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For small farmer, one cow offers enough biogas

Friday May 27 2016

Dedan Nene at his Biogas unit.

Dedan Nene at his Biogas unit in Nairobi. PHOTO | MWAURA SAMORA | NATION MEDIA GROUP 

Mwaura Samora
By Mwaura Samora
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Even with a single cow, one can produce enough biogas for use at home, according to Dedan Nene, the director of Modeline Technologies.

After years of trial and error, Nene has come up with a bio-digester that would be sustained by the sludge produced by one cow.

He did his first design in 2004 using polythene bags fitted with inlet and outlet pipes on both ends and the gas tap at the front.

“The polythene would not last long, so I graduated to using rubber tubes that also had a challenge of getting bloated and bursting after the accumulation of gas,” says Nene, who is a mechanical engineer.

“Before the current design where the rubber is ultra-violet treated to avoid cracking from exposure to sunlight and fibre-strengthened to avoid bloating, there were three generations of designs,” he recounts.

His one-cow bio-digester is a 3 by 30 feet long tubular reinforced rubber buried halfway in a narrow trench. With an initial feed of 2,500 litres sludge, the only daily requirement for the system is a 20-litre bucket refill.


“What makes this digester unique is the fact that it only requires 20 litres of the dung mixed with water at the ratio of 1:1 daily. A single well-fed cow produces around 40 litres.”

Pig dung, he notes, is more productive than cow dung since it has plenty of catalyst bacteria, with two animals being enough to run the digester each day.


Upon installation, it takes about seven days for gas to form and after that the system can produce enough to cook for a family of seven. The digester needs to be inside an enclosure to avoid damage by animals or children who can mistake it for a bouncing castle.

“Assuming breakfast takes two hours, lunch and supper three, there is enough gas to sustain this,” Nene explains. “This is far-much economical than paraffin, electricity or the regular gas given there is no direct monetary input”.

But the quantity of gas produced hugely depends on the type of feeds given to the cow. If the cow is fed good quality feeds, the digester will yield more gas.

“Dry feeds like hay are the most recommended for dairy cows to produce better results in both milk and meat production,” he points out.

“Dry feeds produce more bacteria inside the cow than wet feeds like vegetable leaves and green napier grass. This means the dung will be rich in bacteria, which process the gas faster inside the digester.”

If the dung is short of bacteria, it means the organisms have to be produced inside the digester before any gas can be formed, which takes a longer period.

“The discharge sludge from the digester makes the best fertiliser because it has fermented under anaerobic conditions that make it un-acidic, thus high in nutrient content and cant burn crops.”

At Sh55,000, the farmer gets the digester, the gas pipe and a cooker which, Nene says, is designed to be accessible to the ordinary ‘one-cow farmer’, who is found in the many villages across the nation.