This simply means a tank that biologically digests organic material to produce bio-gas. However, most people think of it as a tank that digests organic material anaerobically without oxygen. The organic material produces methane gas which can be used for cooking, lighting, heating, etc.
Bio-digesters can be installed for simple household uses. It generates bio-gas from animal manure and other organic wastes. This enables families to cook with an environmentally friendly smoke-free fuel.
The digesters also produce a slurry which happens to be very rich in Nitrogen. This makes it a great fertilizer to promote soil health as it contains manure and water. In addition, they save families a lot of money and time.
Bio-gas has become a very important technology in Kenya. This is due to the fact that they give an on-site sanitation system rather than the common smelly sewer system. Bio-digesters never fill up hence you will never need exhauster services. The waste is usually used up in its continuous production.
In Kenya, so many people have no connection to a sewer and for others; they are far from their homes. This is predominantly in the slums and other densely populated areas. Construction of a bio-digester for these people is a great advantage as it will come with added benefits. Free fuel in form of bio-gas is one of them and also a cleaner environment. Urban areas have a growing concern about crowding. This has created the need for a better and improved method of waste disposal and cleaner surroundings.
What is the Cost of Bio-gas
Bio-gas is a renewable source of energy that cannot be depleted making it cheap. This is exceptionally easy for people with livestock. If one constructs their own bio-gas plant then it is basically free. When you use bio-gas, cooking fuel expenses can be reduced by as much as 80per cent. It replaces firewood, charcoal and kerosene.
Majority of Kenyans live below the poverty line. A basic home bio-gas unit costs between Ksh. 50,000 – Ksh. 80,000 which is many Kenyans still cannot afford.
You can also construct your own bio-gas plant. Most constructors charge not more than Sh150,000 to put up a 12m3 bio-gas system.
In Nairobi, people generate about 3,000 tons of waste every day most of which is organic. If all this waste was used to produce bio-gas then there would be fewer problems on fuel and lighting.
Recently, development agencies of German and Japanese governments have been offering Kenyans one-year loans to construct bio-gas plants. All the farmers need to do is to have a source of organic matter. Most keep livestock which gives great waste for methane production. In the meantime, they can sell the cow’s milk to be able to pay back the loan.
As the transition becomes more and more affordable, many poor Kenyans are increasingly switching to bio-gas. Traditional fuels like kerosene and gas cylinders are expensive and the prices keep hiking. Majority of people now prefer bio-gas due to its availability and cheap methods to produce it.
Can Bio-gas be Used for Cooking
There are special stoves made specifically for cooking with biogas. They are called improved cookstoves. They have a valve to pre-mix bio-gas with adequate oxygen. It also has a well-designed burner to hold a cooking pot and combust the mixture. There is a tube that transports bio-gas from the digester to the cooking place.
Bio-gas has no strong odour so it does not keep your home smelling. The flame from it is clean and clear as it has no impurities. This means that your dishes will not end up black with soot.
The improved cookstoves ensure complete combustion and they are more efficient. In a way, they are similar to the cookers used for commercial gas fuels. These stoves can also use wood, charcoal and cow dung as well.
A household using two burners to cook for about three hours every day will use approximately 2.7m3 of biogas per day. This is assuming one biogas burner uses 0.45m3 of biogas per hour.
Normally, a biogas lamp uses at least 0.15m3 per hour. If the same household uses three gas lamps for three hours every day, it will need at least 1.35m3 of biogas per day.
This adds up to 4.05m3 for cooking and lighting. If they are using the 12m3 biogas system, 4.3m3 of biogas will be produced every day.
In the end, the household will have a surplus of 0.25m3 for other purposes or as an allowance for any non-optimal performance.
Anybody who wants to construct a biogas system has a number of considerations to make. These include;
– An efficient bio-digester must have an inlet, an outlet and a means to stir the materials as it grids them.
– To calculate the size of the plant you take Cow dung/cow/day multiplied by the number of cows multiplied by two multiplied by 60, then divide everything by 1,000.
Amount of gas expected
– A cow can produce 15kgs of dung per day. This can generate about 0.5m3 of gas. A farmer can multiply the number of adult cows by 0.5 to estimate the amount of gas in cubic meters per day. An efficient biogas burner uses about 0.5 m3 of gas per hour.
– ensure that open flames are never within six meters of a biogas plant. Before any repairs or inspections, technicians should ensure that all biogas is evacuated from a digester before they enter. This is because biogas can displace oxygen and cause suffocation.
Management of the system
– A digester must be fed regularly for a continuous supply of gas. The feeding frequency could be daily or weekly.
In a domestic system, a tank of 1000 litres is enough to completely digest waste and treat the wastewater. Wastewater comes from toilets, bathrooms, kitchens and sinks in offices and homes. This water contains pollutants like human waste, soaps and detergents, skin flakes, oils and fats and solid particles.
The installation of bio-digesters always starts from the building’s last manhole.