Molecular mechanism of adsorbing triclocarban by the activated sludge in wastewater treatment systems

The ubiquitous use of antimicrobial triclocarban (TCC) has raised widespread concern about the potential im-pacts on wastewater treatment systems, the environment, and the human population. As important constituents of activated sludge secretions, extracellular polymeric substances (EPS) play essential roles in removing micropollutants during wastewater treatment. Here, the adsorption of TCC by sludge and EPS in a multistage biological process was investigated. The EPS was enriched upon TCC stress, and the adsorption by sludge and EPS showed multilayer heterogeneity. The adsorption constant Kf (6.3794-7.6061) of EPS was over 10 times higher than that of sludge (0.5661-0.6200) in all stages, potentially owing to the loose multilayer structure and sub-stantial functional groups (tryptophan-protein as the main binding site) in EPS. TCC significantly inhibited the biological removal of ammonia nitrogen. Notably, TCC once reaching the cell surface, formed a stable complex with ammonia transporter (Amt, binding energy:-73.1 +/- 16.6 kJ center dot mol-1) and bound to the selectivity filter vestibule of Amt (tryptophan 144 and serine 227), inhibiting the transport of ammonia. Our work drew molecular-level insights into the interaction between TCC and activated sludge, and evaluated the adverse im-pacts on treatment performance through an in silico approach, providing new information on the fate and risk of TCC in wastewater treatment systems.

Automated summary

The widespread use of the antimicrobial substance triclocarban (TCC) has raised concerns about its impacts on wastewater treatment systems, the environment, and human health. This study investigated the adsorption of TCC by sludge and extracellular polymeric substances (EPS) in a multistage biological process. The results showed that EPS had a higher adsorption capacity for TCC than sludge, potentially due to its loose multilayer structure and abundant functional groups. TCC also had adverse effects on the biological removal of ammonia nitrogen. Our study provides molecular-level insights into the interaction between TCC and activated sludge, and evaluates the risks associated with its presence in wastewater treatment systems through computational modeling.