Roxarsone exposure jeopardizes nitrogen removal and regulates bacterial community in biological sequential batch reactors.

Roxarsone is widely present in wastewaters of many animal farms in China. However, little is known about how long-term roxarsone exposure influences the nitrogen removal of biological wastewater treatment in agricultural settings. Here we investigated the nitrogen removal performance of a biological sequential batch reactor (SBR) and the changes of bacterial community, upon long-term roxarsone exposure. The long-term roxarsone dosing decreased the SBR nitrogen removal by 52.4%, with an immediate inhibition on denitrification and a delayed inhibition on nitrification. The analyses of bacterial enzymatic activities and 16 S rRNA sequencing revealed that bacterial activities generally decreased, and the nitrogen-cycling bacterial community was changed, particularly by the decrease (Acinetobacter and Methylophilaceae), persistence (Flavobacterium and Methylotenera), and emergence (Aeromonas) of certain bacterial genera. Overall, chronic roxarsone exposure could suppress nitrification and denitrification, which may even have broad implications on the use efficiency and cycling of nitrogen in agroecosystems.