Big energy-savings as giant MBR opens near Seattle

What is claimed to be the world's largest membrane bioreactor (MBR) installation was opened on 24 September 2011 at the Brightwater Wastewater Treatment Plant near Seattle in the US Pacific Northwest.

Built for King County, Washington, the plant will have the capacity to treat an average of 36 MGD (136,000 m³/d) of wastewater. By 2040, treatment capacity will be expanded to 54 MGD (204,000 m³/d). These capacities are for average wet-weather flows.

The plant must also be able to accommodate peak hourly flows of 130 MGD (492,000 m³/d) at start-up and 170 MGD (643,000 m³/d) by 2040.

The plant is at the centre of major county improvements to its regional sewage treatment system, which are needed to handle rapid population growth in the greater Seattle/Puget Sound region. Its energy-saving technology is already earning an energy rebate from the Snohomish County Public Utility District (SCPUD).

SCPUD Board of Commissioners president Dave Aldrich said the utility wanted to recognize Brightwater's approach to saving energy as the plant opens. The utility estimates the energy savings will result in a rebate check of approximately US$ 265,000 by the end of 2011.

"Treating wastewater to high environmental standards requires a large energy footprint, and the state-of-the-art technology King County is using demonstrates it is committed to minimizing that footprint," said Aldrich. "We are impressed with Brightwater's approach to saving energy and look forward to working with King County on more efficiencies once plant operations begin."

The technologies bringing the savings include:

  • Installation of several high efficiency micro turbine blowers that will supply air to the plant aeration system. They are expected to operate 30-50% more efficiently than traditional blowers.

  • Modification of the air-handling system: by optimizing the amount of air required for operation of the GE ZeeWeed MBR, Brightwater expects it can reduce the power consumption by around 50%.

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