Study On The Effect Of Organic Matter On Nitrogen And Phosphorus Recovery From Struvite By Electrochemical Precipitation

With the large-scale and intensive development of livestock and poultry industry,the treatment problem of high concentration organic matter and high nitrogen and phosphorus aquaculture wastewater is becoming more and more prominent.Industrial production still has a great demand for phosphorus and phosphate resources.Therefore,the research on nitrogen and phosphorus recovery from wastewater rich in nitrogen and phosphorus（such as swine wastewater）has irreplaceable significance for the sustainable utilization of nitrogen and phosphorus resources.In this paper,the simulation pig wastewater as the research object,under the conditions of various influencing factors,electrolytic magnesium anode and electrolytically activated serpentine through the electrochemical struvite precipitation method to recover nitrogen and phosphorus in the wastewater,and then select better parameters to explore the mechanism of organic matter on the electrolytic recovery of struvite.The main research conclusions are as follows:First,the experimental results of the recovery of struvite from wastewater by electrolytic magnesium anode show that:（1）The removal rate of PO₄^3--P increased with the increase of current density and electrolytic time,but decreased with the increase of initial p H and P/N,and the removal rate of PO₄^3--P was not affected by the distance between the plates.High current density,high p H and increasing plate spacing will inhibit the removal rate of NH₄⁺in electrolysis for a long time.In addition,the removal rate of NH₄⁺increased with the increase of P/N,and showed a trend of first increasing and then decreasing with the increase of electrolysis time.Under the condition of cathode plate area of 4 and anode plate area of 8,the phosphate removal rate is slightly higher than other conditions.Under the condition of cathode plate area of 8 and anode plate area of 4,the NH₄⁺removal rate is slightly lower than other conditions.（2）The higher the concentration of sodium citrate,sodium alginate and humic acid,the stronger the inhibition effect on the removal of PO₄^3-,the increase of glucose concentration had no obvious effect on the removal of PO₄^3-;The removal rate of NH₄⁺decreased with the increase of the concentration of sodium citrate,sodium alginate,glucose and humic acid.（3）Four different organic matter have a significant effect on the crystal shape of struvite crystals during electrolytic magnesium anode treatment The electrochemical crystallization products with sodium citrate are mainly elongated needles.The electrochemical crystallization products with sodium alginate are mainly short and squarish.The electrochemical crystallization products with the presence of glucose not only have coarse rod-like structure,but also appear more slender square.The electrochemical crystallization products with humic acid are mainly triangular in shape.Secondly,the experimental results of the recovery of struvite from wastewater by electrolytic serpentine show that:（1）There was no obvious trend of phosphate removal and the removal rate was low when Na Cl concentration was electrolyzed with unactivated serpentine.When Na Cl concentration was 1～5 g/L,the removal rate of NH₄⁺increased with the increase of Na Cl concentration.When Na Cl concentration was 7-12 g/L,the NH4+removal rate did not increase with the increase of Na Cl concentration.（2）Ionic bonds in serpentine structural units are destroyed during grinding,and the breaking of the ionic bonds facilitates the dissolution of Mg²⁺and OH^-from solid particles into the aqueous solutions.Under the same conditions,the phosphate removal rate of 1.5 g activated serpentine powder as magnesium source is much higher than that of original serpentine powder,which can reach 95%.The removal rate of ammonia nitrogen is above55%.（3）High current density inhibits phosphate removal.The removal rate of ammonia nitrogen increases with the increase of current density,and the p H value of solution decreases with the increase of current density.The high initial p H value of the solution will cause the phosphate removal rate to take longer to reach the maximum,and the NH₄⁺removal rate increases with the increase of the electrolytic time.The optimal distance between the plates is 2.5 cm.When the electrolytic time is 20 min,the maximum phosphate removal rate is 97.77%,and the maximum p H is 9.04.（4）Overall,the inhibitory effect of organic matter on PO₄^3--P removal was humic acid>sodium alginate>glucose>sodium citrate,and the inhibitory effect on NH₄⁺-N removal was humic acid>citric acid>sodium alginate>glucose.The p H of solution is affected by the concentration of sodium alginate,glucose and humic acid.