Compare: Chemical Reduction Methods For Removal Of Bromate In Drinking Water

This paper used ferrous sulfate reduction, zero-valent iron reduction and iron-carbon micro-electrolysis methods to remove bromate from drinking water. After investigated influencing factors by static experiments, optimal method was selected and used to investigate its continuous operation effects. Finally, the three methods were compared and analyzed in terms of treatment effects, economic costs and technical feasibility.The impacts of FeSO4 dosage, reaction time, pH value, DO and other factors on ferrous sulfate reducting bromate was investigated by static experiment. The results show that: when pH was 8.0-9.0, 60% of the bromate (30μg/L) can be removed after 30min reaction with 20mg/L FeSO4 addition. At the same time, we can see that the reaction was fit for the pseudo-first order reaction kinetics.The study investigated the factors such as surface properties of zero-valent iron, dissolved oxygen, pH, initial concentration of BrO3-, temperature and shaker speed by static experiments. The results show that: the removal efficiency of zero-valent iron was increased significantly after pickling to restore the activation; treating the solution by nitrogen stripping could improve the removal efficiency; low pH could promote the conducting of the reduction degradation reaction; too high bromate concentration would generate competition effects at active sites; the reduction and removal rate of BrO3- was accelerated because of the iron surface covered by a layer of metallic copper. Zero-valent iron powder would appear passive phenomenon in a continuous reaction with bromate. Adjusting the pH of solution to acidic or adding Cl- would make zero-valent iron re-activation.The main influencing factors of removal of iron-carbon micro-electro-reduction include iron-carbon ratio, pH, solution conductivity, shaker speed, reaction temperature and so on. The results show that: the suitable iron-carbon ratio in Fe/C reduction system was 2:1-4:1, add electrolytes into the solution could improve the removal rate of bromate. Increase the speed of shaking could strengthen the transfer process between bromate and reduction system. Iron-carbon micro-electrolysis could maintain a higher processing efficiency at 25-37℃. Under the low pH conditions, the treatment effect of iron-carbon micro-electrolysis was good.Comparing and analysing the above three methods, we can know that iron-carbon micro-electrolysis method is the optimal method. The paper studied the effects of BrO3- removal rate in the iron powder-activated carbon columns and iron filings-activated carbon columns through dynamic small-column tests. Simulating practical engineering, iron-carbon ratio and EBCT were optimized. The iron-carbon bed hardened easily and furthermore influenced the removal rate of BrO3-, therefore the iron-activated carbon column need to be actiated and recoiled regularly.Based on the above static and dynamic experiments study, the analysis and comparison of these three methods focused on the removal efficiency, cost, ease of practical operation, different operating conditions in water treatment plant (unexpected emergency event, normal running, etc.) as well as the activation and maintenance of iron-carbon bed board after hardened. Finally, the suitable methods for different situations were detemined.