water standards.
King County, Wash., in accordance Washington’s Reclaimed Water Act, has launched an aggressive program for reclaiming water to alleviate drought-induced water shortages and to meet its growing water demands. King County currently maintains a pilot technology program and produces reclaimed water at two regional treatment facilities. Future plans include increased reclaimed water production as new facilities are built.
King County’s current reclaimed water program produces 284 million gallons per year of Class A reclaimed water at two regional wastewater plants. Since 1997, King County has used its reclaimed water for in-house treatment plant purposes and for irrigation of parks and athletic fields. Using reclaimed water leaves an equivalent amount of water in local streams and rivers or the municipal water supply, depending on the application.
South Plant
King County’s South Plant can produce up to 1.3 million gallons per day (mgd)of Class A reclaimed water. The facility currently produces 0.25 mgd. The reclaimed water is used for on-site plant processes and irrigation.
King County operates Fort Dent Park as one of the major sport facilities for the county with softball, soccer, cricket, rugby, and play fields. For five years, one softball and one soccer field were irrigated with reclaimed water, saving over 25 million gallons of drinking water. An all-weather soccer field was installed in 2003, so the annual water usage has gone down slightly.
Projects are being implemented to provide reclaimed water to other facilities near the South Plant, such as the Foster Golf Course in Tukwila. Foster Golf Course will irrigate its 4,788-yard, 18-hole golf course fairways, greens, and landscaping with 0.3 mgd of reclaimed water. A reclaimed water hydrant provides water for county and other jurisdiction staff to use for street sweeping, clean drains, catch basins using vector trucks, and to control dust. King County’s Water and Land Resources Division is using the water to irrigate newly planted vegetation for stream restoration and flood control projects. The use of reclaimed water trucks for drought response has allowed King County to get water uses online quickly and gain public support for reclaimed water use.
West Point Plant
King County’s West Point Plant can produce up to 0.70 mgd of Class A reclaimed water. Currently, all of the water, 0.5 mgd, is used internally at the facility, saving $161,000 and over 300,000 gallons of drinking water annually. The West Point facility also serves as an applied research center for King County to evaluate alternative technologies for producing reclaimed water. After thoroughly reviewing
technologies available for reclaiming wastewater, King County chose to investigate alternatives to both standard and advanced treatment processes, including membrane technologies. These studies provided a great deal of data that has been helpful both to King County and to other utilities investigating options
for reclaimed water treatment.
Planning & Outreach
King County is located on Puget Sound and covers more than 2,200 square miles. King County’s metropolitan area includes the city of Seattle and reaches across county lines. With more than 1.5 million people, King County is the 12th most populous county in the United States.
The county’s active support and promotion of reclaimed water began in 1991with proposals that resulted in the 1992 Reclaimed Water Use Act. In 1995, the county completed a water reclamation and reuse feasibility study and began producing Class A reclaimed water. By1999, King County’s 30-year Regional Wastewater Services Plan (RWSP) called for expanding the production and use of reclaimed water as a valuable resource. The county evaluates the potential for both satellite and centralized facilities. King County involves the community and areas affected by any potential upgrade or change to the wastewater treatment system through the following avenues:
• Written and online information
• Public outreach with public
notification
• Speaker bureaus
• Community open houses
• Treatment facility tours
The county evaluated locating a small, reclaimed water satellite facility in the Sammamish Valley. This proposed facility would provide water for a local golf course, athletic fields, nurseries, and crops. Two of the elements of the project involved technology assessment and public outreach. An early action phase of the project combined these elements by building a small pilot scale facility at one of their pump stations and using the reclaimed water produced to irrigate test garden plots that represent the range of water users in the valley.
Instead of a satellite facility, King County is currently exploring a morecost-effective option of producing reclaimed water at a new 36 mgd centralized facility called Brightwater. The proposed Brightwater facility would initially produce about five mgd of Class A reclaimed water when it comes online in 2010. The reclaimed water could be used at the treatment plant site for irrigation, tank washdown, and other processes requiring nonpotable water.
King County plans to make the reclaimed water available to customers along the effluent line and via pipeline to the Sammamish Valley area. The county has the ability to expand reclaimed water production capacity at Brightwater as customer demand grows. King County’s regional reclaimed water program continues to identify potential reclaimed water users near the regional wastewater plants and conveyance systems.
Treatment & Water Quality
Most of King County’s wastewater flows to one of two regional treatment plants — West Point and South Plant. West Point’s maximum design capacity is 133 mgd; its average flow is 108.8 mgd. South Plant’s maximum design capacity is 115 mgd; its average flow is 74.2 mgd. King County’s regional treatment plants use an activated sludge treatment process to treat all of the wastewater to the federal secondary treatment standards before discharge into the Puget Sound.
Only a portion of the water treated at the regional treatment plants is reclaimed for use. The reclaimed water receives additional treatment (beyond secondary treatment) to meet Class A standards. This advanced treatment involves using chemical coagulation and filtering the water through upflow sand filters to remove any remaining particles. A high-level chlorine disinfection process follows the filtration step. Monitoring equipment provides continuous monitoring of flow, turbidity, and chlorine residual to assure that only reclaimed water meeting the required Class A standard is sent to customers.
For new facilities, such as the Brightwater Treatment Plant, King County plans to use membrane bioreactor technology. This unit combines an activated sludge secondary treatment bioreactor and a microfiltration membrane. Membranes are submerged in the aeration tank and water is drawn through the membrane with a low-pressure vacuum, leaving the solids in the aeration tank. The membrane bioreactor can convert screened sewage to clean effluent in a single process — eliminating the need for separate primary, secondary, and advanced treatment. It produces a very high quality effluent meeting Class A criteria (after disinfection). This technology has the potential to significantly reduce plant footprint while producing improved effluent quality.
Financing
The South Plant upgrade to a reclamation facility cost $2.24 million, which did not include distribution to Fort Dent Park and the Boeing Longacres Complex. West Point’s capital cost for its reclaimed water upgrade was $300,000. King County uses a regional funding system for its large regional wastewater treatment system. The county believes that a regional system benefits everyone through increased wastewater capacity, lower wastewater rates, and improved public and environmental health.
For More Information: www.ecy.wa.gov
This article was abstracted from a compilation of case studies published by the Washington State Department of Ecology. The entire publication, titled Case Studies in Reclaimed Water Use, is available for free download at
www.ecy.wa.gov/bib lio/0510013.html.
