Assessment of the suitability of greensand filtration for Mn removal for private wells

Abstract

Greensand filtration is a common treatment option for manganese, sulphide, and iron removal; poor maintenance, however, can compromise effectiveness, leading to increased post-treatment Mn concentrations. A private drinking-water well in exceedance of Health Canada’s maximum allowable concentration for Mn was sampled over a one-year period to assess Mn removal via greensand filtration. Mn concentrations post-treatment were approximately twofold higher than raw well water. Reducing conditions, evidenced by negative oxidation-reduction potential (ORP) of the effluent, were central to transforming solid-phase Mn-oxides to soluble Mn(II). Monitoring revealed that water usage patterns caused variability in post-treatment Mn, with peak concentrations (>3.5x higher than influent water) observed after a 7-day idle period. As inadequate oxidant addition can lead to reducing conditions, monitoring ORP may facilitate proxy surveillance for Mn release. Findings underscore the importance of human factors (e.g., aesthetic concerns, barriers to maintenance, perceived risk) when evaluating overall benefits and drawbacks of treatment systems.