Poop power

If there’s one thing in abundance at a dairy farm, it’s cows, and those cows produce quite a bit of manure—more than 80 pounds per day, according to the U.S. Department of Agriculture’s Natural Resources Conservation Service. And what to do with that manure can be a problem.

Many farmers use it as fertilizer, but runoff from the fields when it rains means a lot of it ends up in our waterways and causes many issues, including algal blooms. University of Nevada, Reno chemical engineering associate professor Charles Coronella is the principal investigator on a research project to convert biomass—the manure—into a solid fuel that can then be used to generate electricity.

“What we are doing now is trying to build a continuous prototype for doing hydrothermal carbonization, so that’s the first step of this process—converting manure into power,” Coronella said. “In hydrothermal processing, what we do is we take—I’m going to call it biomass; it’s a nicer word than manure—take biomass and cook it in hot, compressed water. This is at a temperature of about 250 degrees C, about 500 degrees F. If you keep the pressure high enough—the pressure is about 50 atmospheres—the water will stay as a liquid. So we have liquid water at very high temperature and pressure, which converts the biomass into something that looks an awful lot like lignite or a type of a coal.”

The project is funded for two years by a grant from the Western Sun Grant Consortium. Researchers from the Desert Research Institute, UNR Cooperative Extension specialists, a California-based company that specializes in biomass-fueled generators, a small business interested in commercializing the process, and other UNR researchers are all involved with the project. Coronella said they’re working with biomass from cows at the UNR Cooperative Extension, but he hopes to work with local farmers later on so that they can contribute their experience to the research as well.

Coronella said that university researchers have been looking into hydrothermal carbonization for five or six years now and are optimistic about the results of this project.

“We have the idea of using it for different kinds of wastes,” Coronella said. “My first favorite biomass is wastewater sludge. Definitely can be used there. For example, in Reno, the wastewater treatment plant, they make about 120 tons a day, every day, of sludge, so this could be used to process that instead of sending it out to the landfill. It can also be used for a lot of different kinds of food wastes, so for example, restaurants throw out an amazing amount of food. … This would be an alternative to composting it.”

After the biomass is made into a charcoal-like fuel, it will be put into a gasifier—a partial combustion process that will turn the solid fuel into a fuel gas. That can then be burned in a combustion engine to generate electricity. The goal is to produce 10 kilowatts of electricity. Coronella said that the solid fuel could also be burned and used for cooking, but he doesn’t imagine many people would be interested in using a fuel made from manure for cooking purposes, despite it being odorless.

Anytime you burn something there are emissions of some kind, so the researchers will measure those throughout the project. They will also be doing a life cycle analysis, which will identify any potential environmental impacts, but Coronella said that, if they are successful in generating a renewable fuel, there will be a reduction in carbon dioxide emissions.