Kenya is turning cow dung into electricity

Oct 06, 2011 12:00 AM

by Rosemary Quipp

Mr Dominic Wanjihia has learnt that it does not take much to produce electricity if you know what you are doing.
He has discovered that a little bacteria, warmth of the sun, industrial-strength tarpaulin, and cow dung is all it takes. Add in an understanding of basic engineering and fermentation, and that is all you need to create biogas.

Biogas is released when organic materials such as cow dung rot in the absence of oxygen. If it is captured, the gas can be used to fuel cooking ranges and engines like generators and chaff cutters.
"God gave [the raw materials] to us free of charge," says Mr Wanjihia, the inventor of a new way of collecting biogas. "You just have to put the dung in. It's not rocket science."

Demand for charcoal
Mr Wanjihia has patented the Flexi Biogas system -- a light-weight, portable biogas digester that promises to wipe conventional biogas systems off the map. He says he designed the system after his sister asked him how environmentalists could reduce demand for charcoal, which is causing rapid deforestation in the country.
To prevent the country's forests from disappearing, Mr Wanjihia says charcoal has to be replaced by a more sustainable energy source. Biogas fits the bill, but he is struggling against its bad reputation in the country, as many biogas systems have already been tried -- and failed.

No matter how the system is designed, the principles of biogas production remain the same: organic waste is fed into one end of a biogas digester, where bacteria break down the raw material. Out the other end comes a mineral-rich (and stink-free) slurry, which can be used as fertiliser. In this process, biogas is released and remains in the digester.
Then it is just a matter of piping out the biogas, and using it as fuel. Mr Wanjihia says the science of biogas is not the problem. The problem is how conventional systems -- or, as he calls them, "obsolete systems" -- have been constructed.

Biogas is traditionally produced in permanent digesters made out of stone and concrete, built underground. Instead, Mr Wanjihia's Flexi Biogas system is a large, rectangular balloon made out of industrial-strength tarpaulin which sits on top of the earth.
As biogas is produced, the balloon inflates. The gas can be piped out of the digester to be stored in a second balloon, or used immediately to cook or power a generator.

"You can use anything you've got, and you get gas in situ. It's been a magnificent success," says hotelier Garry Cullen, who uses the Flexi Biogas system at home and at his luxury tented camp in the Mara. "No problems so far."
The system produces more gas than his camp's staff can consume, he says.
"I'm trying to get them to run it out, and they can't do it."

Mr Cullen says the system is superior to existing systems, which are 10 to 20 times more expensive. Conventional designs also pose a series of problems that have given biogas its bad reputation, according to Mr Wanjihia.
First, below-ground systems are permanent, meaning the owner of the system also has to own the land.
Second, the skilled labour and materials involved make them more expensive and time-consuming to construct.
Third, biogas digesters need warmth to run. The bacteria die if temperatures fall below 15 degrees Celsius (or rise above 60 degrees), but Mr Wanjihia says the optimal temperature is about the same as body temperature: 37 degrees.

Easily accessible
Because the earth acts as a cooling system, underground digesters operate at a much lower temperature. To compensate, these digesters require more raw material to produce the same amount of gas as the Flexi system.
Mr Wanjihia says his unit solves all of these issues: it is portable, inexpensive, easily accessible and naturally runs at a higher operating temperature because it is exposed to sunlight -- it can also be erected inside a portable greenhouse to increase temperatures in cooler regions.

The system has a lifespan of 10 to 20 years and costs between Sh 58,500 and Sh 71,500, depending on the capacity of the digester. Schools or businesses may have to buy more than one digester to meet their needs. That cost includes installation and instruction on how to use the digester from Biogas International, Mr Wanjihia's company.
The company has already installed dozens of systems throughout the country. The company is focusing on installing them in schools, children's homes, and clinics in remote areas. Mr Wanjihia says it can be installed anywhere -- from a backyard in rural areas to the roof of an apartment complex in downtown Nairobi.

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