City's Wastewater Plant to Support Power Project

Mike Kuenzi and Todd Vasey

What does a cogeneration plant, a wastewater treatment plant, a geothermal system and free compost have in common? The answer: the City of Klamath Falls, OR.

Klamath Falls has brought these elements together to develop one of the most innovative and aggressive environmental mitigation projects in the Northwest and in the nation. The $350 million, 500 megawatt cogen plant is owned by the city and is being built, operated and maintained by PacifiCorp.

IMCO General Construction, of Bellingham, WA, is giving the city-owned wastewater plant a major upgrade to supply the critically needed cooling water for the cogen plant. In addition, the city currently runs a geothermal system that provides many government buildings and local businesses heat; the upgrade will extend the geothermal loop to include the WWTP. And sludge from the wastewater treatment plant is being mixed with bulking agents (such as tree trimmings) to make compost and then given away to local gardeners and farmers. The city of Klamath has hired IMCO to provide its construction expertise in bringing all these elements together.

Electric Power Plant

In August of 1996, the City of Klamath Falls Cogen Project was awarded an exemption to build a 500-MW power plant. The cogen plant is being financed by revenues from a $300 million bond that was sponsored by the city. The bonds were purchased primarily by institutional investors. The Klamath Falls Cogen Project is the first new major merchant plant built on the West Coast and will service energy-starved California and the Northwest.

The natural-gas-fueled power plant is considered a "cogeneration" facility because it generates two forms of energy: electricity and industrial steam. When in operation, the cogen plant will provide enough energy to serve 400,000 homes and produce enough industrial steam for several local industries.

WWTP Improvements

Integral to the success of the cogen project is its reliance on the city to deliver a consistent flow of low cost, high quality cooling water from the city's wastewater treatment plant, according to Mike Kuenzi, Director of the city's Public Works Department.

"Because the cogen plant is dependent on the cooling water from the treatment plant, we had to design and build backup systems for the plant's processes. This means more pumps, storage, chlorination capabilities and greater operational flexibility," he said.

The city chose IMCO General Construction to upgrade the treatment plant to meet the demands of the new cogen plant. IMCO's $9.4 million contract includes:

• Construction of a 110-foot-diameter secondary clarifier which adds another step in the process of refining the wastewater and making it more suitable for cooling water.
• Construction of a sodium hypochlorite chemical feed facility that disinfects the effluent.
• Upgrading three existing aeration basins by dividing them into six basins and adding new mixers, pumps and gates. New air flow control valves, meters and dissolved oxygen probes are being included to enhance the existing diffusers.
• Construction of a 1,600-square-foot sludge thickening masonry building. The sludge has other composting materials added before the city makes it available for residents to use as fertilizer.
• Construction of a 5 mgd effluent pumping station to serve the cogen cooling towers.
• Construction of a new 4,400-square-foot control building which includes a reception area, offices, conference room, lunchroom and rest rooms.
• Installation of approximately 1,400 linear feet of concrete effluent piping with diameters ranging from 24" to 36". Some of this pipe is connected directly to part of the five miles of pipe going to the cogen plant. There was an additional 8,000 feet of process piping installed that varied from double containment piping to stainless steel air piping.

There have been several unique aspects to this project, according to IMCO Project Manager Todd Vasey. One of the more unusual involved extending the city's geothermal heat loop.

"The city uses the 180° natural geothermal water to heat many of its buildings, sidewalks and even some of the downtown businesses," Vasey said. "In this project, the city wanted to extend the geothermal loop to provide space heating to the WWTP's control, hypochlorite, and thickener buildings as well as provide a more reliable heat source to the digesters. The plan for routing the geothermal pipe even included a number of plant sidewalks to melt the snow. This has been a fascinating project in many ways."

While the wastewater treatment plant is gaining a number of innovative upgrades, the plan does not include increasing its capacity.

"This project is about increasing reliability and operational flexibility so that the WWTP can provide cooling water to the cogen plant 100% of the time." Kuenzi said. "In addition to improved reliability, we have added the ability to 'super-chlorinate' our effluent to mitigate the potential of algae growth in the five-mile-long conveyance pipeline. We have also upgraded the plant to reduce the potential of scaling at the cogen cooling towers through phosphorus removal at the WWTP."

The WWTP will provide the cogen plant with an estimated 2.8 to 4.2 million gallons of water a day, with over 60% being evaporated in the cooling towers. The remainder of the water, called the blow-down, is returned to the WWTP where it is dechlorinated and reduced in temperature prior to discharge into the Klamath River.

"Recycling of the WWTP effluent through the cogen does two things," Vasey said. "One, it alleviates the dependency of the cogen plant on freshwater in its cooling process. And secondly, the evaporation process reduces the amount of discharge going into the river by approximately 2.3 million gallons per day."

"Added to this," Kuenzi said, "is the fact that reuse of the effluent is now essentially a revenue generator because profits from the power sales will come directly back to the city. In addition, profit from the steam sales will go to supporting the on-going maintenance, operation and expansion of the city's geothermal system."

Once the cogen plant is on-line, the city of Klamath also will be able to participate in revenues generated by the cogen plant. Depending on market price of the electricity and once the bonds are paid off, the city could financially benefit up to $10 million to $15 million per year, which is more than annual revenues generated from property taxes.

Frank Imhof, president of IMCO, summarized the attitude of the different groups working on the project by stating, "our company has really appreciated being part of this project and part of a team of people who embrace innovation and strive for quality workmanship. The entire project has so many unique, trend setting aspects to it that it is a privilege to be able to provide our expertise. The team effort by the design engineer for the WWTP, Brown & Caldwell, the construction manager, URS/O'Brien Kreitzburg and the city of Klamath has made this project successful."

About the Authors:

Mike Kuenzi is Director of Public Works for the city of Klamath Falls. He has a bachelors degree in civil engineering from Cal State at Sacramento and Masters degree in environmental engineering for the University of Washington. Todd Vasey is Project Manager for IMCO General Construction, Bellingham, WA. He has a Bachelors degree in construction engineering technology from Montana State University. He has worked in both the consulting engineering and construction industries for the last 15 years.