| In order to remove the disinfection by-production—chlorite by using chlorine dioxide in drinking water. In this paper, the technology combing with conventional drinking water treatment process and three methods of removing chlorite by adding activated carbon, ascorbic acid and ferrous sulfate were studied. Research work included:Firstly, the above three treatment process were studied by single-factor and orthogonal experiments. Secondly, the adsorption mechanism between PAC and chlorite was studied by examining thermodynamic and kinetics behavior. Thirdly, reference to the process data for engineering practice was obtained by examining these impact factors of dynaimic experiment between GAC and chlorite.The results of single-factor experiment showed that pH value, pharmaceutical dosage and reaction temperature had a great impact on the removal of chlorite for the above three treatment process; chlorite initial concentration had a greater influence on PAC removing chlorite than ascorbic acid and ferrous sulfate; with the reaction time, the removal efficiency for PAC and ascorbic acid removing chlorite increased during the first step and then stabilized, the saturation time was 200min and 20min respectively, and ferrous sulfate reacted with chlorite quickly with a few seconds. The optimal conditions of various treatment process were PAC:pH=6, carbon load 25mg chlorite for 1g PAC, the reaction time of 15min, temperature of 35℃:Ascorbic acid:pH=5, ascorbic acid and chlorite mass ratio of 5.5, reaction time of 20min, temperature of 30℃:Ferrous sulfate:pH=5, ferrous sulfate and chlorite mass ratio of 4 and reaction temperature of 40℃The main thermodynamic parameters of chlorite adsorption by PAC were proved that the adsorption was physical mainly and chemical auxiliary process and endothermic in nature, the adsorption thermodynamics meet the Freundlich isotherm model; results of the adsorption kinetics showed that intraparticle diffusion was not the only rate-controlling step; film diffusion may play an important role on the adsorption, adsorption kinetics fitted the laws of pseudo-second-order model.The results of GAC removing chlorite showed that the adsorption saturation time was extended with activated carbon layer height but shortened with liquid flow rate and chlorite initial concentration increasing.The optimal conditions were determined:pH=5, height of GAC layer=7.5cm, chlorite initial concentration=200mg/L, flow rate=30L/min, reaction time=200min. Studies show that these three treatment process can effectively purify the water polluted by chlorite if the optimal control in the best conditions, which will contribute to selection of water treatment process and provide the reference datas for process design. |
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