CLEANING AND DISINFECTION DEMONSTRATION STUDY TO HELP WITH CONVERSION OF A WASTEWATER FORCE MAIN TO RECLAIMED WATER DISTRIBUTION SERVICE

A new wastewater treatment plant, Brightwater, is being constructed by King County in Washington State. The 36 mgd treatment plant will be the third major plant located within the primary area served by King County. Currently, wastewater from the area where the new plant is sited is transferred to existing treatment plants via force mains and gravity interceptors.A distribution system will be required to convey reclaimed water from the new treatment facility to customers being served in the initial phase of the project. Two of the existing wastewater force mains currently in use will not be required for wastewater transmission once the new plant is operational. Two of the existing force mains run from the vicinity of the new plant to the area that will be initially served with reclaimed water. To reduce reclaimed water service startup costs, utilize existing resources, and minimize construction impacts in a built up area, one of the wastewater force mains will be converted for reclaimed water service. Conversion of infrastructure from wastewater to reclaimed water is not a common engineering practice, and delivered reclaimed water must meet stringent water quality standards. Therefore, during the design process a study was carried out at one of the existing King County wastewater treatment plants to test the cleaning and disinfecting procedures recommend for converting the force main from wastewater service to reclaimed water service. This successful testing demonstrated the feasibility of the plan, and gave engineers and operators the opportunity to evaluate and refine the procedures for conversion and disinfection of the existing force main.