Treatment Of High Concentration Ammonia Nitrogen Wastewater By Electrodialysis

The high-concentration ammonia nitrogen wastewater from industrial production has poor biodegradability.If directly discharged,it will cause great harm to the ecological environment and seriously restrict the healthy development of industry and agriculture.Electrodialysis technology was used in this paper,and a small-scale laboratory experiment was carried out to study the simulated wastewater of high concentration ammonia nitrogen in chemical industry(ammonia nitrogen concentration was about 8000-15000 mg/L)by using the recycling treatment process.Through single-cycle tests,the effects of membrane voltage,membrane flow rate of wastewater,liquid differential pressure between concentrated and fresh chambers,and the types of semi-permeable membrane on the nitrogen removal effect of wastewater were studied.Through multi cycle tests,the concentration effect of ammonia nitrogen in wastewater under different initial ammonia nitrogen concentration was studied.The main research results are as follows:1.Treatment of high concentration ammonia nitrogen wastewater by single cycle experiment(1)The higher the voltage,the greater the driving force and the faster the nitrogen removal rate,which could effectively reduce the processing time.The maximum voltage limit of the ion exchange membrane used in this experiment is 25 V,and the working voltage can not exceed the limit value,otherwise the membrane may be broken down.In actual operation,70%of the maximum voltage is taken as the operable voltage.(2)Increasing the flow rate of wastewater through the membrane would shorten the retention time of ions in the membrane,and reduce the efficiency of nitrogen removal,the working time would be prolonged when the ammonia nitrogen concentration in the fresh water chamber reaches the required value.(3)During the operation of the electrodialysis equipment,the concentration difference between the two chambers increased,water permeated from the side with low concentration to high concentration,the solution on one side of the concentration chamber will expand in volume.By adding a control valve at the outlet of the concentrated water chamber,the volume expansion of the concentrated water chamber can be reduced,but the denitrification efficiency can be reduced and the denitrification time can be prolonged.(4)Different types of semi-permeable membranes had different effects on the removal of ammonia nitrogen.In this paper,two types of membrane were used:concentrated ion exchange membrane(CIM)and standard ion exchange membrane(SIM).The results showed that the time-consuming of CIM was longer when the same removal rate of ammonia nitrogen was achieved.Under the same time condition,the ammonia nitrogen removal and concentration effect of SIM were better than CIM.(5)The lower of the initial concentration,the better the treatment effect.When the initial mass fraction of ammonium sulfate was 1.6%-5%(the ammonia nitrogen concentration was 2700 mg/L-8900 mg/L),the concentration rate could reach more than 100%,and the removal rate of ammonia nitrogen could reach more than 90%.2.Treatment of high concentration ammonia nitrogen wastewater by multiple circulation experiment:(1)Replacing the fresh water inlet could increase the number of movable particles in the fresh water chamber and effectively improve the concentration rate of ammonia and nitrogen in the concentrated water chamber.When the initial ammonium sulfate mass fraction was between 1.6%and 8.5%(the concentration of ammonia nitrogen was about 2700 mg/L-15000 mg/L),the concentration rate of total ammonia nitrogen in the three-cycle tests could reach more than 100%,which was about 2-2.3 times of the concentration rate of ammonia nitrogen in the single cycle tests.The lower the initial concentration of the solution,the more obvious the improvement effect of the multi cycle tests on the concentration rate of ammonia nitrogen.(2)The lower the initial solution concentration,the higher the ammonia nitrogen removal rate.The removal rate of the ammonium sulfate solution with an initial mass fraction of less than 13%(ammonia nitrogen concentration was less than 23600 mg/L)could reach more than 50%,which was lower than the result of the single cycle ammonia nitrogen removal experiment.(3)Due to the limited exchange capacity of the ion-exchange membrane,the concentration of ammonia nitrogen in the concentrated water chamber was limited.The concentration limit of the industrial ammonium sulphate solution with the ammonia nitrogen concentration of 15000 mg/L was 43000 mg/L,at this time,replacing the water inlet had no effect on the ammonia nitrogen concentration rate.Therefore,blindly replacing the fresh water inlet and prolonging the reaction time could not effectively increase the effect of ammonia nitrogen concentration.(4)In the process of reaction,with the decrease of the number of transportable particles in the system,the current gradually reduced.The higher the concentration of the solution was,the smaller the resistance of the membrane stack was,the higher the current in the system was,and the power consumption rose with the increase of the initial concentration of the solution.