Study On Synergistic Treatment Of Nitrogen And Phosphorus Wastewater By MAP/electrochemical Oxidation

Total nitrogen and phosphorus control is the key to solve water eutrophication and improve water environment quality.The recovery of nitrogen and phosphorus from wastewater by magnesium ammonium phosphate precipitation(MAP)has attracted much attention.However,the content of NH₄⁺-N in most of the wastewater is much higher than that of PO₄^3-,and the degradation rate of NH₄⁺-N is low in the practical application of traditional MAP process.Therefore,this paper proposes to use the traditional MAP method coupled with electrochemical oxidation method in the same reactor to construct the MAP-electrochemical oxidation coupling process.The excessive NH₄⁺-N in water can be removed through the two processes of electrochemical precipitation denitrification by traditional MAP method and chlorination denitrification by electrochemical oxidation method,and the efficient removal of PO₄^3-can be realized at the same time.The main results are as follows(1)MAP-Electrochemical oxidation coupling process has advantages in the synchronization of efficient nitrogen and phosphorus removal and pollutant degradation.Adding Cl^-can stabilize the final p H value of the solution at about 10.2,inhibit the decomposition of Mg NH₄PO₄·6H₂O precipitation,and keep Degradation rate of NH₄⁺-N at a high level;the degradation rate of NH₄⁺-N increases with the increase of Chloride ion concentration;there is no effect on the degradation rate of PO₄^3-The degradation rate of NH₄⁺-N increased with the increase of current density,but the rate of NH₄⁺-N degradation increased with the increase of current density.Under acidic conditions,the higher the initial p H value is,the faster the electrochemical chlorination denitrification rate of NH₄⁺-N is.Under alkaline conditions,the chlorination denitrification process of NH₄⁺-N is inhibited,and NH₃-N is degraded by blow off reaction.When N:P is 2:1 and 3:1,the degradation rate is first slow,then fast,and finally tends to balance;when the initial NH₄⁺-N concentration is200mg/L,the coupling process has the best effect of nitrogen and phosphorus removal,but has no effect on the degradation rates of NH₄⁺-N and PO₄^3-.(2)The results show that the order of influence of coupling process on Degradation rate of NH₄⁺-N is:current density>Cl^-concentration>initial p H value>N:P>NH₄⁺-N initial concentration;the order of influence on degradation rate of PO₄^3-is:N:P>current density>initial p H value>NH₄⁺-N initial concentration>Cl^-concentration;the optimal process conditions for nitrogen and phosphorus wastewater treatment by coupling process are:N:P=3:1,initial p H=3,current density 15m A/cm²,Cl^-concentration 5000mg/L,NH₄⁺-N initial concentration200mg/L.Under the experimental conditions,Degradation rate of NH₄⁺-N and PO₄^3-were 91.75%and 98.71%respectively,and the reaction time was 40 min.the purity of Mg NH₄PO₄·6H₂O in the precipitate was 44.83%.(3)When there is no Cl^-in the electrolyte,the degradation paths of NH₄⁺-N are direct oxidation,electrochemical precipitation and·Oh indirect oxidation,and the electrochemical precipitation reaction is the main degradation path;when there is Cl^-in the electrolyte,the removal path of NH₄⁺-N increases the indirect oxidation of HCl O on the basis of the former,while the main degradation paths of NH₄⁺-N are indirect oxidation and electrochemical precipitation of HCl O The contribution of chemical precipitation reaction to Degradation rate of NH₄⁺-N is about 30%,and N₂is the main oxidation product of NH₄⁺-N.electrochemical precipitation reaction is the only degradation path of PO₄^3-,and Mg²⁺is provided by sacrificing mg plate in the reaction system.