PFAS reduction during biosolids drying correlates to initial moisture content and is accompanied by detection of PFAS in dryer condensate

Abstract

Land application of biosolids has come under scrutiny for its potential to convey PFAS. Some water resource recovery facilities (WRRFs) have been forced to choose between implementing more extensive biosolids treatment technologies to achieve regulatory limits or altering their biosolids handling approach. Many novel biosolids treatments for PFAS removal include advanced thermal processes such as pyrolysis or gasification. Such processes require drying of biosolids as a preparatory step for treatment. However, little is known about the isolated impact of biosolids drying on the removal of PFAS from biosolids, or what fate PFAS may undergo during the drying process. The objective of this research was to elucidate how biosolids' PFAS profiles change due to drying, and to understand if PFAS can be transported with the gaseous vapor phase into liquid condensate. Biosolids were collected from five WRRFs and dried in a lab-scale oven. Additionally, biosolids from one of the WRRFs were dried in a system that captured and condensed vapor in a methanol impinger. Analysis of the PFAS profiles of the biosolids before and after drying indicated an average of 58% reduction in detectable PFAS across all sites, with the range being 43–74%. A positive correlation was established between the initial moisture content of the biosolids and reduction in detectable PFAS (R² = 0.61). The condensate contained 12–22% of the initial PFAS from the wet biosolids, indicating that PFAS can leave with the gas-phase vapor generated during drying. This research supports the conclusion that biosolids drying can reduce detectable concentrations of PFAS, and operational parameters could be adjusted to optimize dryers for this purpose. Treatment technologies could then be applied to the condensate to destroy the PFAS contained therein.