Plant overhauls filtration system to save 50,000 gal per day
The City of Salida, Colo., stands in the middle of the state in the Upper Arkansas River Valley, settled in the heart of the Rockies. Lonnie Oversole is plant manager for a water treatment facility that serves the approximately 6,000 residents of Salida and supports the influx of visitors that are critical to the area’s economy. Recently, Oversole became frustrated by the consistently short filtration run-times and the large amount of water wasted by the four dual-cell bottom filters used to clean the region’s drinking water. In an area with a history of dry seasons and drought-like conditions, the need to carefully conserve water is critical.
Oversole believed that in order to drive improvement in productivity, he would need to update the entire filtration system, which was installed when the plant was built in 1959. While the filter media was a top priority for replacement, Oversole realized it would also be beneficial to install new underdrains and add air scour to the filters to maximize performance.
The plant worked with SGM Eng. to research and compare the various options and service providers available in order to make recommendations to Oversole regarding the best solution to improve process efficiency. In the end, Xylem’s Leopold Type XATM underdrain with I.M.S. 200 media retainer, new filter media (12-in. silica sand/18-in. anthracite) and wash troughs emerged as a suitable choice. Oversole and his team were particularly attracted to the I.M.S. media retainer, which eliminates the need for the support gravel used with older equipment while increasing the filter depth and freeboard. A smooth installation by Moltz Construction concluded in May 2014.
The underdrain operates by collecting filtered water during the filter run and efficiently distributing air and water during its highly effective backwash cycle, which in turn contributes to longer filter runs, reduced operating costs and improved production of clean drinking water. The low-profile underdrain 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, resulting in a significant reduction in backwash water use. Prior to rehabilitation, the backwash procedure consisted of a hydraulic-only backwash with a high-rate wash cycle of up to 16 minutes. Backwashing each dual-cell filter used approximately 95,000 to 105,000 gal of water. The rehabilitation of the filters with integral air scour reduced the filter high-rate backwash down to only 7 minutes, resulting in a 50% reduction in water usage during the new backwash cycle for each dual-cell filter.
Before rehabilitation, Salida used 5% of its production water for filter backwash purposes based upon an average production rate of 1 to 2 mgd; it is now using less than 2%. With the Leopold filter system, the plant is saving approximately 50,000 gal of water that was previously used for backwash purposes per day.
The I.M.S. 200 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 to 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. The increased liftoff resistance provides additional assurances to the owner that their system will run consistently and reliably throughout a wide range of operating conditions.
Oversole reports that filter runs have tripled. The inefficiency of the previous system resulted in limited filter run times, as the filter media had to be cleaned via backwash every 90 hours. Now the filters can run three times as long before requiring a backwash. The new filters produce higher-quality effluent, and ultimately higher-quality water is delivered to the residents and tourists of Salida. Oversole is pleased with the results, cost savings and overall return on his investment.