HIGH RESOLUTION PER AND POLYFLUOROALKYL SUBSTANCE MASS BALANCE IN A WASTEWATER TREATMENT PLANT POST AQUEOUS FILM FORMING FOAM SPILL

First-generation, PFOS-dominant Aqueous Film Forming Foam (AFFF) concentrate of approximately 200 gallons was released to the sewer system from the Kalamazoo/Battle Creek International Airport on March 30, 2021. The AFFF release migrated to the Kalamazoo Water Reclamation Plant (KWRP), raising plant effluent above the Department of Environment, Great Lakes, and Energy (EGLE) PFOS water quality standard for a total of 46 days post-spill, although the influent concentrations exhibited sharp declines after only 7 days. By sampling influent, effluent, and biosolids daily, the only known long duration, high-frequency PFAS data set of an accidental AFFF release was generated. This study has four primary objectives: (i) identify AFFF released from the airport by comparing influent PFAS composition ratios to those of AFFF from different manufacturers; (ii) perform a plant-wide mass balance to discern how PFAS, and in particular PFOS, moves through and leaves the plant; (iii) provide constraints on the mass balance by estimating the aqueous volume of the AFFF release; and (iv) determine plant mechanisms responsible for 46-day PFOS exceedance of EGLE water quality standard in effluent. This study is the first of its kind to show that a mass balance for an accidental PFAS release is feasible given sufficient sampling resolution and laboratory consistency. Results from the mass balance indicate 1227 grams of PFOS entered the plant as influent, 704 grams of PFOS (54% of total output) discharged into the Kalamazoo River as effluent, and 610 grams of PFOS (46% of total output) sorbed to biosolids and landfilled. PFOS output mass is 84 grams (7%) higher than input PFOS mass; this apparent discrepancy may indicate PFOS generation within the KWRP due to chemical transformations of precursors. Identification of the AFFF formulation and spill volume constrained the mass balance and increase the confidence of the study results. Recirculatory processes are likely responsible for the extended exceedance of the EGLE water quality standard. These findings provide critical insight to wastewater treatment plant operators worldwide for performing PFAS mass balances and developing operational procedures for accidental PFAS releases that minimize PFAS mass releases to the environment.