[Start-up and Characteristics of the Microbial Community Structure of ANAMMOX]

An anaerobic ammonium oxidation (ANAMMOX) reactor was successfully started up in 17 days, with the up-flow anaerobic sludge blanket (UASB) reactor being seeded with mixed anaerobic sludge from laboratory cultures with an ANAMMOX function and aerobic activated sludge from a municipal sewage treatment plant in a volume ratio of 1:2. The processes could be divided into two phases of hydrolysis, enhanced and steady. Anaerobic ammonium oxidation bacteria (AAOB) were enriched by improving the reactor volume load gradually after the steady phase. When the volume load increased from 0.10 kg·(m³·d)^-1 to 0.44 kg·(m³·d)^-1, the removal of total nitrogen (TN) also increased from 0.09 kg·(m³·d)^-1 to 0.42 kg·(m³·d)^-1. The color of the sludge changed from a light red that deepened gradually in the UASB reactor. At that time, the proportion of the sludge particle size greater than 0.2 mm increased from 10.90% to 38.37%.The sludges from the inoculation phase and from the phase when the volume load was increasing were analyzed by high-throughput sequencing, indicating that Chloroflexi, Proteobacteria, WWE3, Actinobacteria, Planctomycetes, and so on were the dominant species. The proportion of Proteobacteriain the denitrification bacteria was gradually reduced from 21.60% to 14.20% with an increase in the degree of AAOB enrichment, while the Planctomycetes increased from 0.73% to 15.50%. Candidatus Brocadia, Candidatus Jettenia, and Candidatus Kuenenia were the main species of Planctomyceteswhen the volume load increased to 0.44 kg·(m³·d)^-1 in the reactor, and the Candidatus Brocadia was the main species of AAOB, which accounted for 13.40%.