Choose the type of biogas system you need

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The choice of biogas system depends on its cost, durability and ease of maintenance. Farmers can choose the system that best suits their pockets. Any farmer with one to three dairy cows housed in a zero grazing unit can collect enough cow dung for biogas production.

There must also be adequate water for mixing with animal waste, which is fed into the biogas digester to produce the gas. All biogas systems have three main components:

a)    A mixing chamber (or inlet) b)   A digester c)    An expulsion chamber (or outlet) where the byproducts or bio-slurry is ejected from the digester.

There are four main types of biogas systems that farmers can use in their farms for biogas production. Below, we give the details of each system to enable farmers choose the type they would prefer to install:

a)    The Fixed Dome Biogas system

 The fixed dome biogas unit has an inlet or mixing chamber where cow dung and water are mixed at a ratio of 1:1. The mixture goes into a dome-shaped digester chamber with a fixed or rigid biogas holder at the top. When the mixture reaches the digester, the material is digested, producing biogas that is stored in the biogas holder. When biogas production starts, the slurry or biogas manure is pushed into the expulsion chamber where it can be collected and used as organic fertilizer in the shamba.


Since the unit is constructed underground, it is protected from physical damage. It also saves space. The fixed dome digester is protected from low or high temperatures during the night and day- as a result, there is not much fluctuation in temperatures making the production of biogas constant.

The construction of fixed dome biogas systems is labour intensive, which provides employment to many people. A well constructed system has a lifespan of 30-50 years. Due to the rising demand for the fixed dome biogas systems, the Kenya National Federation of Agricultural Producers (KENFAP), under the Kenya National Domestic Biogas Programme (KENDBIP) has been helping farmers in construction of Fixed Dome Biogas Systems across the country. The project pays a subsidy of KSh 18,750 and the beneficiary farmers are expected to meet the remaining cost of construction (KSh56,250). The standard size of Fixed Dome Biogas unit has a capacity of 6 cubic metres, which is enough for a farmer with 3 or 4 cows. So far, more than 10,000 Kenyan families have benefited from the programme, which ends this year with a possibility for extension next year.

b)    The Floating Drum Biogas system

 The floating drum biogas system consists of an underground digester and a moving gas holder. The gas holder floats directly above the digester or in a separate water tank. The average size of a floating drum is between 5-15 cubic metres which can produce adequate gas for use in small and medium size farms. A floating drum made of high density polyethylene material is durable but expensive.


The system is simple to operate. The volume of gas produced is visible through the vertical movement of the gas drum. The gas pressure remains constant because it is maintained by weight of the gas drum.


The steel and polyethylene material used in making the gas drum is expensive. If steel is used, corrosion is a problem. Floating drum system has a short lifespan.

c) Plastic Tube Digester Biogas system

The Plastic Tube Digester system is made of an elastic (that can expand and contract) polyethylene tube made of two coats of 300 microns in thickness.


The Plastic Tube Digester (PTD) is a cheap and simple method of producing biogas. The tubes are affordable and available locally. However they have a short lifespan of between 2-5 years. Another disadvantage is that the digesters have low gas pressure and are easily damaged by UV rays from the sun. They can also tear easily if people and animals step on them.


 A standard size of PTD with a capacity of 10 to 16 cubic metres that can produce about 2.4 cubic metres of biogas costs KSh 42,000 (Interested farmers can call Pioneer Technologies Tel. 0722 552 505).

d) Flexigas Biogas system

 Flexigas biogas system is one of the latest Plastic Tube Digesters in the market. The system uses a plastic tube digester housed in a greenhouse to protect it from the effect of the sun’s ultra violet (UV) rays that damage the plastic. The greenhouse also reduces the risk of damage from animals or people. Dominic Wanjihia, the director of Biogas International, the company that markets the system says that unlike other biogas systems, the digester is very efficient in utilization of waste material because the greenhouse helps to maintain the temperatures at between 27°C and 34°C, which speeds up the digestion and biogas production process. “1 cow is enough to produce 1 cubic metre of biogas in a day using the system,” he says. A 5 cubic metre tube system costs Ksh 40,000 inclusive of the gas burner, piping and installation while a 7 cubic metre system inclusive of all the accessories and installation costs KSh 55,000. The system has a lifespan of 10 years. The company is already developing biogas systems that heat chicken brooders and even run machinery such as chaff cutters on the farm. Farmers interested in the system can contact the company Biogas International on 0724 316 992.

Biogas has solved my energy problems

Lucy Wanjiru had for years relied on firewood cut from trees in her 2-acre farm in Muruka village in Kandara, Muranga County. Occasionally, she would buy LPG gas to supplement her energy needs. But, last year she visited a neighbour who had installed a fixed dome biogas plant in her homestead. When she observed the way it was working, she was very impressed by the system. Her husband James Mwangi visited Ecosun Investments, a biogas contractor in Thika Town. He made a down payment and within 7 days, the biogas system had been installed in their homestead.

Saved trees

Since then, her energy problems have been solved. The system came complete with a two-burner cooker and gas metre that helps her monitor the gas levels as she cooks, “It has been a great relief to me and my family. I no longer cut down my trees for firewood and I save a lot of money that I would have spent buying cooking gas. With my 8 cows I have more gas than I need,” she says.

Crop yield tripled

Besides the biogas, Wanjiru says the biogas manure is better than the farmyard manure that she used before. “Our banana yields have tripled since we started using biogas manure, and they are also bigger in size. I no longer buy DAP and CAN chemical fertilizers,” she adds. Her husband, James Mwangi, says that they intend to go into vegetable and fruit production using the high quality biogas manure.

Contact Ecosun Investments Tel 0724 394 699, Thika for biogas installation. KENFAP KENBIP Programme also has a list of certified biogas contractors throughout the country. To get the list, call 020 600 83 324, 020 6000355 0721 203 344, 0722 360 699. TOF can also email the list to interested farmers.

>>Tell us how useful this information is to your farming enterprise. Share your experience by email to, leave a comment below this article or SMS 0715 916 136.

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