Article in UW Oshkosh Northwestern by Jeff Bollier, October 27, 2011
The University of Wisconsin-Oshkosh’s new anaerobic biodigester wants your leaves, your huddled masses of grass clippings, your leftover foodstuffs yearning for a final resting place that’s not a landfill.
With the ability to consume 120 tons of organic material each week and 8,000 tons each year, the biodigester decomposed organic waste to produce methane gas that can generate 53 megawatt hours each year, enough to offset 8 percent of the UWO campus’ electricity use, UWO Director of Sustainability Michael Lizotte said.
In addition to campus waste, what used to sit in a city yard waste drop-off site composting over months and years can now be combined with food waste and used to produce electricity, heat for nearby campus buildings, revenue for UWO Foundation scholarship programs.
The project, the first of its kind in the United States, is drawing national attention for both the university and BIOFerm Energy Systems, the German company that’s trying to introduce widespread “biomass” energy production to the United States.
“We looked at Wisconsin as a state with a lot of agriculture and food processing industries. Basically, any organic material that’s presently being taken to the landfill, we can put it to a better use,” BIOFerm Application Engineer Caroline Chappell said. “It’s a win-win for everyone involved. Before Oshkosh was built and we had people interested, they’d have to go to Germany to actually see it. In general, it is becoming a more interesting market. People are looking at it more.”
How the power plant works is relatively straightforward.
Chappell said 120 tons of organic material gets mixed and crammed into one of four large bays in the main digester building. The material is a combination of discarded foodstuffs from the campus, yard waste from the city and materials other companies can pay the university to get rid of for them.
“Before, it was just a lot of grass clippings, but now it’s grass clippings and the fall harvest: pumpkins, apples. Everything is great food for the biodigester,” Lizotte said. “It completely takes the city’s yard waste and eliminates the need to dispose of it.”
The material is sprayed with a biochemical solution that includes microbes that decompose the material in a sealed bay that has all the oxygen removed and has the heat turned up to more than 100 degrees. Under those ideal conditions, the microbes decompose some of the material and produce methane and carbon dioxide as byproducts.
The methane that is collected and stored in a large, overhead bag. As needed, some of the gas is filtered and pumped into a generator that produces electricity that is sold to Wisconsin Public Service Corp. The generator also produces heat that in the future could be used to heat nearby buildings.
After 28 days, half of the material in the bay is removed and the other half is mixed with a new batch of organic material so methane production continues on a steady pace.
“It helps to have some material that always has those microbes already working,” Chappell said.
The process is repeated with one of the four bays each week to maintain a steady rate of gas production.
Chappell said the UWO biodigester also will tap methane gas the city of Oshkosh’s Wastewater Treatment Plant produces to increase daily electricity production from about 230 kilowatt hours up to 370 kilowatt hours.
Lizotte said the combined use of methane gas from the wastewater plant and the fact the biodigester does not produce any wastewater of its own makes it a nice option for a community that heavily relies on its rivers and lakes for recreation and tourism.
“It’s a really good fit for a watershed like the Fox where phosphorus content needs to be reduced,” Lizotte said.
And even the 80 tons of material remaining after the 28-day cycle finishes doesn’t go to waste. Zillges Spa, Landscape and Fireplace purchases the material, mixes it in with its own compost piles outside the city and then sells it to customers as a soil that helps replenish nutrients in their yards.
“It adds a bunch of nutrients into the soil. It’s the same kind of nutrients you’d find in a Miracle-Gro bag,” company president Tim Zillges said. “It’s all the stuff regular topsoil has had taken out of it over the years. We try to do everything we can to do our part at being green.”
Lizotte said the plant has a projected useful life of 20 years—the digestion process creates an acid that degrades the concrete over time—but a variety of revenue streams should mean the plant pays for itself within eight to 10 years.
He said the sale of electricity to WPS will be supplemented by revenue from contracts with companies like Sanimax that pay a tipping fee to take food waste from supermarkets and from the sale of waste material to Zillges. He said new revenue streams may be identified as the biomass industry grows, but one other thing the university has considered would be to use heat the combined generator creates to warm the Campus Services building to the east of the plant.
“Our hope is in the next 20 years we can develop markets to pump hot water to plants and offices within about a half-mile radius of the plant,” Lizotte said. “The conditions could change over time to become even more profitable than we expect it to be right now.”
A busload of renewable energy company representatives and sustainability professionals will tour the digester Wednesday as BioCycle magazine’s 11th annual Conference on Renewable Energy from Organics Recycling wraps up in Madison. Lizotte said the university and BIOFerm both have already hosted several tours for parties interested in the technology and to possibly offer tours to seniors, elementary, high school and college students in the future.
“When people outside the US look at biomass opportunities in the United States, they look at the Midwest and specifically, Wisconsin,” Lizotte said. “There’s experience with biomass in this region of the country. And with BIOFerm based in Madison, when they have customers, they can bring them up here and show them how it works.”
