Effects Of Amines On The Formation And Degradation Of Chlorinated Nitromethanes In The Process Of UV/Chlorine Disinfection

Halonitromethanes are a kind of typically nitrogenous disinfection by-products,which have strong toxic and carcinogenic properties.Meanwhile,ultraviolet disinfection has been gradually applied to water treatment technology in recent years,but it is generally combined with chlorine disinfection because it has no subsequent disinfection ability.Therefore,three chlorinated nitromethanes with relatively high detection amount in water are selected as the research object in this study.This study explores the photodegradation characteristics of chloronitromethane and dichloronitromethane under low pressure ultraviolet,and the regularity of chlorinated nitromethanes' formation from amines is also studied in the process of ultraviolet/chlorine disinfection,which is of great significance for the control of halonitromethanes in drinking water and sewage treatment.In this study,the photodegradation of chloronitromethane and dichloronitromethane were analyzed by changing the intensity of ultraviolet light,the initial concentration of chlorinated nitromethanes,pH and adding chlorine ion,nitrate and free radical quenching agent.The results showed that UV irradiation promoted the degradation of chlorinated nitromethanes,and the higher light intensity led to the higher degradation rate;With the increase of the initial concentration of chlorinated nitromethanes,the degradation rate will decrease,but in the range of experimental concentration,the photodegradation of chloronitromethane and dichloronitromethane followed the first-order kinetics;At a certain pH range(pH=6.0~8.0),chlorinated nitromethanes were more easily photodegraded under the weak alkali condition;Chlorine ion had no effect on the photodegradation of chloronitromethane,but it had a certain promotion effect on the photodegradation of dichloronitromethane.While the presence of nitrate hindered their photodegradation to some extent;Hydroxyl radical had a positive effect on the photodegradation of chlorinated nitromethanes,but it did not play a dominant role in the reaction.Based on the experimental results and related literatures,the way of chlorinated nitromethanes' photodegradation was deduced.In this study,methylamine(MA),dimethylamine(DMA)and poly-dimethyl diallyl ammonium chloride(PolyDADMAC)were selected as precursors.The effects of precursor's concentration,concentration of free chlorine,light intensity,pH and tert butyl alcohol on the formation of chlorinated nitromethanes were investigated under the condition of ultraviolet/chlorine disinfection;Ultraviolet light played a key role in chlorinated nitromethanes' formation from amines,and the higher the light intensity,the greater the production of chlorinated nitromethanes;In the pH range of the experiment,the production of chlorinated nitromethanes is higher under the acidic condition;Hydroxyl radicals can promote the formation of chlorinated nitromethanes.During the formation of chlorinated nitromethanes from amines,the total nitrogen content decreased in the system,and the concentration of ammonia nitrogen increased gradually,the nitrate nitrogen concentration increased initially but then decreased,while the dissolved organic nitrogen decreased rapidly.It could be speculated that dissolved organic nitrogen had an important effect on the formation of chlorinated nitromethane.Based on the above experimental contents and related literatures,the formation paths of chlorinated nitromethanes had been inferred under UV/chlorine disinfection conditions.