Study On Enhancing Denitrification Of Domestic Sewage By A~2/O~2 Process

More and more attention has been paid to the environmental problems caused by nitrogen pollution in water conservancy,and the removal of nitrogen pollution is a difficult problem in water environmental treatment.At present,the A2/O process is basically used in sewage treatment plants in China.The A2/O process has the advantages of simple process,less hydraulic retention time and low operation cost.However,A2/O process also has some shortcomings,which leads to the low efficiency of denitrification in A2/O process.Especially when the C/N of domestic sewage is low,the removal rate of TN is usually not high and the denitrification effect is unstable.The purpose of this project is to add a micro-oxygen tank in front of the aerobic tank of A2/O process to make it become A²/O² process,so that it can remove COD,ammonia nitrogen and TN in domestic sewage stably and effectively,and strengthen the denitrification effect of domestic sewage.It lays a foundation for upgrading and transformation of A2/O process wastewater treatment plant.Sludge inoculation and equipment start-up were carried out,and the influencing factors DO,p H and temperature of nitrification and denitrification were studied.In order to determine the optimum operating conditions,response surface experiments were carried out in a suitable range.Kinetic analysis of nitrification and denitrification in A²/O² process and analysis of bacterial community structure were also carried out.The research results are as follows:The sludge was domesticated and stabilized.The removal of COD,TN and ammonia nitrogen was 4770 mg/d,1073.25 mg/d and 3975 mg/d respectively.The influencing factors DO,p H and temperature of A²/O² process were optimized by single factor and response surface analysis.The optimum process conditions for nitrification and denitrification were DO=0.5?0.6 mg/L?0.57 mg/L as far as possible?,p H=7.5?7.6?as close as possible to 7.52?,temperature=27?28 C?as close as possible to 27.6 C?.The removal rate of ammonia nitrogen,TN and nitrite was 92.82%,83.84% and 88.68% respectively.By calculating the material balance in each area of A²/O² process and combining with Monod equation,the nitrification kinetic model in micro-oxygen zone was obtained.The undetermined coefficient Vmax of the equation was 0.114 mg NH₄⁺-Nmg VSS-1D-1,KS was 25.38 mg NH₄⁺-NL^-1.The kinetic model of denitrification in anaerobic tank was also obtained.The undetermined coefficient Vmax of the equation was 0.013 mg NO₂^--Nmg VSS-1.D-1,KN was 0.016 mg NO₂^--NL^-1.The microbial species in activated sludge of micro-aerobic tank,anaerobic tank and anoxic tank were analyzed respectively.It was found that Nitrosospira?1.44%?,Nitrospina?0.81%?and nitrite bacteria accounted for a large proportion in the sludge of micro-aerobic tank;Paracoccus?4.67%?was the main microbial species in the sludge of anaerobic tank,and denitrifying bacteria accounted for the majority;microbial species in the sludge of anoxic tank were the main ones.Paracoccus?4.30%?and denitrifying bacteria accounted for the majority.