John E. Tobiason
The focus of this research was to determine the performance of different types of media for a post-filter second-stage contactor for the removal of manganese from a drinking water source. The Aquarion Water Company’s Lantern Hill (LH) water treatment facility in Stonington, CT served as the motivation for this study. The groundwater at this site contains significant concentrations of manganese, averaging 0.2 mg/L, as well as iron, 2.3 mg/L, and total organic carbon (TOC), 3.5 mg/L. Currently, the Lantern Hill facility is using a combination of pH adjustment, potassium permanganate, chlorine, and cationic polymer addition prior to down flow through a dual media, anthracite over green sand, direct filtration process.
Levels of prefilter chlorine required to maintain a filter effluent manganese concentration of 0.02 mg/L or less result in unacceptable levels of disinfection byproducts (DBPs), specifically trihalomethanes (THMs) and haloacetic acids (HAAs). Prior UMass/AWC research has shown that a two-stage approach, with a first-stage dual media (DM) filter for the removal of particulate matter, including oxidized iron and some TOC, followed by a second-stage media contactor for manganese removal, is effective. Addition of chlorine after the first-stage filter results in much lower DBP levels compared to the addition of chlorine to the raw water at a level that yields effective manganese control. The design of a facility upgrade is in progress, which requires more information on media performance.