Study On Treatment Of High Ammonia Wastewater By Vacuum Membrane Distillation

With the high-speed evolution of society,the wastewater has been in a rising state,in which ammonia nitrogen wastewater is a large part of the adverse environmental impact has become increasingly serious.In view of the shortcomings and limitations of traditional ammonia removal methods,such as high cost,easy to produce secondly pollution and low efficiency,it is impending to seek an efficient and convenient method.As the vacuum membrane distillation technology of membrane distillation technology has stable treatment result,flexible operation,low energy consumption,and achieved good results in the removal of volatile substances in the application,for the treatment of ammonia wastewater,it has high feasibility.In this paper,the high concentration ammonia wastewater was disposed by the vacuum membrane distillation system,and the change of the membrane flux was investigated by changing the operating conditions(the temperature of feed liqiud,the pressure of reducing pressure side and the flow rate of liquid).The results show that membrane flux by the feed temperature and the change trend is particularly evident when the temperature increases,the rising trend of membrane flux is very obvious;there was a positive correlation between the flow rate of liquid and decompression pressure with transmembrane flux.In other operating conditions(the flow is 20 L/h,the decompression side pressure is 80 kPa,the initial pH value of feed solution is fixed),the feed liquid temperature of 60?,the maximum membrane flux of 6.05kg·m-2·h-1.By changing the initial pH value,liquid feed temperature,feed flow rate,permeat side pressure and studied its ammonia removal efficiency,mass transfer coefficient and selectivity coefficient change,polarization phenomenon and system heat loss,and the influence of the salt effect on the ammonia separation process.The higher the ammonia removal efficiency is,the better the removal efficiency of ammonia is,the higher the mass transfer coefficient is,the better the mass transfer performance of the system is,and the higher the selectivity coefficient is,the better ammonia in mass transfer than water is.Research shows that increasing the pH value of initial liqiud,the rate of ammonia removal,selectivity coefficient and mass transfer coefficient enhanced significantly;mass transfer coefficient and the ammonia removal efficiency will rise due to rising feed temperature,therefore the opposite selectivity coefficient reduced;when the feed flow rate rise will also increase the mass transfer coefficient with the ammonia removal efficiency,change of selectivity coefficient is relatively small;the vacuum degree is positively related to the removal efficiency and mass transfer coefficient of ammonia and permeate side,but the selectivity coefficient is negative correlation.The variation of CPC/TPC is relatively small,the export temperature is always lower than the import temperature,the temperature range is between 1-4?.Under the optimal operating situations,adding calcium chloride will produce salt soluble effect,adding sodium sulfate to produce salting out effect,and increasing the salt contant of the liquid will reduce the membrane flux.Under the optimal handle situation,the membrane flux changes during the experiment were studied.The results showed that the membrane fouling was increased due to the passage of time.On this basis,to explore the improving methods of membrane pollution,obtained Deionized water + hydrochloric acid +EDTA to control membrane pollution better,After cleaning,the membrane flux was recovered to 98.3% of the former,and the membrane lifetime prolonged.