Performance, microbial community and inhibition kinetics of long-term Cu²⁺ stress on an air-lift nitritation reactor...

Biological nitrogen removal process could be affected due to the presence of heavy metals owing to their toxicity and accumulation in the sludge. In this study, the impact of Cu²⁺ shock on a long-term nitritation operation was investigated in an air-lift reactor with self-recirculation. Both the dynamics of microbial community and inhibition kinetics under Cu²⁺ stress were ascertained. The results showed that Cu²⁺ exerted severe inhibition on nitritation performance of an air-lift reactor (ALR) at 25 mg/L. The corresponding NH₄⁺-N removal efficiency decreased to below 50%, which was mainly due to the variation of microbial community structure, especially the inhibition of nitrifiers like Nitrosomonas (the relative abundance decreased from 30% to 1% after Cu²⁺ inhibition). Kinetic parameters were obtained and compared after fitting the Haldane model. The long-term Cu²⁺ stress on the ALR aggravated the ammonium affinity and the resistance to substrate self-inhibition of the nitritation sludge, but reduced the resistance to Cu²⁺ inhibition. Furthermore, Cu²⁺ acted as uncompetitive inhibitor on nitritation process. Our results provide new insights into the nitritation characteristics under long-term Cu²⁺ stress.