Research On Biological Removal Of Nitrogen By Paracoccus Versutus LYM Under Aerobic Condition

The traditional biological nitrogen removal usually consists of two processes as nitrification and denitrification, which have opposite tolerance to dissolved oxygen and carbon sources. The researchers found that some heterotrophic bacteria could perform aerobic denitrification, which made it possible that both nitrification and denitrification processes could occur under the same conditions.Paracoccus versutus LYM, identified from sea sludge, was a facultative bacterium. P. versutus LYM had been once confirmed to be able to convert nitrate or nitrite to N2in anaerobic conditions. Besides, less study about such kind of strain characterized with the ability of aerobic denitrification was found. The aims of the research were to study bacterial characteristics in aerobic nitrate conversion, its mechanisms of heterotrophic nitrification aerobic denitrification, and the process of simultaneous nitrification and denitrification with the presence of ammonium and nitrate (nitrite) in the solution. The main results were concluded into three parts as the following:1) P. versutus LYM was capable of aerobic denitrification. To be precise, it could convert95%NO3-N (approximately400mg/L) to N2via NO2-N in the shaking condition (150rpm,30℃). Through the optimizing experiments of aerobic denitrification, it was concluded that sodium lactate was the optimized carbon source, the ratio of C to N (w/w) was10and the incubation biomass was0.593g DCW (Dry Cell Weight)/L.2) P. versutus LYM was characterized with the function of heterotrophic nitrification aerobic denitrification. During the process, the NH4+-N removal efficiency was74.5%, and N2was the sole denitrification gaseous product. Besides, there were few accumulations of intermediate in the solution. After performing nitrogen balance tests and detecting the enzymes involved in the process, the nitrogen pathway of heterotrophic nitrification aerobic denitrification process was concluded as NH4+â†'NH2OHâ†'NO2-â†'NO3-â†'NO2-â†'N2.3) When NH4+and NO3-were present in the medium, P. versutus LYM removed both nitrogen compounds simultaneously, although there was high concentration of NO2-accumulated. Fe2+was added in the system and helped the accumulating NO2-further convert. And when sufficient carbon sources were supplied, NO2-was further removed completely. When NH4+and NO2-were present in the medium, P. versutus LYM also achieved completely nitrogen removal in the system. Nevertheless, in the absence of NH4+1-, NO2-could not be converted and the bacteria didn’t grow, either.