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7.4 <br />7.4.1 <br />7.4.2 <br />Other options for iron and manganese removal are chemical oxidation followed by membrane <br />filtration or reverse osmosis. Both of these options are very expensive from a capital cost and <br />operations and maintenance standpoint and are not being considered further. <br />Hardness Removal <br />Hardness in water is caused by excess calcium and magnesium ions in the water. Hard water <br />causes scaling on fixtures and can plug pipes. Hardness can be removed from water on a <br />municipal scale by lime softening or ion exchange softening. <br />Lime Softening <br />Lime softening involves adding lime to water to raise the pH to a point where the calcium <br />carbonate is no longer soluble in the water. By forming calcium carbonate precipitate; the <br />calcium can be removed by filtration. A lime softening water treatment plant requires <br />sedimentation, clarification, and filtration and is very expensive. The capital cost of a lime <br />softening water treatment facility for Ramsey could be as much as $50 million. The operation <br />and maintenance (O&M) of a lime softening water treatment facility would also be significantly <br />more than an iron and manganese removal water treatment facility. Higher O&M for a lime <br />softening plant is due to a larger facility and more chemical processes. It should be noted that a <br />lime softening water treatment plant would also remove manganese and iron, and would not <br />require a separate treatment process. <br />Due to the high capital and O&M costs associated with a lime softening water treatment plant, it <br />is not recommended for the City of Ramsey. <br />Ion Exchange Softening <br />Ion exchange softening involves exchanging calcium and magnesium ions for sodium ions with <br />an ion exchange resin. This is exactly the same process that is used in a home water softener. <br />To regenerate an ion exchange softener, the resin is flushed with a concentrated solution of <br />brine. This regeneration process uses large quantities of salt. A municipal ion exchange water <br />softening system treating 3.5 MGD (Ramsey's 2040 average day demand) would use as much as <br />6 tons of salt every day. <br />The capital cost of adding an ion exchange water softening treatment process to a new water <br />treatment facility would be approximately $5 million. This cost would be in addition to an iron and <br />manganese removal water treatment plant. <br />The operation cost for salt and wasted water for an ion exchange softening process is <br />approximately $500 per million gallons of water treated. This is independent of whether it is done <br />by the City or by a resident. <br />An ion -exchange softening process would add approximately 3 tons of chloride to the wastewater <br />system which is ultimately discharged to the Mississippi River. While the MCES Metro <br />Wastewater Treatment Plant currently meets its discharge limits, chlorides have received more <br />regulatory scrutiny recently. Operating a municipal scale ion exchange softening process may <br />become less feasible in the future due to chlorides in wastewater. In addition, municipal scale ion <br />exchange softening might not be considered environmentally responsible. Due to the higher <br />operation and maintenance costs, potential future regulations, and environmental responsibility, <br />an ion -exchange softening process is not recommended. <br />FEASIBILITY STUDY RAMSY 154354 <br />Page 28 <br />