Isolation And Characteristics Of Nitrogen Removal Bacteria

A ammonia-oxidizing bacteria named CM-NRO14and a denitrifying bacteria named CM-NRD3were isolated from urban domestic wastewater treatment plants.16S rDNA sequences were analyzed to identify the strains. Effects of substrate concentration, pH and temperature on the reaction activity of the strains were studied in the batch culture. Process of two-stage A/O was conducted to study the value of strains in removing nitrogen. A sufficient amount of bacteria were obtained by continuous culture in fermentation tanks.Strain CM-NR014and strain CM-NRD3were identified as Nitrosomonas eutropha and Stenotrophomonas sp. respectively through morphological feature, biochemical/biophysical characteristics and16S rDNA sequence analysis. The maximal ammonia oxidation rate of CM-NRO14was24.54mg·(L·d)-1under the optimal ammonia concentration331.2mg·L-1.Km and Ki for ammonia were45.66mg·L-1and2401mg·L-1,respectively. K; for nitrite was1524mg·L-1.The optimal pH for ammonia oxidation was7.79.The optimal temperature was34℃. When cultured in the conditions of ammonia nitrogen180mg/L, pH7.79and34℃, strain CM-NRO14removed91.6%of ammonia in4days. Doubling time of the strain was2.94d. Strain CM-NRD3was able to use either sodium nitrate or sodium nitrite as electron acceptor to oxidize organic matter. The maximum denitrification rate by using nitrate as electron acceptor was19.86mg·L-1·h-1, which is much higher than that of nitrite (4.05mg·L-1·h-1). Therefore, the optimal electron acceptor was nitrate. Growth dynamics test revealed that the optimal pH and temperature for CM-NRD3were7.36and33.5℃, respectively. Under the optimal conditions (NO3--N140mg/L, acetate served as sole organic carbon source, pH7.36and33.5℃), strain CM-NRD3in the exponential phase was obtained after10h, and the doubling time was9.9h. The nitrate removal efficiency was up to95%in48hours.Amount of bacteria were obtained by continuous culture that was of high quality and efficiency, which can supply sufficient bacteria for project application. By the process of two-stage A/O, the strains successfully achieved shortcut nitrification and denitrification in which more than99%of NH4+-N,80%of TN and90%of COD were removed totally. Volume load for NH4+-N and TN were0.084kg/(m3· d) and0.047kg/(m3· d), respectively. The process produced less sludge in which much energy was saved compared to the general activated sludge process. The strains have high value in removal of nitrogen in wastewater, and it can be used to reform municipal wastewater treatment plant.