Morris, Minn. — Taking care of bugs is part of Dori Coler’s job description.

Coler is a biologist at DENCO, an ethanol processing plant in Morris. One of her jobs is to make sure the bacteria in the plant’s anaerobic digester are healthy and happy. The bacteria clean the plant’s wastewater and give off methane as a byproduct.

DENCO is one of several Minnesota ethanol plants using anaerobic digestion to boost efficiency, says Gerald Bachmeier, manager of DENCO, a 353-member limited liability company with annual sales of $30 million. Eventually, the digestion process will provide the plant with supplementary fuel as well.

Wastewater from the plant flows into a 30,000-gallon bioreactor, which looks like a tall, silver silo. Inside the reactor is a floating bed of hardworking bacteria. These “methanator bugs” break down chemical wastes in the water, removing more than 90 percent of the impurities that interfere with ethanol processing. The water is left clean enough to be reused in fermentation, Coler says.

The DENCO plant, which is working with AURI on new product development, produces about 18 million gallons of ethanol a year. The digester has boosted fermentation efficiency by 15 percent, Bachmeier says. “It cuts our disposal costs and lets us reuse more water.” The $300,000 system paid for itself in less than a year, he says.

The “methanator bugs” that clean DENCO’s wastewater also produce between 4 and 20 cubic feet of methane per minute. Currently, this gas is flamed off.

But later this year, Bachmeier says, the methane will be captured and used to run drying equipment. Bachmeier expects the plant’s homegrown methane to offset about seven percent of the natural gas needed for drying.

Manure to methane:

does it pay?

By E. M. Morrison

As interest in manure digesters grows, the key question for farmers is: Does it pay?

The answer: It depends.

That’s according to a 2000 report from Project Minnesota, a rural economic development organization that examined the performance and financial viability of Haubenschild Farms’ plug-flow digester.

The report, available at www.mnproject.org, identified several variables that affect digester profitability, including:

  • size and type of livestock operation,
  • type and age of facilities,
  • manure collection and storage methods,
  • farm electricity expense,
  • excess power sales opportunities,
  • expansion plans,
  • capital investment needed, and
  • financing costs.

The Haubenschild Farms’ 900-cow digester, for example, cost $355,000 to construct. It was built with $278,000 in government grants and zero-interest loans as part of a research project sponsored by the State of Minnesota and AgSTAR, a federal environmental program. Haubenschild Farms contributed equity of $77,000.

Traditional lenders were unwilling to finance the project, says Dennis Haubenschild.

Projections based on ten months of data from the Haubenschild operation show that, even with financing costs, a “900-cow digester will pay for itself in a reasonable time period — four to six years,” according to the Project Minnesota report. Haubenschild projects a five-year payback on his 760-head operation.

However, digesters are probably not feasible for smaller livestock operations, according to Peter Ciborowski, an official at the Minnesota Pollution Control Agency. Ciborowski recently finished a detailed financial analysis of anaerobic manure digesters for MPCA. The report will be available later this year.

Ciborowski’s research suggests that dairy farms need at least 500 cows and six cents a kilowatt hour to operate a digester profitably. Economic thresholds for swine manure digesters are much higher — at least 5,000 finishing hogs, he estimates.

Clearly, manure digesters are not right for every Minnesota livestock farm, says Jack Johnson, AURI engineering services director in Waseca. Still, he adds, there’s a growing recognition that digesters could help control odor and contribute to energy self-reliance, and their viability improves as energy costs rise. “There’s great potential for this technology.”

Ciborowski agrees. He predicts that within a decade, up to 30 percent of Minnesota dairy farms will be large enough to operate profitable digesters. “It’s a win-win,” he says. “A pollution control technology that can be cost effective, too.”

For digester farmer wannabes

Would a manure digester make financial sense on your farm? A new program from AURI helps sort out the benefits and risks of installing a manure digester.

The program, called “A Self-screening Assessment and Checklist,” is available from AURI at www.auri.org/research/digester/digchck.htm

The Assessment and Checklist can calculate the capital investment that would be needed to build a manure digester, and helps estimate operating costs and returns. The site also explains the different methods of manure digestion and offers links for more information and technical assistance.

The Minnesota Department of Agriculture is also offering zero-interest loans to farmers interested in demonstrating anaerobic manure digestion technology on their farms. These competitive loans are available in amounts up to $64,000. Applications will be accepted until July 31, 2001. For more information, call Matt Drewitz, of the Minnesota Department of Agriculture Development Division, at (651) 296-3820.