The Mdewakanton Sioux community in Minnesota, has experienced tremendous growth during the past 10 years. To keep up with water demand, the Tribe turned to Tonka Water for assistance. Like many upper Midwestern groundwater sources, their raw water contains iron and manganese at concentrations exceeding the recommendations of the Ten States Standards. The decision was made in 1994 to design a state-of-the-art iron and manganese removal water treatment plant around a 400-gpm Dualator® III, which would meet Minnesota state standards. Two additional 600 gpm Dualator® III units were installed in 2001, allowing the community to continue providing quality water for the increasing population.
Tonka Water’s Dualator® III is a low-profile water treatment system that incorporates aeration, detention, and filtration in a single packaged unit. The treatment process begins as the raw water enters the aerator section of the Dualator® III where iron oxidation takes place. Following aeration, the water flows through a static mixer located between the aerator and the integral detention section. Chlorine and potassium permanganate are added at the static mixer for oxidation of hydrogen sulfide and manganese. The chemical reactions are completed while traveling through the 30-minute detention section. In addition, a portion of the iron and manganese precipitate settles to the detention chamber floor, contributing to lengthening filter runs. Water from the detention section is uniformly collected and transferred to the filter, where it is distributed in the filter. The chemically-treated water flows through a dual media consisting of manganese greensand and anthracite where the iron and manganese precipitates are removed. The water is then pumped from the Dualator® III filter by high-service pumps out to the distribution system.
The raw water analysis summarized below reflects moderate concentrations of iron and calcium hardness. The Dualator® III has been highly efficient in delivering the effluent water quality.
|Iron (Fe)||1.2 mg/L||Not Detected|
|Manganese (Mn)||0.3 mg/L||< 0.02 mg/L|