Removal Of Bromate From Drinking Water By Nanoscaled Zero-valent Iron Supported On Chelating Resin

In recent years, the pollution of drinking water sources aggravated due to the development of industrialization and urbanization. With the improvement of drinking water health standards, the conventional water technology has been unable to meet requirement of drinking water quality. Therefore, many advanced treatment technology such as ozone oxidation were used to treat the polluted drinking water. Ozone can effectively remove organic compounds and trace pollutants and has been widely used in water treatment. However, bromate is formed during the ozonation of bromide-containing potable water, which is a carcinogenic disinfection byproduct (DBP). Bromate is classified as a class2B (high carcinogenic potential) potential carcinogens by the International Agency for Research on Cancer (IARC)。 According to standards for drinking water quality(GB5749-2006), the maximum contaminant level (MCL) for bromate is10μg/L. In this thesis, zero-valent iron nanoparticles (nZVI) were immobilized within a chelating resin containing pyridine functional groups (Dowex M4195) for removal of bromated. synthesized of composite materials which chosen nitrogen chelating pyridine resin (DOW3N) as the carrier with the reduction method and carried out the research on the reduction of bromate. The main contents and results are as follows:(1) Fe3+was loaded on Dowex M4195and reduced with NaBH4liquid phase, then the nano zero-valent iron composite materials were prepared with the largest amount of iron loading of147.13mg/g. The XPS spectra confirmed that ZVI particles were successfully attached on the resin. TEM images indicated that the ZVI particles were nanoscale (10nm～100nm) and spherical shaped. The four nZVI-Resin composites (nZVI-R1, nZVI-R2, nZVI-R3and nZVI-R4) with different Fe loadings were obtained by preparing Fe(III) solutionin in the0,30,50, and70%(v/v) ethanol aqueous, respectively. The results found that the Fe content of nZVI composites and the size of iron nanoparticles increased with increase of the concentration of ethanol.(2) The batch experiments conditions of bromate reduction by four nZVI-R composites were:pH=6.1,speed=200rmp,T=25℃,initial DO=9.0mg/L.The removal efficiency of bromate by four nZVI-R composites had the following order: nZVI-R1>nZVI-R2>nZVI-R3>nZVI-R4, which shows negative correlation with size of iron nanoparticles. The kinetics of bromate reduction by nZVI-resin composites can be described by pseudo-first-order model very well.The mass balance of total bromine indicated that the removal of bromate was dominantly attributed to the reduction by nZVI instead of adsorption by DOW3N.(3) The removal efficiency of bromate were affected by the intial concentration of dissolved oxygen, and pH value. Bromate reduction rates and Kobs declined when the DO level increased from Omg/L to5mg/L and9mg/L. The pH value have evident influence in bromate reduction rate. In this experimental condition, the bromate removal efficiency by three nZVI-R composites (nZVI-R1、nZVI-R2and nZVI-R4) decreased by9%,28%and47%, respectively, with increasing intial pH value from4.5to9.5.(4) The commom oxyanions and humic acid (HA) also have effect on bromate removal. Bromate removal rate decreased by addition of40mg/L sulfate. Nitrate can be reduced by Fe0and inhibit the reduction of bromate seriously. The removal efficiency of lmg/L bromate by three nZVI-R composites reduced from100%,94%and75%to49%,45%and34%, respectively, when10mg/L nitrate was added to the solution. Phosphate and carbonate can form inner-sphere complexes with Fe0and iron oxides and influence the reactivity of nZVI particles. When PO43--P concentration in the solution is0.5mg/L, the removal rate of bromate by nZVI-R1、nZVI-R2and nZVI-R4within180min were only62%38%and34%. The removal rate of bromate by nZVI-R1、nZVI-R2and nZVI-R4were96%、86%and74%with presence of60mg/L bicarbonate. The HA has insignificant effect on bromate removal efficiency, the removal rate of bromate by nZVI-R1、nZVI-R2and nZVI-R4declined by8%,4%and2%with adding lOmg/L of HA.(5) The removal of bromate in the fixed bed of nZVI-R composites was discussed. The composite materials with different amount of iron loading showed good ability to remove the bromate. The treatment capacity of nZVI-R4(147.13mgFe/g) for1mg/L of bromate solution was up to3500bed voume, i.e,1mL composites can treat3500mL of1mg/L bromate to10ug/L. The higher capacity for bromate removal was obtained as the iron loading on resin increased.