ROCKY MOUNTAIN WATER MAY 2017 | 17 FEATURE So the plant worked with SGM Engineer-ing to research and compare the various options and service providers available in order to make informed recommen-dations regarding the best solution to improve process efficiency. In the end, Xylem’s Leopold® Type XA™ Underdrain I.M.S® 200 media retainer, new filter media (12 inch silica sand/18 inch anthra-cite), and wash troughs, emerged as the top choice. Oversole and his team were particularly attracted to Leopold’s new technology, which eliminates the need for the support gravel used with older equip-ment while increasing the filter depth and freeboard. Installation was performed by Moltz Construction, concluding in May 2014. The benefits of the new, state-of-the-art system were quickly evident and continue to deliver significant improvements. Additional security and ease of installation are a result of the innovative grout pocket built within the Type XA underdrain. The underdrain provides maximum uplift resistance and can withstand pressures up to 30 psi. The underdrain operates by collecting filtered water during the filter run and distributing air and water during its backwash cycle, which contributes to longer filter runs, reduced operating costs, and improved production of clean drinking water. A low-profile underdrain of this type also increases filter depth for additional driving head and media expansion within the filter. The air scour process allows for a collapse pulse cleaning of the filter media, creating a more efficient filter backwash that results in a significant reduction in backwash water used by the plant. Prior to the filter rehabilitation the backwash procedure consisted of a hydraulic only backwash in which the high-rate wash cycle would last up to 16 minutes. Backwashing each dual cell filter used approximately 95,000 to 105,000 gallons of water. The rehabilitation of the filters with integral air scour reduced the filter high-rate backwash to just 7 minutes, using approximately 44,800 gallons for each dual cell filter. “Before the rehabilitation we were using five percent of our production water for filter backwash purposes. We are now using less than 2 percent of our production water,” Oversole said. The facility on average is producing 1–2 mgd, and with the new filter system the plant is saving approximately 50,000 gpd that was previously used for backwash purposes. The new media retainer also proved to be extremely valuable to the plant’s new filter system. By replacing the gravel support structure the media retainer increased the vertical profile of the filter system allowing the filter to operate at increased headloss levels, extending filter run times. The equipment’s rigid construction and precision-engineered, injection-molded slots directly support the sand and anthracite above the underdrain and provide uniform distribution of backwash air and water adding to the overall system efficiency. Oversole reports filter runs have tripled. The inefficiency of the previous system resulted in limited filter run times, because the filter media had to be cleaned via backwash every 90 hours. Now the filters can run for 270 hours before requiring a backwash. The new filters produce higher quality effluent and ultimately higher quality water delivered to the residents and tourists of Salida. The utility has realized cost savings and an overall return on its investment. As Oversole looks to keeping the plant oper-ating at full speed and relying on the latest advances in water treatment, he appreci-ates that updated equipment means less time spent on upkeep and repairs. “I now feel confident knowing that ongoing maintenance and water waste will both be minimal, and that the Salida community will be well supplied with healthy water and prepared for any future dry seasons,” Oversole said. Bruce Wolfe is Senior Sales Engineer, Leopold, a Xylem brand. He joined the Leop-old team in 1994 as a field service technician before moving on to product development, applica-tion engineering, and his current position for the Rocky Mountain states.
RMW - May 2017
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