[Community Structure and Activity Analysis of the Nitrifiers in Raw Sewage of Wastewater Treatment Plants]

The communities and activity of nitrifiers collected from the raw sewage of the 2^nd and 3^rd wastewater treatment plants (WWTP) in Xi'an were investigated. FISH results indicated that the (AOB+NOB)/EUB percentages were (5.35±2.1)% and(6.0±2.8)% in the 2^nd and 3^rd WWTP, respectively. The dominant AOB was Nitrosomonas europaea/Nitrosococcus mobilis lineage and the dominant NOB was Nitrospira, the sub-dominant NOB was Nitrobacter, and coexisted with Nitrococcus, Nitrospina. Respirometric assays showed that the influent nitrifiers were active following a 2-16 hour period of metabolic induction. The ammonium utilized rate was (0.32±0.12) mg·(L·h)^-1 and (0.43±0.17) mg·(L·h)^-1, nitrite utilized rate was (0.71±0.18) mg·(L·h)^-1 and (0.58±0.27) mg·(L·h)^-1 for nitrifers in raw sewage fed to the 2^nd and 3^rd WWTP, respectively. Therefore, nitrifiers were present and active in the raw sewage, and played the role of natural continuous seeding in the activated sludge system. Based on the nitrification activity, the estimated continuous seeding intensity of AOB and NOB was 0.08-0.09 g·(g·d)^-1 and 0.11-0.24 g·(g·d)^-1, respectively.