Abstract
Microbial community structure in a G3-type Down-flow Hanging Sponge (DHS) reactor was investigated by rRNA approach. Cloning analyses indicated that the microbial community structure was successionally changed along with the height of the reactor. Dechloromonas sp. was predominant at the upper portion of the reactor, indicating contribution of this group to organic removal. Ammonia-and nitrite-oxidizers were quantified by quantitative real-time PCR, which revealed that the populations of both groups gradually increased along with the height of the reactor. A part of reasons for stable treatment of the DHS reactor is found by the microbial community structure analysis.