Preliminary Study On The Formation Regulation Of NDMA From The Reaction Of PDMDAAC With Chloramine

The ammonia nitrogen is generally one of polluted components contained in the tiny-polluted raw water in China,and it could form chloramine with chlorine used as a pre-oxidation agent or disinfectant in the process of raw water treatment for producing drinking water.In this case,a carcinogenic substance of N-Nitrosodimethylamine(NDMA)as a disinfection by-product might be formed by the reaction between chloramines with one of NDMA precursors,the small molecules or polymers containing dimethylamine functional groups like Poly(dimethyldiallylammonium chloride,PDMDAAC),which existed in the raw water or were added as the water treatment agent.In this paper,the reaction process of PDMDAAC with mono-chloramine was taken as the research object.The concentration change of both PDMDAAC and chloramine with reaction time and the formation tendengcy of product NDMA were investigated,respectively,on the basis of the existing literatures,preliminary experiments and then the corresponding established detection method of NDMA.Moreover,the kinetic equation and activation energy of the reaction were acquired.The main progresses achieved were shown as follows.Firstly,the NDMA formatiom rule under a higher concentration with the adding dosage of 100mg/L PDMDAAC was verified,and the NDMA detection method with 200ng/L level reported in the literature was meanwhile verified and further applied practically.The results showed that the precisions of the method in the determination ranges 0.2?1.0mg/L and 2.0?10.0mg/L were 0.51 ±0.03mg/L and 5.13±0.20mg/L,respectively,while the recovery rates were all 98.2%?99.8%.The influences of various factors such as reaction time,mono-chloramine concentration,reaction temperature,pH value and PDMDAAC intrinsic viscosity as well as dosage on the formation of NDMA,then after were investigated repectively,under the reaction condition of 100mg/L PDMDAAC with 125mg/L mono-chloramines and via using the verified method.The results showed that when other conditions were kept unchanged,the formation of NDMA increased with the concentration of mono-chloramine,contact time and temperature,respectively,within the experimental range.While,PDMDAAC of the medium and low intrinsic viscosity reacted at the 25 ?C for 12h,the NDMA formation concentration increased from 0.8?g/L to the maximum 9.00?g/L when pH value rose from 5 to 8 and then decreased to 6.4?g/L at pH=9.In addition,it was found that on the same condition of above,the maximum formation concentration of NDMA decreased from 9.0?g/L to 7.1?g/L when the value of the PDMDAAC intrinsicviscosity increased.Secondly,in order to research on the formationsof NDMA under the condition of treating real tiny-polluted raw water,a new NDMA detection method with a detection limitation of 10ng/L was established based on an improvment,moreover its precision and recovery rate were tested.The effects of changing various factors under the actual conditions of treating real tiny-polluted raw water on the formation of NDMA were further explored.The results showed that the precision of the method was 50.2±0.80?g/L,the recovery rate was 98.2%?104.2%,indicating the improved NDMA detection method was feasible.Using this method,the NDMA formation regulation was researched under the reaction condition of the 0.5?4.0mg/L chloramine and 0.5-3.0mg/L PDMDAAC.The results showed that the formation of NDMA increased with the contact time,the concentration of reactant and temperature,respectively.While,the NDMA formation concentrationdecreased from 36.3ng/L to 14.9ng/L when the PDMDAAC intrinsic viscosity value increased from 0.5dL/g to 3.0dL/g,similarly,NDMA formation concentration increased from 8.6ng/L to 27.0ng/L when pH value rose from 5 to 8,and then decreased to 13.7ng/L at pH=9.Finally,the reaction kinetics was researched in order to know the reaction process of PDMDAAC with chloramine.The initial concentration method was used to exploring the reaction kinetics equation and activation energy of the reaction of PDMDAAC with chloramine.The result showed that the degradation of both mono-chloramine and PDMDAAC were conformed to be independently the first order reaction(R2>0.9989).When the reaction temperatures were 15,25 and 35?,the total reaction orders of the reaction of PDMDAAC with chloramine were 1.964,1.947and 1.951,and their average reaction rate constants were 7.30×10-6,1.17×10-5and 2.39×10-5(mol·L-1)-1h-1,respectively,and the reactive activation energy Ea was 44.23kJ·mol-1 approximately.These work mentioned above could provide a series of basic experimental data for the NDMA formation possibility and generation content prediction under the condition that prechlorination and chlorination were employed at the same time with the composite coagulants containing PDMDAAC for enhanced coagulation in the treatment of the tiny-polluted raw water in China.