Removal Of TCS In Two Typical Sewage Treatment Systems

Triclosan (TCS) is a kind of synthetic chlorinated aromatic compound which is widely used in industrial and personal care products as a broad-spectrum antibacterial and antifungal agent. The worldwide TCS application exceeds 1500 tons per year, and it has been detected in various environmental samples. Owing to its high hydrophobicity, biological cumulative, persistence and biological toxicity, TCS is harmful to the aquatic organisms, mammals, human, and even the soil ecosystem. Environmental issues caused by TCS have become one of the environmental focuses. Because conventional wastewater treatment plants are lack of specific technology for TCS, concentrations of TCS in the effluent is still high, so a better way for TCS removal need to be learned.The main objective of this study was to assess the TCS removal performance in two typical sewage treatment systems:constructed wetland and simultaneous nitrification and denitrification (SND) system. Three species of wetland plants-emergent plant (Cattail), submerged plant (Hornwort) and floating plant (Lemna minor) were used to build constructed wetlands, individually. TCS removal mechanisms in these constructed wetlands and SND systems were studied and the main conclusions are as follows:(1) TCS removal efficiencies from water in three constructed wetlands were all greater than 97%. The contribution rates for TCS removal by sorption of sediments and plants in Tornwort and Lemna wetlands were 44.78% and 40.25%, which were significantly higher than that in the Cattail wetlands (29.12%), suggesting that sorption played an important role for TCS removal in Tornwort and Lemna wetlands.(2) Cattail wetlands had the highest microbial community richness and diversity. Some bacteria that were shown to correlate with TCS biodegradation, like beta-Proteobacteria, gamma-Proteobacteria and Bacteroidetes were detected and their OUTs in Cattail wetlands is 20.98%-117.92% more than in Tornwort and Lemna wetlands. This shows that microbial biodegradation had significant correlations with TCS removal in Cattail wetlands.(3) TCS removal efficiencies were more than 93% in stabilized SND systems. And the contribution rate for TCS removal by the water effluent, sludge sorption and biodegradation are 1.27%,6.46% and 92.27%, respectively. Firstly when TCS was added, it was removed through sorption to the sludge solids. After the adsorption of TCS saturated and microorganisms in SND gradually adapted to TCS, biodegradation gradually contributed more to TCS removal.(4) Water quality deteriorated in SND systems after TCS was added, as removal rate of NH4+-N droped from 100% to 88.3% and COD decreased from 95.15% to 65.81%. Then they gradually recovered and stabilized on the 14th day when the bacteria were gradually adapted to TCS. Furthermore, microbial community richness increased after TCS was added. OUTs of alpha-Proteobacteria, beta-Proteobacteria and Bacteroidetes that were related to TCS biodegradation increased by 4.79%, 19.13% and 13.31%, respectively.