Study On The Treatment Of Nitrate Polluted Groundwater By Using A Novel Denitrifying Bacterium

Nitrate contamination has become one of the most serious water pollution issues in China, due to excessive application of chemical fertilizers and pesticides during the process of modern agricultural production, as a consequence, the nitrogen especially nitrate content in the arid farmland groundwater increased greatly thus further impact the ground and surface waterbody in the whole region which is tremendously harmful to the people health and environment. The important approach for solving this problem is in situ biological land remediation using the denitrogenation of nitrobacteria and denitrifying bacteria. The groundwater drainage from the drainage canal system unique in Xinjiang is not only high in nitrate content but also very high in salinity. The key technical solution for microbial denitrogenation land remediation would be selection of salt tolerant high efficient aerobic denitrifying bacterium and application of it prior mixture with other functional bacterial communities. Unlike anaerobic denitrifying bacteria, the aerobic ones can simultaneously proceed to denitrification with nitrification from aerobic nitrifying bacteria since its superoxide dismutase to remove free radical under aerobic conditions and special conformation of denitrifying enzyme-substrate complex, therefore the denitrogenation efficiency in the reaction system could be improved significantly.In this study, twenty eight denitrifying bacteria were isolated from cold spring sediment unique in Xinjiang by using selective plate dilution method. From which, one aerobic denitrifying bacterium isolate named NSA4 with stronger denitrification ability and salt tolerance was screened. Through systematical study on the morphologicai observation, physiological and biochemical characteristics, and 16S rDNA sequence homology analysis, the taxonomic and phylogenic status of this isolate was confirmed. The results showed that NSA4 is a Gram negative short rod bacterium and its similarity with Pseudomonas brassicacearum was 99%。Its optimal growth temperature was 30℃, optimal growth pH was 7 and optimal growth salt content was 1%. For study the effect of different environment factors on denitrifying efficiency of the strain under aerobic condition, alkaline potassium persulfate oxidation-UV spectrophotometric method, Nessler reagent spectrophotometric method, phenol disulfonic acid UV spectrophotometric method, and Griess-salt zma spectrophotometric method were used for determination of TN, NH4+-N, NO3--N, and NO2--N respectively. The results showed that the optimal denitrifing temperature was 30℃, pH was 7, and salt content was 10%. And the optimal carbone resources were sodium potassium tartrate, sucrose, amylum, and lactose with their denitrification efficiency at 50.9%,50%,52.9%, and 46.2% respectively. Strain NSA4 has stronger denitrifying effect compared with others.For testing its actual effect, NSA4 suspension was inoculated into water samples collected from the farmland lateral drainage canal near Urumqi. The result showed that the treatment NO3--N and TN removal rates were 10%～40% and around 10% higher than the control. Thus, this aerobic denitrifying bacterial strain can significantly improve the nitrate removal rate in groundwater, and has great potential application for the treatment of nitrate polluted farmland groundwater and land remediation in the future.