Fate of triclosan, triclocarban, and their transformation products in wastewater under nitrifying conditions

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: Journal of Water Process Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2019
Publication Date: 2/2/2019
Citation: Armstrong, D.L., Lozano, N., Rice, C., Ramirez, M., Torrents, A. 2019. Fate of triclosan, triclocarban, and their transformation products in wastewater under nitrifying conditions. Journal of Water Process Engineering. 28:144-151.

Interpretive Summary: Many waste water treatment plants (WWTPs) have installed nitrification/denitrification steps in the treatment systems to reduce nitrate releases from their discharges. Few studies exist on the extent to which these systems separately contribute to enhanced removal of trace contaminants that are released in discharges from WWTPs. This study was designed to separately study the nitrification stage. Bench scale bioreactors were loaded with sample materials collected just prior to entry into the in-plant nitrification/denitrification stage and substrate nitrification was contintued at neutral and basic pH ranges for 7 days. Rates of removal of triclosan (TCS) where similar to published studies and formation of the metabolite, methyltriclosan, was also observed. Both of these reactions were faster in the basic pH treatments. No other metabolites of TCS were observed. However, TCC did not degrade at either pH which contrasts with whole system nitrification/denitrification reports where TCC degraded. The results suggest that plant operations would gain improved removal of TCS using basic pH in the nitrification reactor stage, however, only moderate removal would occur with longer retention times. This information will be useful to scientists devising waste water treatment strategies.

Technical Abstract: The nitrification process was simulated using benchtop bioreactors to gain insight into the fate of the antimicrobials, triclosan (TCS) and triclocarban (TCC), as well as their transformation products, during wastewater treatment. Reactors were run using samples collected from a large municipal wastewater treatment plant at two pH ranges (6.5 – 7.5 and 8.5 – 9.5) for 171 hours to simulate an extended hydraulic retention time (HRT). TCS was degraded under both pH conditions; with a 28.5% overall reduction of TCS in solids samples when the range was 6.5 – 7.5 and an overall reduction of 83.2% in TCS in solids samples when the pH ranged 8.5 – 9.5. Methyltriclosan (MeTCS) was formed during both treatment configurations. Concentrations of MeTCS in solids during nitrification increased at a rate of 0.00985 ± 0.007 h-1 for the first 98 h under a pH range of 6.5 – 7.5, while at a pH range of 8.5 – 9.5 MeTCS was formed at a rate of 0.0174 ± 0.005 h-1 during the first 25 hours of treatment and a rate of 0.00190 ± 0.002 h-1 thereafter. Levels of 2,4-dichlorophenol, a TCS photolysis product, and TCC did not change over the 171 h treatment period, indicating that nitrification is not an effective treatment for reduction of these compounds.