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It’s a whale of a job replacing the membrane filters at Brightwater Treatment Plant

By October 18, 2023November 16th, 2023No Comments


Two male operators hold a long ribbon of white strings as they move it to be placed into a giant metal frame. The frame already has a wall of ribbons installed, and various empty connectors can be seen along the edges of the frame. The white ribbon like items are membrane filters and are part of a special filtration system at the plant. Various empty frames sit in the background.

Brightwater utility worker Andre Brown and a Veolia field service representative work together to install new membrane filters.

What do whales and wastewater treatment have in common? A visit to Brightwater Treatment Plant in Woodinville explains it all.

Inside the wastewater treatment plant, giant baleen-like filters are on rare display as King County Wastewater Treatment Division staff begin replacing the plant’s 48 membrane-filtration modules. Brightwater’s state-of-the-art membrane filtration system filters out bacteria and viruses from wastewater – much like whale baleen – as a last step in cleaning water before it’s piped to Puget Sound.

This is the first time Brightwater is replacing its membrane modules since the plant came online in 2011 to serve various Eastside towns. The work will stretch for three years and won’t be replaced again for another 10 to 20 years.

“This is a first for everyone at Brightwater,” says Brightwater’s plant manager, Matt Nolan. “It’s so unique and rare, so we’re going to learn a lot from it.”

A male worker in a yellow safety vest, black hardhat, and clear safety glasses stands to the right of a large, metallic, frame filled with tons of white strings. The frame is being attached to a metal brace by a man on a ladder. The brace is connected to a large yellow crane that sits overhead. A partly cloudy sky makes up the background.

Brightwater operator-in-training, Justin Estes, and maintenance mechanic Blaine Rambough, work together to reinstall the freshly assembled membranes back into the basin.

Insane in the membrane!

Whales with baleen – such as humpbacks, blues, and greys – feed by gulping large amounts of water and straining out tasty morsels of krill, plankton, and small fish through dense, hair-like baleen. Similarly, Brightwater’s membranes remove the smallest of particles left over from the treatment process by sucking up to 40-million gallons of water a day like a straw.

Each membrane filter is built with numerous micro-sized pores, which are smaller than a red blood cell. Water is pushed through the pores to separate out material so small that individual bacteria can be removed in the process, but it is important that the water be as debris-free as possible, as the filters are delicate and are not meant to deal with anything other than extremely fine material.

“Nothing should be getting to the membranes other than treated water,” says Joseph Rheaume, a senior operator who’s helping assemble the connectors for the cassettes at Brightwater. “Material can cause a lot of damage to the filters, so we have to be extra careful when doing work with or around the membrane system so that nothing gets into the filters.”

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Million membrane mission

The membrane filters are contained in large metal frames called cassettes and housed within Brightwater’s eight active aeration basins, where air is added into wastewater to help microbes decompose pollutants.

During the work, each cassette is lifted out of the basin to be stripped of the old membranes and pressure washed. Crews then begin to reassemble them with all the components, starting with new pipes and connectors. Once those are placed, the new filters are carefully installed.

Brightwater has 160 membrane cassettes, each one holding 48 individual filtration modules, and each module holding 2,200 membrane fibers. In total, over 17 million membranes make up the stringy walls of these cassettes. When finished, over 2.6 million square feet of membranes will have been replaced. That’s enough to completely cover 45 football fields!

If that isn’t impressive enough, think of this — if each membrane were to be placed end to end, it would stretch around the entire diameter of the Earth!

The work requires plant staff to collaborate with Veolia North America, the manufacturer of the system.

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The membranes are so delicate they can’t be touched and must be kept moist at all times. Crews installing them have to work carefully, efficiently, and also in stages over the course of the next three years to keep service uninterrupted at Brightwater.

Sixteen cassettes have been finished as of the start of October, with another 72 due to be replaced in the summer of 2024. Once they’re all installed by 2025, the membranes won’t be making a return for at least a decade!