Treatment Of Nitrogen And Phosphorus Wastewater Using Seawater Coagulation Based On MAP Method

Based on the demand for the future sustainable utilization of resources, this study aimedto recover nitrogen and phosphorus from the wastewater. Through single factor tests andthermodynamic equilibrium analysis based on Medusa software, the treatment effect ofnitrogen and phosphorus wastewater by typical magnesium ammonium phosphatehexahydrate process and seawater coagulation process was studied; the influence of pH andthe molar ratio of precipitation agent was analyzed; the impact on the generation of MAP ofCa²⁺, Na⁺and K⁺brought in by seawater was investigated in detail; and the feasibility andefficiency of seawater coagulation process was evaluated.The influence factors of nitrogen and phosphorus recovered from wastewater by typicalMAP process were analyzed. The optimum opereating conditions for MAP process were: theMg:N:P molar ratio was1:1:1, pH was9-9.5. For PO₄^3--P removal purpose, the optimumMg:N molar ratio was1.2:1.The impact on the generation of MAP of Ca²⁺, Na⁺and K⁺brought in by seawater wasinvestigated. Due to the presence of Ca²⁺, Na⁺or K⁺, the existence of hydroxyapatite,potassium magnesium phosphate hexahydrate or magnesium sodium phosphate heptahydratewhould decrease and improve the removal efficiency of NH₄⁺-N and PO₄^3--P respectively.The influence factors of nitrogen and phosphorus treatment by seawater coagulationprocess were analyzed. For NH₄⁺-N removal purpose, the optimum opereating conditionswere: the Mg:N:P molar ratio was0.8:1:0.8, pH was8-9. For PO₄^3--P removal purpose, theoptimum opereating conditions were: the Mg:P molar ratio was1-1.2:1, pH was9.5-10.In conclusion, the seawater coagulation process recovered nitrogen and phosphoruseffectively and decreased the emission of nitrogen and phosphorus to aquatic environment.However, due to the higher content of Ca²⁺and of Na⁺in seawater, the removal efficiency ofNH₄⁺-N and PO₄^3--P was decreased and improved respectively.