By Mike Lutz, P.E., and Alan Pratt, P.E.
When the Parker Water and Sanitation District (PWSD) was established in 1962, it would have been difficult to envision the transformation of this rural community, set along Colorado’s Front Range. At the time, the district served fewer than 300 residents in a quiet town sustained by an agricultural economy.
Parker is located just 20-mi southeast of downtown Denver, however, and the rapid growth of the metropolitan area led to a steady increase in the community’s population over the following decades. Today, PWSD serves more than 50,000 residents within a 43-mi² service area. The population is projected to reach 120,000 by 2050.
While the demand for district water has grown exponentially, the supply—primarily groundwater—has declined. Early on, PWSD officials recognized that increased customer demand could eventually lead to critical water shortages, with an unsustainable rate of water extraction from local aquifers. In 1985, the district launched a 30-year plan to shift from the exclusive use of groundwater to a renewable water supply. The plan identified the year 2015 as a target for the completion of a multi-phase capital improvement program that would create the infrastructure for the capture, storage, treatment, and distribution of water from renewable sources.
With the opening of the $51.5-million Rueter-Hess Water Purification Facility (RHWPF) in mid-2015, the implementation of the district’s ambitious plan has now been fully realized. The new, 10-mgd treatment plant, which can be expanded to 40-mgd, produces potable water using surface water, groundwater, alluvial well water, and reclaimed wastewater stored in the nearby Rueter-Hess Reservoir, which was completed in 2013.
PWSD’s long-term planning effort allowed for a careful examination of potential treatment processes within the new plant. PWSD officials recognized that the plant’s source water—including surface runoff from nearby Cherry Creek (a tributary of the South Platte River), alluvial water from Cherry Creek, and reclaimed wastewater effluent from two water reclamation facilities—would likely result in a high organic content that would easily foul membranes during the filtering process, potentially requiring frequent cleaning and replacement.
In 2007, as planning for the facility began, project team representatives visited several plants in Japan and Australia to assess various treatment options. At the time, many Japanese water treatment plants had been equipped with ceramic membrane filter modules—the first such application in the world.
While ceramic membranes had been used on a smaller scale in industrial applications, such as food and pharmaceutical filtering processes, the technology had not previously been used for municipal drinking water filtration. In the 1990s, recognizing the potential for greater durability and efficiency, the Japanese developed the technology to make the ceramic filters large enough to be commercially viable for water plants. More than 115 plants in Japan are now using it successfully.
The representatives toured several facilities in Japan, included the NGK plant in Nagoya—approximately two hours south of Tokyo by train—where the ceramic membrane modules were being manufactured. The team also visited water treatment plants in Oshio and Shimizu, observing the treatment process and reviewing the maintenance of the modules with local plant representatives. In each case, PWSD officials and Dewberry engineers were assured of the ceramic membrane modules’ long-term durability and ease of maintenance.
The team did consider the more standard polymeric membrane filters, and visited a plant in Sydney, Australia, to explore that option. Ultimately, though, the advantages presented by the ceramic membrane filters were persuasive. The team determined that RHWPF would become the first drinking water plant in North America to implement the technology. The ceramic elements and the stainless steel housing in which the ceramic elements were installed were manufactured by Metawater (formerly NGK) in Japan. The stainless steel filter skids, including all the connecting piping, valves, and controls, were manufactured and assembled by Kruger Inc. in the United States.
RHWPF is also unique in that the plant uses a trio of state-of-the-art, sequential processes. The treatment begins with ballasted sedimentation followed by recirculated powdered activated carbon (PAC), and culminating with the ceramic membrane filtration. The treatment removes a high percentage of dissolved organic compounds (DOC) from the raw water, minimizing the formation of disinfection byproducts. Organic chemicals such as pharmaceuticals and other emerging contaminants that may be regulated in the future are removed through this process as well.
The treatment process begins as a new 50-cfs diversion pump station conveys water approximately 3-mi from Cherry Creek to the Rueter-Hess Reservoir. With 1,170-acres and a storage capacity of 72,000-acre-ft, the new reservoir was another key component in the district’s long-term development plan. The reservoir feeds raw water to RHWPF, where the innovative treatment takes place.
In the first filtration step, the Actiflo Turbo system, a ballasted sedimentation process is combined with a lamella clarifier. Developed by Kruger, the technology consists of compact chambers in which coagulation, flocculation, and sedimentation produce a high-rate of clarification that removes turbidity, metals, and a portion of the DOC from the raw water. The second step, Kruger’s Actiflo Carb process, features a recirculating PAC chamber that adsorbs most of the remaining organic matter. While PAC is used in many conventional treatment plants, RHWPF’s unique recirculating process, which sends used PAC back through the system, is one of the first such applications in the United States. The process reduces costs and improves the treatment by increasing the contact time between PAC particles and DOC for a more efficient and aggressive treatment.
The representatives toured several facilities in Japan, included the NGK plant in Nagoya—approximately two hours south of Tokyo by train—where the ceramic membrane modules were being manufactured.
The third step pumps the treated water through the ceramic membrane filters. The RHWPF plant features 560 8-i diameter by 1.5-m long ceramic modules, which remove any remaining particles larger than 0.1- μm, including algae, bacteria, and pathogenic protozoans (such as Giardia and Cryptosporidium), as well as any remaining microsand or PAC. The technology consists of monolithic extruded porous ceramic cylinders with parallel tubular channels that extend through the length of the cylinders, with each inner surface coated with a thin aluminum oxide ceramic membrane layer.
Up to 100 ceramic membrane modules are contained in each of the six skid-mounted filtration systems at RHWPF. While polymeric membranes typically deteriorate within six to 10 years, the ceramic membranes are anticipated to last 20 years or longer—as the plants in Japan are now demonstrating.
The skid-mounted ceramic membrane filters were delivered fully assembled and placed by a crane into the filter building ready to be connected to the plant piping and electrical systems. The filters are fully automated and require minimal operator attention. (For military applications, skid-mounted ceramic membrane filters could be moved from one location to another by truck to provide drinking water treatment at remote locations).
Ceramic membranes can be cleaned to like-new condition using stronger acid and chlorine solutions than polymeric membranes. Additional advantages include ceramic membranes require less frequent backwashes; the design flux rate is close to double that of a polymeric system; and they have lower transmembrane pressure losses. Overall, the ceramic membranes have a longer service life than a polymeric system. While the initial capital cost is higher—about double that of the polymeric membranes—the installation is practical in terms of long-term value and performance.
The overall efficiency of the processes yielded another key benefit: a smaller building. The shorter water detention times allowed for a single enclosed building, currently sized at 33,000-ft². The facility is designed to be expanded incrementally to 20-, 30-, and 40-mgd, with the building itself expandable to 65,000-ft². The control room, operations lab, and accessory spaces are located on an upper level, providing a clear view of the treatment processes.
Construction began on RHWPF in 2012 and the plant became fully operational in July 2015, following several months of successful, full-scale testing. An open house and dedication in October brought civic leaders and community members together to celebrate the delivery of one of the nation’s most advanced treatment plants.
With a realistic goal of operating with a water supply that is 75 percent renewable and 25 percent non-renewable, PWSD is setting a strong, sustainable example to help address water shortages throughout the country.
Mike Lutz, P.E., is Principal Engineer and Alan Pratt, P.E., is Principal Engineer, Dewberry. They can be reached at email@example.com; and firstname.lastname@example.org.