Formatted Title
Use of High-Pressure Membranes for the Industrial Pretreatment of PFAS in Semiconductor Wastewater
Background/Objectives
Publicly-owned treatment works (POTWs) may soon be subject to discharge limits of per- and polyfluoroalkyl substances (PFAS). While treatment at the plant is possible, many technologies for PFAS removal were developed for relatively clean groundwater sources and may be negatively impacted by the elevated levels of dissolved organic carbon (DOC), nutrients, and other compounds present in municipal wastewater. To minimize the burden of treatment on POTWs, efforts should be made to address high concentration industrial discharges prior to their release into the collection system. One potential point source of PFAS to POTWs is effluent from semiconductor fabrication facilities (FABs). A variety of PFAS, including ultrashort compounds whose fate is poorly understood, are present in chemical additives that are used in the manufacturing process and acceptable non-fluorinated replacement compounds have not been identified for many applications. Implementation of technologies for industrial pretreatment that effectively remove the broadest range of PFAS is essential to limit the mass of PFAS in the source waters of POTWs.
Approach/Activities
Laboratory-scale experiments with synthetic FAB wastewater were performed using a flat sheet filtration cell to compare rejection of PFAS and pertinent co-contaminants by multiple membranes. The optimum membrane was then used in a pilot-scale system employing spiral wound membrane modules to treat synthetic and real wastewater collected from an operating FAB in the U.S. Pilot system experiments evaluated the impact of varied operating conditions and strategies for maximizing water recovery. Additional experiments were performed to identify the impact of carbon chain length, adsorption, and charge on PFAS rejection. These data were incorporated into empirical and mechanistic rejection models to develop an improved understanding of relationships between feed water composition, membrane characteristics, and system performance.
Results/Lessons Learned
A tight nanofiltration (NF) membrane was identified as the optimum membrane due to its high PFAS rejection and lower required feed pressure when compared to reverse osmosis membranes. The membrane was able to achieve >97% rejection of all PFAS evaluated at the bench scale including the ultrashort chain compound trifluoromethane sulfonic acid (TFMS). The collected FAB wastewater was dominated by shorter chain perfluorocarboxylic acid (PFCAs) including the C1 compound trifluoroacetic acid (TFA). High PFAS rejection was also seen in the pilot system, with improved rejection in the real wastewater when compared to the synthetic wastewater at water recoveries up to 90%. Additional data on the rejection of ultrashort chain compounds will be presented along with results from the modeling efforts. Use of high-pressure membranes for the removal of PFAS presents an opportunity for pretreatment of industrial waste streams, decreasing the level of treatment required at POTWs.