Form Distribution Of Nitrogen In Source Water And Removal Characteristics Of DON By Adsorption And Filtration

Eutrophication degree of water body in our country is not optimistic,and nitrogen pollution plays an important role in it.Nitrogen exists in water in different forms,and one of the main forms is dissolved organic nitrogen（DON）.In recent years,researches on nitrogen forms briefly focus on those in rivers and offshore waters,few researchers take attension on forms and compositions and distributions of nitrogen in lakes and reservoirs.DON,one of nitrogen forms,has attracted attention as the precursor of chlorination disinfection by-products（DBPs）.There are some DON in source water,which results in a threat to the safety of drinking water.Unfortunately,any accurate monitoring method and effective removal technology of DON in water body have not been found yet.We have taken a source water reservoir as an example,and investigated the form distribution of nitrogen in it,and also analyzed the distribution characteristics of different form nitrogen in this thesis.Through experiments,the removal effects of DON in water have been studied by activated carbon absorb,nano-filtration and combination of the absorb and filtration.Based on the investigation and experiment,the following conclusions have been obtained.（1）The nitrogen in the drinking water reservoirs are composed of inorganic nitrogen（accounting for about 84%）and organic nitrogen（accounting about 16%）.And the inorganic nitrogen consists of ammonia nitrogen（accounting for about 49%）and nitrate nitrogen（accounting for about 51%）.The main composition of nitrate nitrogen is NO₃-N,which accounts for more than 97%,while NO₃-N is very little,less than 3%.（2）The composition of nitrogen forms varies from region to region in the reservoirs.In the water inlet area,the proportion of inorganic nitrogen is higher than that of the effluent area,while the proportion of organic nitrogen is lower than that of the effluent area.（3）Removal effect of DON,which was simulated with aspartic acid,is obvious if walnut shell activated carbon has been taken as absorbent,and the removal rate can be up to 57%.The absorption effect may be influenced by the dosage of walnut shell activated carbon,adsorption time and pH value of the water.The optimum adsorption conditions have been found as follows:temperature of 30°C,dosage of 1g/L,pH near4.7;And the adsorption is basically balanced if the absorption time reaches 200min.（4）The removal efficiency of DON by nano-filtration membrane is obvious.When the pressure is 0.95MPa,the effluent flow rate is about 0.6L/min and the removal rate in DON is up to 85%.（5）The removal efficiency of DON by combining activated carbon adsorption and Nanofiltration amounts to 94%in slightly polluted source water,and the removal efficiency of inorganic nitrogen also reached more than 70%.