Fate of Triclocarban, Triclosan and Methyltriclosan during wastewater and biosolids treatment processes

Abstract

Triclocarban (TCC) and Triclosan (TCS) are two antibacterial chemicals present in household and personal care products. Methyltriclosan is a biodegradation product of TCS formed under aerobic conditions. TCC and TCS are discharged to Waste Water Treatment Plants (WWTP) where they are removed from the liquid phase mainly by concentrating in the solids. This study presents a thorough investigation of TCC, TCS and MeTCS concentrations in the liquid phase (dissolved + particulate) as well as solid phases within a single, large WWTP in the U.S. Total TCC and TCS concentrations decreased by >97% with about 79% of TCC and 64% of TCS transferred to the solids. The highest TCC and TCS removal rates from the liquid phase were reached in the primary treatment mainly though sorption and settling of solids. The TCC mass balances showed that TCC levels remain unchanged through the secondary treatment (activated sludge process) and about an 18% decrease was observed through the nitrification–denitrification process. On the other hand, TCS levels decreased in both processes (secondary and nitrification–denitrification) by 10.4 and 22.6%, respectively. The decrease in TCS levels associated with observed increased levels of MeTCS in secondary and nitrification–denitrification processes providing evidence of TCS biotransformation. Dissolved-phase concentrations of TCC and TCS remained constant during filtration and disinfection. TCC and TCS highest sludge concentrations were analyzed in the primary sludge (13.1 ± 0.9 μg g−1 dry wt. for TCC and 20.3 ± 0.9 μg g−1 dry wt. for TCS) but for MeTCS the highest concentrations were analyzed in the secondary sludge (0.25 ± 0.04 μg g−1 dry wt.). Respective TCC, TCS and MeTCS concentrations of 4.15 ± 0.77; 5.37 ± 0.97 and 0.058 ± 0.003 kg d−1 are leaving the WWTP with the sludge and 0.13 ± 0.01; 0.24 ± 0.07 and 0.021 ± 0.002 kg d−1 with the effluent that is discharged.