By Falguni Vyas, World Ark contributor
Photos by Olivier Asselin

A biogas project in Uganda leaves nothing to waste. Through the use of simple technology, animal manure is transformed into fuel, fertilizer and electricity. 

GOMBE, Uganda—The day starts early for Edith Kalale, 45. She wakes before the sun is up and has made her day’s wages by 6 a.m. Kalale is the proud owner of a biogas digester, which she uses to make pancakes to sell to children on their way to school. “I start making the pancakes at 4 a.m. By 6 a.m. I am done with everything.” 

The money she earns from the pancakes keeps her home running and her family fed. Kalale and her husband, Henry, the pastor at Glorious City Church in Gombe, had six children. Only their four girls are still living. One son died of AIDS at the age of 23, and the other from suspected poisoning when he was two-and-a-half. Their daughters are grown and gone to work in Kampala, but the Kalales still care for their nephew, Peter Mulema, 19, and grandsons Michael, a curious three-year-old, and Smile, a cautious one-year-old. 

Peter Mulema, 19, spreads bio-slurry to fertilize crops.
Peter Mulema, 19, spreads bio-slurry to fertilize crops.

Mulema’s parents died of AIDS nearly 11 years ago; he has lived with Edith and Henry ever since. To them he’s like a son. And Mulema treats the Kalales like he would his own parents. Once Edith has finished her morning pancake duty, Peter takes over and finishes up the rest of the day’s chores. 

On three acres of land they grow all the beans, maize, cassava and bananas they need. They have four cows and are able to sell more than a gallon of milk a day through the local co-op, which gets them a little less than a dollar a day. 

With the milk and pancake sales, the family makes enough to sustain their daily needs. But Mulema has dreams of becoming a doctor, and at $9 a semester, medical school is an expense beyond his reach. “I pray to God to help me get enough money to pay my university course,” he said.


Mulema is a man of faith and believes in miracles. He said his belief was confirmed two years ago when the Kalale family got a biogas digester. The contraption allows the Kalale family to spend less time collecting firewood and more time making money by selling pancakes. 

Mason Isaac Muckhwana lays bricks to build a biogas digester.
Mason Isaac Muckhwana lays bricks to build a biogas digester.

Biogas is a renewable energy source. Technically speaking, it’s methane-rich gas, produced through anaerobic (without air) digestion of organic waste. Simply stated, when organic waste, like cow dung, is trapped in an oxygen-free environment, bacteria breaks it down. The result is a biogas that is about 60 to 70 percent methane and 30 to 40 percent carbon dioxide. Used for both cooking and electricity, the gas saves trees from being used as firewood and brings electricity to rural families who wouldn’t have it otherwise. 

Once you have a digester, the process of creating biogas is simple. There’s another benefit, one that Mulema is counting on to bring him closer to his goal of earning enough money for school. Bio-slurry, a rich fertilizer that is a byproduct of biogas production, can dramatically boost crop yields. Mulema expects he will soon be able to sell bumper crops of maize, bananas, potatoes and beans.

Effluence = Affluence

Effluence, or bio-slurry, is the muck that’s left behind after the biogas digestion process. And it’s safe to say that this stuff is pretty much sludgy, black liquid gold. The undigested slurry, a mixture of dung and water that’s fed into the digester, undergoes a series of anaerobic digestion processes, or fermentation, to become combustible biogas. 

The residual bio-slurry retains all nutrients originally present in the undigested slurry, which in the case of many small-scale farmers in Uganda is cow dung. When applied correctly, bio-slurry is a potent organic fertilizer providing higher crop yields than just plain old manure. And, as a bonus to the environment, the slurry serves as a solution for addressing nutrient depletion in agricultural soils in developing countries.

Hadija Nekesa, 80, has an easier time cooking thanks to her biogas system.
Hadija Nekesa, 80, has an easier time cooking thanks to her biogas system.

Now We’re Cooking

Like Edith Kalale, Hadija Neseka, 80, wakes up each day before daybreak. As the head of her household, she is responsible for milking the cows for the morning tea, cooking and collecting firewood. All this is done in the darkness and, with Neseka’s failing vision, is not an easy task. As she gets older, Neseka is finding it more difficult to get around.

“I cannot move as I want!” she says with a hearty laugh as she sits on the front stoop of her home in Kinyole Village. “I cannot get as much firewood as I need. I want a stove and light in my house.” 

Years of cooking on a traditional wood-burning stove has caused her vision to fail. Her eyes water almost constantly from damage caused by so much exposure to smoke, and she has to take medication to reduce the watering. 

Biogas stoves reduce indoor air pollution. The gas flame is clear and does not emit any smoke. Women like Neseka no longer have to breathe in dangerous wood smoke, which is a major cause of respiratory and eye diseases in the developing world and is responsible for an estimated 1.6 million deaths each year.

For years, Neseka saved money from milk sales and finally has the $52 she needs for a stove and lamp. In Kinyole, Heifer participants must pay for some of the cost of labor and help with construction. Partners in the field support the project by supplying the sand, bricks and cement neededfor construction. Heifer International Uganda provides training, maintenance help and quality control for one year. 

Biogas digesters are installed underground, so a hole has to be dug first. Actual unit construction takes 6-10 days, but once the digester is built, it needs to settle for three months before it’s used. Neseka’s digester is six cubic feet, and she’ll need about 100 pounds of dung a day to feed it, which is perfect for her because her cows produce 100-130 pounds on average every day. The digester must be fed daily to build up gas stores. 

A well-maintained unit has a lifespan of up to 30 years and is relatively inexpensive to troubleshoot if something breaks. When something goes wrong, Heifer Uganda dispatches someone who is trained to make repairs, and that person also trains owners of the unit so they can handle future minor repairs and maintenance. Most often the trainers are called upon to help fix broken light bulbs, clear out stove blockage due to oxidation and drain away condensation.

Jamira Webisa Nalyaka, 62, cooks mandaz on a burner fueled with biogas.
Jamira Webisa Nalyaka, 62, cooks mandaz on a burner fueled with biogas.

More Time, More Money

Jamira Webisa Nalyaka makes mandaz to sell to children as a mid-afternoon snack. Mandaz is a sticky, sweet fried dough ball, Uganda’s answer to the donut. 

Seated next to her biogas stove, Nalyaka mixes one bag of flour with sugar and baking soda. Quietly and with great efficiency, she fries the dough. She averages one mandaz every 30 seconds, making about 80 mandaz a day. Before she had a biogas stove, she would wake up at 6 a.m. to collect wood so she could cook, making sure the donuts were ready by 10 a.m. Today, she wakes up at 7 a.m. and is done within the hour.

Money made from the mandaz sales pays for her children’s school uniforms. Her other source of income is banana sales, which doubled since she began using bio-slurry as fertilizer. 

Nalyaka credits her good friend and neighbor Zaina Muyobo, 49, for introducing her to biogas. Muyobo learned about biogas in 2010 through a commercial on the radio. Today, not only is she a proud owner of her own biogas digester, but she also works as a biogas promoter in her village in the Manafwa district. 

Muyobo earns $20 for every digester she sells. As a promoter, she invites local farmer families to her home for biogas stove demonstrations. As one of ten promoters in her district, she does one presentation a day.

“People are most interested in the bio-slurry and what it can do,” she said. 

Muyobo credits the slurry with her success as a coffee farmer. Not only does she sell enough coffee to afford a comfortable lifestyle for her and her family, but her coffee plants are of such high quality that the Uganda Coffee Development Authority, a government agency created to regulate Uganda’s coffee industry, buys her seeds and has made her a nursery coordinator, allowing her to sell her seedlings to nurseries around the country. 

Farmers who cannot afford a biogas digester can still reap the rewards of bio-slurry. Muyobo sells her slurry at $2.60 a bag. 

Heifer Uganda and Kampala’s Makerere University are teaming up to see if bio-slurry is a commercially viable form of fertilizer. If so, there is opportunity in creating a bio-slurry value chain, allowing farmers to team up and form co-ops to aggregate and sell their slurry to larger markets. 

In the meantime, plenty of farmers already know the value of biogas and bio-slurry. When asked what her favorite thing about biogas is, Muyobo, delighted and proud, shouted,” It’s free gas! It’s free fertilizer! It’s free money!”

Biogas Basics

Biogas Basics

By Jason Woods

Biogas digesters can be a key component of an integrated farm, turning organic waste into rich fertilizer and combustible methane gas. The gas is used to generate light for the house and heat for cooking. Children can study past sunset thanks to the lighting, and time once spent fetching fuel can go to other tasks. Heifer International Uganda initiated a biogas program to address deforestation, which is a serious problem in the country.

Additionally, biogas digesters:

  • Reduce air pollution from smoke, and associated respiratory diseases and eye ailments 
  • Create more free time for families, particularly female members of households, who no longer have to collect firewood • Generate opportunities for local employment through construction of biogas digesters 
  • Control greenhouse gas emissions from livestock in a responsible way

Bio-slurry, a biogas production byproduct, is used to improve agricultural yields and restore soil fertility. Heifer Uganda is also testing the use of bio-slurry as a repellent to protect both livestock and dogs from pests. 

Although biogas digesters are expensive — fixed dome digesters, like those primarily used in Uganda, cost $800-$1,000 — families no longer have to buy or collect fuel. Time in the kitchen is often reduced as well (for example, the cooking time for beans is reduced from one hour to 30 minutes after a switch to biogas). 

Through the biogas initiative, Heifer Uganda has supported the construction of digesters for more than 500 farmers. In addition to Uganda, Heifer International supports the use of biogas digesters for farmers in Bangladesh, Cambodia, Cameroon, China, Honduras, India, Nepal, Nicaragua, the Philippines, Rwanda, Senegal, Tanzania and Vietnam.