The city of Elkhorn, WI made the decision to replace an aging pressure filtration water treatment plant with a custom gravity system. The new water treatment plant features aeration, detention, and filtration within a single vessel, in addition to separate ion exchange vessels that are similar to those in use at the previous plant. The water system serves a population of about 10,000, through nearly three miles of distribution lines. The existing plants feature removal of radium, ammonia, and iron from well water, through aeration and pressure filtration. The new plant continues those removal needs, with iron removal related to aesthetic considerations.
The Tonka Water, a U.S. Water Brand Dualator® III pre-treatment system has a rated capacity of 1,100 gpm, and features process viewing hatches with 2 ft.-wide curbs. The aeration phase helps to provide for iron removal, via oxidizing soluble iron. Chemical feed additions, prior to the detention phase, help provide for ammonia removal, as well as arsenic. Raw water then spends approximately 25 minutes in the detention phase, before entering four gravity filter cells with dual media of 12 in. of anthracite, and 18 in. of Greensand Plus™. Three layers of graded gravel, and a layer of torpedo sand, provide the necessary support for the dual filtration media. Filtered water proceeds to three 9 ft.-diameter ion exchange vessels (softeners), accounting for design loading of 7 gpm/sq. ft., and where there is room to expand to a fourth vessel. The ion exchange phase helps provide for radium (radionuclide) and hardness reduction.
Dualator systems are designed to meet USEPA, Ten States Standards, and Canadian requirements for iron, manganese, and arsenic removal applications. They also have the capability of meeting a large range of flow rates, from 80 gpm to 2 MGD in one process train.