Removal of triclosan during wastewater treatment process and sewage sludge composting-A case study in the middle reaches of the Yellow River

Triclosan (TCS) is widely used as an antibacterial disinfectant in personal care products, especially in rapidly-urbanizing countries, such as China. Almost all TCS enters wastewater treatment plants (WWTPs), but the fate of the TCS in the WWTPs is unclear. TCS may be present in sewage sludge or in effluent, and the discharge of TCS into an ecosystem can pose environmental risks. In the present study, influent, effluent, and sewage sludge were collected from four typical urban WWTPs, and the fate of TCS in the plants was investigated. The study was conducted in Zhengzhou, a city in the middle reaches of the Yellow River in China. The sewage sludge was used for aerobic composting to study the influences of different ventilation treatments on the biodegradation effects of TCS and the changes in the microbial community during the composting process. The results showed that the mean concentration of TCS in the influent of the four typical WWTPs was 397.1 ng/L. The mean level of TCS in the effluent was 8.0 ng/L. The mean concentration of TCS in the sewage sludge was 814.4 ng/g. For the four WWTPs, the percentages of TCS removal were 97.6% (Nansanhuan), 97.6% (Xinzheng), 98.8% (Wulongkou), and 97.9% (Chenyu), respectively. The sewage sludge enrichment rates for TCS ranged between 36.4% and 49%. Therefore, there is a need to focus on the environmental risks from sewage sludge. During aerobic composting, the TCS was effectively degraded under three ventilation strategies. Thus, improved ventilation could enhance the degradation rate of TCS. Moreover, TCS degradation occurred in the mesophilic period and in the early stage of the thermophilic phase period. Finally, the degradation rates of TCS in sewage sludge samples composted with low-, medium-, and high-ventilation treatments were 48.1%, 59.0%, and 59.5%, respectively. Thus, high ventilation could provide enough oxygen for the pile and enhanced microorganism activity, benefiting the degradation of TCS. In addition, the microbial communities change during the composting process, and a diversity index of the changes can help explain the composting process.