Nitrogen Removal Characteristics And Simultaneous Nitrification And Denitrification Capacity Of A Cold And Alkali Resisting Aerobic Denitrifier

Human activities,such as excessive use of artificial fertilizer,excessive throwing of fish feed and improper discharge of livestock waste or industrial effluents,lead to nitrogen accumulation in water environment.Different forms of nitrogen have different effects and hazards,excessive nitrogen in water bodies may do harm to both aquatic life and human beings.For instance,ammonium damages the liver and kidney of fishes,nitrate destroys the immune system of fishes,and nitrite can cause severe health problems like methemoglobinemia in infants and even cancer in humans.Biological method,which has the advantages of low-cost,high efficiency and good sustainability,has been widely used in city sewage treatment.However,most aerobic denitrifiers areextremely sensitive to environmental stresses such as low temperature,extreme pH,and high load nitrogen.Many aerobic denitrifiers conduct denitrification at the temperatures of 15?and above,and denitrification bacteria below 15?,especially 5?,are rarely reported.And bacteria can efficiently conduct denitrification under conditiongs of strong alkaline or high-concentration nitrogen are also seldome reported.Therefore,the exploration and study of denitrifying bacteria which are resistant to cold,alkali,high load nitrogen and can remove different nitrogen sources have important implications for treating sewage in extreme environmental conditions.In this study,the isolated denitrifying bacteria Y-12 could quickly and efficiently remove nitrite nitrogen and total nitrogen at the temperature of 15?.Strain Y-12 was identified by morphological observation,specific phospholipid fatty acid detection and 16Sr RNA gene sequencing,in combination with various identification methods,the bacterium was identified as Pseudomonas putida Y-12.The optimum conditions for nitrogen removal of strain Y-12 were investigated under laboratory conditions.The effects of different temperatures,initial pH,shaking speed,inoculated quantities,carbon source type,and initial nitrite nitrogen concentration on the denitrification of the strain Y-12 were studied.The experimental results showed that the optimum denitrification conditions of the bacteria were as follows:carbon source of sodium succinate,shaking speed of 150r/min,temperature of 20?,pH of 7.0-8.0,inoculated quantities of 2.0×10⁸ CFU.And strain Y-12 was cultured under this condition,after 48 h,the removal rate of nitrite nitrogen and total nitrogen was 100%and 81.8%respectively.When the temperature was as low as 5?,strain Y-12could still remove nitrite nitrogen and total nitrogen,and the nitrite nitrogen and total nitrogen removal rates were 33.0%and 24.0%respectively.Strain Y-12 could hardly grow in acid environment when pH<7,but still had good denitrification effect in alkaline environment when pH>8,and he removal rate of nitrite nitrogen is above 99%.Strain Y-12 showed good tolerance to low temperature environment and alkaline environment.Strain Y-12 was a cold and alkali resistant aerobic denitrifier.At 15?,the denitrification characteristics and denitrification process of strain Y-12 with different sole nitrogen source were studied.The results showed that strain Y-12 can efficiently remove both low and high concentrations of ammonium,nitrat and nitrite nitrogen at low temperature.When removing low congcentraions of sole nitrogen,the remvoal ratios of ammonium,nitrate and nitrite nitrogen were 100.0%,99.7%and 99.9%,respectively;and the total removal raios were 46.2%,53.6%and 57.7%,respectively.When removing low congcentraions of sole nitrogen,after 4 days of cultivation,the concentration of ammonium nitrogen decreased significantly from208.14 mg/L to 2.40 mg/L,the concentration of nitrate nitrogen decreased from 204.66 mg/L to54.03 mg/L,and the concentration of nitrite nitrogen was lowered from 199.00 mg/L to 45.49 mg/L,the removal ratios of ammonium nitrogen,nitrate nitrogen,and nitrite nitrogen of strain Y-12 were98.8%,73.6%,and 77.1%,respectively,and the total nitrogen removal rate reached exceed 32%.The average nitrification rate and denitrification rate were 2.14 mg NH₄⁺-N/L/h and 1.57 mg NO₃^--N/L/h or 1.60 mg NO₂^--N/L/h.The accumulation of intermediate products were at low level while hydroxylamine nitrogen was not detected.According to the detected nitrate nitrogen and nitrite nitrogen,the heterotrophic nitrification process of strain Y-12 might be NH₄⁺??NH₂OH??NO₂^-?NO₃^-.The aerobic denitrification process might through NO₃^-?NO₂^-?NO?N₂O?N₂.The mediums with different concentrations of mixed nitrogen sources were used to investigate the simultaneous nitrification and denitrification at 15?.When the mixed nitrogen source in the medium was at a low concentration,5 mg/L ammonium nitrogen and 5 mg/L nitrate nitrogen or 5mg/L ammonium nitrogen and 5 mg/L nitrite nitrogen,strain Y-12 could efficiently remove ammonium nitrogen and nitrate nitrogen or nitrite nitrogen,and it could remove 100.0%of ammonium nitrogen,and above 90%of remove nitrate nitrogen or nitrite nitrogen.The total nitrogen removal rate reaches more than 50%.When the concentration of the mixed nitrogen source in the medium increases,100 mg/L of ammonium nitrogen and 100 mg/L of nitrate nitrogen or 100 mg/L of ammonium nitrogen and 100 mg/L of nitrite nitrogen,strain Y-12 still had a high removal effect on ammonium nitrogen with removal ratios of 99.7%and 99.3%,respectively,But the removal rate of nitrate nitrogen or nitrite nitrogen is reduced,and the removal ratio of nitrate nitrogen or nitrite nitrogen was 61.6%or 69.5%,and the removal ratios of total nitrogen were 31.8%and 24.7%,respectively.Strain Y-12 exhibited the characteristics of simultaneous removal of ammonium nitrogen and nitrate nitrogen or nitrite nitrogen in different concentrations of mixed nitrogen sources.When the mixed nitrogen source was at a low concentration,the removal effect was the best.When the nitrogen source was in high concentration,the removal ratio of nitrate nitrogen or nitrite nitrogen was lower,but strain Y-12 could also perform simultaneous nitrification and denitrification under low temperature conditions.The intermediate product accumulates at a low level.Strain Y-12 could conduct nitrification,denitrification,and simultaneous nitrification and denitrification.In the presence of other nitrogen sources,strain Y-12 could rapidly reduce high-concentration ammonium nitrogen in low-temperature water,and could be used in alkaline wastewater treatment in autumn and winter.Strain Y-12 could be provide as the optional strains of wastewater denitrification,which are of great significance for the protection of environmental water bodies and the reuse of water resources.