Study On Formation Mechanism And Control Technologies Of Trichloroacetamide,Disinfection By-product From Asparagic Acid In Chlorination

With the increasing attention to the safety of drinking water,it is found that there are many disinfection by-products(DBPs)in drinking water.They have carcinogenic,teratogenic properties which seriously affect human health.Therefor,it has great practical significance to study the formation and control methods of these disinfection by-products to ensure the drinking water safety and human health.The detection method of trichloroacetamide(TCAcAm)was established by liquid-liquid extraction and gas chromatography(LLE-GC).We use methyl tertiary butyl ether(MTBE)as extractant and 1,2-dibromopropane as internal standard,respectively.The target and internal standard were well separated by this method.And the measurement method for TCAcAm was highly accurate with the recovery rate between 100.1%and 105.1%,the relative standard deviation(RSD)between 0.41%and 3.24%,and the minimum detection limit(MDL)was less than 1 μg/L.The results show that:in the experiment on the formation of TCAcAm,with the increase of reaction time the amount of production increased first and then remained unchanged at last began to slow down,under the acidic conditions(pH=4～6),the amount of production were the largest,when pH=7 the amount of production first increased rapidly but soon decreased due to the hydrolysis of TCAcAm,when the increase of pH to the alkaline condition.With the highly hydrolysis of TCAcAm the concentration of TCAcAm increased slowly and then decreased.With the temperature increased from 15 to 25,the amount of TCAcAm increased,but when the temperature increased from 25 to 35,the amount of TCAcAm decreased rapidly with the increase of temperature due to the high rate of hydrolysis.The formation of TCAcAm from aspartic acid in the process of chlorination involved a series of reactions such as substitution,decarboxylation,hydrolysis and so on with a total of 6 steps.The TCAcAm adsorption process on NaOH-GAC could be divided into three stages,namely,the fast adsorption stage,the slow adsorption stage and the dynamic equilibrium stage.In the condition of the experiment,with the increase of the dosage of NaOH-GAC,the adsorption effect increased.For the TCAcAm solution with the initial concentration of 45 μgg/L,when the dosage of NaOH-GAC was 0.7g/L,the removal rate of TCAcAm was 86.5%.Keep increase the dosage of NaOH-GAC,the removal rate was not obvioused.With the increase of the reaction temperature,the adsorption effect increased.With the increase of pH,the adsorption effect changed not obviously.The removal rate of TCAcAm decreased with the increase of initial concentration,and the amount of adsorption increased gradually.The adsorption of NaOH-GAC on TCAcAm agreed with the Freundlich adsorption isotherm equation and accords with the pseudo second-order adsorption kinetics.The TCAcAm removal efficiency of Fe/Cu mixture was obviously higher than that of elemental iron.The reaction of Fe/Cu on TCAcAm accords with the first-order kinetic equation.In the condition of the experiment,with the increase of the dosage of Fe/Cu,the removal efficiency also increased.When the dosage of Fe/Cu increased from 2g/L to 11g/L,the removal rate increased from 53.6%to 71.4%.With the increasd of the temperature,the removal rate of TCAcAm also increased obviously.The removal rate of TCAcAm increased with the increase of the initial concentration of TCAcAm.When the initial concentration of TCAcAm was increased from 15 g/L to 65 g/L,the removal rate of TCAcAm increased from 77.4%to 83.6%.When the initial concentration of TCAcAm was increased from 65 g/L to 85 g/L,the removal rate was not obvious due to the removal of the removal agent into saturation state.