Now they're turning that manure into biogas at the Bioproducts, Sciences and Engineering Laboratory on the Richland campus of Washington State University Tri-Cities.
It is a process that Vilma Zuniga, an environmental assistant, and Harold Gamboa Morillo, an engineer, believe can be duplicated by Honduran coffee farmers.
"It's a real win-win for the community," said Keith Thomsen, assistant director of the WSU center for Bioproducts and Bioenergy.
Producing biogas from waste would not only improve the quality of life for small coffee been farmers in Honduras, but it also would help reduce an environmental problem.
Now most Honduran coffee farmers sell "green" coffee beans because they don't have the energy-intensive capability to process it into more profitable "golden" coffee beans.
The beans must have pulp removed and the jellylike mucilage around the seed washed off. After that, they must be gently dried.
Typically, the pulp is stockpiled but can wash into creeks and rivers when it rains. The musilage-contaminated water also goes back into waterways. Too much of either can kill fish and make the water undrinkable.
Thomsen and Birgitte Ahring, director of the WSU center, have been tapped by the U.S. Department of Agriculture to help develop a biogas-production demonstration project in Honduras to help solve the problem. It will be based at Honduran Cafe Institute, a nonprofit, that employs Zuniga and Gamboa Morillo.
The project is planned to demonstrate that pulp and musilage can be turned into biogas that farmers can use to dry coffee, Zuniga said.
"Farmers will develop more," she said. "By drying coffee, they could get a better price for coffee."
Coffee is seasonal, and during the rest of the year, the digesters that produce biogas could be fed with manure or chopped-up green waste, Thomsen said. Farmers are constantly removing brush to maintain coffee production and in some cases banana production from trees that are used to shade the coffee plants.
When not needed for coffee processing, the biogas could be used for heating or cooking, both of which now may be done by burning wood. Using biogas instead would not only reduce the smoke inside Honduran homes, but also help prevent deforestation.
Zuniga envisions the biogas eventually used to produce electricity for communities.
Ahring and Thomsen have worked on similar projects in other countries, and Thomsen said a simple digester could be made by a farming cooperative for $5,000 to $10,000.
"It's very affordable, very deployable," he said.
This week at WSU Tri-Cities, Zuniga and Gamboa Morillo first learned to mix compost with water to feed into a laboratory digester.
It will grow the microbes that will convert biomass into a biogas. After about a day, Zuniga and Gamboa Morillo should be able to start feeding the manure they collected into the digester, and the bacteria will convert it into a biogas of about 65 percent methane and 35 percent carbon dioxide.
Left over will be nutrients that can be used for fertilizer, said Rajib Biswas, a WSU Tri-Cities doctoral student.
"We're just here learning how to get started," Zuniga said. But next year, Honduran Cafe Institute should have a demonstration digester to start testing the process.
It's projects like this one that improve the lives of people that motivated Thomsen to become an environmental engineer, he said.
"It really lifts the community, and they do it themselves," he said.