Water Treatment Process

Rock Creek Water Resource Recovery Facility

The Rock Creek Water Resource Recovery Facility, located in Hillsboro near Hillsboro High School, is an award-winning, state-of-the-art facility serving Washington County residents in Hillsboro, portions of Beaverton, Aloha, and unincorporated Washington County.

Today, the facility cleans 37 million gallons of wastewater on an average day to among the highest safety and quality standards in the nation. Through advanced technology and processes, the Rock Creek facility treats and removes valuable resources from water collected from homes and businesses, as well as excess flows from the Forest Grove and Hillsboro facilities sent by pipeline during the wetter winter months. This water flows through a strategic process of liquids and solids recovery. The water is then returned to Washington County’s only river — the Tualatin. The returned water is so clean, it improves the river’s water quality.

Cleaned water is also used for local irrigation, and natural byproducts of the treatment process are converted to electricity and heat and used as soil amendments. Captured methane gas, a byproduct of anaerobic digestion, supplies electrical power for the facility. A nutrient recovery facility built at Rock Creek through a partnership with Ostara Nutrient Recovery Technologies captures 80% of the phosphorus from the recycled wastewater stream and converts it into a premium, slow-release fertilizer used in agriculture and nurseries.

Rock Creek began operations in 1978 to reverse decades of severe water pollution in the Tualatin River and its tributaries, and to meet the demands of a growing population. The facility centralized a scattered system of inefficient wastewater treatment plants, creating one of the most efficient and advanced facilities in the world.

Aerial image of Clean Water Services' Rock Creek Water Resource Recovery Facility with the view of the mountains in the background and Rock Creek, a main tributary to the Tualatin River, in the foreground.

Rock Creek Water Resource Recovery Facility Process

At the Rock Creek Water Resource Recovery Facility, used water flows through a series of processes (PDF): preliminary, primary, secondary, tertiary, disinfection, and effluent discharge.

Nutrient Recovery

In 2009, the Durham Water Resource Recovery Facility became the first in the United States to recover fertilizer using the Ostara struvite recovery system. In 2012, Clean Water Services opened the world’s largest municipal nutrient recovery facility at the Rock Creek Water Resource Recovery Facility in 2012.

Ostara Nutrient Recovery Technologies Inc. developed a technology that simplifies the treatment process by directly removing phosphorus and ammonia from wastewater. Traditional methods involve sending water through multiple cycles, which increases operating costs and takes up capacity while also forming struvite that can coat pipes, valves and other equipment. Instead this proprietary technology, called the PEARL™ process, diverts the phosphorus and other nutrients to a reactor that converts them into a premium, slow-release, environmentally friendly commercial fertilizer called Crystal Green®. This product is made from a renewable resource — wastewater — and is the most environmentally responsible source of phosphorus available.

In addition to the benefits to our water resource recovery facilities, it takes one-seventh the amount of energy to create Crystal Green® as it takes to create an equal amount of conventional fertilizer. Crystal Green® is certified by the Oregon State Department of Agriculture. Its unique slow-release characteristics provide a steady, season-long supply of phosphorus and magnesium that is always available to the plants when they need it. It’s also a key ingredient in Clean Water Grow® Plant Food, our retail fertilizer product.


  • Pollution reduction and reduced greenhouse gas emissions through reduced energy usage
  • Reduced chemical use
  • Revenue generation from the sale of Crystal Green® fertilizer
  • Increased water resource recovery facility reliability and capacity
  • Reduced operations and maintenance costs 
  • Generation of carbon credits

Rock Creek Facility Facts

  • Provides a higher level of treatment that 98% of the facilities in the nation
  • Meets over 1,000 permit conditions, including monthly, weekly, and daily limits established to protect the Tualatin River
  • Operates 24 hours a day, 365 days a year
  • Serves a growing population of 300,000 residents and a significant flow from high-tech industry
  • Cleans an average of 37 million gallons of wastewater per day
  • Recycles more than 18 dry tons of biosolids daily for use as a soil amendment
  • Produces approximately 300 tons of Crystal Green®
  • Meets 30% of facility electrical needs through the self-generation of energy
  • U.S. EPA National Clean Water Act Recognition Award (2006) for the best operated and maintained large, advanced treatment facility in the nation
  • National Association of Clean Water Agencies (NACWA) Gold Award for 100% permit compliance achieved over multiple years