Research On Removal Of Manganese From Groundwater By Chlorine Dioxide/Manganese Sand

Groundwater, an important part of water resources, is used for irrigation, production and in life owing to its worldwide distribution, good quality, stable water and low vulnerability of pollution. However, the excessive iron (Fe2+) and manganese (Mn2+) ions will bring much trouble or even harm to people’s life and production. The content of Fe2+and Mn2+differs greatly with the different depositional environment of regional geology. And low iron and high manganese is the typical one, namely, its iron is conformed to the health standards (≤0.3mg/L), while the manganese is far beyond the standards. This kind of water is difficult to treat. Therefore, the more effective and economical methods are needed. Recently, strong oxidation has been generally used in many European big cities, as it is efficient, timely, fast and thorough in target pollutants removal. So chlorine dioxide (ClO2) was widely used for drinking water pre-oxidation and disinfection process.According to the character of low iron and high manganese, the ClO2and manganese sand filtration process was applied in this study. The effects of ClO2on Mn2+removal and its influential factors were mainly observed, and the by-product chlorite ion (ClO2) forming and control on the Mn2+removal by ClO2pre-oxidation were investigated in the experiment. The results show that at the original Mn+concentration of3.5mg/L, the removal efficiency is up to92.8%, when the optimal addition of ClO2, pH and filtration rate are5mg/L,6.5～8.0and8m/h respectively. What’s more, the existence of iron has a positive effect on Mn2+removal. The higher the initial concentration of iron, the better the Mn2+removal efficiency is. When the concentration of Fe+rises from0.05mg/L to0.3mg/L, the efficiency nearly increases by20%. Additionally, if the pH is properly controlled, the oxidizing performance of ClO2and its by-product ClO2-will give its full play, which may reduce the residual concentration of ClO2-and greatly reduce the actual dosage of ClO2. Results reveal that above pH6.9, if ClO2/Mn2+was0.5, the Mn2+can be reduced to0.1mg/L effectively. And ClO2-can give full oxidizing performance and minimize the ClO2-accumulation. According to the above pH range, it can be concluded that the optimal pH is from6.9to8.0in the experiment.Low level Mn2+containing groundwater was also investigated in the study. Results indicate that by manganese sand filtration the removal efficiency of Mn2+reaches86.5%and the effluent concentration is far lower than the limits of Standards for Drinking Water Quality. At the filtration rate of12m/h, the continuous operation of manganese sand filtration column has a stable effect on Mn2+removal. The oxidizing ability of disinfectant chloramines is less than liquid chlorine, so it can avoid the black and black brown precipitate MnO2forming. Moreover, when the mass ratio of ClO2and nitrogen is4:1, the disinfection effect is best.