Experimental Study On Removal Of Ammonia Nitrogen In Electroless Nickel Plating Wastewater

With the maturation of electroless nickel plating technology,its application is becoming more and more extensive,and the scale of production of electroless nickel plating is also expanding.However,the waste disposal failed to attract enough attention,and even some manufacturers directly discharged liquid waste,which has caused serious environmental impact.At present,the nickel in the electroless nickel plating wastewater has been well recovered and utilized.The research of other wastewater treatment technologies is mainly focused on the removal of organic pollutants in the wastewater.Ammonia nitrogen is an important factor in the emergence of eutrophication in water,but it is often overlooked.In addition,the domestic wastewater discharge standards are continuously improving,and the requirements for removing ammonia nitrogen from wastewater are also more stringent.Therefore,the removal of ammonia nitrogen has become a major problem that needs to be solved in the wastewater treatment of the electroplating industry.For the characteristics of high ammonia nitrogen concentration in electroless nickel plating wastewater and difficulty in removal,the actual electroless nickel plating wastewater that has not met the standards after the existing process is tested,the wastewater quality is as follows:pH=6⁷,total nickel is lower than 0.08 mg/L,SS is lower than 20 mg/L,but ammonia nitrogen concentration is still higher,100mg/L¹20mg/L.In this paper,sodium hypochlorite oxidation method and magnesium ammonium phosphate precipitation method were used to remove residual ammonia in wastewater,and the effect of integrated MBR membrane bioreactor on removal of COD and ammonia nitrogen in electroless nickel plating wastewater was investigated.The suitable conditions for the NaClO oxidation method are as follows:the amount of sodium hypochlorite solution is 1800 mg/L,the reaction time is 30 minutes,the initial pH value is 6.0 to 7.0,the reaction temperature is 10℃³0℃,and the magnetic stirrer speed is 300 r/min.Under this condition,the ammonia nitrogen removal rate of wastewater effluent reached over 91%,and the residual ammonia nitrogen concentration was 10 mg/L,which was lower than 15 mg/L,meeting the emission requirements of ammonia nitrogen in Table 2 of GB 21900-2008 Emission Standard of Pollutant for Electroplating.The suitable conditions for ammonium magnesium phosphate precipitation method are as follows:n（Mg）:n（N）:n（P）is 1.1:1:1.2,initial pH is 10.5,reaction time is 50 min,and reaction temperature is 20℃⁴0℃,magnetic stirrer speed is 100r/min.Under this condition,the ammonia nitrogen removal rate of wastewater effluent is as high as 88%,and the residual ammonia nitrogen concentration is about 14 mg/L,which meets the emission requirements for ammonia nitrogen in Table 2 of GB21900-2008.The test proved that the Fe²⁺/NaClO oxidation method is feasible for the pretreatment of the water in the MBR membrane bioreactor.When the integrated membrane bioreactor is used to treat the electroless nickel plating wastewater after pretreatment,the optimum process parameters of the plant operation are as follows:The hydraulic retention time was 10 h,the aeration volume was 3.0 L/min,the carbon to nitrogen ratio was 3:1,and the temperature had no significant effect on the treatment effect within a certain range.Under this condition,the COD concentration of the effluent of the reactor can be maintained at 52 mg/L,and the residual ammonia nitrogen concentration of the effluent is 17 mg/L.