Perfluoroalkyl acids (PFAA) are a persistent and potentially toxic group of chemicals whose presence is increasingly detected in drinking water across the United States, especially in potable reuse systems. Among several technologies evaluated for mitigating PFAA, sorption onto granular activated carbon media has been found to be a promising treatment technique. In this work, bench-scale testing of biochar, a potential alternative adsorbent and a low-cost carbon residue derived from the pyrolysis of waste biomass, was conducted to determine its sorption ability for two PFAA, perfluorooctanoic acid (PFOA), molecular weight of 414.07 g/mol and perfluorobutanoic acid (PFBA), molecular weight of 214.04 g/mol. Sorption of PFBA and PFOA to two biochars, pinewood and hardwood biochars was evaluated in batch sorption experiments using advanced tertiary treated wastewater effluent from a full-scale wastewater treatment facility and Lake Mead water in Nevada. Sorption kinetics of PFOA and PFBA on both biochars was determined by spiking 1000 ng/L PFOA or PFBA into sample bottles containing the tertiary treated wastewater effluent, and mixing the solution with 50 mg of biochar on a shaker for 30 days. PFOA sorption capacity of pinewood and hardwood biochars in different water matrices was also evaluated in batch sorption isotherm experiments using 0.01 – 100000 µg L-1 PFOA solution. Results from the batch sorption kinetic experiments showed that PFOA was better sorbed on pinewood and hardwood biochars than PFBA. Pilot-scale tests were performed to compare PFAA removal efficiency on hardwood biochar to two other carbon media; anthracite, and granular activated carbon. For the pilot tests, the same tertiary-filtered wastewater used in the batch tests was fed to a Pilot filtration skid located at the full-scale water treatment facility in Las Vegas. Each of the three filter columns containing the three carbon media were operated at the same target flow rate of 1.77 GPM (gallons per minute) and loading rate of 9 GPM/ft2. Ambient PFAA levels in the aqueous phase across the filters were monitored by collecting monthly samples from the filter influent and effluents over a 1 year period. Break-through and performance data from the pilot tests suggest that the fate of PFAA during sorption on granular carbons is dependent on the carbon media type and the structural properties of PFAA such as functional groups, carbon chain length, and hydrophobicity/hydrophilicity.

Removing perfluoroalkyl acids from potable reuse systems using carbon adsorbents: Bench-scale and pilot testing

251st National Meeting (2016)

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