No abstract

The effects of alkalinity addition with different strategies on the start-up, performance, and microbial community of completely autotrophic nitrogen removal over nitrite (CANON) were investigated over 450 days. In phase I, the alkalinity was increased gradually from 300 to 2,000 mg/L to obtain the optimal range. In phase II, the reactor was restarted to verify the appropriate alkalinity value of 1,600 mg/L. The fact that it only took 90 days (phase I: 170 days) to complete the start-up of CANON in phase II demonstrated that an alkalinity value of 1,600 mg/L was suitable when the influent NH 4 + -N concentration was 200 mg/L (alkalinity/NH 4 + -N = 8:1). The slope (k = 2.00) of NH 4 + -N concentration decrease in phase II during the start-up process was significantly higher than that in phase I (k = 1.50). High removal efficiencies of NH 4 + -N (98%) and TN (80%) were attained in both phases. Specific anaerobic ammonium oxidation (anammox) activity tests showed that the anammox activity of the two phases reached 3.31 and 5.31 mg TN/(g VSSÁh), respectively.High-throughput sequencing analysis revealed that appropriate alkalinity could promote the enrichment of Candidatus Brocadia, C. Jettenia, and C. Kuenenia (total abundance of 31.96%) while effectively inhibiting Nitrospira (abundance of less than 0.50%). Practitioner Points• An alkalinity/NH 4 + -N ratio of 8 promoted the rapid start-up and stable performance of CANON. • NH 4+ -N and TN removal efficiencies of 98% and 80%, respectively, were obtained. • High alkalinity promoted the enrichment of Candidatus Brocadia, Candidatus Jettenia, Candidatus Kuenenia and inhibited Nitrospira.