Kenyan Startup Uses the Sun to Turn Human Waste into Cooking Fuel

A Kenyan startup scales up its processing of human waste with a new continuous flow system creating a new fuel stream for cooking

5 min read
A collection of Sanivation's poop-based fuel briquettes
Sanivation's poop-based fuel briquettes finish cooling and drying on racks.
Photo: Sanivation

In August 2015—after a couple of years of testing—a company in Kenya began commercially treating human poop with the sun’s heat to create an environmentally friendly fuel source. This week, Sanivation plans to turn on a new continuous-flow system that will help it scale up to support many more customers than it could previously.

“We can treat thousands and multi-thousands of peoples’ shit continuously,” says Sanivation CTO Emily Woods.

In developing countries, the International Energy Agency estimates that about 2.5 billion people cook with biomass: charcoal from forests, agricultural waste, animal dung, and other sources. In Kenya, charcoal provides about 82 percent of the energy in urban households and 34 percent of the energy in rural households, according to the Kenya Forest Service. Yet its use is leading to major deforestation2013 research found that the demand for charcoal was about 16.3 million m3, but there was only a supply of about 7.3 million m3. Not to mention that the air pollution from inefficiently burning solid fuels such as charcoal can kill about 4.3 million people a year.

One solution to these problems could be switching to cleaner cooking stoves, but some research points out that new technology adoption is difficult. Instead of swapping stoves, changing fuel is another possibility—research by the United Nations University Institute for Water, Environment, and Health concluded that the electricity generated from the world’s collective human feces could power up to 138 million households, for example.

And that’s where Sanivation steps in—providing an alternative cooking-fuel source to local small businesses and restaurants. Woods says Sanivation’s sun-treated poop fuel briquettes can burn two times longer than normal charcoal, yet release about one third of the carbon monoxide and particulate matter emissions. Each metric ton of the briquettes saves about 88 trees yet they are “comparable” in cost even with charcoal’s rapid price fluctuations.

Before this week, the team of about 50 was able to process about 2 metric tons of waste every month in batches. In the new continuous-flow system coming online this week in Naivasha, Sanivation estimates it will be able to process 6 to 8 metric tons of waste every month, decreasing the amount of physical space required for processing, and increasing the number of customers from hundreds to hopefully many more.

The process starts with fecal waste that the company collects from latrines and ends with a fuel briquette.

The first stage is treatment. Sanivation applies heat to sanitize the waste—waiting in a container—and remove any harmful pathogens.

Sanivation's waste treatment system: a solar concentrator with a receiver that heats up fecal matter

Photo: Sanivation
Sanivation’s waste treatment system uses a solar concentrator to heat up fecal matter. Primary components include the Scheffler dish reflector (mirrored surface), the beige hopper to load the poop, and the large-bore-pipe heat exchanger.

A glass and steel parabolic disk with an area of about 5 m2 acts like a solar concentrator. When the sun’s rays hit the disk, it reflects the light and focuses it onto the glass side of an approximately 13- by 13-centimeter receiver containing the waste. The waste starts warming up to about 60° C—the other sides of the receiver prevent the heat from escaping because they are insulators: cement or fiberglass.

The trick to the treatment is that once poop gets hot enough, pathogens disappear. One estimate says this happens after waste is heated to 60° C for one hour. Woods says many researchers are working on finding the lowest possible temperature and time to sanitize waste, but for now Sanivation errs on the side of caution and goes to 60° C for three hours.

Before this week, the team would check that the batches went above safety requirements and then mix the product with waste materials such as charcoal dust or sawdust. Feces have a high fiber content, so when cooled and dried after heat treatment, a hard and solid briquette forms. (Woods says the details of the processing are “kind of our secret” but “you get a nice, solid, very dense, very flammable material.”)

Sanivation's agglomerator

Photo: Sanivation
Sanivation’s agglomerator acts like a cement mixer to combine ingredients and apply tumbling pressure to the feces binder and the carbonized agriculture waste.

In the new continuous-flow system, the waste heats up for about five to 10 minutes, and is routed via pipes to insulating cement and fiberglass containers, where it sits for a total of three hours before moving into the briquette production stage. Sensors throughout the container monitor the temperature.

Woods says rolling out a new system like this is hard, because it’s difficult to get equipment such as a seal fixed or replaced due to the availability of parts and manufacturing quality limitations. “We can’t just swing down to the Home Depot and pick up a new seal,” she says.

Still, this week should be the week it goes live. “I think we’re about ready to put some poop in it,” she says.

Salim Mayeki Shaban, the founder and president of the African Christians Organization Network in Kenya, creates charcoal from an invasive species called water hyacinth instead of trees. He sells special stoves that can use and produce his charcoal sustainably—primarily as a fertilizer ingredient but also for fuel.

He writes in a Skype message that maybe about 70 percent of the people in Kenya still use normal charcoal in part because of cost deterrants but mostly because of a “lack of knowledge” that could be improved by going out in the field with demonstrations and training. He writes that most people switch to alternatives once they learn about them.

Björn Vinnerås, an environmental engineer at the Swedish University of Agricultural Sciences in Uppsala, develops on-site sanitation systems in Sweden, Africa, Asia, and Latin America. One of his projects collects poop and urine—but instead of converting it into fuel, he, like Shaban, also creates a fertilizer for plants. “If you can really turn the waste you have to manage into a resource,” he says, “I see a really big benefit of it.”

Unlike other alternative charcoal sources, Vinnerås says, Sanivation’s system addresses the problem of where to put waste that overfills latrines: if it winds up in a landfill, it act as a pollutant. He says the image of human manure might make it difficult to receive public acceptance, but at the same time, some people in rural areas already use cow dung as fuel. “So it can be found within the culture already,” he says.

Woods says people always bring up the poop imagery, but she says Sanivation hasn’t found it to be a problem. “Once people try it, they rarely still have a problem with it.” The company is upfront about it, but the briquettes don’t smell or look like poop. 

Besides social and political obstacles of not being from Kenya, she says the main challenge is quality of supply. The other materials Sanivation uses to create the briquettes are often filled with contaminants such as dirt that can lower the briquette quality.

She says Sanivation is doing particularly well with local businesses because it meets sustainability regulation—most of the charcoal sold in Kenya, she says, has been created illegally, so business owners don’t have to worry about the company suddenly disappearing like traditional fuel providers. In October, Sanivation sold about 8 metric tons of briquettes to about 20 small businesses and restaurants.

The company has targeted small businesses and restaurants first because they buy in bulk: a business would buy between about 200 kilograms to 2 metric tons of briquettes while a household could only buy kilograms. However, the company plans on expanding to the household market because households “will pay more.” Woods also hopes to reach out to more municipalities, both about the fuel briquettes and the custom toilets Sanivation sells to improve sanitation conditions.

“It’s all pretty simple technology, and that’s actually key to working and operating in Kenya,” she says.

Future improvements could include switching to conveyor belts to move the feces and other waste products around. Next year, the team hopes to get the system processing 30 metric tons per month.

“These other forms of fuel, they’re just so needed,” she says.

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