Microbial characteristics of a CANON reactor during the start-up period seeding conventional activated sludge.

An up-flow oxygen-controlled biofilm reactor filled with volcanic filter was used for a completely autotrophic nitrogen-removal over nitrite (CANON) process. The reactor was successfully established by seeding conventional activated sludge at ambient temperature without additional biomass inoculation. An average total nitrogen (TN) removal rate of 1.1 kg·(m(3) d)(-1) was achieved after 180 days' operation. The bacterial morphology, community structure and spatial distribution of nitrogen removal microorganisms were analyzed by using some molecular biotechniques. Denaturant gel gradient electrophoresis (DGGE) profiles showed a distinct community shift of nitrite oxidizing bacteria (NOB) during the start-up period, which was not the same as that of aerobic ammonium-oxidizing bacteria (AerAOB) or anaerobic ammonium-oxidizing bacteria (AnAOB). Phylogenetic results indicated the predominance of Nitrosomonas, 'Candidatus Brocadia fulgida' and Nitrobacter for nitrogen removal in the system, all of which coexisted without a distinguishable niche on the biofilm.