New cogen system triples energy output from biogas at Oregon WWTP

By Katie Fletcher | May 05, 2016

On May 4, Clean Water Services, Energy Trust of Oregon and the Oregon Department of Energy formally announced the implementation of a new cogeneration system that converts wastewater and grease into renewable energy. The innovative system, which is part of Clean Water Services Durham Treatment Facility, is the third cogeneration system in Oregon to codigest fats, oils and grease (FOG).

Amongst the people in attendance of the renewable energy facility opening were Andy Duyck, chair of Clean Water Services of Washington County; Michael Kaplan, director of the Oregon Department of Energy; and Betsy Kauffman, renewable energy sector lead of the Energy Trust of Oregon.

Since 1993, Durham has operated a 500-kW cogeneration system using biogas from the communities’ wastewater to offset its own energy usage. By replacing this smaller engine with two new Jenbacher 848-kW engines, Durham now has a 1.7 MW cogeneration system fueled by biogas produced from the anaerobic digestion (AD) of municipal wastewater solids as well as FOG from Washington County restaurants, commercial food processors and others. Average gallons of FOG codigested per week will start at 70,000 gallons and is expected to increase to 100,000 gallons within the next six months. The Durham campus hosts two, 1.3 million gallon digesters.

Prior to being fed to the engine, the biogas will need to be treated with a gas treatment system made by Unison Solutions that will remove hydrogen sulfide particulates, siloxane and moisture from the raw biogas.

“Clean Water Services Durham took the steps very deliberately and smartly to design a system that works for increasing the production of biogas to help maximize generation at the plant,”  said Dave Moldal, senior renewable project manager with the Energy Trust of Oregon. Modal added that like other plants, CWS didn’t have complete information or full confidence that there was sufficient FOG available in the marketplace, but they proved there is sufficient FOG available not only for this facility, but for many others in Oregon. “They’re really pioneers in proving that bumping biogas through codigestion, in this case primarily with FOG, can yield tremendous economic and energy benefits,” he said.

Bruce Cordon, business opportunities manager with Clean Water Services, attributes one of the reasons to install a new cogeneration system to population growth. Prior to implementing the new system, CWS was flaring a fair amount of excess gas, since the engine wasn’t large enough to handle the amount being generated. “We knew we had to do something, the engine was also starting to age a bit, so we set our sights on a bigger, more modern cogen system,” he said. “Energy is the most expensive operating cost we have after labor, and it’s very important to us to be able to manage it wisely, and so one approach to managing it, of course, is to generate your own.”

The new systems’ cogeneration output when coupled with its existing 403-kW solar electric system will generate 60 percent of the electricity needed to run the wastewater treatment plant (WWTP) and resource recovery facility, nearly tripling what the facility had the capacity to generate before. However, Cordon said there are a few challenges if the facility would ever hope to generate 100 percent of its electricity needs. “One of the challenges we face is that our treatment plant is required to meet treatment standards that are extremely high, much higher than most WWTP in the U.S.,” he said. Cordon said this is partly due to Oregon’s reputation as a green state, but also because a high amount of energy is needed to make the wastewater stream clean enough to meet the high standards. The Durham Treatment Facility cleans wastewater for nearly 250,000 residents of Beaverton, Tigard, Sherwood, Tualatin, Durham, King City, and portions of Clackamas and Multnomah Counties.

Cordon added, “I think a bigger problem is that our state has a 2 MW limit on self-generated power for folks like us, and we’re already there with this new system and our existing solar system, so we really can’t expand self-generation unless that law is somehow changed.”

Still, where it’s at today, the facility has the ability to generate more than half of its own energy needs from biogas and solar, which reduces greenhouse gas (GHG) emissions and helps Oregon meet its carbon reduction goals. Combined with the solar electric system, CWS expects to generate more than 12,800 MWh per year—enough electricity to power 1,100 homes and avoid producing 6,000 tons of CO2.

“From our perspective, this is another classic example of the evolution of wastewater treatment plants to resource recovery facilities,” Moldal said. According to Moldal, the first generation was really about protecting public health and the second generation of WWTP—in the ‘70s, ‘80s—began producing value-added products like water, soil amendments and also generating power. “Cogeneration is not new, but this is really the third generation, where we’re using this facility’s existing infrastructure to achieve GHG reduction goals.”

The $16.8 million project was funded by CWS. The agency received $3 million in cash incentives from Energy Trust and tax credits for combined-heat-and-power from the Oregon Department of Energy in the amount of $2.8 million. The project is expected to cut CWS’ operating costs saving ratepayers money. Around $690,000 savings in electrical costs in the first year is expected and $100,000 savings in heating costs. The project will generate $340,000 annually in tipping fees for FOG disposal.

CWS also operates the Rock Creek WWTP in Hillsboro. Cordon said the company is looking at implementing renewable natural gas for transportation use at this facility. Other projects the company is looking at include making plastic from methane gas, as well as cellulose recovery from the toilet paper that ends up in the sewage system.