Uganda: The Benefits of Biogas

Generating enthusiasm for a new kind of technology is key to its long-term success. Rebecca Larson, a CALS professor of biological systems engineering, has already accomplished that goal in Uganda, where students at an elementary school in Lweeza excitedly yell “Biogas! Biogas!” after learning about anaerobic digester systems.

Larson, a UW–Extension biowaste specialist and an expert in agricultural manure management, designs, installs and upgrades small-scale anaerobic digester (AD) systems in developing countries. Her projects are funded by the Wisconsin Energy Institute at UW–Madison and several other sources. Community education and outreach at schools and other installation sites are an important part of these efforts.

Children get excited by the “magic” in her work, she says. “It’s converting something with such a negative connotation as manure into something positive,” Larson notes. In an AD system, this magic is performed by bacteria that break down manure and other organic waste in the absence of oxygen.

The resulting biogas, a form of energy composed of methane and carbon dioxide, can be used directly for cooking, lighting, or heating a building, or it can fuel an engine generator to produce electricity.

Larson’s collaborators in Uganda include Sarah Stefanos and Aleia McCord, graduate students at the Nelson Institute for Environmental Studies who joined forces with fellow students at Makarere University in Kampala to start a company called Waste 2 Energy Ltd.
Along with another company, Green Heat Uganda, which has built a total of 42 digesters, Waste 2 Energy has helped install four AD systems since 2011.

“Most of these digesters are locally built underground dome systems at schools and orphanages,” Larson explains. Lweeza’s elementary school is a perfect example.

The AD systems use food waste, human waste from pit latrines and everything in between. The biogas generated by the digester is run through a pipeline to a kitchen stove where the children’s meals are prepared. Compared to traditional charcoal cooking, the AD systems greatly reduce the school’s greenhouse gas emissions.

Larson and her team are now focusing on enhancing the efficiency and environmental benefits of these systems. Their goals are to improve the digester’s management of human waste, reduce its water needs, increase the amount of energy it produces and generate cheap fertilizer to boost food crop yields.

“Our overall goal is to create a closed-loop and low-cost sustainability package that addresses multiple local user needs,” Larson says.

The beauty of the project is that all these needs can be met by simply adding two new components to the existing systems: heating elements and a solid-liquid separator.

To help visualize the impact of the fertilizer, Larson set up demonstration plots that compare crop yields with and without it. Down the road, a generator could be added to the system to provide electricity in a country where only 9 percent of the population currently has access.

As a next step, Larson hopes to replicate the project’s success in Bolivia. She is finalizing local design plans with Horacio Aguirre-Villegas, her postdoctoral fellow in biological systems engineering, and their collaborators at the Universidad Amazonica de Pando in Cobija.

Of Cows and Climate

ON A SUBZERO FEBRUARY day, Mark Powell stops his vehicle on the road a few miles outside Prairie du Sac. He’s been explaining that cows actually enjoy the polar weather—and as if to prove it, a frisky group in the barnyard across the road turns toward us and rushes the fence.

As a USDA soil scientist and CALS professor of soil science, Powell is focused on the ground beneath their hooves. A few years ago he led a survey of manure handling on Wisconsin dairy farms. He and his colleagues knew how much cows left behind—about 17 gallons a day—but had only educated guesses about the ultimate environmental impact of barnyard design. In open yards like this, says Powell, they found that 40 to 60 percent of the manure ends up uncollected. “It just stays there,” he says. In the decade since his survey, the manure challenge has only grown, both in Wisconsin and nationwide. Water quality has been the major concern, but air quality and climate change are gaining.

A few minutes later we turn into the 2,006-acre U.S. Dairy Forage Research Center farm, and the talking points all turn to plumbing. There’s an experimental field fitted to track how well nutrients from manure bond to the soil. Parallel to one barn are nine small yards with different surfaces, each monitored to measure gasses emitted and what washes out with the rainwater.

The manure pit is frozen over, but circumnavigating the complex—shared by CALS and the U.S. Department of Agriculture—we arrive at the southern terminus of the barns. Uncharacteristic ventilation ducts adorn the walls and roofline. Inside are four unique stalls that can contain up to four cows each. The manure trough is lined with trays so that each cow’s waste can be set aside for further experiments. When the cows return from the milking parlor, airtight curtains will drop, isolating each chamber.