Study On Removal Of Nitrate Nitrogen From Secondary Effluent Of Sewage Treatment Plant By Ion Exchange Resin

With the aggravation of water pollution and the improvement of environmental protection awareness,the comprehensive upgrading of sewage treatment plant is imminent.The secondary biological treatment has limited effect,resulting in high nitrate nitrogen content,which is the main reason for the difficulty in reaching the total nitrogen standard.Moreover,a large amount of nitrate nitrogen in the secondary effluent will cause eutrophication and threaten human health when it enters the water,so a good method is urgently needed to remove it.Ion exchange resin has been widely used to remove nitrate nitrogen from groundwater due to its high efficiency,stability,and regeneration.In order to find ion exchange resin suitable for the removal of nitrate nitrogen from the secondary effluent of sewage plant,commercial resin 201×7 and D407 were selected in this paper,and their static and dynamic adsorption properties were studied in different environments,and their practical application was preliminarily explored.The main conclusions are as follows:（1）Study on static adsorption performance:At 30℃,when the dosage is 2.5g/L and the initial NO₃^--N concentration is 12mg/L,the equilibrium time and equilibrium adsorption capacity of 201×7 and D407 resin are 60min,4.537mg N/g and 75min,4.642mg N/g,respectively.And the initial p H and temperature have little effect.In comparison,the adsorption effect of D407 resin is better at low concentration.The pseudo-second-order kinetic and the Freundlich model can describe the adsorption behavior of the 201×7 resin,while the D407 resin is more in line with the pseudo-second-order kinetic and the Langmuir model,and the theoretical maximum adsorption capacity are 34.843mg N/g and 30.120mg N/g,respectively.The adsorption process of the two is controlled by chemical action,intraparticle diffusion is the main rate-controlling step,and adsorption is a spontaneous,entropy-increasing endothermic process.（2）Study on the influence of soluble components:Dissolved inorganic matter has a greater effect on the adsorption of NO₃^--N by 201×7 resin,while D407 resin is less affected;Dissolved organic matter has different degrees of influence on the adsorption of NO₃^--N by 201×7 resin and D407 resin.（3）Study on dynamic adsorption performance:In the simulated secondary effluent,the adsorption performance of D407 resin is obviously better than that of 201×7 resin.Thomas model predicts that the maximum adsorption capacity is 12.531mg N/g,which is close to the experimental value of 12.758mg N/g.The overall performance is better after the inlet water is pretreated with macroporous resin SD500.（4）Application of practical secondary effluent:SD500 combined with D407 resin has excellent removal effect on NO₃^--N.The average effluent concentration before the breakthrough point(C^-_NO3-N=1.2mg/L)is 0.383mg/L,and the water inflow at the breakthrough point is 920 times the volume of D407 resin.When using the preferred low-concentration regeneration solution 3%Na Cl+0.5%Na OH solution for regeneration,the desorption rate is as high as 99.3%.The study in this paper will provide reference and data support for the application of ion exchange resin in the secondary effluent of sewage treatment plant,which is of great significance in reusing the secondary effluent and improving the quality of the water environment.