09/05/2007 Council Packet - Laserfiche WebLink

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DRAFT 8 -17 -07 VIII. WATER PLANT OPTIONAL PROCESSES The 2004 City of Lino Lakes Comprehensive Water System Plan as prepared by TKDA had a section regarding water treatment for Lino Lakes. As Lino Lakes water supply is from the Jordan aquifer, recommending it has iron and manganese levels that exceed the secondary maximum contaminant levels (SMCL) of the safe Drinking Water Act as discussed in Section II of this report. There are three typical types of water treatment plants built for iron and manganese removal. They include a gravity open filter type plant, manufactured gravity filters in closed units and pressure filters. For this study we chose to do a preliminary layout and cost estimate for the manufactured gravity filters and the pressure filters. The manufactured gravity filters and pressure filters are modular in nature and are delivered with most of the internal components and piping attached. These processes are described below in more detail. A. MANUFACTURED GRAVITY FILTERS Gravity filtration is one of the oldest, most basic processes for water treatment. It involves allowing water to flow through a media, such as sand, to remove particulate matter in the water. Initially filters were large basins made of concrete with several feet of sand media that had limited capacity and required frequent cleaning. Advances in filtration technology have resulted in filters that are more compact with automated operation. For the proposed Lino Lakes treatment plant, we used manufactured filters that use silica sand and anthracite (granular coal) media for the preliminary layout of the gravity filter facility. The iron and manganese are oxidized by chemical addition forming a precipitant, which is removed in the filters. Different types of media and chemicals can be used to oxidize and filter the iron and manganese. The optimum approach is generally determined by pilot testing during the actual design. Figure 1 shows the preliminary layout for the gravity filter facility. Each filter is approximately 10 feet wide by 34 feet long and has the capacity to treat approximately 1.5 MGD of water per day (MGD). To meet the projected year 2030 peak demand of 6.0 MGD, four filters would be required with a fifth filter for redundancy. Ten State Standards require the system to meet the maximum day demand with one filter out of service. This allows the plant to maintain full capacity while one filter is backwashing or out Water Treatment Plant Study 12 13843.000