Screening, Identification And Nitrogen Removing Character Of A Heterotrophic Nitrification-Aerobic Denitrification Bacteria SLWX₂ From Sea Water

In recent years, eutrophication problems caused by nitrogen pollution become increasingly serious, which means strengthening the wastewater denitrification research is particularly urgent. Compared with the chemical method, biological nitrogen removal is more widely used because of its economy, effective, simple and less secondary pollution. The discovery and research of heterotrophic nitrification and aerobic denitrification bacteria have broken people’s understanding on traditional biological nitrogen removal theory, which makes it possible that nitrification and denitrification can be completed under aerobic conditions at the same time. This achievement has gradually become a hotspot in research of biological denitrification,because it has a great significance in building synchronous nitrogen removal system of wastewater treatment. In this study, an efficient heterotrophic nitrifying- aerobic denitrifying bacteria strain SLWX2 was isolated from stichopus japonicus culture ponds. Species identification, nitrogen removal characteristic and nitrogen load tolerance ability research was implemented on the strain, in order to enrich the biological nitrogen removal theory and the strain resources, and to provide theorial basis for the application of this kind of bacteria strains in wastewater treatment engineering. The main experimental results are as follows:(1) A bacterial strain SLWX2 with efficient heterotrophic nitrifying- aerobic denitrifying ability was screened, which is identified as Bacillus hwajinpoensis through morphologic observation, physiological characteristics and 16 S rDNA sequence analysis. Its removal rate in 24 hours of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen reached 100%, 99.5% and 85.6%, respectively.(2) When the ammonia nitrogen, nitrite nitrogen and nitrate nitrogen is used as the only nitrogen source, respectively, the removement of the 3 forms of nitrogen mainly happened in logarithmic phase of strain SLWX2. NO2--N and NO3--N werebasicly undetectable during the removal process of ammonia nitrogen. Neither NH4+-N nor NO3--N was accumulated during the degradation process of nitrite nitrogen. NH4+-N was almost undetectable during the degradation process of the nitrate nitrogen, while the concentration of NO2--N rised first and then decreased.When the 3 kinds of inorganic nitrogen exist at the same time, strain SLWX2 utilized ammonia nitrogen firstly, suggesting it can achieve simultaneous nitrification and denitrification itself.(3) Ammonia nitrogen, nitrite nitrogen and nitrate nitrogen was used as a nitrogen source respectively and each kind of nitrogen was set up by 7 different concentrations to explore the tolerance ability of strain SLWX2 to different nitrogen sources. The results indicated that SLWX2 could tolerate ammonia and nitrate nitrogen of 500 mg·L-1, nitrite nitrogen of 300 mg·L-1. The strain showed perfect nitrogen removal ability when the ammonia load was not above 500 mg·L-1, nitrite load was not above 100 mg·L-1and nitrate load was not above 200 mg·L-1,the maximal removal measure of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in 96 h reached 180 mg, 30 mg and 120 mg, respectively. Moreover, there was no NO2--N accumulation during nitrification. This strain showed great potential in biological nitrogen removal of wastewater with high nitrogen from mariculture and industries.(4) The influence of 4 environmental factors(temperature, pH, C/N and salinity)to the growth and nitrogen removal performance of strain SLWX2 was analyzed with the glucose as carbon source and the ammonium sulfate as nitrogen source. The examination indicated that the tolerance ranges to environmental factors those strain SLWX2 required for growth and nitrogen removal were wide. In the environment of weak acid, neutral and weak base and in the conditions of 28 ℃ to 40 ℃, C/N 5 ~30, pH 6~8.5, NaCl 0~25 g·L-1, Strain SLWX2 showed great growth characteristics and nitrogen removal performance. The best conditions are as follows: Temperature is30 ℃, C/N is 25, pH is 8.0, salinity is 25.