Raymond, New Hampshire is a growing community east of Manchester. The town’s existing two wells had high levels of iron and manganese, which led to consumer complaints of staining and colored water. In addition, due to a lack of supply capacity, they wanted to add a third well. The Town determined a new groundwater supply source was needed and a new water treatment plant would be designed to eliminate the iron and manganese as well as remove radon gas from the water supply. The Town worked with Tonka Water to design New England’s first Dualator® VI treatment plant. The plant successfully opened in 2004.
The treatment process consists of three steps in one compact system—aeration, detention and filtration. The aeration step is for radon/CO2 stripping and iron oxidation. Calcium hypochlorite and potassium permanganate are added after aeration for oxidation of manganese. The detention tank allows full oxidation of both iron and manganese to an insoluble state. The final step is filtration through a four-cell filter system using a dual-media filter bed of manganese greensand and anthracite. The anthracite cap serves to capture the larger iron and manganese precipitates, while the greensand removes the smaller manganese dioxide solids that pass through the anthracite.
Tonka Water customizes each Dualator® VI treatment plant to meet the requirements of each application. During the final stage of design, the state reviewing authority asked if we could modify our design to allow the operation of the system with one filter cell out of service. We responded by customizing the Dualator® VI filter section into an isolated cell design.
The raw water analysis summarized below reflects low concentrations of iron and high concentrations of manganese existing in the water. Since start-up the treatment process has been highly effective in delivering quality water as indicated below.
|Turbidity||0.35 mg/L||0.01 mg/L|
|Manganese (Mn)||1.3 mg/L||0.03 mg/L|