The “Big Stomach”: Turning Waste to Energy

When Vianney Tumwesige sees a blue flame in the kitchen of a farmhouse in Uganda, he gets a little giddy. There’s a good chance the gas fire comes from one of his “big stomachs.”

The big stomach is Tumwesige’s term for the digester he and his team came up with to turn organic waste into fuel and fertilizer, firing cooking stoves and nourishing crops. He developed it when he was still in university.

Tumwesige is the founder of Green Heat International, a for-profit company, with a mission of helping farmers improve their crop yield while at the same time bringing a clean-burning fuel to their households.

His journey of turning organic waste into energy began while Tumwesige was still in the university, after handing in a bachelor thesis in 2007. He had a chat with his professor and began experimenting with an early biogas digester.

In Uganda, the use of other biogas resources meant that citizens didn’t have to purchase wood for fuel, a material that was becoming more scarce and expensive. Wood was being used in 90 percent of the households.

“I love to see that blue flame,” said Tumwesige. “That means organic waste is being used for cooking, piped in through the digester near the house.”

Organic waste is waste from any biodegradable organism, from banana peels and corn stalks and paper to human and livestock waste. It is all fed into Tumwesige’s “big stomach” digester.

The big stomach is Tumwesige’s term for the digester he and his team came up with to turn organic waste into fuel and fertilizer, firing cooking stoves and nourishing crops.

However, there was only one problem with the original digester technology: It needed too much water to mix with the organic waste, and farmers—mostly women— found it was an inconvenience to haul 80 liters of water each day. Many gave up on the digesters within a year.

“We found that while we had solved an energy problem, we had created another problem—a water problem,” said Tumwesige. “We went back to the drawing board and figured out how to separate and reclaim the water.”

Tumwesige explains the entire process in understandable terms: “The stomach (digester) is airtight, so it gives the right conditions for bacteria to produce gas that is fed through a pipe into a family’s kitchen. When it is not flowing into the kitchen as gas, it decomposes. We separate the water so the solid waste remaining can be used as fertilizer.

“It’s a natural fertilizer and doesn’t harm or deplete the soil,” he said. “We don’t have fertilizer plants here, but this compost can be put directly onto the farm fields,” he added.

Today, the digesters use 80 percent less water than previously and Green Heat has installations in other African countries (Cameron, Rwanda, Mozambique, Ethiopia) and as far away as the Caribbean in Haiti.

Green Heat is both a technology company and one that provides installation of their systems with about 1,200 in operation. We offer support for six months after installation.

The cost of the know-how and equipment ranges from a one-time charge of $1,000 for a family of six which provides about six hours of cooking a day. The larger models cost $500 more.

“The process is becoming more and more acceptable,” said Tumwesige. “One might think there would be a reluctance of energy from waste products, but it’s not.

“If they have cheap fertilizer and cooking gas, they are happy,” he said.

USAID, Sweden through the Swedish International Development Cooperation Agency, and the Governments of The Netherlands and South Africa invested $35 million in Securing Water for Food (SWFF) to promote science and technology solutions that enable the production of more food with less water and/or make more water available for food production, processing, and distribution.

This story was developed through the SWFF Social Impact Storytelling Initiative which was established to document innovator journeys and social impact as they work to improve the way water is being used for agriculture. #socialimpact #innovation #agriculture #water