| Nitrogen and phosphorus pollution is the main cause of eutrophication in water bodies. How to control nutrients pollution efficiently and economically has become an important problem to be solved urgently at present. No traditional removal but modern recovery in the sewage treatment system is emphasized by more and more researchers and governments today.In this paper, a study was carried out on the recovery of phosphorus and nitrogen in upper liquid of digested sludge and landfill leachate by magnesium-ammonium phosphate precipitation. The effects of pH value and the molar ratio of ammonia nitrogen, phosphate and magnesium on nitrogen and phosphorus recovery were studied with simulated wastewater. Through the analysis of the composition of practical sewages, investigations of upper liquid of digested sludge and landfill leachate by this method were accomplished. The results indicated that the magnesium-ammonium phosphate precipitation was effective in the recovery of nitrogen and phosphorus in wastewater. 99.3 percent of phosphorus in upper liquid of digested sludge containing 60.1mg/L PO43--P was translated into magnesium-ammonium phosphate under 9.5 of pH value, adding chemicals according to 1:1:1.1 mole ratio of N:P:Mg, and phosphorus content for the remainder was 2.44mg/L. 87.5 percent of ammonia-nitrogen in landfill leachate containing 1670mg/L NH4+-N was translated into magnesium-ammonium phosphate under 9.5 of pH value, adding chemicals according to 1:1.1:1.1 mole ratio of N:P:Mg, and ammonia-nitrogen content for the remainder was 209.09mg/L. The precipitate was proved struvite (MgNH4PO4·6H2O) by X-ray diffraction analysis.The research showed that the means of magnesium-ammonium phosphate precipitation is effective in recovery of nitrogen and phosphorus from wastewater. The recovery of the nutrients will bring greater environmental protection, resources benefits and economic efficiency.
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