| In recent years, the emergency pollution of drinking water source of city occurred frequently. Hexavalent chromium was a kind of common emergency pollutant in drinking water. Traditional treatment process of water supply plant was suitable for relatively clean water source. It could not ensure the safety of drinking water for residents once the water source was contaminated by hexavalent chromium. The iron-carbon method has great application prospects in the treatment of Cr(â…¥) pollution in drinking water due to its low cost and simple operation. In this paper, the optimal conditions of iron-carbon method to treat Cr(â…¥) in drinking water were determined and reaction kinetics were analyzed. The reaction mechanisms were analyzed through the studies of reaction product characterization, changes of pH and ion concentration. The application prospects of iron-carbon method in the treatment of emergency Cr(â…¥) pollution were analyzed and the continuous experiments were carried out according to the optimal conditions. In addition, the ultrasonic strengthen and electrolysis strengthen iron-carbon method were proposed and studied due to the shortcomings of traditional iron-carbon method and the improvement of treatment effect. The research results were as follows:(1) The increase of dosage, reaction time, reaction temperature was advantageous to the hexavalent chromium removal. Iron-carbon method to remove hexavalent chromium pollution in drinking water without having to adjust the raw water pH can achieved better treatment effect. When iron carbon mass ratio of 7:3, activated carbon particle size was 2-4 mm, the hexavalent chromium removal effect was best.(2) The reaction process was follow the first-order kinetics. As the increase of dosage and reaction temperature, the apparent propagation rate constant increased. In neutral and acidic conditions, the apparent propagation rate constant was larger.(3) The reaction mechanisms were analyzed through the studies of reaction product characterization, changes of pH and ion concentration. And the main mechanisms were galvanic effect, reduction, the adsorption effect of activated carbon and flocculation.(4) The iron-carbon reactor could operate for 17 days with the iron-carbon mass ratio of 7:3, the iron-carbon total amount of 350 g, HRT of 50 min and Cr(â…¥) concentration of 1 mg/L. The reactor could operate for 61 days after backwashing and the total iron concentration of effluent reached the standard of the Standards for Drinking Water Quality in 2006 (GB5749-2006). The emergency treatment device of iron-carbon could be set before conventional treatment process in water supply plant to deal with the sudden hexavalent chromium pollution of drinking water. In addition, the raw material cost of iron-carbon method was 1.17 yuan/ton.(5) The removal rate of Cr(â…¥) increased from 61.96% to 66.38% when the voltage strength increased from 0 V to 24 V with the iron-carbon dosage of 3 g/L. The improvement of removal rate of electrolysis strengthen iron-carbon method was not obvious while the power consumption was evident. The removal rate of Cr(â…¥) could reach to 98.64% and the residual concentration of Cr(â…¥) was far less than 0.05 mg/L when the ultrasonic power was 80%, so the effect of ultrasonic strengthen was more obvious. The Cr(â…¥) attenuation rate of electrolysis strengthen and ultrasonic strengthen iron-carbon method were 1.26 times and 2.26 times as the traditional iron-carbon method, respectively, with the iron-carbon dosage of 3 g/L, the voltage strength of 18 V and ultrasonic power of 40%.(6) The ultrasonic strengthen iron-carbon method could not only enhance the removal rate of Cr(â…¥), but also prevent the problem of harden and channel flow in practical application, so it was feasible to remove Cr(â…¥) for water supply plant. |
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