July 7, 2011

Designed to be a good neighbor

When King County was seeking public input during the Brightwater siting process, people clearly expressed an interest in sustainable design and how the plant could employ new technologies and design features to maximize its environmental benefit.

The team of CH2M Hill, Brown and Caldwell, and Mithun has worked with King County to site, environmentally evaluate, design and support construction of the regional wastewater treatment plant. Brightwater will serve the northern portion of the county’s service area when it goes into operation later this year.

Image courtesy of King County [enlarge]

Wastewater runs through cassettes as part of the MBR process.

The Brightwater project includes a state-of-the-art advanced wastewater treatment and reclamation facility on a site that formerly hosted wrecking yards and other industrial uses. The site is being transformed into a park-like area with streams, wetlands, trails, overlook structures, and even an environmental education/community center.

Innovative design delivery

Building a plant that is a good neighbor — with advanced odor control and environmentally conscious features — required a dedicated and focused design team to put plans on paper. Early design tasks included screening and selecting technologies, authoring a facilities plan required by the state Department of Ecology, refining the treatment plant layout, and preparing schematic designs.

The team developed construction documents consisting of more than 6,000 drawings and supporting specifications, organized into multiple contract packages. Drawings were prepared using 3-D modeling software that provided detailed images of process facilities. The design team made extensive use of 3-D visualization tools to enable county staff to optimize facility layouts for functionality and ease of maintenance.

The 3-D model files also were provided to the construction contractors to aid in planning and execution of their work.

The Brightwater design was completed in January 2007. Construction is nearly finished, with a public grand opening set for Sept. 24.

The MBR process

What is a membrane bio-reactor? An MBR uses filtration to separate bacteria from treated water. Bacteria are essential to the treatment process.

It’s a state-of-the-art technology that was originally developed for the drinking water industry but is now used increasingly to provide advanced levels of wastewater treatment.

The filter or membrane is used in lieu of relying on gravity to separate bacteria from treated water in a large basin or clarifier, which is typical of conventional wastewater treatment. The MBR process gets wastewater seven to 10 times cleaner than conventional secondary treatment, which already does an excellent job at meeting or exceeding Clean Water Act standards.

The MBR process was chosen over conventional treatment following an extensive evaluation of cost, engineering, operation and maintenance, environmental and community factors. The primary reasons for selection were the significant improvement in effluent quality and reduced footprint offered by the MBR, at equal or less cost of competing processes. A portion of the MBR effluent will be reused as Class A reclaimed water, the highest quality recognized by the state for reuse.

Brightwater also will use chemically enhanced primary treatment to allow the plant to handle high peak flows exceeding the MBR capacity that may be experienced during short durations.

Primary treatment uses gravity to settle the solids in the incoming sewage. Like the name implies, chemically enhanced primary treatment uses chemicals to increase the amount of solids that can be settled out. This process allowed the county to optimize the size of the MBR to make it cost-effective and enable its use at Brightwater while still providing better overall effluent quality than a conventional treatment plant.

The use of MBR at Brightwater will significantly reduce the annual pollutant discharge to Puget Sound compared to a conventional treatment plant.

When Brightwater comes online, it will be the largest MBR treatment plant in North America, according to membrane manufacturer GE/Zenon.

Resources from wastewater

Brightwater solids-handling facilities include the ability to treat the solids from the primary treatment process and the separated bacteria that are left over from the treatment process. These facilities include digesters where “anaerobic” bacteria — bacteria that thrive in an environment without oxygen — provide treatment and reduce the amount of solids in the process.

Methane gas, a natural by-product of the digestion process, can be used to heat and power plant process units, reducing the need to buy electricity. The treated solids will be dewatered and turned into nutrient-rich biosolids that will be beneficially reused as a soil amendment for farms and forests. Eastern Washington farmers who grow wheat and hops are especially fond of this product.

To ensure we’re also being a good neighbor, all treatment processing facilities, including the biosolids truck-loading bay, are fully enclosed, with air conveyed to the odor control facilities where it is scrubbed before release to the atmosphere.

Brightwater’s odor control will be virtually unsurpassed. King County invested $65 million in odor control to keep its promise to the community that there would be no odors past the fence line. These are the most stringent air quality standards for any treatment plant in the U.S.

Resource recovery/reuse

One of the greatest benefits of Brightwater is that nearly all the wastewater will be treated to Class A reclaimed water standards, so there are many opportunities to make this water available for irrigation, industry and almost any other use except drinking.

Brightwater initially will produce 7 million gallons of reclaimed water each day. Space is reserved on-site for facilities which would increase reclaimed water production to 21 million gallons a day.

Brightwater’s reclaimed water will initially be used on site for irrigation, tank cleaning and other activities to conserve and reduce potable water use. Reclaimed water will also be distributed off site for use at other King County facilities and privately owned land. The county is studying ways to make the reclaimed water even more widely available.

Biosolids from the treatment plant will be digested and dewatered for beneficial use off site, primarily through agricultural application.

Other Stories:

• Brightwater design weds form and function
  
• Public process helped make Brightwater a reality
  
• Crews worked quickly to install marine outfall
  
• A look around Brightwater
  
• A place for hands-on environmental education