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Farmer slashes power costs using homemade biogas system

Friday July 21 2017

Alphonce Njau runs a chaff-cutter powered by biogas chop napier grass for his dairy animals.

Alphonce Njau runs a chaff-cutter powered by biogas to chop napier grass for dairy animals in his farm in Kiambu. He also uses the biogas-powered system to heat his bathroom water and in cooking. PHOTO ERIC WAINAINA | NATION MEDIA GROUP 

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It’s around mid-morning as we are ushered into the compound of a homestead with a well-manicured lawn in Kiambu.

At one end of the compound stands a cowshed and inside it something can be heard rattling.

A man dressed in an orange apron and black gumboots carrying a bunch of green nippier grass on his shoulder can be seen entering the shed.

As we approach the shed we see the man feed the napier grass to a running chaff cutter, chopping the grass into small pieces to be used as fodder for his cattle.

From the look of things, there is nothing out of the ordinary, considering most zero grazing farmers in the area use electric or petrol powered chaff cutters to make their work easy.

But this rattling machine is different from the other chaff cutters.

The chaff cutter in Alphonce Njau’s farm at Kanunga Village in Kiambu town sub-county doesn’t run on petrol or electricity.

It uses a bio gas-operated engine which Njau, who has kept dairy cattle for the last 15 years, improvised four years four years ago.

Njau who was introduced to dairy farming by his father, who gave him one cow as a start, said he bought a petrol powered chaff cutter to make his work of preparing fodder for his increasing number of cows easy.

He and his wife, Josephine, he said, could not manage to work on the fodder manually hence the need for the machine.

But as the venture grew, so did the challenge of cleaning mud deposited around by the cows. Njau says the dung would accumulate in the shed fast.

Disposing it became a challenge since his is a small farm and all the waste can’t be fully turned into manure, releasing a stench around the farm and attracting flies and other insects.

His neighbours soon pointed out that his venture was making their lives uncomfortable and he needed a solution real quick. Luckily for him he didn’t have to wait for long.


As a remedy, he installed a bio gas digester, which apart from generating gas for domestic use would help him manage cleanliness because the organic residue does not emit smell, and can last for a long time before being used in the farm in form of organic fertiliser.

The farmer who has a background in mechanics said he learnt how to remodel his chaff cutter from petrol-powered to a biogas-ran engine from tourists from the Netherlands, a country that is credited for advanced dairy farming practices.

Njau's wife, Josephine also the uses biogas for her cooking at their home.

Njau's wife, Josephine also the uses biogas for her cooking at their home. Njau has installed a de-sulphuriser with an inbuilt gauge in the system to his house to purify the gas, clearing the stench away. PHOTO | ERIC WAINAINA | NATION MEDIA GROUP

Njau, a freelance tour guide, met the tourists at Maasai Mara Game Reserve, and during their holiday, their discussions included topics on dairy farming.

“They narrated to me about how they do their dairy farming and I also shared my experience. It was during our discussion that they told me about how they use bio-methanol gas generated from slurry to power chaff cutters and other farm machines.

“At first it sounded untrue,” he said.

The tourists then introduced him to their colleagues in Arusha, Tanzania, who were training people on how to convert fuel operated chaff cutter to use bio gas.

Njau got trained for free for two months and he immediately put the skills into use by remodeling the small petrol-powered chaffcutter on his farm to run on bio gas that he was generating.

The task, he said entailed modifying the fuel jets of the Lister engines by expanding them to accommodate the gas to enable the carburettor use it instead of petrol.

Thanks to his mechanical training, he also improvised the pulley in the lister engine which runs the chaff cutter wheel that has two cutting blades.

He then set up a piping system to feed the carburettor with the gas directly from the bio digester system. The system worked and it zero-rated his running cost since he no longer incurs any electricity or petrol costs to operate the machine which runs for at least 45 minutes daily.


Within the 45 minutes, Njau said he chops enough fodder to feed his animals for a day, adding that the wheel speed can be controlled using the valves he has installed in the piping system.

It does not require petrol or electricity to ignite the engine, Njau said.

Njau indicates at the sludge that is fed into the bio-digester for biogas formation.

Njau indicates at the sludge that is fed into the bio-digester for biogas formation. The bio-digester helps him manage farm cleanliness as the organic residue does not emit smell and can last long being used in the farm as organic fertiliser. PHOTO | ERIC WAINAINA | NATION MEDIA GROUP

The machine is smokeless, and has no maintenance cost, and Mr Njau said since he started using it four years ago, he has never spent a cost on it.

Previously, he spent at least Sh2,000 on electricity per month, or at least Sh120 worth petrol every day.

To start the engine, you only have turn on the gas valve and then manually turn the chaff cutter wheel once or twice to kick start the Lister pulley.

He also uses the system to heat his bathroom water and in cooking.

To ensure the gas used in the kitchen is clear of the cow dung stench, Njau has installed a desulphuriser with an inbuilt gauge in the system to his house to purify the gas.

Njau currently has three lactating Friesian cows, each producing an average 25 litres on milk per day which he sells at a cost of between Sh40 to Sh50 per litre,.

Until recently, the farmer had five dairy cows, but sold two of them to enable him upgrade the breeds.

After successfully installing the system, Njau decided to help interested farmers to set up a similar system in their farms at a cost of Sh45,000.

A farmer is required to purchase the ordinary chaff cutter, and using his knowledge and expertise, he modifies it to convert it to run on, biogas. He says that so far, he has done modifications to at least 20 chaff cutters.