Joining Hands

The City of Edmonton’s membrane ultrafiltration plant supplies a local refinery with reclaimed effluent for production processes.
Joining Hands
The 82 mgd Gold Bar Wastewater Treatment Plant in Edmonton operates an ultrafiltration membrane treatment process as part of a treatment train that supplies reclaimed water to an oil refinery.

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Business is thriving in Edmonton, capital city of the Canadian province of Alberta. Forecast to be one of the country’s fastest growing economies over the next four years, its boom is driven by expansive oil sands projects.

But with an exploding population, outpacing the national growth rate, Edmonton’s demand for water also continues to rise. The concern for water supply and quality was a primary driver for the region’s substantial investment in a new wastewater membrane treatment plant.

The facility was commissioned in 2005; its main impetus was Suncor Energy’s Edmonton refinery and its need for more water. Located in the North Saskatchewan River Valley, the refinery at the time processed 135,000 barrels per day of crude oil into a wide range of consumer products. It was planning a major upgrade, switching to handle heavier crude mixtures. This meant the company was reconfiguring how the refinery worked and could explore better ways to use and reuse water, and reduce water consumption.

The best choice

Suncor considered a variety of alternatives and came down to a choice between building its own system to treat water from the river or entering into an agreement with EPCOR, the utility serving Edmonton, for the supply of water from the city’s 82 mgd Gold Bar Wastewater Treatment Plant, which then served a population of 700,000.

After a thorough cost-benefit and environmental evaluation, the company decided to partner with the city and EPCOR to build and operate Canada’s largest membrane-based water reuse facility, using advanced ultrafiltration membrane technology.

The arrangement called for the city to design, build and operate a membrane treatment facility at the Gold Bar plant for ultimate production of up to 5.5 mgd of water. In addition to the treatment facility, the project would include a 3.4-mile pipeline through two city parks located along the river valley and through a provincial park to carry effluent to the refinery.

Filter fibers

At the heart of the new membrane treatment plant are more than a million tiny tubes. Packed into filtration cartridges, membrane fibers draw clarified wastewater into their hollow centers under an applied vacuum. Pores on the membrane service measuring 0.04 micron filter out microscopic impurities to make the water clean enough for industrial uses.

The membrane fibers are part of a ZeeWeed ultrafiltration unit from GE Energy. For further treatment, the effluent passes through GE PRO 450 reverse osmosis (RO) units to remove molecular-level impurities, such as dissolved salts. The purified water is then used to help produce hydrogen and steam at the Edmonton refinery, and to replace 30 percent of cooling tower makeup water that was originally supplied via a river intake system.

After passing through 800-micron strainers used to protect the membranes, the secondary effluent is pumped to an elevated membrane flow distribution channel, which distributes the flow evenly between the eight ultrafiltration membrane trains. The membranes are contained within isolated concrete tanks, increasing the redundancy, reliability and flexibility of the system. The division of the system into eight identical units simplifies operations and maintenance.

Permeate pumps draw from a common suction header and provide the typical -1 and -8 psi vacuum that draws water from the outside in through hollow fiber membranes, leaving the lids behind. Periodically, the flow of permeate is reversed in a backwash to remove accumulated fouling from the fiber pores. The membrane surface is also scoured by air introduced through a coarse-bubble diffuser at the base of the membrane module. The air causes a high shear across the fiber surface that sweeps away highly concentrated solids.

Effluent from the ZeeWeed system flows through the pipeline to the refinery and hydrogen and steam supplier. A chlorine residual between 0.5 and 1 mg/L is maintained in the pipeline for biofilm control. Two 400 gpm RO systems at the steam plant reduce the conductivity of the treated effluent from about 1,000 micromoles to 10-15 micromoles.

Benefits add up fast

With an investment of $25 million to build the membrane plant, the pipeline to the refinery and the RO facility, the benefits are substantial. Suncor now uses about half the water previously required for refining, diverting 4 mgd — about 5 percent of Gold Bar plant’s outflow — to the Edmonton refinery, and saving more than 700 million gallons of water since commissioning. The refinery previously ran three pumps to fill its holding ponds and now only uses one. As an indicator of the heavier blends now processed and upgraded, the refinery collects 400 tons of sulfur daily, versus 40 tons when the refinery only handled light oil.

Though boiler feedwater treatment systems were still required at the refinery, these systems could be reconfigured to handle consistent-quality recycled municipal wastewater throughout the entire year instead of dealing with the extreme variations in raw river water quality. Supplying the eventual boiler feedwater system with consistent feedwater saves in capital cost for additional pretreatment. Further, since space is no longer required to expand the water treatment system, the refinery can now use the land for hydrocarbon processing equipment.

Edmonton’s Gold Bar plant membrane project pioneered an approach to water reuse for Canada, winning several awards that recognize leadership in water conservation and recycling. Perhaps the most valuable reward is the plant’s readiness to meet the water needs of future industries — a win/win for today and for tomorrow.

About the author

Jennifer Pawloski, M.Eng., P.E., is ZeeWeed 500 product manager with GE Power & Water —  Water & Process Technologies.


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