A Bright IdeaA Bright Idea

After 40 years of paying the local power company for electricity to run their dairy, the Aragi family will be producing their own power.
April 1, 2010
Dairy Farmers of America

Like all good dairymen, Louis Aragi, Jr. has learned how to make money off the milk produced on his farm in Sheffield, Mass., where he raises 1,000 head of cattle. Now, with increased production costs, this Dairy Farmers of America, Inc. member is venturing into a new way of making money from his operation. Aragi will complete construction next winter of a $1.3 million digester that will input manure and output power at Pine Island Farm, the dairy he operates with his father, Louis “Chico” Aragi, Sr.

Aragi knew he was entering unfamiliar territory, but was willing to learn something new if it would offer him the opportunity to be more environmentally conscious and allow him to offset energy expenses and generate a different revenue stream.

According to the National Sustainable Agriculture Information Service (ATTRA), anaerobic-digestion systems are used to convert livestock manure into a fuel for heating or cooling a portion of the farm operation or for further conversion into electricity for sale to a utility. North Carolina State University’s Cooperative Extension Service indicates that a well-insulated, three-bedroom home that requires 900,000 Btu/day for heating in cold weather could be served by a 50-cow dairy. The solids that are left after the digestion process can be used to amend the soil.

The types of anaerobic digesters include:

  • Covered lagoon – a pool of liquid manure topped by a floating cover.
  • Complete mix – a silo-like tank where solid and liquid manure is heated and mixed. According to ATTRA, this is the most expensive system to install and operate, but it works well for operations that wash out manure.
  • Plug flow – a cylindrical tank that handles both solid and liquid manure, in which the gas and other byproducts are pushed out one end by new manure being fed into the other end.

Despite the benefits, anaerobic digesters are not without maintenance considerations and require regular and frequent monitoring.

Figuring out the details
To determine what size digester was appropriate for their farm, the Aragis commissioned a feasibility study. The study, conducted by the Massachusetts Technology Collaborative, indicated that the best system for Pine Island Farm would be a mixed plug flow digester, with manure routed through the digester vessel and heated to 100 degrees, accelerating the bacterial breakdown.

Aragi says manure entering the digester takes 21 days to become its end product. Once the production becomes constant, the feasibility study suggests that 700 mature cows can support a substantial generator and turn out 973,000 kilowatt hours a year. After powering the digester itself, the generator also will be used to provide power for farm buildings and residences on the family’s 671 acres, and the surplus electricity will be transferred to a power grid.

Good timing
Both the Massachusetts state government and federal government have emphasized the importance of renewable energy and made grants available that allowed Aragi to take advantage of funding to supplement his own investment in the digester.

In addition, the rising price of powering the dairy farm gave him an incentive.

“It seems to make more sense now with high energy costs,” he says.

Along with these factors, the technology that drives this biomass system has improved to a point of more acceptable efficiency. Earlier attempts at the manure-to-methane conversion met with less favorable results, Aragi says, and bad word of mouth by farmers followed.

“They would turn their heads when you talked digester,” Aragi says.

Fortunately, the poor reviews only concerned the machinery used in the process. Technology has improved since the 1970s and systems installed since the 1990s are better designed.

An anaerobic digester actually simulates a biological process that occurs in nature — organic waste being destroyed by bacteria where oxygen is excluded. The digester being installed by the Aragis will speed the process, with biogas, most prominently methane, being the byproduct.
The methane then powers an electricity generator.

The cost of an anaerobic digester, though, can be pricey and is not cost effective for all farms. ATTRA estimates the cost of an anaerobic-digestion system can vary dramatically depending on its size, purposes and sophistication. A covered lagoon system can cost as low as $25,000 for 150 swine to $1.3 million for up to 5,000 cows. Plug flow digesters range from $200,000 for 100 dairy cows to $1.8 million for up to 7,000 dairy cows.

The future of digesters
Jackie Klippenstein, DFA vice president of industry and legislative affairs, says DFA supports its members’ initiatives in working toward energy conservation and production.

“As the price for dairy products turns around and the dairy economy rebounds, I expect more producers will be in a position to use available state and federal incentives to take advantage of opportunities to use this technology either for their own farm’s use or to market to others interested in green energy,” she says.