Degradation of triclosan and triclocarban and formation of transformation products in activated sludge using benchtop bioreactors

Authors: ARMSTRONG, DANA - University Of Maryland; LOZANO, NURIA - University Of Cantabria; Rice, Clifford; RAMIREZ, MARK - District Of Columbia Water & Sewer Authority (DCWASA); TORRENTS, ALBA - University Of Maryland

Submitted to: Environmental Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2017
Publication Date: 1/10/2018
Citation: Armstrong, D.L., Lozano, N., Rice, C., Ramirez, M., Torrents, A. 2018. Degradation of triclosan and triclocarban and formation of transformation products in activated sludge using benchtop bioreactors. Environmental Research. 161:17-25.

Interpretive Summary: Waste Treatment Plants (WWTPs) are looking for ways to improve trace contaminant processing, especially in view of recent reports that large numbers of pharmaceutical and personal care products are escaping from these plants. Activated sludge treatment is a common step at most treatment plants. These processes normally last less than a day. Modifying this process by lengthening treatment and temperature was researched by us as a tool for improved removal of two high-release personal care products, triclocarban and triclosan. To conduct the experiment, two commercial bioreactor systems were run with activated sludge for up to 8 days and at 20 and 30 degrees centrigrade. TCC was found to only decrease in quantity at the higher temperature while TCS disappeared from both reactors, and at an increased rate with the higher temperature. A substantial transformation of TCS to MeTCS was also observed after 4 days, especially at the higher temperature. Six other degradates of these two compounds were sought but only 2,4-dichlorophenol from TCS and 4-chloroanline from TCC were observed at very low concentrations. The increased removal of these compounds at longer treatments and higher temperatures is encouraging as a way to clean effluents. However, the high production of MeTCS is problematic since this compound has a high bioaccumulation potential and is known to have endocrine disruption properties.

Technical Abstract: Benchtop bioreactors were run aerobically with activated sludge samples collected from a large municipal wastewater treatment plant (WWTP) to understand how increased hydraulic retention time (HRT) and varying treatment temperatures (21°C and 30°C) impact concentrations of the endocrine disrupting antimicrobials triclosan (TCS), triclocarban (TCC), and their transformation products. Samples from the reactors were collected periodically over a 122 to 196 h period and the solid and liquid fraction were separately quantitated for TCS, TCC, and methyltriclosan (MeTCS), and scanned qualitatively for six other transformation products. Results indicated that TCS, TCC and MeTCS were predominately associated with the solids fraction of the activated sludge with only nominal concentrations in the liquids fraction. TCS was degraded in the solids fraction, with increased rates at 30°C (-0.0224 ± 0.007 h-1) when compared to reactors run at 21°C (- 0.0170 ± 0.003 h-1). Conversely, TCC concentrations did not significantly change in solids samples from reactors run at 21°C, while an increase in reactor temperature to 30°C resulted in TCC degradation at an average rate of -0.0158 ± 0.012 h-1. Additionally, MeTCS formation in the solids fraction was observed in three out of four reactors run, indicating a notable transformation of TCS. Qualitative appearance of 2,4-dichlorophenol and 4-chloroanaline was observed in the liquids fraction of all reactor samples. The remaining four qualitatively analyzed compounds were not detected. These experiments demonstrate that increased HRT and temperature result in enhanced removal of TCS and TCC from wastewater during the activated sludge process. Furthermore, a substantial transformation of TCS into MeTCS was observed.