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Advanced Water Treatment for PFAS removal: Membrane Treatment using Closed Circuit RO and Membrane Distillation
Citation:
Lee, T. AND M. Nadagouda. Advanced Water Treatment for PFAS removal: Membrane Treatment using Closed Circuit RO and Membrane Distillation. North American Membrane Society, Tuscaloosa, AL, May 13 - 17, 2023.
Impact/Purpose:
Reverse osmosis (RO) has demonstrated remarkable capability in removing per- and poly-fluoroalkyl substances (PFAS) from water. However, managing PFAS-rich RO rejects water residuals may be a significant challenge in the future due to their adverse effects on the environment and human health, what this may mean in terms of future discharge permit requirements along with any concerns regarding potential liability. In this study, we evaluated closed-circuit RO (CCRO) and membrane distillation (MD) as methods to reduce the volume of the RO residual further to reduce the compliance costs and improve the efficacy of viable residual treatment options such as advanced oxidation, crystallization, and granular activated carbon (GAC).
Description:
Reverse osmosis (RO) has demonstrated remarkable capability in removing per- and poly-fluoroalkyl substances (PFAS) from water. However, managing PFAS-rich RO reject water residuals may be a major challenge in the future due to their adverse effects on the environment and human health, and what this may mean in terms of future discharge permit requirements along with any concerns regarding potential liability. Development of effective PFAS treatment techniques for RO brine streams is an important area of research to assure that public water systems can continue to maintain discharge permits in a changing regulatory environment, and to maintain peace of mind regarding avoiding future disputes with downstream communities. In this study, we evaluated closed-circuit RO (CCRO) and membrane distillation (MD) as methods to further reduce the volume of the RO residual with the aim of reducing the compliance costs and improving the efficacy of viable residual treatment options such as advanced oxidation, crystallization, and granular activated carbon (GAC). CCRO enables high-recovery operation by recirculating the RO concentrate, while continuously recovering clean permeate water through pressure-driven membrane processes. A bench-scale RO-GAC hybrid system was constructed to demonstrate CCRO's applicability for treating RO residuals. MD is useful for treating difficult-to-treat water sources since the process is thermally driven and not limited by high osmotic pressure or concentration polarization. However, studies have found that the presence of PFAS in the feed water may cause premature membrane fouling and pore wetting due to the rapid surface diffusion of PFAS. We evaluated the benefits of crosslinking a polytetrafluoroethylene (PTFE) membrane with polyvinyl alcohol (PVA) and sulfosuccinic acid (SSA) to impart an anti-wetting property by limiting the hydrophobic interaction of PFAS's hydrophobic tails with MD membranes.