Manganese removal from groundwater: characterization of filter media coating

Removal of manganese in conventional aeration-filtration groundwater treatment plants (GWTPs) results in the formation of a manganese oxide coating on filter media. The formation of this coating is an essential prerequisite for efficient manganese removal. Different manganese oxides have varying affinities for autocatalytic adsorption/oxidation of dissolved manganese. The aim of this study was to characterize manganese oxide(s) on filter media from successfully operating manganese removal plants. Characterization of filter media samples from full-scale groundwater treatment plants and identification of manganese species was carried out by X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-radiation (SEM-EDX), Raman spectroscopy and electron paramagnetic resonance (EPR). The results showed that the manganese oxide present in the aged coating was poorly crystalline. Results from the Raman spectroscopy and the detailed EPR analysis show that the manganese oxide in the ripened coating was of a Birnessite type, and of physicochemical origin. The results transpiring from this research suggest that the presence of Birnessite in the coating is essential for effective manganese removal in conventional aeration-filtration treatment plants, since Birnessite has a considerable ability to adsorb and oxidize dissolved manganese.