AWWA JAW57437

A high manganese (Mn) concentration in source water is a common problem faced by water utilities. Utilities often remove this Mn by oxidation of the manganous ion (Mn2+) to manganese oxide (MnO2(s)) using an oxidant, such as chlorine dioxide (ClO2). Excess MnO2(s) may remain in the water after treatment, causing brown staining on plumbing fixtures and laundry. Many water utilities experience Mn problems from effluent concentrations as low as 20 ug/L, leading some utilities to strive for finished water Mn2+ concentrations <10 ug/L. Most studies reported in the literature have not fully explored oxidation of low initial Mn2+ concentrations (60-200 ug/L) and the dose requirements of the primary oxidants, ClO2, potassium permanganate (KMnO4), and ozone (O3). The overall objective of this study was to evaluate these oxidants for the oxidation of low initial Mn2+ concentrations to Mn2+ <10 ug/L. Bench-scale experiments were performed by applying different doses of each oxidant to a raw surface water and measuring Mn2+ residuals over time. The study found that it was more difficult to remove Mn when the initial concentration was low, regardless of the oxidant used. ClO2, however, consistently produced final Mn2+ to <10 ug/L, generally within 60-120 s. All oxidants produced final Mn2+ <10 ug/L when the initial Mn2+ concentration was high (1,000 ug/L). The conclusions indicate that ClO2 may be a viable treatment alternative for water utilities wishing to reduce Mn concentrations in finished water to <10 ug/L. Includes 17 references, table, figures.