Comparative Study On Treatment Methods For Ammonia Nitrogen Wastewater With Middle-high Concentration

This study investigated pretreatment of ammonia wastewater before biochemical treatment by the methods of chemical precipitation,break point chlorination and air stripping.Ammonia nitrogen wastewater was treated to meet the requirements of biochemical treatment unit in the purpose of pretreatment.And the ammonia experimental wastewater with middle-high concentration?200-500mg/L?was taken as the experimental object.From the perspective of treatment effect and economic cost,the main conclusions were as following:The optimal conditions of precipitation method were:Mg Cl₂?6H₂O as magnesium salt,Na₂HPO₄?12H₂O as phosphate salt,n?Mg?:n?N?:n?P?=1:1:1,p H=9.5,30min reaction time;100r/min stirring speed.Under optimal conditions,removal rate was 86%,and residual ammonia nitrogen concentration was 28mg/L.Sodium hypochlorite solution with sufficient amount can completely remove the ammonia nitrogen.The optimal conditions of break point chlorination were:n?Cl₂/NH₃-N?value is 1.5,p H=8,30min reaction time,stirring speed is 300r/min.The residual ammonia nitrogen concentration under this condition will be able to satisfy the requirements of biochemical treatment unit.The ammonia nitrogen removal rate was 93.9%and the residual ammonia concentration was 12mg/L.The striping method is more limited by temperature.The optimal conditions were:p H=11,30?of the reaction temperature,90min of reaction,6000 of air liquid ratio.Under this conditions,the removal rate of ammonia nitrogen was 88%and the residual concentration was 24.8mg/L.In this paper,the actual cost of chemical precipitation,break point chlorination and stripping method under their own optimal conditions,were 14.22,15.36,and15.3 yuan per ton of wastewater respectively.Calculating the economy profit of MAP product recovery,the cost of treatment would be 10.53 yuan per ton.Chemical precipitation and break point chlorination,which were high adaptable to temperature,can be selected as emergency ammonia treatment under low temperature condition.Air stripping is economical and has stable treatment effect for treating wastewater with high concentration and low influent quantity,when wastewater temperature is suitable?above 20??and equipments are adequate.For high-salinity wastewater containing calcium,iron and other competing phosphate ions,chemical precipitation method demonds higher medicament dosage and may reduces treatment effect.So break point chlorination is preferred.For high organic content wastewater,break point chlorination probably brings about CBPs?chlorine disinfection by-products?increased dramatically.Therefore,chemical precipitation or air stripping is preferred.