This proof-of-concept project aims to advance the application of the ultra-violet (UV)/sulfite system in the destruction of concentrated per- and polyfluoroalkyl substances (PFAS) in sorbent regeneration waste brines and membrane rejects. The direct goal is to use a limited amount of thermal energy (i.e., heating the water up to 95°C) to significantly enhance the treatment effectiveness and energy efficiency of reductive PFAS degradation in challenging water matrices that contain high concentrations of salts and organic solvents. Successful treatment of PFAS in those waste streams will significantly lower the operation and material costs of physical removal modules (carbon adsorption, ion exchange, and nanofiltration) in the Department of Defense’s (DoD's) treatment operations. The outcome will benefit the sustainable recycling of PFAS-laden materials and the deployment of membrane systems. The project team will collect a comprehensive set of performance data and forward the UV/sulfite technology to field demonstration in the near future.
Three technical objectives include:
- Achieving near-complete defluorination from a majority of PFAS structures by thermal-enhanced reductive and alkaline defluorination;
- Achieving rapid decay and deep defluorination of highly recalcitrant short-chain sulfonic acids and fluorotelomers;
- Minimizing the consumption of electrical energy and chemicals.
The project team will elucidate detailed reaction mechanisms for thermal-enhanced PFAS degradation and provide a new perception of the effects of thermal energy produced in a photochemical system.
A series of bench-scale experiments will be conducted to systematically compare and understand the thermal-enhanced rate and extent of PFAS degradation by the UV/sulfite treatment. The reaction kinetics and transformation products will be characterized under a series of variable reaction conditions (including temperatures, PFAS structures, salt concentrations, organic solvent concentrations, chemical doses, and UV irradiation energies and intensities) to optimize the treatment system to maximize PFAS destruction and minimize the overall energy and chemical consumption. Also, an anaerobic collimated beam system will be built with well-controlled photochemical parameters, temperatures, and sample volumes to accurately estimate the overall energy efficiency. If necessary, special analyses, such as nuclear magnetic resonance characterization and theoretical calculations in selected cases, will be conducted to obtain a good understanding of the transformation products and thus the reaction mechanisms.
The results from this project will contribute to both fundamental science and practical engineering regarding the deep or near-complete destruction of concentrated PFAS in challenging water matrices. In particular, the positive roles of the thermal energy generated from photochemical systems will be elucidated in great detail. The electrical energy per order of the UV/sulfite system will be further and significantly lowered from the current <11 kWh m–3 (for all perfluorocarboxylic acids and long-chain sulfonic acids) to <2 kWh m–3. Also, the fate of residual C−F bonds will be elucidated after a deep reductive defluorination and how to further cleave them without using oxidation. The results will strongly promote knowledge transfer to a field demonstration project through the collaboration with the remediation industry, to the PFAS research community, and to a solid student course training for the emerging need of PFAS treatment workforce in the real world. (Anticipated Project Completion - 2022)