| Disinfection by-products(DBPs)in drinking water have highly carcinogenic,teratogenic and mutagenic properties,which seriously affect human health.Therefore,it has great practical significance to study the disinfection by-products in drinking water.Dibromoacetonitrile(DBAN)is one kind of disinfection by-products from aspartic acid during the drinking water chlorination.In this study,the quantitative analysis of DBAN by liquid liquid extraction(LLE)and gas chromatograph(GC)on the extracting agent of methyl tertiary butyl ether(MTBE)and using 1,2 dibromopropane as internal standard was firstly established with the recovery rate of DBAN between 99.8% and105.7%,the relative standard deviation(RSD)between 1.09% and 2.43%,and the minimum detection limit(MDL)less than 1μg/L.According to the DBAN formation mechanism,the studies on influencing factors,degradation process and kinetics were carried out by Fe/Cu catalytic reduction method and powdered activated carbon adsorption to remove DBAN.The results showed that DBAN production was less at acidic conditions(pH=4~6)and with the further increase of pH,the amount of production gradually increased and then tended to be stable.When pH value was higher than 9,the amount of production decreased due to the hydrolysis of DBAN.The impact of temperature on the formation was minor mainly because of the combined effects of increased molecular energy and accelerated DBAN hydrolysis with the increase of temperature.It was also found the DBAN concentration increased with the increase of bromide ion concentration.The formation of DBAN from aspartic acid in the process of chlorination included a series of reactions,such as substitution,decarboxylation and oxidation with a total of 8 steps.The DBAN adsorption process on PAC consisted of three stages,namely the fast phase,the slow phase and the dynamic equilibrium stage.In the rapid phase,adsorption and mass transfer power were high due to the presence of a large number of active sites on the PAC surface and the high concentration of DBAN,,so that the DBAN removal rate at this stage was relatively fast.However,with the decrease of active sites and the DBAN concentration,the adsorption efficiency of PAC decreased in the slow phase.PAC adsorption saturation was obtained in the dynamic equilibrium stage.During the test,the adsorption effect increased with the addition of PAC.For the DBAN solution with an initial concentration of 50μg/L,when the dosage of PAC was 0.6g/L,the removal rate reached 86.48%and the efficiency did not improve a lot with the further addition of PAC.The increased temperature was helpful to the adsorption effect,while the increased pH value had a negative effect.With the increase of the initial concentration of DBAN,the removal rate of DBAN decreased gradually,but the adsorption capacity was more and more large.The adsorption of DBAN on PAC agreed with the Freundlich adsorption isotherm equation,which conformed to the pseudo second-order adsorption kinetics.The DBAN removal by iron was not obvious,while Fe/Cu mixture had greatly improved the removal efficiency of the DBAN,especially the increased Fe/Cu dosage.When the Fe/Cu dosage increased from 2g/L to10g/L,the removal rate increased from 56.26% to 90.34%.This is mainly because that the content of zero-valent iron and copper increased with increasing dosage,and the contact area and contact amount of DBAN with iron and copper were raised as well.The higher temperature was also found to benefit the removal rate of DBAN dramatically.The removal rate of DBAN increased with the increase of initial DBAN concentration.When the initial concentration of DBAN increased from10μg/L to 50μg/L,the removal rate of DBAN was enhanced from 82.4%to 89.28%.When the initial concentration of DBAN was further increased to 100μg/L,the efficiency improvement wass not obvious.The reaction of Fe/Cu and DBAN was in accord with the first order kinetic equation. |
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