A treatment plant expansion for two wastewater districts in Oregon is designed to deliver environmental, economic and social benefits


Rapid growth, tighter regulations and aging infrastructure were challenging the wastewater systems in Clackamas County, Ore. In response, two wastewater districts teamed up to expand the Tri-City Water Pollution Control Plant in Oregon City.

Designed with extensive public input, the $90 million expansion includes everything from advanced membrane bioreactor (MBR) technology to bike trails and wheelchair-accessible plant tour routes.

The 2-year construction project started with six years of public discussion that sent a clear message: The community wanted sustainable features built into the new facility, operated by Clackamas County Water Environment Services.

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“There are three pieces of sustainability: environmental, economic and social,” says technical support consultant Dale Richwine, president of Richwine Environmental of Beaverton. The plant, serving about 66,000 customers, went online in February 2011. It serves the Tri-City Service District and the neighboring Clackamas County Service District #1. The Clackamas district’s Kellogg Creek treatment plant had exceeded its design capacity and was leasing capacity from the Tri-City plant, which was also nearing its operational limits.

Both districts, in suburban Portland, now have adequate treatment capacity for at least 10 years and have avoided a building moratorium that could have been enforced by the state Department of Environmental Quality.

 

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Efficient treatment

Clackamas County chose the GE-Zenon membrane bioreactor (MBR) with hollow-fiber membranes from GE Water & Process Technologies.

“It’s producing effluent that is almost drinking water quality,” says Doug Harbaugh, county water quality manager. “It’s unbelievable how clean it is. The operators are happy to work on the cutting-edge of membrane technology. We’re one of the biggest MBRs on the west coast.”

The process is supported by high-efficiency equipment, such as WEMCO-Hidrostal pumps from Weir Specialty Pumps/WEMCO Pump. The UV disinfection system from Ozonia (Infilco Degremont) uses vertical tubes to minimize power use. “It can be turned down to 7 percent of total output rather than the normal 30 percent, and it automatically matches the UV dose to what is needed,” says Richwine. “We put out virtually zero coliform.”

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The new buildings were laid out to allow for modular expansion without increasing the plant’s footprint. Expansions, planned about every three to five years for the foreseeable future, should keep the plant adequate through 2050. Incremental revenue from fees paid by new users will pay for the expansions.

As part of the expansion, five 300 hp aeration blowers were replaced with 250 hp high-speed turbo blowers from HSI to serve both the old and new facilities. The blowers use 17 percent less energy while increasing airflow by 50 percent, boosting performance and making it unnecessary to add a blower building for the new plant. That saved $7 million and brought in a $183,000 efficiency rebate from the Energy Trust of Oregon.

A three-level lighting design allows the plant staff to use only the amount of lighting necessary. The first level uses skylights for daylighting, adequate for most tasks on sunny days. High-efficiency fluorescent lamps provide two more levels of lighting, operated by separate switches. At night, all exterior lights are controlled by motion sensors to minimize energy use and reduce light pollution.

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A Caterpillar 2.5 MW backup generator is connected to the Portland General Electric (PGE) utility grid under the utility’s dispatchable power program. “They can turn it on anytime for peak shaving,” says Richwine. The utility controls the generator and can use it for up to 400 hours a year. In exchange, PGE pays all maintenance and fuel costs and provided $575,000 toward the $1.3 million cost of the generator.

The plant’s HVAC system was designed for conversion to hot-water heating. It will use reclaimed heat from an engine-generator as part of a future expansion of the solids-handling system. The buildings are automatically ventilated to maintain a slight negative pressure, stopping the escape of odors while optimizing power use.

 

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Voice of the people

The plant expansion had to fit in a small footprint because the property is confined by the Willamette and Clackamas rivers to the north and west, an old landfill to the south, and a major freeway to the east.

“On the west is Clackamette Cove where a developer is planning to build a $100 million condominium project within 100 feet of the plant,” says Richwine. “It came down to how we could enhance the neighborhood. We’re very proud of the end product.”

Citizens in both districts and in the three communities served by the plant were consulted from the start. One advisory committee included various city professionals, while another included citizens and elected officials from each community. All meetings were open to the public, and several community surveys helped identify priorities and keep the committees on task.

“They wanted this plant to be as sustainable as possible while remaining cost-effective,” says Richwine. Rate impact was fourth among priorities, and water quality came in third. The most important elements were open space for public access and links to bike trails in the area.

“An MBR was selected because it can be built indoors with a small footprint,” says Richwine. “The new buildings have a commercial look and screen the old plant from the condo development next door. In addition, the modular design means the districts can add additional capacity in a just-in-time fashion, mitigating the need to invest in large capacity construction that would likely sit idle waiting for future customers to show up”.

 

Public education component

In line with residents’ wishes, the plant was laid out to accommodate educational and public tours and to be wheelchair accessible. The Oregon Museum of Science and Industry in Portland designed displays and interactive exhibits in and around the facility. “People can see how the screening system operates, touch membranes and learn about stormwater management,” says Richwine.

Tours end by going through a 72-inch pipe removed from the plant’s outfall during construction. A local artist created a mural inside with signage to illustrate flow levels. “They can get a feel for how much flow really comes through the treatment plant,” says Richwine.

Equipment manufacturers such as JWC Environmental, maker of the Muffin Monster grinder, and GE Water & Process Technologies provided funding and materials and helped with the design and content of the displays. General contractor Slayden Construction donated display installation, including concrete.

Harbaugh says operators enjoy the tours: “They really enjoy being able to share their work with people. This is a chance to showcase what we do for a living, how we protect the environment and public health, and how we provide a great service for ratepayers.”


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