Isolation And Nitrogen Removal Characteristics Of A Heterotrophic Nitrifying Bacterium YL

In recent years, since excessive nitrogenous wastewater discharges randomly that cause increasingly serious water environmental pollution. The biological nitrogen removal is one of the most economical and effective ways in nitrogen removal field. The traditional nitrogen removal method based on the processes of aerobic autotrophic nitrification and anaerobic heterotrophic denitrification. However, this system usually exhibits the disadvantages of long procedure and low efficiency. Recently, more and more heterotrophic nitrification bacteria have been isolated. These bacteria usually exhibit higher growth rates and biological activities, can use extensive substrates as carbon sources, and most of them have the ability of heterotrophic nitrification and aerobic denitrification simultaneously. Therefore, heterotrophic nitrification has become the research focus in nitrogen removal field. In present study, a heterotrophic nitrification–aerobic denitrification bacterium YL was isolated from a Sequencing Batch Reactor(SBR) with efficient nitrification and denitrification ability. Meanwhile, its characteristics of nitrogen removal were investigated through the single–factor experiments and orthogonal test. Furthermore, the application potential of strain YL in synthetic wastewater treatment was investigated, which provide the theoretical basis for future practical applications. The main research results are as follows:(1) A heterotrophic nitrifying bacterium YL was isolated and was identified as Pseudomonas aeruginosa YL through morphological observation, biochemical characteristics and molecular biological identification.(2) The preferred conditions of heterotrophic nitrificationby strain YL were succinate as the carbon source, C/N ratio of 10, pH of 7.0, temperature of 30℃, and the shaking speed of 160~200 r/min. And strain YL was able to tolerate the high-strength of ammonium concentrations. Meanwhile, the hydroxylamine could be metabolized by strain YL with the intermediate products of nitrite and nitrate. After 48 h cultivation, the removal efficiencies of hydroxylamine and total nitrogen were 94.8% and 90.4%, respectively.(3) Stain YL had the abilities to utilize high concentration of nitrite(200 mg/L) and nitrate(200 mg/L). The accumulation of intermediate products, ammonia and nitrate, were observed in the process of removal of nitrite. By 48 h, the removal rates of nitrite and total nitrogen were 92.7% and 91.9%, respectively. In the process of removal of nitrate, the formation of nitrite was detected, and the removal rates of nitrate and total nitrogen were 93.6% and 63.4% after 48 h cultivation, respectively. In addition, orthogonal test showed that the most important influencing factor on aerobic denitrification of strain YL was C/N ratio. Under the optimal conditions(C/N=10, T=30℃, r=200 r/min, pH=7), the removal rate of nitrate and total nitrogen were 94.6% and 76.3%, respectively.(4) Under the conditions of 30 °C, pH 7.5, C/N 10 and 160 rpm and succinate as carbon source, the growth of strain YL was faster in ammonium than the other nitrogen sources. The specific growth rate of strain YL was 0.19 h-1, the removal rates of ammonium and TOC were respective 5.05 mg/g/h and 45.95 mg/g/h, and the removal efficiencies of nitrogen and TOC were 100% and 90.8%, respectively. Further, there was no accumulation of nitrite and nitrate during the culture period.(5) Activated sludge formed by strain YL was adopted to treat synthetic wastewater. In the period of 8 ~20 d when the system working steady, the number of strain YL was 43 percent of total bacterial count, and the removal efficiencies of TOC, ammonia nitrogen and total nitrogen maintained about 85%, 96%~100%, and 90%, respectively. The performance of the system was obviously superior to the conventional activated sludge system(P=0.005, 0.002<0.05). Not only the ammonia nitrogen was completely removed, but also there were no obvious accumulation of nitrite and nitrate in the process. These results indicated that strain YL was more competitive, could help get steady efficiencies in this system.