Fate of PFAS Through a Biosolids Drum Dryer With Regenerative Thermal Oxidizer Emissions Control

Thermal dryers are commonly used for biosolids volume reduction and stabilization, but the fate of PFAS in these systems is not well understood. Triplicate samples from a full-scale rotary drum dryer were evaluated, including gas-phase emissions before and after a regenerative thermal oxidizer used for emissions control. Substantial PFAS removal between the feed and dried solids (60.0% on a total molar basis for targeted PFAS) was observed. PFAS did not accumulate in the drain water from wet scrubbers treating dryer exhaust. The scrubbed exhaust contained six orders of magnitude less PFAS than the dewatered feed solids on a total molar mass basis. The destruction or removal efficiency of PFAS across the RTO was complicated by contaminant-prone and thermally unstable HFPO-DA, achieving 93.5% when including the suspect compound and 99.3% when not. Further research is needed to identify potential transformation mechanisms and products to close the PFAS balance across drying processes.