Biogas is a by-product of anaerobic (without oxygen) breakdown of organic matter like animal manure and crop waste.
These materials are readily available on the farm since most Kenyans engage in farming, particularly in rural areas.
Other waste can come from dairies, brewing, distilleries, vegetable oil refining and slaughterhouses.
The anaerobic digester will partially convert the organic matter into energy in the form of biogas.
The main and most important component is methane, a flammable gas. Others include carbon dioxide and minor gases like hydrogen, nitrogen, and traces of water vapour and hydrogen sulphide.
Biogas is generally a clean and environmental friendly renewable fuel, which can be used to run engines like chaff-cutters, generation of electricity, for cooking and heating hot water systems and even refrigeration. Certainly, biogas is an alternative solution to the current energy crisis.
The energy content of the gas is directly related to methane gas concentration, where a typical cubic meter of methane gas has a calorific value of about 20 mega joules (MJ) per m3 and burns with 60 percent efficiency on the conventional biogas stove.
This in turn implies that a household that uses two burners for cooking for about three hours daily will use approximately 2.7m3 of biogas per day, assuming a single biogas burner uses maximum of 0.45m3 of biogas per hour.
Usually, a biogas lamp uses approximately 0.15m3 per hour. Therefore, if the same household uses three gas lamps for three hours daily, it will require approximately 1.35m3 of biogas per day.
This gives a total of 4.05m3 for cooking and lighting activities. When using the 12m3 biogas system, 4.3m3 of biogas will be produced per day.
The household will, therefore, have a surplus of 0.25m3 for other purposes or give allowance for non-optimal performance, if any. Most families pay between Sh1,200-Sh1,500 electricity bill per month for lighting only. Majority of biogas constructors charge not more than Sh150,000 to put up a 12m3 biogas system.
If you are paying Sh1,500 per month, you need about Sh18,000 per year to settle your power bills. Therefore, in about seven years, you will exceed the cost of setting up a 12m3 biogas plant.
Remember the plant has an expected useful life of not less than 30 years. Currently, most of biogas producers rely on cows for manure. The question most people ask is how many cows they need to produce biogas.
For the 12m3 we based our calculations on, you need about six cows. However, for the smallest biogas capacity of 4m3, two cows are enough to produce biogas that you can comfortably use at home for cooking or lighting.
To set up a biogas system, go for a qualified digester designer, builder or equipment supplier. Besides financial capability, manure-power consumption rate determines the size of biogas, and, therefore, what one can invest.
The qualified designer should guide you the costs determined by principle components such as foundation, digester effluent storage, roof, gas pump, boiler, hydra-ram manure pump with hydraulic unit, supplies and labour.
The costs also vary depending on local prices and the choice of components one chooses to include in the system.
A well-constructed biogas should be user friendly and sensitive to the safety of workers and visitors around the system.
Areas of concern to owners during production and handling of biogas include gas releases that are flammable, liquid tanks that may result in drowning, children and unaware visitors who come close to areas of danger.
Opinya is based at the Department of Animal Science, Egerton University.
To beat high cost of power, fuel I made my own biogas system
Sonokwek in Litien, Bomet County, is a lacklustre village like any other across the country, making one believe that nothing exciting happens in the hamlet.
But that is until you step into Bernard Kemei’s dairy farm, some four kilometres from Litien.
The farmer is busy feeding freshly harvested napier grass from his farm into a chaff cutter when Seeds of Gold team meets him.
Soon, he completes the task and Kemei opens the machine’s fuel tank, pours some 10ml of diesel into the engine to jump-start it before letting the gadget run on biogas.
The machine starts to slice the fodder into tiny pieces before he stops it and feeds more napier.
“This machine runs on biogas that I generate from my cows,” says Kemei, with a smile on his face, noting the machine has greatly lessened his work.
The innovative dairy farmer has improvised a mechanical biogas system that has improved his work operations and cut his expenses greatly.
Kemei began rearing dairy cows in 2010 with a traditional cow. However, it wasn’t a profitable enterprise especially because he used practice free — range system.
“I improved the breed of my animals slowly, taking up Friesians. In 2015, I started using biogas to power my chaff cutter. I learnt from other farmers that biogas can be used for cooking but I later adopted and tried on my machines and it is working,” says Kemei, a keen observer who looked at the way things work, put them to test and they worked.
He has a 12m3 digester that collects and converts manure from the cows to biogas, which he then pipes to the chaff cutter.
He has modified the machine’s petrol engine in such a way that he uses the small drops of fuel to jump-start the engine which roars before it automatically switches to use the biogas.
Kemei has grown different fodder on his three-acre farm, which include napier grass, sorghum, desmodium, lucerne and sweet potato vines.
The feeds cater for his seven cows — four that he milks, two heifers and a calf — and have helped him increase milk production from seven litres per cow a day to 25 litres.
INNOVATIVE TO CUT COSTS OF POWERING MACHINES
The farmer improvised the biogas unit after realising he was spending more on fuel, at least three litres every day on the machine.
“I bought a chaff cutter, a great improvement from the improvised machete that I was using to chop napier grass and maize and sorghum stalks, but I realised it was consuming plenty of fuel,” says Kemei.
From the zero-grazing unit, the waste from the cows flow to the biogas digester where he adds a bucketful of water before stirring.
He then removes materials such as fodder that may have entered the digester and can block it.
Later, he opens up a small valve to allow the slurry flow to his farm. The gas from the mixture then flows to the storage tank ready for use.
Atop the zero-grazing unit he has placed a water tank which is connected to the several pipes running from the facility to the water troughs for his cows.
“I decided to put it up there to ensure that the water becomes warm due to solar heat. I was taught that cows require warm water.”
Next to the water tank hangs a small bottle that is tied to the tank by a tiny string. The bottle enables him to know when the tank is empty and requires to be refilled.
In one of the water troughs, he has put a floater that fills and re-fills with water from the tank without human presence. It is all mechanical.
“With this, I don’t have to be here all the time. When the water level goes down, clean water from the tank fills by itself into the tank,” says Kemei of the systems that he set up himself, spending at least Sh200,000 on both.
Evans Kiplagat, the Bomet County assistant director of livestock production, says with petrol and electricity prices skyrocketing, farmers have to be innovative to cut the cost of powering machines.
“Chaff cutters are necessary on any modern dairy farm because they make work easier when it comes to chopping fodder to make silage or for the animals to feed on them directly. So, it is for farmers to find a way of making the machines efficient.”
Kemei says it would cost him Sh200 a day to hire a worker to assist him to chop fodder and he would spend at least Sh200 a day on fuel if he had not developed the system.