Nitrification and nitrifying bacteria in the Chengdu section of middle Min river (China)

The Min River is one of the most important tributaries of the upper Yangtze River. Its middle reach, below Chengdu city, receives large numbers of effluents from Sanwayao wastewater treatment plant (WWTP), where ammonia concentration raises significantly. In this study, the situation of ammonia pollution, nitrification and nitrifying bacteria in the Min River was studied during the year 2007 to 2008. Nitrifying activity was assessed under optimum conditions based on the background ammonia concentration and abundance of nitrifying bacteria was measured by the real time quantitative-polymerase chain reaction (RTQ-PCR). The community composition of ammonia-oxidizing bacteria (AOB) was investigated with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S ribosomal DNA fragments. The results showed that the ammonia contamination of the Chengdu section of the middle Min River was severe. Nitrification mainly takes place in the 30 km reach of the lower river, where the numbers of nitrifying bacteria are relatively more than those in the upper river do. The sequence analysis of the DGGE bands reveals that the majority of AOB presenting in the river belong to lineage 2, represented by Nitrosomonas oligotropha-and Nitrosomonas ureae-like bacteria. The rest of the AOB population is represented in minor proportions by Nitrosospira-like species.