Construction Of Autotrophic Denitrification System For Pyrite Tailings And Study On The Removal Efficiency Of Nitrogen And Phosphorus Pollutants From Municipal Wastewater

At present,the eutrophication of natural water bodies caused by excessive nitrogen and phosphorus nutrients has attracted wide attention.In the process of rapid urbanization,the aging of the original municipal sewage treatment facilities and the singleness of the process cannot effectively control the nitrogen and phosphorus content in the tailwater.The excessive nitrogen and phosphorus in the tail water of the water plant enters the water body,which speeds up the process of water eutrophication and forms the potential environmental risk.Therefore,the upgrading of existing water plant process should carry out deep treatment of nitrogen and phosphorus in wastewater.Deep bed filter,as a common deep bed treatment process,has a good effect on the treatment of pollutants in water.As the filter material of deep bed filter,pyrite can provide electrons for the denitrification process,so it has a more extensive application prospect.In this study,raw pyrite ore,pyrite tailings and magnetite were selected as the research objects.Based on the characteristics that ores can be used as electron donors for autotrophic denitrification,organic matter contained in the secondary effluent of waterworks and ores were used as electron donors for denitrification,and the energy efficiency of simultaneous removal of nitrogen and phosphorus pollutants in water by three kinds of ores was compared.On this basis,the effects of particle size and glucose-coated iron pyrite tailings on the efficiency of simultaneous nitrogen and phosphorus removal in the heterotrophic and autotrophic denitrification system of iron pyrite tailings were investigated.The main research results are as follows:（1）The raw pyrite ore and its tailings in the experimental group had similar NO₃^-nitrogen removal effects,with 69%and 60%of NO₃^-removed in sewage within 132 h,respectively,while the magnetite ore group only had a better removal effect in the first 36 h,with a NO₃^-removal rate of 35%.All the three experimental groups were able to degrade the low concentration of PO₄^3-in sewage to below the detection limit within 48 h,and with the progress of the reaction,the concentration of PO₄^3-in sewage was below the detection limit.In the experimental group of pyrite and pyrite tailings,the reaction by-product SO₄^2-increased rapidly at 12 h at the beginning of the reaction.During the process from 12 h to 132 h,the concentration of SO₄^2-in the two experimental groups was always in an increasing trend.（2）In view of the shortcomings of slow reaction rate and low removal rate of pyrite tailings in the experimental group,the effects of particle size change and glucose-coated denitrification system on simultaneous nitrogen and phosphorus removal were investigated.The results show that with the decrease of particle size,the pyrite tailings are more easily oxidized,the removal rates of NO₃^-and PO₄^3-in water are slightly accelerated,and the concentration of SO₄^2-generated in the initial reaction stage increases.（3）The physical and chemical properties of pyrite tailings changed after the coating of glucose-coated pyrite tailings.The pH decline rate slowed down in the reaction process,and the removal effect of NO₃^-was better.PO₄^3-could be completely removed in 24 h,and the generation of reaction by-product SO₄^2-could be reduced.（4）The denitrification process of pyrite tailings in the heterotrophic autotrophic denitrification system is divided into two parts.In the first 36 h,the residual organic matter in water is mainly used for heterotrophic denitrification,and the removal of NO₃^-is mainly carried out by Betaproteobacteria.During the 36 h to the end of the reaction period,The autotrophic denitrification was mainly carried out by using pyrite tailings through Epsilonproteobacteria.No phosphorus-accumulating bacteria was detected in the sludge after the reaction,indicating that biological removal did not contribute much to the phosphorus removal of pyrite tailings system.Fe³⁺in water could react with PO₄^3-to form Fe PO₄,or Fe³⁺could be hydrolyzed into Fe（OH）₃,and Fe（OH）₃could form complex precipitation with PO₄^3-to achieve the purpose of removing PO₄^3-.The results of this study provide a theoretical basis for the removal of nitrogen and phosphorus pollutants in the water by the heterotrophic-autotrophic denitrification system of pyrite tailings,which is of great significance for the solution of the excessive nitrogen and phosphorus in the secondary effluent of sewage treatment plant and the alleviation of eutrophication of water bodies.