Response of partial nitritation-anammox process to substrate concentration and temperature variations in a single-stage airlift circulation system: Performance and microbial community dynamics

Abstract

Low-strength ammonia and temperature challenge the application of partial nitritation-anammox (PNA) process in the treatment of mainstream wastewater. In this study, we operated a single-stage PNA process under various substrate concentrations (250, 150, and 50 mg/L) and temperatures (32, 25, 15 °C). Changes in nitrogen removal performance, biochemical reaction rate, and specific activity were investigated via the long-term continuous experiment and batch tests. Microbial diversity, community structure, and metabolic pathways in response to the various conditions were explored. When the temperature declined to 15 °C, the nitrogen removal efficiency decreased from 83.9 % to 51.5 % with the influent of 50 mg-NH4/L, while the nitrogen removal rate dropped to 0.33 kg N/m3/d. Meanwhile, the relative abundances of Candidatus Brocadia and Nitrosomonas reached 14.1 % and 1.5 %, respectively. The results showed that the mechanisms of performance degradation caused by low ammonia concentration and low temperature were significantly different. Moreover, the substrate concentration mainly affected the reaction rate and activity of anammox bacteria and hardly affected the relative abundance of functional bacteria. But temperature reduction resulted in a significant decline in the relative abundance of anammox bacteria. Changes in metabolic pathways suggested that this PNA system may respond to low substrate concentrations and low temperatures by facilitating substance transport and reducing energy consumption. These results provide a deep insight into the microbial community dynamics and interactions in the treatment of mainstream wastewater by PNA process.