Nitrogen Removal Characteristic And Differential Mechanism Of Immobilized Efficient Mixed Aerobic Denitrifying Bacteria

In recent years,lake eutrophication caused by excessive nitrogen has become increasingly prominent.The discovery of aerobic denitrifying bacteria has broken the concept that denitrifying can only be carried out under anaerobic/anoxic conditions,and provided a new idea for in-situ denitrification of natural water bodies.In order to avoid the loss of effective bacteria and strengthen the effect of bacteria on nitrogen removal in the process of nitrogen removal,the efficient mixed aerobic denitrifying bacteria was screened from Baiyangdian sediment,and immobilization was carried on based on volcanic rock and polyester fiber sponge carrier,respectively.Moreover,the nitrogen removal performance and impact resistance were investigated through influencing factors,Baiyangdian source water and impact resistance experiments,respectively.This study would provide support for the application of aerobic denitrifying bacteria in biological nitrogen removal in low C/N water.The main conclusions are as follows:1)The screening of mixed aerobic denitrifying bacteria in immobilized system and its influencing factors were studied.In this study,the collected Baiyangdian sediments were used as samples.Through enrichment,preliminary screening and rescreening,efficient mixed aerobic denitrifying bacteria were obtained and reached 98.77%of NO₃^--N removal.The highly efficient mixed aerobic denitrifying bacteria were immobilized using volcanic rock and polyester fiber sponge as immobilized carorier.Under the condition of C/N of3.5,the NO₃^--N removal efficiencies of volcanic rock and polyester fiber sponge immobilized system reached 88.74%-99.11%and 85.38%-90.84%,respectively,showing good aerobic denitrification ability.The single factor experiment showed that sodium acetate was the best carbon source for the mixed aerobic denitrifying bacteria in volcanic rock and polyester fiber sponge immobilized system,and it had strong adaptability to C/N（2-8）.2)The temperature response characteristics of denitrification by mixed aerobic denitrifying bacteria in immobilized system were analyzed.The immobilized system had strong adaptability to temperature at low C/N（C/N=3.5）.At 5℃,15℃and 25℃,94.64%-98.25%and 89.71%-98.14%NO₃^--N were achieved by mixed aerobic denitrifying bacteria in volcanic rock and polyester fiber sponge immobilized system,respectively.The relatively stableα-diversity and the dominant genus Magnetospirillum（84.41%-98.36%）of the mixed aerobic denitrifying bacteria in volcanic rock and polyester fiber sponge immobilized system at different temperatures were the potential causes of efficient nitrogen removal at different temperatures.3)The contribution and mechanism of nitrogen removal by mixed aerobic denitrifying bacteria in immobilized system at different temperatures were elucidated.The NO₃^--N removal by the carrier（volcanic rock/polyester fiber sponge）immobilized mixed aerobic denitrifying bacteria accounted for 41.18%-82.47%of NO₃^--N removal by the immobilized system,which played a major role in NO₃^--N removal.And the lower the temperature,the higher the contribution of the carrier to NO₃^--N removal.The reasons for the differences in nitrogen removal were as follows:theα-diversity of carrier immobilized mixed aerobic denitrifying bacteria was higher than that of free bacteria and polyethylene shell immobilized mixed aerobic denitrifying bacteria at the same temperature,and remained relatively stable with the decrease of temperature;the types and relatively abundance of OTUs positively correlated with NO₃^--N and TN removal in the carrier immobilized mixed aerobic denitrifying bacteria were higher than those of free bacteria and polyethylene shell immobilized mixed aerobic denitrifying bacteria;the carrier immobilized mixed aerobic denitrifying bacteria obtained higher niche breadth.4)The nitrogen removal mechanism of source water and impact resistance of mixed aerobic denitrifying bacteria in immobilized system were studied.In the experiment of source water,the concentration of NO₃^--N in volcanic rock immobilized system decreased from 2.37 mg·L^-1 to 0.77 mg·L^-1,and that of NO₃^--N in polyester fiber sponge immobilized system decreased from 2.34 mg·L^-1 to 0.87 mg·L^-1,showing a good nitrogen removal effect in source water.When the immobilized system was re-used after 7 d,15 d and 60 d of stagnation,the NO₃^--N removal efficiencies of the mixed aerobic denitrifying bacteria in the immobilized system could be stabilized in the range of 92.82%-96.61%within 72 h.Under different nitrogen loads of 5.67 mg·L^-1,15 mg·L^-1 and 40 mg·L^-1,the NO₃^--N removal efficiencies of volcanic rock and polyester fiber sponge immobilized systems reached 97.47%-99.15%and 88.00%-99.63%,respectively.The mixed aerobic denitrifying bacteria in immobilized system has good impact resistance under accident stagnation and different nitrogen source concentration loads.