Research On Control Strategies Of Trichloroacetonitrile,Disinfection By-product In Drinking Water

Most disinfection by-products in drinking water have the effect of"three-induced"(carcinogenic,teratogenic and mutagenic),posing a serious threat to the health of the human body.Therefore,the study on the control of disinfection by-products is of great value to human health,social stability and economy development has a profound impact.In this paper,the trichloroacetonitrile(TCAN),a by-products of disinfection,was studied.The control technology of TCAN was mainly discussed.The effects of TCAN removal by powdered activated carbon,potassium ferrate and Fe/Cu catalytic reduction technology,influencing factors and mechanism kinetics.In this study,liquid-liquid extraction-gas chromatography method was used to establish a TCAN detection and analysis method,so that the target and the internal standard have been well separated.The recoveries of spiked samples were between 92.9%and 103.86%,the relative standard deviations were between 3.88 and 7.96%,and the detection limits were between 0.60?g/L and 2.61?g/L,which indicated the accuracy and precision were higher.Powder activated carbon(PAC)adsorption TCAN process is divided into three stages,fast stage,slow stage and dynamic equilibrium stage.The rapid adsorption of TCAN by PAC is mainly due to the large number of active sites on the surface of the PAC and the large mass adsorption and mass transfer.Therefore,the removal rate of TCAN is rapidly increasing.The slow phase is mainly due to the reduced active sites on the PAC surface,resulting in a decrease in the efficiency of PAC adsorption of TCAN.In the dynamic equilibrium phase,PAC has been saturated adsorption.As the dosage of PAC increases,the removal rate of TCAN increases and the adsorption effect increases.For the TCAN solution with initial concentration of 50?g/L,the removal rate of TCAN reaches 87.5%when PAC dosage is 0.7 g/L.When the dosage of PAC increased to 0.7 g/L,the removal rate of TCAN did not increase obviously even though the dosage of PAC was increased.With the increase of temperature,the adsorption effect has increased.With the increase of pH,PAC removal efficiency of TCAN is reduced,because alkaline conditions are not conducive to PAC adsorption.As the TCAN initial concentration increased,the TCAN removal rate was declining despite the increasing TCAN adsorption.The reason is mainly that PAC has a limited number of active sites and no adsorption effect after adsorption is saturated.Up to the adsorption equilibrium stage,as the initial concentration increases,the adsorption amount of TCAN increases due to the increase of initial concentration kind of driving force,reducing the mass transfer resistance of TCAN between aqueous solution and PAC.The adsorption of TCAN by PAC was better than the Freundlich adsorption isotherm equation,and the reaction process of PAC adsorbed TCAN was in accordance with the quasi-second order adsorption kinetics.For TCAN solution with initial concentration of 50?g/L,the removal rate of TCAN increased with the increase of potassium ferrate dosage when the dosage of potassium ferrate was constant.After 30min,the removal rate reached 64.18%in a stable.The addition of potassium ferrate has a significant effect on the removal of TCAN.When the dosage of ferrate is increased from 0.01 g/L to 0.09g/L,the removal rate of TCAN is increased from 41.08%to 81.06%.For the TCAN solution with initial concentration of 50 ?g/L,the removal rate of TCAN increased with the increase of pH when potassium ferrate dosage was 0.05g/L and temperature was 25 ?.When the pH was 6.5 and the dosage of potassium ferrate was 0.05g/L,the removal rate of TCAN reached 64.23%after 30 min reaction.Potassium ferrate degrades TCAN in accordance with the first order reaction kinetics.For TCAN solution with a concentration of 50?g/L,the effect of elemental Fe on TCAN removal was general,removal efficiency was 48.72%,the effect of Fe/Cu mixture on the removal of TCAN was better,and the effect of Fe/Cu(mass ratio of 8:1)the removal rate was 89.28%.With the increase of Fe/Cu dosage,the removal efficiency of TCAN by Fe/Cu also increased.When the dosage of Fe/Cu(mass ratio 8:1)increased from 1g/L to 5g/L,the removal rate increased from 55.08%to 87.76%.As the temperature increases,TCAN removal rate also increased significantly.The reason is that when the temperature is raised,the activation molecules in the solution will increase,and the probability of collisions between molecules will also increase,thereby increasing the removal rate of TCAN.The removal rate of TCAN increased with the increase of TCAN initial concentration.When TCAN initial concentration increased from 10?g/L to 50?g/L,the removal rate of TCAN increased from 83.70%to 87.76%.However,when TCAN initial concentration was increased from 50?g/L to 90?g/L,the removal rate did not increase obviously.