Per and polyfluoroalkyl substances (PFAS) have been notoriously known for their high environmental persistence. Driven by government regulations, PFAS manufacturers have gradually shifted to relatively short-chain PFAS and emerging PFAS alternatives. Among the developed PFAS treatment technologies, UV/Sulfite (UV/S) process has unique advantages in treating all chain-length PFAS because the reaction occurred in a homogeneous environment. However, the UV/S process still faced challenges from (i) incomplete defluorination (e.g., 40%~70%) after reduction reactions, (ii) relatively slow reaction kinetics, and (iii) unknown feasibilities for the emerging PFAS alternatives.To address the incomplete PFAS defluorination from UV/S reduction (Red) process, we demonstrated for the first time that incorporating the subsequent advanced oxidation (Ox) process further cleaved the residue C−F bonds in reduction products to elevate the overall treatment performance. The integrated Red and Ox process reported >97% defluorination for major PFAS categories (e.g., CnF2n+1−COO−/SO3− and CnF2n+1−CH2CH2−COO−/SO3−). To resolve the relatively slow reaction kinetics for persistent short-chain perfluoroalkyl sulfonate in UV/S, we achieved accelerated PFAS degradation by adding iodide (UV/S+I). The highlight of the UV/S+I system is the substantially improved degradation kinetics (e.g., up to four times increase) and significantly enlarged treatment capacity for concentrated PFAS wastes (e.g., 300 mg/L PFAS mixture), with fewer chemical dosages and shorter reaction time. Using ether-based PFAS (e.g., Nafion-related ether sulfonates, PFESAs) as emerging PFAS alternatives, we further investigated the role of critical structural features (e.g., linear vs. branched and introduction of C−H bond) in PFAS degradation potential in UV/S+I and evaluated the feasibility of integrated Red and Ox process. The results showed that the introduction of branched structure (e.g., −CF3), C−H bond and −COO− group improved PFAS degradation potential. Previously proposed the integrated Red and Ox process achieved >98% defluorination for these emerging PFESAs structures. Finally, we comprehensively evaluated membrane separation performance for a wide spectrum of PFAS compounds. The results showed that perfluoroalkyl sulfonamides (FOSAms) are distinctively different from the other PFAS compounds, with noticeably higher transmission percentages in the permeate solution in NF270 filtration. We also proposed enhancement strategies for FOSAms removal, including switching to “tighter” membrane NF90, elevating solution pH to ~9, and fully peroxidation of FOSAms to the well-rejected PFAS acids.