| Chlorination is commonly used in drinking water treatment,which can effectively kill bacteria and viruses.At the same time,liquid chlorine also reacts with the natural organic matter(NOM)in the water,resulting in the disinfection by-products(DBPs)which have carcinogenic,teratogenic,and mutagenic effects on human health.Therefore,the study of DBPs has very important practical significance.The liquid-liquid extraction(LLE)-gas chromatography(GC)methods for the detection of dichloroacetamide(DCAcAm)was established by using methyl tert-butyl ether as the extractant and 1,2-dibromopropane as the internal standard in this experiment.And then the formation mechanism and control methods of DCAcAm produced from aspartic acid were discussed.The detection method was accurate and effective with the recovery rate of DCAcAm,the relative standard deviation(RSD)and the minimum detection limit(MDL)of 100.46%~102.20%,1.25%~2.02% and less than 1.24ug/L,respectively.Experimental results indicated that in the formation test of DCAcAm,when the concentration of aspartate was 1mmol/L and the chlorine dosage was 4mmol/L,the concentration of DCAcAm increased first and then decreased with the prolongation of the reaction time.The pH value had a great influence on the formation process of DCAcAm,and the yield of DCAcAm increased with the increase of pH under the condition of weak acidity(pH=4~5.5),while when the pH increased from 5.5 to 10,the production of DCAcAm gradually decreased.In addition,the yield of DCAcAm increased with the increase of sodium hypochlorite.And the increase of temperature was beneficial to the generation of DCAcAm.The chlorination process of aspartic acid to form DCAcAm included three reaction steps,substitution,decarboxylation and hydrolysis.When the granular activated carbon(GAC)was modified by NaOH solution,the specific surface area of modified GAC was increased by 34.08%.When the addition amounts of GAC and modified GAC were all 0.75g/L,the adsorption removal of DCAcAm by the modified GAC was 63.51% with the initial DCAcAm concentration of 50?g/L,which was 1.40 times greater than that by GAC,so the adsorption effect was greatly improved after modification.The adsorption process of DCAcAm by the modified GAC could be divided into three periods: rapid adsorption period(0~2.0h),slow adsorption period(2.0~3.5h)and dynamic balance period(3.5~4.0h).And the removal rate of DCAcAm increased with the increase of modified GAC dosage,temperature and pH value.With the increase of initial concentration,the DCAcAm adsorption by modified GAC was increased in the beginning and then decreased.This adsorption process could be well described by the Freundlich adsorption isotherm equation and also conformed to the pseudo-second order adsorption dynamics equation.The removal efficiency of DCAcAm was not satisfactory by the single Fe,while it was found that CuO could greatly promote the removal effect of DCAcAm by Fe.When the initial concentration of DCAcAm was 50?g/L,the removal rate of DCAcAm by Fe/CuO was 1.90 times higher than that by single Fe.Especially when the dosage of CuO increased from 0.2g/L to 0.4g/L,the removal rate of DCAcAm significantly increased from 58.21% to 74.26%.The removal rate of DCAcAm by Fe/CuO increased with the increase of reaction temperature and zero-valence iron.And the initial concentration of DCAcAm has little effect on the removal rate.The results also showed that the removal rate of DCAcAm reached 90.46%,74.26% and 84.78% when the pH was 4,7 and 10 with the zero-valence iron and CuO dosage of 14g/L and 0.4g/L,respectively.While the DCAcAm removal was poor when pH was neutral.The reaction process of DCAcAm by Fe/CuO followed the first order kinetics equation. |
PDF Full Text Request