Comparison of O3BAC combination and conventional processes on removal of pollutants for treating drinking water

The treatment effect of the combination process (pre-ozonation→high-density clarifier→sand filter→post ozonation→biological activated carbon(BAC) filter) was much better than that of the conventional process in treating the Huangpu River water, which is especially suit to high organic material and NH4+-N in water. The removal efficiencies of CODMn and NH4+-N by the post ozonation-BAC process were up to 30.4% and 18.9% respectively. And as the pre-ozonation process played a better role than pre-chlorination process in aid-coagulation, the removal efficiencies of CODMn and NH4+-N were up to 29.6% and 81% respectively in traditional part of combination process. However, the removal efficiencies of CODMn and NH4+-N were only 22.3% and 61.5% in the conventional process. In addition, the concentrations of algae toxins, trihalomethanes, bromate, molecular weight distribution and the related parameters of the BAC effluent were also investigated. The results show that the organic material with low molecular weight can be more easily removed by the post ozonationBAC processes (removal efficiency of organic material with molecular weight less than 1 kD is more than 70%). Tihalomethanes formation potential is 41% less than that of the conventional process. Besides, the microcystin and bromate concentrations are lower than drinking water standards in China. Moreover, the free chlorine disinfection can be used because the NH4+-N can be mostly removed by the combination process, which can avoid the generation of nitrosamine as well as the odor and test problem by chloramine disinfection. However, the combination process also has some disadvantages such as the growth of algae on the purification structures during high-temperature season as the reaction time of ozone is relatively short. This problem may be solved by the combinated pre-ozonation and pre-chlorination process.