Research On Deep Denitrification Process Of Autotrophic And Autotrophic-heterotrophic Synergistic Denitrification In Secondary Effluen

The large amount of secondary biochemical effluent of urban sewage treatment plants,low C/N and high nitrogen content are one of the important factors affecting the environmental quality of surface water,and it is urgent to carry out targeted deep denitrification treatment.However,the deep denitrification process of the existing sewage plant is mainly heterotrophic denitrification,which has problems such as large carbon source,high operating cost,and easy to produce secondary pollution.Therefore,the development of economical and efficient new secondary biochemical effluent depth nitrogen removal technology has important practical significance.In this study,the efficiency and decontamination mechanism of autotrophic denitrification deep denitrification were systematically studied by constructing autotrophic denitrification deep denitrification filters and using a variety of sulfur sources as electron donors,using a variety of sulfur sources as electron donors,in order to provide technical reference for the development of a new deep denitrification process.The main research contents and results are as follows:（1）The experiments of deep denitrification of different sulfur sources show that the optimal working conditions of sodium thiosulfate as the sulfur source are:the dosage is 1.5 times the theoretical value,HRT=2h,the influent p H=7.5,and the removal rate of NO₃^--N can reach 97%.The optimal working conditions of sodium sulfide as sulfur source are:the dosage is twice the theoretical value,HRT=4h,the influent p H=7.5,and the removal rate of NO₃^--N can reach 96%.The optimal working conditions for elemental sulfur as sulfur source are:the filling ratio of ceramic grain to sulfur is 2:1,HRT=2h,influent p H=7.5,and the removal rate of NO₃^--N can reach 98%.Compared with the NO₃^--N concentration and NO₂^--N accumulation of different sulfur from the effluent of the nursing denitrifier,it can be found that when Na₂S is used as the sulfur source,the nitrogen removal effect is more susceptible to the influence of sulfur source dosage and HRT,and when the sulfur source supply is insufficient or HRT is short,NO₃^--N and NO₂^--N are easy to remain in the effluent.From the analysis of nitrogen removal effect alone,autotrophic denitrification with elemental sulfur and sodium thiosulfate as sulfur sources is more advantageous.（2）The optimal working conditions for autotroph-heterotrophic synergistic denitrification with sodium thiosulfate as sulfur source and sodium acetate as carbon source are:sulfur source dosage is 1 times the theoretical value,carbon source dosage is 0.9 times the theoretical value（residual nitrogen content after autotrophiacy）,HRT=1.5h,influent p H=7.5,the removal rate of NO₃^--N can reach 96.8%,the system can achieve good nitrogen removal effect,and there is almost no accumulation of NO₂^--N;The effect of autotrophic denitrification and nitrogen removal can reach 83%.Carbon source dosing not only increases the heterotrophic denitrification and denitrification pathway of the system,but also improves the autotrophic denitrification capacity and accelerates the denitrification process.And with the increase of carbon source dosage,the effect of autotrophic denitrification and nitrogen removal first increased and then decreased.（3）Based on the Monod model,a kinetic mathematical model of autotroph,autotroph-heterotrophic synergistic denitrification was constructed,and the kinetic parameters and stoichiometric coefficients were determined,which could better simulate the degradation process of pollutants.Compared with autotrophic denitrification,the maximum growth rate of Thiobacillus denazuris in the mathematical model of autotroph-heterotrophic synergistic denitrification kinetics decreased the maximum growth rate,indicating that with the addition of carbon sources,the activity of obligate autotrophic bacteria in the system decreased,and heterotrophic denitrification occurred in the system.