Filtration and manganese removal

Manganese removal through a filter bed is generally carried out and accepted by practitioners and researchers as occurring through catalytic oxidation at the surface of MnO₂ coated media, although manganese passage through a coated media filter has been little investigated. To better understand the kinetics of Mn removal through a naturally coated filter, a pilot plant consisting of four filter columns packed with various sand and coal media was used to investigate manganese removal using different chlorine species, viz. chlorine, calcium hypochlorite and sodium hypochlorite, in water of pH 6.6–8.0. Outcomes of the investigation were a clearly observed association of the bulk of Mn removed with the build-up of carbonaceous material in the filter column, and the observation that while Mn was removed through the filter column, 75–85% of such removal took place in the top 20–40 mm of the media column of 0.9–1.0 m overall depth. This investigation suggests that commonly held beliefs regarding the design of catalytic filters should be revisited and the actual removal mechanisms contributing to the overall removal be reassessed. Considerable savings in operation/pre-conditioning of filters may be possible with an improved understanding of the Mn removal through the filter column.