Brightwater Treatment Plant – a clean water treatment facility

The process

Preliminary

Preliminary treatment removes large objects from the untreated wastewater (influent) as it enters the treatment plant. The equipment includes screens for removing debris and grit facilities for removing sand, gravel and other inorganic matter.

Primary

Primary treatment is the process where most of the suspended solids settle out of the wastewater. The conventional primary system consists of rectangular clarifier units equipped with collection systems on the top and bottom. Most of the flows coming into the plant wil be treated here.

Advanced secondary treatment - membrane bio-reactor (MBR) technology

Secondary treatment is the process where soluble and fine suspended dissolved materials not already removed at primary treatment are removed. As an alternative to conventional secondary processes (knows as conventional activated sludge), the Brightwater project uses Membrane Bioreactor (MBR) technology.

The MBR process includes:

• Fine screens which remove remaining debris and inorganic material larger than 2 mm from the wastewater
• Aeration basins that promote the growth of microorganisms that consume organic matter, thereby creating wastewater that has less organic matter that can decompose
• Membrane tanks, which separate the liquids from the solids

MBR technology provides substantially better effluent quality than conventional secondary treatment. MBR effluent is suitable for irrigation of golf courses, playfields, and for industrial heating and cooling. Learn more about the MBR system being used at Brightwater (PDF).

Split Flows

During times of high flows, flows above a certain design threshold will be split off after preliminary treatment, processed using an enhanced primary treatment and recombined with MBR effluent for disinfection and discharge to Puget Sound. As with the MBR effluent, this combined effluent also provides substantially better effluent quality than conventional secondary treatment.

Disinfection

The purpose of disinfection is to kill remaining pathogens in the effluent to a level that complies with water quality discharge permits. At Brightwater sodium hypochlorite is being used for disinfection.

Odor Control

King County is committed to operating Brightwater with no detectable odors. Stringent design and performance criteria have been established for odor prevention at the facility. All treatment facilities are covered, including the influent wet well, screening and grit handling, primary clarifiers, aeration basins, membrane tanks, and disinfection. The headworks and solids handling equipment are also fully enclosed.

Air is collected from these enclosed areas and is then routed to the odor control systems. This air is then treated by multistage chemical and biological scrubbers, followed by a final polishing stage of carbon adsorption. Each stage treats the process air to a greater degree.

Learn more about odor control at Brightwater.

Reclaimed Water

Washington state identifies standards for four classes of reclaimed water, with Class A being the highest. Class A reclaimed water can be safely used for many purposes that do not require drinking water, such as industrial processes; irrigation of edible crops, gardens and landscaping; and irrigation of public areas such as parks and recreational fields.

Brightwater will produce about 7 million gallons of Class A reclaimed water each day for off-site uses, and eventually up to 21 million gallons per day as demand requires. The reclaimed water is also being used on-site for irrigation, tank cleaning, and other processes that do not require potable water.

Biosolids

Biosolids are the nutrient-rich organic material produced by treating wastewater solids. After processing and treatment, they can be beneficially recycled as a fertilizer and soil amendment. King County has been safely recycling biosolids for more than 25 years. In 2010, more than 28,000 dry tons of biosolids from the county's two regional treatment plants were used for agriculture and forestry applications, and a portion was composted for use in landscaping and gardening.

Biosolids production include thickening, anaerobic digestion and dewatering of the wastewater solids. The stabilized, dewatered biosolids are hauled offsite and beneficially used along with biosolids from the West Point and South Treatment plants. The biosolids facilities will have odor control systems.

Visit the Resource Recovery site to learn how King County recovers and recycles beneficial resources from the wastewater treatment process.