Pilot Studies of Per- and Polyfluoroalkyl Substances (PFAS) Removal From Drinking Water with Membranes and Treatment of Membrane Concentrate

Per- and poly-fluoroalkyl substances (PFAS) are man-made fluorinated compounds of emerging concern in the water industry. PFAS are persistent and stable in the environment due to the strong chemical bond between carbon and fluorine atoms. The City of Greensboro (City) in North Carolina detected PFAS in their finished drinking water as a result of the Third Unregulated Contaminant Monitoring Rule (UCMR) with combined levels of PFOS and PFOA sometimes exceeding 100 ng/L. The City utilizes a surface water source and treats water using conventional treatment. The City desires to reduce PFAS in their drinking water by constructing an advanced treatment process after dual-media filtration. As part of this effort, HDR and the City is performing a pilot study to evaluate nanofiltration (NF) and reverse osmosis (RO) membranes among other technologies for the removal of PFAS, 1,4-dioxane and other emerging contaminants. NF and RO were selected for evaluation because of their ability to produce permeate with very low concentrations of multiple contaminants. To avoid the reintroduction of PFAS into the environment, membrane concentrate from the pilot is conveyed to a pilot column system, known as the “membrane concentrate pilot”, which will operate alongside the membrane pilot. This is the first known pilot-scale study performed for the removal of PFAS from membrane concentrate. Pilot test planning is complete and procurement/installation is in progress, and the pilots will operate for one year starting from October 2021. The membrane pilot simulates a two-stage 2:1 array membrane system and receives 16 – 30 gallons per minute of filtered water from the WTP. Part of the pilot study includes operating at various recoveries to determine the impact of recovery on membrane performance and recycling concentrate to evaluate higher PFAS loadings.

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