| Because of the contamination of the water quality at the resource and the frequently happened burst water pollution incidents, especially the more stringent drinking water quality standards in china, which has a contradiction with the traditional drinking water treatment technology, the application of ozonation in drinking water deep treatment is widespread. But ozonation will generate bromate, a by-product which is carcinogenic. Bromate has been classified as a group2B or possible human carcinogen by the International Agency for Research on Cancer, and according to drinking water quality standards in china (GB5749-2006), the maximum contaminant level for bromate is10μg/L. Therefore it is urgent to study the removal of bromate in drinking water. Nanoscale zero-valent iron (NZVI) hasa advantage of small particle size, large surface area and high reactivity, which leads to an effective removal of bromate. Howere, due to the high reducibility led itself easily oxidized, NZVI is instability, the modification is need to maintain reactive. For the above problem, this paper conducted research on modification of NZVI to achieve the purpose to improve the effect of removal of bromate.Firstly, the effect of modified NZVI on the removal of bromate was studied. Three materials including PVP, Cu and ethanol were selected and the modified NZVI were prepared by the liquid phase reduction method, then batch experiments were conducted to compare the effect the effect on removal of bromate. The experimental results showed that all the modify materials could improve the effect in low dissolved oxygen (DO) condition. Under the condition that pH was7.0,20℃, and DO was0.1mg/L, the modified NZVI could reduce bromate from100μg/L to less than10μg/L. Under normal DO content, the effect differs:PVP could improve the removal efficiency; Cu would reduce the removal; Ethanol could improve the removal within a certain proportion; The effect of PVP with Cu together would be between the independent one.On the basis of comparison of different modified NZVI, nanoscale Fe/Cu were selected to study for the removal bromate, considering the impact of different factors. These factors include: nanoscale Fe/Cu dosage, initial concentration of bromate, the DO content in the solution, the initial solution pH, reaction temperature, and coexisting ions (nitrate, nitrite, chlorate, phosphate, sulfate). The results showed that removal rate would increase with the increase of dosage and the reaction temperature. PH had a dual effect, nanoscale Fe/Cu could effectively reduce the bromate within a certain range and alkaline conditions were unfavorable for removal. According to DO would oxidize nanoscale Fe/Cu particles and generated passivation layer to prevent the reaction of bromater, the presence of DO caused a significant reduction in the removal rate of bromate. The presence of anions could inhibit the removal. The impact of nitrate, nitrite and chlorate was a result of its oxidability and competing with bromate. Sulfate could corrode NZVI, thereby weakening the effect. Phosphate and iron ions could form complexes covering the nanoscale Fe/Cu surface, resulted in the greatest impact for removal of bromate in all experimental ions.The process of reducing bromate by nanoscale Fe/Cu occurred on the reactive sites of nanoscale Fe/Cu’s surface. During the reaction process, bromate is reduced to bromide ions without generating intermediate products. Cu plays a catalytic role in the bromate reduction by NZVI. Several means such as SEM, TEM, XRD and BET were used for characterization of the NZVI and nanoscale Fe/Cu particles. The prepared particles had an average particle diameter of about90nm. Major substance was iron and it was coated by Cu particles. Nanoscale Fe/Cu had a relative larger specific surface area. |
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