New Anaerobic Digester at MSU Will Produce Energy From Waste

Apr 17, 2012

Michigan State University is ready to start work on a new anaerobic digester.  The system will use microorganisms to turn tons of manure and food waste into electricity for some MSU buildings south of the main campus.

The Board of Trustees has approved $5 million for the digester.

Dana Kirk is managing the project.  He’s a specialist with MSU’s Department of Biosystems and Agricultural Engineering.  WKAR’s Gretchen Millich spoke with Kirk at the site of a smaller anaerobic digester already used for research at MSU.

DANA KIRK:  On a daily basis, we get manure from the Dairy Farm, about 1,000 or 1,500 gallons a day.  We get the pulped food waste from Brody, the cafeteria on campus. We also are getting pre-consumer food waste on campus, and that’s the bins that you see, from three other dining halls on campus.  That we take and pump in into the digester, and we warm it to about 105 degrees.  Anaerobic digestion is the breakdown of organic matter in a warm environment, and it also is an environment that doesn’t have oxygen or has very limited oxygen. 

When we break down the plant material, the carbon that’s released actually will match up with hydrogen and create methane. The microbes that are responsible for anaerobic digestion are naturally occurring, and the nice thing about being right here at the Dairy Farm is that dairy manure is rich with the anaerobic community of bacteria that we’re looking for to break down this waste.  Essentially this is an extension of a cow’s stomach.  The cow is a natural anaerobic chamber, and so we’re just using what’s left over in the waste from the cow to enhance this process and drive it.

GRETCHEN MILLICH:  There’s going to be a new anaerobic digester, a larger one.  How will that differ from this research digester?

KIRK:  This digester is actually a configuration that we call plug flow. There’s no mixing inside of this tank.  The material goes in and essentially moves down by the new material being added behind it.  So, every day, it’s pushed down by new material that comes in.  The proposed digester is actually a complete mixed digester.  It’ll be about three times as large as this, and we’re going to take a much larger variety of feed stock.  So, we’re going to look at more dairy manure, other manure from campus, more food waste from campus, as well as other organic waste from campus. 

Then we’re going to look at partnering with some local businesses in the community to take their organic waste, their food processing waste and their fats, oils and greases. Unlike this system, that one will be producing electricity every hour, 24 hours a day, all year round.  The liquid that comes out of it will again be treated for fertilizer.  So, we’ll use that here on the south campus farms, as well as export it to neighboring farms.

MILLICH:  I understand that this is not exactly new technology, that some type of anaerobic digestion has been used since the 17th century.

KIRK: Yeah, the technology is very old.  I mean, anaerobic microbes have been around probably since the beginning of time, and using them as waste treatment has been around since the 17th or 18th century. Using anaerobic digestion for energy production became more common in the 19th century, and then in the 1970’s, we saw a number of digesters built in the United States to produce energy from livestock manure.  Then again in the 2000’s, we start to see more of a trend in using anaerobic digestion to treat livestock waste in the U.S. for odor control, to reduce greenhouse gas emissions, to generate energy and to stabilized the waste. 

Today, in the U.S., there are about 170 to 180 systems on farms.  There’s hundreds or thousands of systems that are used in waste water treatment plants.  In Europe today, I think there are about 6,000 on-farm anaerobic digesters in Germany alone. So, the technology has evolved over the last 20 or 30 years, and you see a lot of use of this technology to convert organic matter into energy and usable fertilizers.

MILLICH:  Five million dollars has been allocated to pay for the proposed digester.  How long will it take to pay for itself in terms of producing energy?

KIRK:  What we’re currently looking at is about 12 to 15 years to pay that system back.  The revenues are going to be from the energy that we produce, from some fertilizer sales, but also from tipping fees that we hope to collect with our partners, because they are currently paying to dispose of their materials in landfills or wastewater.  So, there’s revenue there. We won’t know the exact final payback until we finalize those contracts, but we believe it’s in the range of 12 to 15 years at this point.