Laserfiche WebLink
7.3 <br />7.4 <br />7.4.1 <br />7.4.2 <br />maximum day demand nearly triples the average day demand. The projected 2040 maximum <br />day water demand is 10.3 MGD. <br />The recommended capacity of a water treatment plant for Ramsey is 10 MGD under normal <br />conditions with the ability to operate up to 15 MGD for shorter periods. This will allow the City to <br />comfortably treat maximum days through 2040 and possibly beyond. <br />Manganese and Iron Removal Options <br />The most common and most cost effective option for manganese and iron removal is chemical <br />oxidation followed by sand filtration. In groundwater, the manganese and iron ions are in <br />solution. When a strong oxidant is added to the water, it converts the manganese and iron to <br />filterable solids. <br />The oxidant that is added for iron oxidation is typically oxygen via aeration or chlorine. The <br />chemical oxidant that is added for manganese oxidation is typically sodium permanganate. <br />Chlorine is a less expensive chemical oxidant, but the reaction with manganese is too slow to be <br />used in a filtration process. Options for gravity and pressure filtration are presented later in this <br />chapter. <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 riot <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 />FEASIBILITY STUDY -DRAFT RAMSY 154354 <br />Page 26 <br />