Removal Of Bromate Using Nanoscale Zero-valent Iron Supported On Activated Carbon

When the concentration of bromide ion (Br-) in water is over20μg/L, bromate canbe formed as one of disinfection by-products (DBPs) after the ozonation treatment.Bromate is a potential human carcinogen, which has been classified as a group B-2carcinogen by the International Agency for Research on Cancer (IARC). The maximumcontaminant level (MCL) for bromate in drinking water established by World HealthOrganization (WHO) and United StatesEnvironmental Protection Agency (USEPA) is only10μg/L (0.078μmol/L). According to Standards for drinking waterquality (GB5749-2006) and Drinking natural mineral water (GB8537-2008)，themaximum contaminant level (MCL) for bromate is also10μg/L in China. Thereby theresearch of bromate removal is extremely urgent. In this paper nanoscale zero-valent ironsupported on modified activated carbon (nZVI/MAC) was proposed for bromate removal.Combined with the great specific surface area, high reactivity of nanoscale zero-valent ironand the strong adsorption ability of activated carbon, nZVI/MAC showed the perfectperformance to quickly remove bromate from the water.This paper is divided into three parts. In the first part, nanoscale zero-valent iron(nZVI) and nanoscale zero-valent iron supported on modified activated carbon(nZVI/MAC) were synthesized using liquid phase reduction method. The nZVI/MAC wascharacterized by X-ray diffraction (XRD), scanning electron microscope (SEM) andtransmission electron microscope (TEM). The results suggested the presence of α-Fe0inboth nZVI/MAC and unsupported nZVI. The nanoparticles dispersion of the nZVI/MACwas good, and the average particle size of immobilized nanoscale zero-valent was abouthalf of that of unsupported nZVI.The second part discussed the effect factors of bromate removal by nZVI/MAC. Theresults indicated that the process of bromate removal by nZVI/MAC followed pseudofirst-order kinetics model and nZVI/ACHNwas the optimal material for bromate removal,and95.66%bromate removal could be obtained in5minutes when DO was0mg/L and pHwas6.8at room temperature. The removal efficiency of bromate increased with theincreasing of nZVI dosages, and also rized with decreasing initial pH (except extremelyacid conditions). However the removal efficiency of bromate rapidly decreased with theincreasing of the DO. In addition, the extension of nZVI/ACHNstorage time and the existence of coexisting ions in the solution would also compromise the bromate removalefficiency. The Kobsdecreased with the increase of the bromate concentration, but theinitial rate constant increased.At last, the bromine mass balance and mechanism of bromate removal by thenZVI/ACHNwas investigated. The bromine mass balance was in the range of96.24-101.17%during the experimental course and bromide was the only product forbromate reduction. Bromate removal by nZVI/MAC was accomplished via two-stepmechanism. Firstly, bromate in solution was absorbed quickly on the surface ofnZVI/MAC, which increased the local concentration of bromate. Then, the adsorbedbromate was reduced by nZVI and the reduced product, bromide, entered into the solution.