Removal Of Bromate By-Products In Ozonation Technology By Nanoscale Zerovalent Iron

With the increasing contamination of drinking water resource and the more stringent drinking water standards, conventional water treatment technology appeared its lack in efficiency, the application of ozonation in deep treatment drinking water is widespread. Although the ozonation is effective for contaminated drinking water, a new broblem about by-products is appeared. Bromate is formed following ozonation of water containing bromide, which is classified by the International Agency for Research on Caner (IARC) as a Group 2B or "possible human" carcinogen. According to "Standards for drinking water quality" (GB5749-2006), the maximum contaminant level(MCL)for bromate in China is 10μg/L, thereby the research of control and removal of bromate is important. As the present technologies for bromate control or removal have some deficiencies, bromate reduced by nanoscale zerovalent iron(NZVI) is discussed in this paper. NZVI have the characteristics of small diameter, high specific surface area to mass ratios and greater surface reactivity, which will resulted in a higher removal efficiency of bromate.NZVI was prepared by the liquid phase reduction method, and was characterized by SEM, TEM, XRD and BET techniques. Batch experiments for bromate reduction by NZVI were conducted in this paper, and the main conclusions are as follows:1. The reduction of bromate by NZVI is a surface reaction. NZVI has larger specific surface area (20.9824m2/g) than normal iron powder, so the reaction rate is faster and NZVI dosage was much lower.2. A series of experiments of bromate reduction by NZVI were carried out and discussed. It has been found that the efficiency of bromate reduction were affected by the amounts of NZVI, initial bromate concentration, pH valve, reaction temperature, mixing rates and the concentration of dissolved oxygen. The reduction rate increased with the increasing of NZVI dosages, reaction temperature and mixing rates. The pH valve has dual influence in bromate reduction rate, and the appropriate pH valve can lead to the rapid bromate reduction rate. If the NZVI addition is over dose, initial bromate concentration has little influence on bromate reduction. The existence of dissolved oxygen in water decreased the bromate reduction rate.3. The effect of the normal ions on bromate consumption rate was quantitatively discussed. It was found that nitrate and chlorate in the reaction medium decreased the nitrate disappearance rate, while the presence of nitrite increased the reduction rate of bromate. Carbonate and phosphate can be adsorbed on the iron surface and formed complex compounds with iron, thereby decreaced the bromate removal efficiency. The presence of sulfate also decreased the bromate reduction rate by promoting corrosion of iron. The presence of NOM has slightly effect on bromate removal. The bromate reduction rate was significantly decreased in tap water, and a greater amount of NZVI was required for the reduction of bromate completely.4. The bromate reduction over NZVI could be described by pseudo-first-order reaction kinetics. According to the Arrhenius equation, the superficial activation Energy, Ea, was calculated to be 23.2kJ/mol and the Pre-exponential factor (A) was 1933.4min-1.