Denitrification Characteristics And Application Of Salt-tolerant Heterotrophic Nitrification Aerobic Denitrification Bacterium N07

At present,nitrogen pollution caused by excessive discharge of wastewater during urbanization and industrial and agricultural development in China seriously damages the ecosystem and threatens human health.For special wastewater treatment with high salt content,denitrification treatment is more difficult.Therefore,screening and research of high-salinity tolerant high-efficiency denitrification microorganisms is a key measure for the treatment of high-salinity wastewater.Heterotrophic nitrification-aerobic denitrification(HN-AD)bacteria have attracted much attention for their simple nitrogen metabolism pathway and strong stress resistance,but there are few studies on salt-tolerant HN-AD bacteria.It is of great significance to screen out hn-AD bacteria with strong salt tolerance and discuss its denitrification characteristics and application effect in practical wastewater.The main contents and results of this study are as follows:(1)A strain with salt tolerance and high nitrogen removal efficiency was screened from high-salt chemical wastewater.Morphological observation showed that it was gram-positive bacteria with straight rod shape.Molecular identification showed that Bacillus megaterium was named N07.(2)Strain N07 could grow and remove nitrogen normally in 8%high salinity environment,and the highest removal rates of total nitrogen,nitrate nitrogen,ammonia nitrogen and nitrite nitrogen were 85.95%,70.62%,44.55%and 85.56%,respectively.(3)When the carbon source was sucrose,C/N was 20:1,p H was 8,rotation speed was 160 rpm,and temperature was 28?,the best denitrification performance was achieved.Response surface experiments showed that when the initial ammonia concentration was 150 mg/L,the total nitrogen removal rate of strain N07 could reach 72.56%.(4)High concentration of calcium ions(?5 mg/L)inhibited the denitrification ability of the bacteria;Magnesium ion is a necessary trace element in denitrification process.When the concentration of Cu²⁺exceeds 0.5 mg/L and Cd²⁺exceeds 2.5 mg/L,the strain is toxic.(5)Strain N07 could simultaneously remove ammonia nitrogen,nitrate nitrogen and nitrite nitrogen.Ammonium nitrogen was preferentially used when mixed nitrogen sources existed.The degradation rate of different nitrogen was in descending order:NH4⁺>NO2^->NO3^-.(6)Nitrate reductase gene Nas,nitrite reductase major subunit gene Nir B,nitric oxide reductase gene Nor B and nitrous oxide reductase gene Nos Z were successfully cloned from strain N07genome,further verifying the aerobic denitrification ability of N07.(7)Using N07 strain to treat nucleic acid production wastewater,the nitrogen in wastewater can be removed 100%;The strain could remove all nitrogen from the domestic sewage with the initial total nitrogen concentration of 74.24 mg/L and the nucleic acid production wastewater with the total nitrogen concentration of 498.53 mg/L within 6h.The strain had great application potential for nitrogen removal in practical sewage.