Quaternary Ammonium Compounds in Wastewater Influents, Effluents, and Biosolids: Analysis from Twelve Wastewater Treatment Plants from 2020 to 2023

Quaternary ammonium compounds (QACs) are high production volume chemicals used in consumer and industrial products, including disinfectants. Influent, effluent, and biosolid samples were collected from 12 wastewater treatment plants (WWTPs) from 2020 to 2023 and analyzed for 21 QACs to assess influent loadings and discharges to the environment via effluent and biosolids. The median total QAC concentrations in liquid influents ranged from 18 to 194 μg/L, while liquid effluent concentrations were substantially lower (0.15 to 1.1 μg/L). Median biosolid concentrations were substantial (26–430 mg QAC/kg solids dry wt; maximum ∼1 g/kg). For many WWTPs, the mass loadings of QACs in biosolids were of similar magnitude as those in influents, indicating that sorption plays a large role in the removal of QACs. At most plants, ≥98% of QACs were removed by a combination of sorption (9–72%) and degradation (28–91%). One plant that used aerobic digestion had only 1% of the initial QACs in the biosolids. On a national scale, 1900 tons of QACs were estimated to enter WWTPs in liquid influents annually, 30 tons were estimated to be discharged with liquid effluents, and 770 tons were estimated to leave with biosolids, of which 640 tons are land applied or landfilled.