Characteristics Of The Nitrifying Bacteria Population In Biofilm Of Chloraminated Drinking Water Distribution System

The nitrification occurs widely in the chloraminated drinking water distribution systems, and it leads many adverse effects, including attenuation of disinfector,the regrowth of HPC and decline of water quality. The object of this study was investing the nitrifying bacteria in the biofilm of the chloraminated drinking water distribution systems in Minhang district of Shanghai city, containing ammonia-oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). Meanwhile, the relationship between the living conditions of nitrifying bacteria and correlative parameters were studied. The main contents of this study were as follows:We sampled from the actual chloraminated drinking water distribution systems. We counted the nitrifying bacteria in biofilm by MPN-Griess method, and used other methods to analyze water parameters such as pH,temperature,ammonia-nitrogen,nitrite-nitrogen,nitrate-nitrogen,disinfector and biofilm parameters such as heterotrophic bacteria (HPC),dissoluble organic carbon (DOC) etc. The results indicated that: (1) AOB widely occurred in this chloraminated drinking water distribution systems, and its cell density was rather high, while NOB occurred only in a few of biofilm samples. (2) The disinfector had an obvious negative-effect on the cell density of AOB, also AOB promoted the decomposition of disinfector. (3) AOB had a positive effect of the growth of HPC. (4) The cell density of AOB increased as temperature and pH increased, and it promoted the increase of the nitrite-nitrogen. Meanwhile, AOB had a negative relationship between the concentration of nitrate-nitrogen and the pipe diameter.We used molecular biology techniques including PCR,DGGE and DNA sequencing to analyze the diversity of nitrifying bacteria, and studied the relationship between the diversity of nitrifying bacteria and correlative parameters. The results indicated that: (1) NOB widely occurred in all of the biofilm samples, that was obviously different from the result of MPN-Griess. (2) We had obtained 27 species of AOB and 23 species of NOB from the biofilms of this drinking water distribution system. (3) Some species of AOB, including Nitrosolobus sp., Nitrosomonadaceae bacterium, and some species of NOB, including Nitrococcus sp., Nitrite-oxidizing bacterium, existed in these water distribution systems, those were hardly detected in other drinking water distribution systems. (4) There were obvious positive relationships between the diversity of nitrifying bacteria and some environmental parameters, such as the concentration of disinfector,temperature and pH.For predigesting the environmental condition, we used simulant experiments to study some important characteristics of nitrifying bacteria, including the effect of AOB on the attenuation of disinfector, the promotion of the regrowth of HPC and the conglutination of AOB. The results indicated that: (1) Mainly, AOB had stronger resistance of disinfector than HPC. The mechanism of AOB promoting attenuation of disinfector was different from HPC, because AOB can live on chloraminate. (2) AOB can produce organic substances during its growth, and those organic substances can be used by HPC for its growth, so AOB has potential role of accelerating the regrowth of HPC. (3) The adsorption of AOB was also stronger than HPC.