Study On Immobilized Aerobic Denitrifying Bacteria Enhancing Simultaneous Nitrification And Denitrification Of Biological Sponge Iron System

In recent years,with the rapid development of China’s economy,environmental protection work has continued to strengthen,so that wastewater treatment capacity has been continuously improved,and the main target pollutants of wastewater treatment have also changed from COD to nitrogen and phosphorus.Biological nitrogen removal technology has become an irreplaceable method for wastewater nitrogen removal with its economic and efficient advantages.Simultaneous nitrification and denitrification（SND）can complete the nitrification denitrification reaction in the same reaction area,which has the advantages of simple process,less investment,convenient operation and management,and effective use of carbon sources in sewage compared with the traditional denitrification process.The biosponge iron system（BSIS）is a complex system formed by involving sponge iron into activated sludge in a certain way,which is an organic combination of iron-carbon micro-electrolysis and activated sludge method.Our research group has shown that there are a variety of aerobic denitrifying bacteria in BSIS,so that BSIS has a certain SND ability,so it is of great significance to improve the SND ability of BSIS by bioenhancement means so that it can better complete the nitrification denitrification process under aerobic conditions.In this work,activated sludge in well-run BSIS was selected as inoculated sludge,and aerobic denitrifying flora was domesticated by adding different amounts of sponge iron under the condition of NO₃^--N and continuous aerobic nitrogen source in the influent water.Sodium alginate（SA）and diatomaceous earth were used as immobilization materials,and Ca Cl₂solution was used as crosslinking liquid to embed and immobilize aerobic denitrifying bacteria to make gel balls.The orthogonal test was used to optimize the material ratio of gel balls,determine the mechanical strength,mass transfer efficiency,adsorption performance and stability of gel balls,optimize the effects of temperature,shaker speed and p H on the denitrification efficiency of gel balls by response surface method,and describe the degradation process of gel balls from NO₃^--N by kinetic fitting.Finally,free aerobic denitrifying bacteria and immobilized aerobic denitrifying bacteria were added to BSIS,and artificial simulated domestic sewage was used to explore the strengthening effect of aerobic denitrifying bacteria themselves and their immobilization on the SND ability of BSIS.（1）The activated sludge domesticated aerobic denitrifying flora in BSIS,which was well operated in our group,was found to show that the removal ability of aerobic denitrifying flora to NO₃^--N was positively correlated with the amount of sponge iron.After 60 days of acclimation operation,the average removal rate of R₄（sponge iron dosage of 135 g/L）to NO₃^--N reached 91.83%after reaching the stable period,corresponding to R₁-R₃（sponge iron dosage of 0,45,90 g/L）and NO₃^--N were 40.16%,69.39%and 83.78%,respectively.At the same time,the amount of iron sponge added had little effect on the removal efficiency of COD in aerobic denitrifying flora.The specific oxygen consumption rate（SOUR）of R₁-R₄before and after the acclimation operation increased by 2.36,3.10,3.75 and 4.11 times,respectively.Therefore,the domesticated aerobic denitrifying flora in R₄ was selected for subsequent experiments.（2）Orthogonal tests showed that the optimal material ratio combination for making gel balls was 3 g/100 m L SA+2 g/100 m L diatomaceous earth+3 g/100 m L Ca Cl₂+2 g/100 m L bacterial group embedding amount,corresponding to NO₃^--N removal rate of 94.93%,among which the bacterial group embedding amount had the greatest influence on the ability of gel balls to remove NO₃^--N.The response surface method showed that temperature had the greatest influence on the denitrification efficiency of the gel ball,followed by shaker speed,and finally p H.The prediction results show that the optimal process conditions for gel balls are shaker speed=109.6 rpm,temperature=31.5°C,p H=7.4,and the maximum total inorganic nitrogen（TIN）removal rate is predicted to reach 90.58%,and the TIN removal rate in the verification experiment is 91.08%,indicating that the fitting model results are good.The kinetic fitting results showed that the degradation process conformed to the first-order kinetics when the initial reaction substrate concentration was low（30,50 mg/L）,and the degradation process conformed to the zero-order kinetics when the initial reaction substrate concentration was high（100,200 mg/L）.（3）Run 1#（BSIS）,2#（BSIS+free aerobic denitrifying flora）,3#（BSIS+immobilized aerobic denitrifying flora）to explore aerobic denitrification flora and its immobilization to enhance the SND ability of BSIS.The results showed that both free and immobilized aerobic denitrifying flora could effectively improve the SND capacity of BSIS.During stable operation,the average TIN removal rates of the 1#-3#reactor reached 47.83%,70.96%and 96.04%,respectively.The average removal rate of TIN by the 3#reactor reached 96.04%,which was 25.08%higher than that of the 2#reactor.The immobilization technology effectively retains the aerobic denitrifying flora in actual operation,so that it can better play the aerobic denitrification effect,thereby strengthening the SND ability of BSIS.