Isolation And Nitrogen Removalcharacteristics Of A Heterophic Nitrification-aerobicdeni Trificationbacterium

In this article,a bacterium strain XY-1 with capacity of heterotrophic nitrification-aerobic denitrification was isolated from the river bottom sludge,which was subsequently identified with 16S rDNA sequencing and assigned to Citrobacter freundii.The heterotrophic nitrifying and aerobic denitrifying ability of the strain XY-1 was investigated as well as the influence of various environmental factors.The potential denitrification mechanism of strain XY-1 was proposed preliminarily and its application potential in the denitrification treatment of actual wastewater was evaluated as well.The main results are as follows:(1)Single factor experiments show that:Strain XY-1 preferred to utilize small molecular organic acids rather than the commonly used carbohydrates,such as glucose,and cannot utilize inorganic acids.Strain XY-1 can remove more than 85%NH4+-N in the temperature range from 15? to 35?;with different initial pH values(5?8),XY-1 can also remove more than 90%NH4+N;in the terms of low dissolved oxygen scenario(DO 0.16 mg/L),XY-1 can remove as high as 96.92%of NH4+-N;with different initial ammonia nitrogen concentration:300 mg/L,400 mg/L and 500 mg/L,the growth(OD600)of strain XY-1 was 2.680,2.947 and 2.632,while the ammonia removal rate was 94.8%,86.5%,and 65.4%,respectively.(2)The optimal culture conditions for heterotrophic nitrification-aerobic denitrification of strain XY-1 were showed as following:sodium succinate was used as carbon source,the C/N was set as 10,the initial pH of medium was adjusted to 7.0,and then XY-1 was cultured at 30? with a oscillation speed of 160 r/min,which leading to the highly denitrification(99.42%of NH4-N and 90.03%of TN),and without nitrite accumulation.(3)The aerobic denitrification denitrification gene of strain XY-1 was identified as the periplasmic nitrate reductase gene(Nitrate reductase,napA),and N2 and N2O were the denitrification products,the proposed nitrogen removal pathway of XY-1 follows as the nitrification process of NH3?NH2OH?NO2-?NO3-.The aerobic denitrification of NO3-was mediated by napA,which was finally converted to N2 as the following pathway NO3-?NO2-?NO?N2O?N2.(4)Activated sludge was bioaugmented by strain XY-1 for simulated domestic wastewater treatment.When the hydraulic retention time was higher than 12 h,the obtained total nitrogen removal rate was over 81.6%;Citrobacter freundii was the dominant strain in the microbial community and presented a relative abundance of 65.91%.(5)Bioagumented multi-media biological filter with strain XY-1 were constructed to treat Tail water of sewage treatment plant,When the hydraulic retention time was set as 18 h,the total nitrogen concentration in outlet consequently decreased to 1.96 mg/L,which meets to the water standard V required by the Surface Water Environmental Quality Standard(GB3838-2002).