Study On The Performance Of Denitrification Of Modified PVA-Boric Acid Embedding Immobilized Nitrobacteria-Denitrifying Bacteria

In this paper, through selecting efficient denitrification bacteria to build efficient denitrification bacteria. By examining the morphology and performance characteristics of modified carrier material, selected a suitable modified carrier material. Using polyvinyl alcohol- boric acid prepared immobilized microorganisms and optimize the performance parameters of immobilized microbial denitrification via response surface analysis, build ammonia degradation mathematical models to determine the optimum process conditions. Simulating the process of denitrification in the bioreactor, further analysis of immobilized microbial denitrogenation performance, provide theory basis for immobilized microorganisms used in wastewater treatment.Screening nitrite bacteria, nitrate bacteria and denitrifying bacteria from the sewage treatment plant sludge of secondary sedimentation tank; named YN-1, N-2, DN-2. YN-1 of ammonia nitrogen removal was 50.47%. N-2 of nitrogen removal rate was 36.23%. DN-2 of nitrogen removal rate was 83.25%. When the volume ratio of three strains is 1:1:1, the removal rate of ammonia nitrogen were higher than others. After activated carbon and straw powder combined modification, the elastic coefficient of immobilized microorganisms is 163.3 N/m, and after 24 hours, the breaking rate is 0, expansion coefficient is 77.7%, the degradation rate is over 80% after repeated use of three times. Performance index is superior to other material’s immobilized microorganisms. Meanwhile in SEM graph, the phenomenon of agglomeration of immobilized microorganisms has disappeared; there are many holes inside modified immobilized microorganism, which communicated with each other, forming intricate spatial networks, to enhance the mechanical strength of immobilized microorganisms and adsorption capacity of the bacteria source. The response surface optimization experiments of modified immobilized microorganism calculated the best experimental conditions for ammonia nitrogen degradation rate were: temperature is 30 degree, pH is 7.8, rotate speed is 160r/min, and the maximum theoretical degradation rate of ammonia is 77.9%. The degradation rates of ammonia interaction among the factors affect the experiment is: the interaction effect of temperature and pH value is obvious. The modified immobilized microorganisms were added to the bioreactor to simulate experiments, the result was, when the dissolved oxygen concentration is 4.2 mg/L, C/N is 6, pH value is about 8.0, the total nitrogen removal rate can reach 60%, ammonia nitrogen removal rate is nearly 90%. Nitrogen in the bioreactor mainly exists in three forms: ammonia, nitrite nitrogen, nitrate nitrogen. In the denitrification process, ammonia nitrogen overall decline, when it was up to a certain value, it no longer changed. The concentration of nitrite nitrogen is lowest, generally less volatility; there will be a small increase in the low temperature or hypoxia state. The concentration of nitrate nitrogen rises in the overall, and has certain accumulation in reactor; the concentration is higher in effluent.