Performance evaluation, enzymatic activity change and metagenomic analysis of sequencing batch reactor under divalent zinc stress.

Divalent zinc (Zn) are widely detected in domestic and industrial wastewater, and it is essential to evaluate the effect of Zn on wastewater biological treatment process due to its bio-toxicity. In this study, the nitrogen removal rates and their corresponding enzymatic activities of sequencing batch reactor decreased with the increase of Zn concentration. The Zn accumulation in activated sludge caused significant antioxidant response, and the reactive oxygen species (ROS) production and antioxidant enzymatic activities were positively correlated with Zn concentration. The presence of Zn inhibited the metabolic pathways related to energy production and electron transport. The abundance decreases of nitrification and denitrification functional genes led to the deterioration of nitrogen removal performance under Zn stress. The correlation analysis between functional gene modules and microbial genera revealed that Zoogloea had obvious Zn resistance. This study can provide the insights into the influencing mechanism of Zn on the biological nitrogen removal process.