Study On The Effect Of Ammonia-releasing Compounds On Chloramine And NDMA Production

Nitrosodimethylamine(NDMA)is a new type of nitrogen-containing disinfection by-product with strong carcinogenicity.It is formed by the reaction of dimethylamine group-containing compounds with disinfectant inorganic chloramines.China’s raw water treatment system for drinking water generally does not use inorganic chloramines as disinfectants.However,tiny-polluted raw water in China generally contains a certain amount of ammonia nitrogen,and when pre-chlorination(usually chlorine)is used for enhancing treatment,inorganic chloramines may be formed.In this case,if the dimethylamine group-containing compound is existed in the raw water,it constitutes a necessary condition for the formation of a disinfection by-product NDMA.The literature suggested that the appropriate contact method between the two was a sufficient condition for forming NDMA.Inorganic salt/PDMDAAC is a superior composite coagulant for the coagulation treatment of tiny-polluted raw water and has unique advantages.However,when tiny-polluted raw water is treated with both pre-chlorination and composite coagulants to enhance the coagulation process,NDMA may be formed if ammonia nitrogen,chlorine,and PDMDAAC containing a dimethylamine group in the composite coagulant exist at the same time.However,presently in China,concerning the study of precursors,accelerators,and formation mechanisms related to the formation of NDMA disinfection by-products,there have been lack of the systematic studies on the effect of ammonia-releasing compounds,i.e.the precursors of ammonia nitrogen widely existing in raw water,on the formation of chloramines and further NDMA.Based on this reason,nine typical ammonia-releasing compounds(glycine,phenylalanine,glutamic acid,histidine,cysteine,urea,and humic acid)were selected in this paper for the investigation of the effect of typical ammonia-releasing compounds on the formation of chloramine and NDMA.The details are as follows.Establishment of NDMA analysis method under the experimental conditions Based on a existing method of testing micro amount NDMA(detection limitation of 200 ng/L)in our group,and according to the typical regional surface raw water quality model and the enhanced coagulation process conditions using composite coagulants,the effects of three typical ammonia-releasing compounds(glycine,urea,and humic acid)on the detection of micro amounts of NDMA were investigated by UV scan,liquid chromatography,and SPE-HPLC methods.Further,the effects of ammonia-releasing compounds on the precision and spike recovery of a new method of solid-phase extraction-high performance liquid chromatography which can test a trace of amount NDMA(detection limitation of 10 ng/L)were investigated.The results showed that when the concentration of typical ammonia-releasing compound was set to 10 mg/L,it was found that the selected three kinds of ammonia-releasing compounds displayed the certain interference on the UV absorption and liquid-phase detection results of NDMA,and then the interference can be eliminated after solid-phase extraction.Moreover,in the new method with NDMA detection limitation of 10 ng/L,the relative standard deviations RSDs obtained were 1.258%,and 1.251 to 1.655%,respectively.And the recoveries for the spiked standards were 98.22 to 104.16%,and 96 to 105%,respectively.Therefore,the new NDMA detection method was still accurate and reliable in the presence of ammonia-releasing compounds,and was suitable for the detection and analysis of trace amount of NDMA in reaction systems containing ammonia-releasing compounds under experimental conditions.Exploration of the possibility of chloramine formation from ammonia-releasing compounds and chlorine In order to investigate the effect of ammonia-releasing compounds on chloramine formation,a static chlorination method was designed to independently explore the possibility,regularity,and mechanism of the formation of chloramines from each of 7 types of 10 mg/L typical ammonia-releasing compounds.The results showed that under the conditions of equal mass concentration of them,when any one of six ammonia-releasing compounds reacted chlorine,none of six typical ammonia-releasing compounds,glycine,phenylalanine,glutamic acid,histidine,cysteine and humic acid(HA is the main components,the same below)could not form detectable inorganic chloramines,only urea could form 0.0-0.4 mg/L inorganic chloramine.For organic chloramines,in addition to cysteine and humic acid,the other five ammonia-releasing compounds glycine,phenylalanine,glutamic acid,histidine,and urea could form 0-7.6 mg/L of organic chloramines.It could be seen that the different kinds of ammonia-releasing compounds interact with chlorine,resulting in the difference of both the formation amount and types of the formed chloramine.The effect of the ammonia-releasing compounds on the reaction of PDMDAAC with chloramine to form NDMA Based on the selected parameters of the micro-polluted raw water quality model and the enhanced coagulation process conditions,three kinds of ammonia-releasing compounds-chloramine systems were separately designed,and then PDMDAAC was added in to study the effect of ammonia-releasing compounds on the reaction of PDMDAAC with chloramine to form NDMA.The experimental results showed that 7 kinds of 10 mg/L typical ammonia-releasing compounds added,after reacting with the same concentration of chlorine,reacted with 2 mg/L PDMDAAC,respectively,no NDMA production was detected for each after 72 hours of reaction time.The independent existence of 0.1 mg/L various ammonia-releasing compounds had few effect on the formation amount of NDMA produced by the reaction of 3 mg/L ammonia nitrogen,5 mg/L chloride,and 2 mg/L PDMDAAC.Based on the micro-polluted raw water quality model,when the sum of various ammonia-releasing compounds was approximately 3 mg/L,the effect of their existence on the reaction to generate NDMA was:after adding PDMDAAC for 1 h,the producing amount of NDMA decreased from 25.45 to 17.93 ng/L,in comparision with without their existence.It could be seen that although ammonia-releasing compounds were the precursors of ammonia nitrogen,their existence should be a hindrance to the formation of NDMA in certain existent.The above research results could provide powerful theoretical and experimental basises for the control and elimination of the formation of disinfection by-product NDMA in the application of PDMDAAC-containing composite coagulants in the enhanced treatment of micro-polluted raw water.