A pump station at Clean Water Services treatment plant is the first of its kind to receive certification as a green facility


Office buildings, schools, hotels, homes, banks and government buildings dominate the list of LEED certified buildings in the United States: buildings designed or refurbished to meet sustainability and energy efficiency standards.

 

And now there is an influent pump house on that list of nearly 2,000 buildings. “We wanted to see if it could be done with a process facility,” says Mark Poling, director of the Wastewater Treatment Department for Clean Water Services, the water resource management utility for the half-million customers in the Tualatin River Watershed in northwest Oregon.

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Completed in July 2008, the $38 million, 180 mgd pump station is the first ever to win a Leadership in Energy and Environmental Design award with its Silver certification. It is part of the Durham Advanced Wastewater Treatment plant in Tigard, a suburb of Portland, the city with the second-most LEED certified buildings in the country, according to the U.S. Green Building Council, which developed the LEED standards.

 

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LEED as the goal

Led by project consultant MWH Global, headquartered in Broomfield, Colo., the design focused on LEED factors such as energy and water conservation, site selection, stormwater management and building materials.

 

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Poling says the pump station uses significantly less energy than a standard design: the annual 1.2-million kWh saved is equivalent to that used by 109 average homes and eliminates carbon emissions equal to cutting 1.4 million miles of automobile driving.

 

The annual electricity cost savings will be about $77,000. The Energy Trust of Oregon (ETO) rewarded the plant with an efficiency rebate of $415,791 to help fund the use of variable-frequency drives and premium-efficiency motors. The project also qualified for $214,000 in Oregon Business Energy Tax Credits, which Clean Water Services is able to sell to qualifying third parties.

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A Siemens Water Technologies programmable logic controller (PLC) manages two 40 mgd pumps and four 25 mgd pumps manufactured by ITT Water & Wastewater - Flygt with variable-frequency drives from Siemens that operate the pumps at maximum efficiency.

 

Precise control

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The building’s air-handling unit, also with variable-frequency drives, keeps the motor control room at the optimal temperature, humidity and pressure. Automated pressure sensors control return air fans to maintain positive pressure. “VFDs are very sensitive to hydrogen sulfide, and pump stations have a lot of it,” says Poling. “Positive pressure prevents pulling air from the process area and prevents the sulfides from corroding the circuit board and other components in the VFDs.”

 

The pump station contains two wet wells because of the wide range of flows experienced throughout the year. “We get a lot of rain in the winter, and that’s when we get our highest flows,” says Poling. “But it’s extremely dry in the summer.” Summer flows average about 20 mgd versus peak flows of over 100 mgd in winter.

 

The wet wells are self-cleaning, a feature added to the design after operators and maintenance staff saw that capability in other facilities they visited. “The wet wells go through a cleaning cycle once or twice a week to remove the buildup of grease and debris and move it through the system in small amounts rather than getting a big flush during high flows,” says Poling. “And we don’t have to send operators to muck out debris.”

 

Operators like the new pump station because it is easier to control and more reliable, especially during high flows. “The old pump station was a little touchy and it was difficult to get the maximum flow out of it,” Poling says. “It was hard to stage pumps because we had three sizes of pumps. Some were old and some were newer, some were variable-speed and some weren’t.”

 

Design challenges

The LEED system assigns points for efficiency and sustainability, but many credits do not apply to a process facility like a pump station. That made it challenging to get the certification.

“You need someone who really understands the LEED certification process and can find where you can get points,” Poling says. Clean Water Services turned to Brightworks, a West Coast sustainability consulting firm with an office in Portland.

 

“Because wastewater plants are such huge energy consumers, we had a lot of opportunity to get points there,” Poling says. But other criteria, such as access to public transportation, parking capacity, bicycle storage, do not apply.

 

Site selection is another LEED category, and while Clean Water Services may not have scored many points there, the location offered some unique design challenges. “This is the plant’s outward face to a public park. It’s quite prominent because it’s three stories built into a hillside,” Poling notes.

 

Part of the design was to make the building fit the look of the neighborhood. “The roof mimics the park building roofs,” says Poling. “We pre-planted trees and shrubs that we knew wouldn’t be disturbed by the construction and got those growing early to provide some visual screening from most of the park.”

 

Along with the city park next door, the Durham plant is surrounded by a residential neighborhood, an elementary school, a high school and another park, so odor control was important.

At the former pump house, crews used bleach to scrub out odors. To save energy and cut chemical use, the design team selected a soil biofilter, sometimes referred to as a Bohn filter. Variable-frequency drives pull air from the wet wells and pass it through soil containing microorganisms that digest the odorous compounds. “We don’t need chemicals — it’s a much softer way of treating odors,” Poling says.

 

Other green projects

Clean Water Services has been working closely with Portland General Electric (PGE) and ETO since 2002 to reduce energy demand, boost energy efficiency and save ratepayers money. “We’ve replaced a lot of the lighting fixtures throughout our facilities,” Poling says. “When we need to replace motors, we’ve gone to premium-efficiency motors, and ETO has provided rebates.”

Nearly 4 percent of the nation’s electricity use goes toward moving and treating water and wastewater, according to the Electric Power Research Institute. Poling points out that Clean Water Services is one of PGE’s largest customers in Washington County. “Conservation is probably the greenest alternative because you don’t have to generate the power in the first place,” says Poling.

 

The Durham facility, one of four treatment plants in the district, also recycles more than 100 million gallons a year of cleaned wastewater for irrigation and more than 14 tons of biosolids daily for use as a soil amendment. It burns methane to generate more than 4 million kWh of electricity per year, enough to power 330 homes for a year.

 

“We’re in the environmental business,” says Poling. “This was a good direction for us to go. Our staff and the consultants did a superb job of building a large, sustainable facility.” Information about LEED certification can be found at www. usgbc.org.


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