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Feasibility Study <br />Water Treatment Plant <br />City of Lino Lakes, MN <br />WSB Project No. 015822-000 Page 20 <br />The advantages of a Pressure Filtration system include: <br />1.) Can be constructed on one floor level. <br />The disadvantages of a Pressure Filtration system include: <br />1.) Pressure filters are not open to view and difficult to access internally. This <br />reduces the observation, operation, and maintenance of the filter cells and <br />associated components. <br />2.) Usually does not have an upstream detention tank to effectively oxidize and treat <br />manganese and iron. <br />3.) Odors in drinking water are more difficult to remove without a full aeration <br />process. <br />4.) Strong dehumidification is needed to reduce corrosion of the filters due to high <br />humidity and sweating of the pressure filters. <br />5.) Steel filters need to be sand blasted and repainted every 20 years like a water <br />tower. <br />6.) Less flexibility when disruption to normal operation occurs during routine <br />maintenance procedures. <br />6.4.4 Recommended Filtration Option <br />A Conventional Gravity Filtration system that is modified to provide for biological filtration <br />with an initial treatment capacity of approximately 6,000 gpm is recommended for the City <br />of Lino Lakes. A gravity filtration system offers many more advantages over a pressure <br />filtration system while biological filtration will significantly reduce chemical costs, provide <br />longer filter runs, and save many millions of gallons of water each year for the City. A <br />water treatment pilot study should be conducted as the first step to verify the <br />effectiveness of the full scale treatment process. Ten States Standards requires filtration <br />rates from 2 to 4 gpm per square foot (ft2) of filter media when determining the size of a <br />filtration system. A typical filtration rate is 2 to 3 gpm/ft2 for manganese and iron <br />removal. For a filtration rate of 6,000 gpm under normal operating conditions, the facility <br />will require 3,000 ft2 of filter media at a filter loading rate of 2 gpm/ ft2 or 2,000 ft2 of filter <br />media at a loading rate of 3 gpm/ft2. To allow each filter to be thoroughly backwashed <br />and to provide operational flexibility, four to six filter cells will be required depending on <br />the results of the pilot study and the filter loading rate needed to provide efficient <br />treatment of manganese and iron. <br />Water Treatment Pilot Plant Pilot Plant-Laboratory Trailer