Electrochemical Precipitation Of Magnesium Ammonium Phosphate-Electro-Oxidation Integration Removal Nitrogen And Phosphorus For High-Concentration Nitrogen And Phosphorus Wastewater

The high-strength nitrogen and phosphorus wastewater is mainly derived from industrial,domestic sewage and agricultural wastewater,which has the characteristics of wide source,large discharge and strong harm.Generally,the concentration of ammonia nitrogen water is much higher than phosphate in such waste.And traditional biological treatment is difficult to achieve the desired effect,physical and chemical treatment methods have the problem of only removing a certain pollutant in the wastewater.In this respect,this paper studies a new integrated nitrogen and phosphorus removal method for high-strength nitrogen and phosphorus wastewater,in one reactor,Sacrifice the magnesium plate anode to provide magnesium salts,and the phosphate and some ammonia nitrogen in the wastewater with magnesium are precipitated as magnesium ammonium phosphate（MAP）to recovery resources,further use of ruthenium-plated titanium mesh（DSA）anode electrochemical oxidation the rest ammonia nitrogen and nitrate nitrogen,which achieve the removal nitrogen and phosphorus integrated.On the one hand,the studies can recover nitrogen and phosphorus,which provides a reference to achieve sustainable development of resources.the other hand,it also provides new ideas for the harm control of water eutrophication.The studies has important practical significance,and the main conclusions as follows:（1）In an electrochemical precipitation MAP system with magnesium plate anode and titanium plate cathode,the initial pH,electrolysis time,and current density have an important effect on the removal of phosphate and ammonia nitrogen.When the initial pH is7.5,the removal rates of phosphate and ammonia nitrogen reach 97.03%and 7.49%,respectively;Increasing the initial pH will reduce the phosphate removal rate and increase the removal rate of ammonia nitrogen;when the electrolysis time is 20 min,the phosphate removal tends to be saturated,at 30 min,the removal rates of phosphate and ammonia nitrogen reached 98%and 7.63%respectively;higher current density would increase the removal rates of phosphate and ammonia nitrogen,at 20 m A/cm²,the removal rates of phosphate and ammonia nitrogen reached 95.54%,12.26%,but excessive current density will lead to the decomposition of MAP,which is not conducive to phosphate removal;the electrode spacing,electrode area,coexisting potassium ions and coexisting sodium ions have no significant effect on the removal rate of phosphate;However,when the Na⁺concentration is higher than 1500 mg/L,the ammonia nitrogen removal rate is only 0.48%;the electrochemical precipitation MAP method is also applicable to low strength nitrogen and phosphorus wastewater.When the waste water is diluted 8 times,the removal rates of phosphate and ammonia nitrogen reach 99.8%,37.83%respectively.Response surface optimization analysis results with phosphate removal rate as the response value show that,the initial pH is the main influencing factor for the denitrification and dephosphorization by electrochemical precipitation MAP method.The initial pH interacts with the electrolysis time and the current density.It is 7-8,the electrolysis time is 15-20 min,and the current density is 15-20 m A/cm²,the phosphate removal rate has a peak value of 99%.（2）XRD,SEM and FTIR characterization analysis results show that the initial pH and K⁺or Na⁺have a significant effect on the precipitation.The initial pH is 7.5 and the precipitation is typical MAP;the initial pH is 10.5 and the precipitation becomes hydroxide Amorphous materials such as magnesium;when the concentration of K⁺or Na⁺is more than 1500 mg/L,the surface of the obtained precipitate will obviously adhere to other amorphous crystals.When the concentration of K⁺or Na⁺is more than 2500mg/L,the main body of precipitation is Mg KPO₄and Mg Na PO₄.（3）In an electrochemical oxidation denitrification system with ruthenium-plated titanium mesh（DSA）anode and titanium plate cathode,the main removal route of ammonia nitrogen and total nitrogen is anodic oxidation.The initial pH,electrolysis time,current density and chloride ion concentration has an important effect on the removal of ammonia nitrogen and total nitrogen.Increasing the initial pH will increase the indirect oxidation capacity,when the initial pH is 10.5,the removal rates of ammonia nitrogen and total nitrogen reach 84.86%and 89.5%respectively;a longer electrolysis time and a larger current density before the saturation of the denitrification reaction are beneficial to removal of pollutants,60 min and 45 m A/cm²are the electrolysis time and current density at which ammonia nitrogen and total nitrogen removal reach saturation;the increase of chloride ion concentration is conducive to the removal of ammonia nitrogen;the plate spacing and area have no obvious effect on the removal of ammonia nitrogen and total nitrogen.The removal of nitrate nitrogen is mainly the reduction of the cathode,and the active area of the cathode plate is the main influencing factor.The response surface optimization analysis results with the total nitrogen removal rate as the response value show that the electrolysis time is main influencing factor of the system;electrolysis time interacts with the initial pH and current density,the initial pH is 9.5-10.5,and the electrolysis time is 54-66 min,the current density is 50-60 m A/cm²,the total nitrogen removal rate has a peak value of 72%.