Catalytic Media (Greensand)

Catalytic media solve the slow-manganese problem. Manganese-dioxide-coated greensand (and modern pyrolusite-type media) catalyse the oxidation of iron and manganese at the grain surface and filter the product in a single bed — regenerated continuously by a trace oxidant or periodically by permanganate, giving reliable manganese removal in a compact pressure filter.

Catalytic filter media — manganese-dioxide-coated greensand and modern equivalents that catalyse and capture iron and manganese in one bed.

Borehole and groundwater supplies are chemically reducing, often free of oxygen, and characteristically carry dissolved iron and manganese, sometimes arsenic, fluoride, ammonia or hydrogen sulphide. Because the raw water is clear at the wellhead and only discolours after contact with air, treatment is designed around controlled oxidation followed by filtration — converting dissolved metals into a filterable floc before they reach the distribution network.

Iron and manganese removal is governed by oxidation kinetics and pH. Iron oxidises readily by aeration above pH 7; manganese is far slower and usually needs a higher pH, a stronger oxidant, or a catalytic filter media that adsorbs and auto-catalyses the reaction. Where biological iron and manganese removal is used, naturally occurring bacteria perform the oxidation within the filter at lower chemical dose, producing a compact, backwashable bed.

Arsenic and fluoride demand specific chemistry: arsenic is best removed after oxidising As(III) to As(V) followed by adsorption or co-precipitation onto iron oxides, while fluoride responds to activated alumina or bone-char adsorption. Continuous water-quality monitoring at the wellhead and post-filter closes the loop, confirming that breakthrough is detected before it reaches consumers and that backwash is triggered on differential pressure or run-time.