Living, Learning Lab

Besides edging toward sustainability goals, a unique biodigester on the University of Wisconsin Oshkosh campus will also provide learning opportunities, and eventually financial assistance, for students.
By Lisa Gibson | July 28, 2011

It’s the first of its kind on this side of the globe; an opportunity to train university students for renewable energy careers; and a potentially  lucrative source for scholarship funds. The University of Wisconsin Oshkosh's dry fermentation anaerobic digester is the whole package.

In the midst of finishing touches and final construction details, the plant will be operational in late summer or early fall. Described as a warehouse with steel garage doors, it isn’t a typical anaerobic digester. While the facility will employ the same biological process as tank digesters that are fed slurry, it will carry out its biological conversion on dryer, solid feedstock in enormous concrete chambers, hence the name “dry fermentation anaerobic digester.” It is the first commercial-scale system in the Americas, according to its developer BIOFerm Energy Systems.

“They look to me like they’d be really fine parking garages for 18-wheel trucks,” says Mike Lizotte, UW Oshkosh director of sustainability, describing the concrete chambers. Inside each of the chambers is a floor drain and overhead nozzles to help recirculate the fluids, collecting and reusing what’s drained from the pile of feedstock on the floor, Lizotte explains. “That’s full of really great microbes and nutrients and that all recycles back,” he says. Solid steel doors on the chambers keep detrimental oxygen from seeping in and corrupting the process.

But unlike the doors, which Lizotte calls “pretty fancy,” handling systems for the operation are surprisingly simple, due entirely to the solid nature of the feedstock.

Front-Loader Feeding

No pumping mechanisms are required because the UW Oshkosh system will be fed by front-loaders, tasked with piling up the material inside the concrete chambers, directly after it’s delivered by truck, according to BIOFerm application engineer Caroline Chappell. “Instead of it being pumped through a series of tanks, it’s pretty low tech,” she says.

The largest portion of the system’s feedstock, at least in the first year of its 20-year operation, will come from supermarkets, Lizotte says. The food will be delivered unpackaged and will consist of meat, dairy, bakery waste, fruits, vegetables and other outdated or otherwise unsalable products. The next largest fraction will consist of yard waste collected from the 66,000-person city of Oshkosh, followed by winter bedding waste from a local dairy farm. Lizotte is quick to point out that the material from the farm will not include wet manure. Finally, about 5 percent of the anaerobic digester’s feedstock will be food and yard waste from the university itself.

“One unique aspect of this system, because it’s urban, is we promised the community we wouldn’t store anything outdoors,” Lizotte says. “So we have to operate with on-time delivery.” The plant will have a relatively small area for feedstock storage, but it will be strictly limited to use for yard waste and other feedstocks that come in dry and don’t break down.

That leads Lizotte to his next point: some material will inevitably be too wet for the process, and since this specific installation of BIOFerm’s equipment includes no drying apparatus, the perfect balance can be tricky. “One of the challenges is you can find rich feedstocks but they can be too wet and they break down, therefore you end up with a soup rather than a pile,” he says. “The idea is to just have something to mix it with [to maintain the system’s integrity]. There’s some art and science to making the right mix of feedstocks.”

The plant is designed to handle 8,000 tons of feedstock per year, Chappell says, and will produce 2.32 million kilowatt hours of power annually. In addition, the plant’s combined-heat-and-power unit, developed by technology manufacturer 2G-Cenergy, will produce up to 7,900 million Btus of heat for at least one university building, and perhaps more down the line. “We’re hoping for more heat customers, but heat is still a foreign idea to purchase,” Lizotte says. While the hot water distribution system is not yet in place, it will definitely be a component of the project.

As for the electricity, options are open but for now, 100 percent of the power generated will be sold to the grid through a 10-year power purchase agreement (PPA) with Wisconsin Public Service. The PPA, Lizotte says, was difficult to negotiate until WPS offered a biogas rate that was a little better than its standard rates. “They sat down and said, ‘This is the rate. Take it or leave it,’” he says.

But debate over pricing swirled within the university, as well. Lizotte says the school was reluctant to lock in to one rate price for an entire decade in the face of so many ongoing changes. But as many project developers and owners learn, that signed output contract is crucial to getting monetary support. “Having this agreement worked out in our favor when it came to going out and getting financing,” he confirms.

During a break from filling out financial paperwork for the project, Lizotte says the university is applying for $500,000 in U.S. DOE funds. In addition, the school will receive another $250,000 from the Wisconsin Focus on Energy program. Both funding sources, however, are reimbursement-based and therefore could not be used for the roughly $3.7 million construction. Enter: University of Wisconsin Oshkosh Foundation.

Supporting Students

As current owner of the facility, the University of Wisconsin Oshkosh Foundation has funded the construction through bond debt and loans, according to foundation President Arthur Rathjen. Once that debt is paid off, and Rathjen says he’ll have a better idea of that timeframe in about 18 months, the foundation will funnel revenue earned to a useful and meaningful cause: student financial support.
“Through energy sales, we can not only cover the expenses of our bond debt and our yearly payment, but we also plan on spinning off income toward scholarships and financial aid help for the students,” he says.

The university has an ambitious energy independence goal, Rathjen says, and the AD plant was a prime opportunity for the foundation to partner with it and boost progress toward its core sustainability goals, while assisting its students. “We had seen it as not just a chance to go ahead and help the university advance one of its goals or mission objectives, but also there was an opportunity to turn some of this income into a way to help students further their education.”

Although financial aid may be benefit enough, the plant will supplement the education offered at the school through the Living Learning Laboratory program for both faculty and students. “They’re going to be doing a lot of research around this, building some curriculum around teaching students how to run the digester,” Chappell says. “That’ll be the future workforce.”

Two of the strongest programs at the university are microbiology and chemistry, Lizotte says, and students in both programs have the potential to glean knowledge about the plant and renewable energy from on-site experience. “They got pretty excited about the opportunity this presents to do projects for these students and so the lab’s pretty full this summer,” he says, adding that projects include bench- and pilot-scale versions of the process that allow for testing feedstocks, looking at microbial communities, studying chemical amendments, and other aspects that could enhance the process. The plant will help the university give its students a future in working for firms geared toward renewable energy principles, Rathjen adds.

In the future, Lizotte hopes the plant will be a training ground for similar operations, showing technicians how to run such facilities.

A German History

In the meantime, UW Oshkosh remains the only location in the Americas to have a commercial-scale model, Chappell says. The most common country for siting BIOFerm’s facilities is Germany, she adds, attributable for the most part to electricity rates. “In Germany, it’s highly subsidized, so the payback looks a lot better,” she explains. In addition, the U.S. does not have a developed infrastructure for source separated organics. “It’s preferable if the material is as free as it can be of contaminants,” she says, adding that the feedstock delivered to the UW Oshkosh system will be presorted and completely usable.

The university’s application has garnered attention for the process, however, in a variety of sectors including composting operations and municipalities, Chappell says. BIOFerm hopes the successful operation of its first installation here will attract even more interest and opportunities to reduce waste while producing energy.

The university is a perfect candidate for a premiere, she says, because of its sustainability and carbon reduction goals. “The university is really focused on sustainability across the board in a lot of different aspects,” Chappell says. There’s no question that the school has a challenge ahead of it to become energy independent, he adds, and he and the University of Wisconsin Oshkosh Foundation are more than happy to play their role.

The digester is a concrete example of the school’s commitment to establishing itself as one of the greenest universities in the country, Rathjen says, adding that it goes beyond just aiming to be the strongest and greenest university, but represents an evolution. “It demonstrates that if you’re serious about renewable energy programs and sustainability, you need to make investments in that infrastructure that will change the way people think.”

Author: Lisa Gibson
Associate Editor, Biomass Power & Thermal
(701) 738-4952
[email protected]