Manganese removal in groundwater treatment: practice, problems and probable solutions R. Buamah, B. Petrusevski, D. de Ridder, T. S. C. M. van de Wetering and J. C. Shippers ABSTRACT R. Buamah B. Petrusevski J. C. Shippers Department of Urban Water and Sanitation, UNESCO-IHE, Institute for Water Education, Westvest 7, Delft 2611 AX, The Netherlands E-mail: r.buamah@unesco-ihe.org D. de Ridder Kiwa Water Research, Groningenhaven 7, Nieuwegein 3433 PE, The Netherlands T. S. C. M. van de Wetering Brabant Wate, Magistratenlaan 200, ’s-Hertogenbosch 5223 MA, The Netherlands Most drinking water production plants use rapid sand filters for the removal of manganese from groundwater. The start-up of manganese removal on newly installed sand media is slow, taking several weeks till months. Reducing this period in order to prevent the loss of water during this phase has become an issue of concern. In this study pilot and bench scale experiments were conducted to investigate the mechanism, influence of operational conditions (e.g. filtration rate, manganese loading) and measures that enhance manganese removal capacity of the sand media. Other filter media were investigated with the objective of finding suitable substitutes for the sand. The development of the adsorptive/catalytic coating the sand media in a pilot plant was very slow, notwithstanding the relatively high pH of 8. Low manganese concentration and more frequent backwashing resulted in a longer start up period of the manganese removal. It can not be excluded, that nitrite has a negative effect as well. Measurements in the lab and bench scale tests show that the rate of adsorption/oxidation of manganese in the top layer of the filter bed is too low to explain the complete manganese removal in the filters. It is likely that the adsorptive catalyst in the top layer has partly been covered with ferric hydroxide. From the Freundlich’s isotherms determined for 6 different filter media, a crushed medium consisting of mainly manganese dioxide and some silica, iron and aluminium (Aquamandix) followed by iron oxide coated sand, containing some manganese, demonstrated highest adsorption capacities at pHs 6 and 8. These materials can therefore be potential substitutes for sand in situations of slow start-up of manganese removal. Key words | adsorption, catalytic, filter media, manganese, oxidation INTRODUCTION Groundwaters generally contain one or more contaminants like iron, manganese, ammonium, methane and natural organic matter e.g. humic acid. For drinking water supply purposes, these contaminants need to be removed or reduced to acceptable levels. High manganese levels in drinking water can give rise to aesthetical and health problems. Together with dissolved iron, manganese (II) could flocculate and form sediments in distribution lines. If the flow in the distribution lines increases (daily peak demand), the sediment can become re-suspended and may result in customer complaints of incidents of ‘black’ or ‘brown’ water. These ‘black water’ incidents may occur when manganese concentrations in treated water is as low as 0.02 mg/L (Sly et al. 1990; MWH 2005). To exclude the possible health hazard as a result of chronic exposure to manganese, a health-based guideline of 0.4 mg/L for the occurrence of manganese in drinking water has been recommended by WHO (2006). doi: 10.2166/ws.2009.009 89 Q IWA Publishing 2009 Water Science & Technology: Water Supply—WSTWS | 9.1 | 2009 Downloaded from http://iwaponline.com/ws/article-pdf/9/1/89/419083/89.pdf by guest on 27 November 2023