Profiting from dairy pollutants

PULLMAN — A professor at Washington State University is researching the best ways for dairies to manage their cow manure.

Economics Professor Richard Shumway used computer modeling to determine which methods of nutrient management, or combination of methods, would be the most profitable for dairies.

Dairies can contribute to greenhouse gas emissions, water and air pollution. Anaerobic digester technology can significantly reduce greenhouse gas emissions, odor and pathogens, while producing renewable energy, according to Shumway’s working paper.

“Anaerobic digestion has such powerful benefits to the environment,” Shumway said.

Anaerobic digesters process the cow manure to separate out the nutrients. The digesters also capture the methane gas from the manure, which is sometimes used to produce electricity.

However, these digesters are expensive, and Shumway’s team determined that anaerobic digesters by themselves are not typically economically feasible.

“Right now there are no standalone anaerobic digester technologies that are economically viable for any of the small dairies,” Shumway said.

Shumway and a graduate student, Gregory Astill, found that digesters equipped to output compressed natural gas (CNG) have the greatest potential for profitability. Compressed natural gas can be used in place of gasoline and produces fewer greenhouse gases when burned.

The location of the dairy can determine how profitable producing CNG is. Storing CNG is costly, so most owners of anaerobic digesters who produce it establish a connection to a national CNG pipeline. Pipeline connection fees vary depending on the site, and are usually determined by the distance to the existing pipeline.

Dairies can also use combined heat and power to generate electricity from their digesters. Most dairies do not need all the electricity produced by this method, so they connect to a municipal grid to sell the excess electricity. Like CNG, the connection fees vary widely and largely determine the economic viability.

Another way to make anaerobic digesters more profitable for dairies is a method called codigestion. Food waste produces higher amounts of methane. Adding food waste to the manure can optimize the efficiency of the digester, said Shumway.

Dairies can collaborate with restaurants or food processing plants by taking their food waste for a tipping fee. According to Shumway’s paper, these fees can generate a large portion of income for anaerobic digester owners.

The cost of building an anaerobic digester would be difficult to manage for a small dairy, but Shumway said by combining technologies, it could be profitable for some of the smallest dairies.

“The conventional wisdom seems to view 500 cows as the lower end for any of these technologies, I’m not sure that it needs to be that high with some combinations,” he said.

WSU’s Center for Sustaining Agriculture and Natural Resources (CSANR) works to provide dairy owners up-to-date information on anaerobic digester technology, said CSANR Director Chad Kruger.

The CSANR website has a budget calculator meant for dairy owners to determine if an anaerobic digester is the right decision for their particular situation. Kruger said the center is currently working on a technical manual, composed of a series of fact sheets about anaerobic digesters for dairy owners.

Kruger said he hopes the manual will be completed and published on their website by the end of the year.

Shumway said he expects that anaerobic technology to improve and become less costly.

“Once that’s done, then you’d expect to have widespread adoption,” he said. “That’d be a great benefit to the nation, world, everybody.”