Experimental Research On Simultane Ous Nitrification And Denitrification In Biological Aerated Filter

In recent years, China has made great efforts on water pollution control. However, there is still large amount of wastewater discharged to aquatic environment without enough treatment. Considering the current situation of China, developing wastewater treatment technologies with low energy consumption and high-efficient nutrient removal is of strategic importance.The primary advantage of the BAF is biological treatment and solids separation in the same reactor eliminating the requirement for separate secondary clarification. As a consequence, the technology could reduce the space requirements, capital investment and energy consumption.In this study, BAF was used to treat sewage collected from the sewer of residential section in Harbin Institute of Technology.The effects of hydraulic loading, ratio of air to water, pH and COD/NH₃-N/TP on simultaneous nitrification and denitrification were investigated in BAF.The result shows,when hydraulic loading was 0.5m³/(m²Â·h),ratio of air to water was 2:1,pH varied from 7.0 to 8.0, system had an excellent simultaneous nitrification and denitrification effect.The degradation of COD occurred mainly at the beginning 0 - 60 cm range of the filter bed, and COD removal efficiency in this range account for 88.9% of the total COD removal efficiency. Nitrifying bacteria mainly distributed above 40cm of the filter bed. COD/NH₃-N dramatically affected the removal efficiencies of NH₃-N and TN. NH₃-N removal efficiency declined with the rising of COD/NH₃-N and when COD/NH₃-N was 8, TN removal efficiency reached the maximum value of 54.9%.COD removal efficiency declined with the rising of COD/TP. When COD/TP was below 100/0.4, COD of the effluent was less than 50mg/L; When COD/TP varied from 100/0.6 to 100/1.0, NH₃-N removal efficiency was stable above 90% and the NH₃-N concentration of effluent fluctuated narrowly around 3.2 mg/L; When COD/TP was 100/0.4, lack of TP inhibits the growth and reproduction of microorganisms, and TP became a critical factor for the inhibition to nitrification.In this study, the combination of gas and permeate backwashing was employed in BAF backwash. After backwash, the pollutants removal efficiency of BAF had different degrees of reduction. Heterotrophic bacteria and nitrifying bacteria had strong self-restoring capacity ,but denitrifying bacteria restored slowly during the experiments.Kinetic model of organics removal in BAF was investigated in this study. Based on a large amount of experimental data, a kinetic equation of the organics removal was deduced.