USING A BIOGAS DIGESTER
The use of biogas for day-to-day activities is something that happens on a large scale worldwide. In countries like China and India the waste produced by large factories and households flats etc is being used to produce biogas. It has also helped to reduce environmental pollution. This document concentrates on small-scale domestic biogas digesters. Our objective is to build awareness on how to properly maintain a small biogas digester and what needs to be done when minor malfunctions occur. The reason being as the result of research carried out suggesting that the majority of biogas digesters become inefficient due to minor malfunctions. The production of biogas is: An easy method of obtaining combustible fuel required for domestic consumption though the systematic management of waste. When do you use a biogas digester? 1. As a substitute for firewood or LP gas used for cooking.
2. As a substitute to the traditional oil lamps used to light the household.
3. If the biogas digester is large it
can be used as a substitute for the fuel used to run an engine.
4. As a method of obtaining fertiliser that can be used instead of chemical fertilisers used for cultivation.
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5. To manage waste, which pollutes the air, and transform that waste into something beneficial to the environment.
What are the special advantages of using a biogas digester? 1. You do not need firewood or LP Gas for cooking. (This means you need not cut down trees. The environment will be preserved. There is no need to spend time collecting firewood or to spend money on LP Gas. This means it is good for the pocket too). 2. You do not need kerosene oil to light the house. This means the money spent on Kerosene is saved. Also, the hazards and dangers of using kerosene are reduced.
3. There is no smoke and there is
no soot when cooking. This means it is better for your health.
4. In the end you receive a very high quality fertiliser (the advantages of using fertiliser is endless. It especially saves money. Apart from this, as you are producing organic vegetables that do not use chemical fertilisers they can be sold at a higher price). Disadvantages The initial cost is a little high (but it is very cost effective in the long-term).
Introduction to the biogas digester
There are three main types of biogas digesters. There are:
1. The Indian biogas digester
This is a digester with an expandable gas cylinder or dome. As shown in the picture the waste is being sent and collected from drains on either side. The digester is made using bricks and cement. The cylindrical dome is made of metal sheets and moves up and down as it stores and releases the gas.
Gas Mixture Floating dome Collection pit for digested waste material
Central wall Inlet pipe for water material Outlet for digested waste material
The Chinese biogas digester
The bio digester and the composter are made together using cement and bricks and it is a permanent structure. The biogas is collected in the upper chamber and the waste decomposes in the lower chamber. Just as in the Indian digester this has two drains to feed waste and to collect the composted waste.
Upper concrete ring Input for raw material P.V. C pipe Manhole Output for removing digested waste
Entry pipe for raw material Digester Bottom concrete ring
Removal pipe for digested material
In both the Indian and Chinese digesters the waste needs to be:
Put in daily.
Therefore the best option is to connect the digester to the cattle shed or pigs sty.
In both methods the toilets that we use daily can also be used to produce biogas. This gives extra sanitation advantages.
The following table gives the information about the amount of waste that is needed and the output. The capacity of a digester (square meter) 1 2 3 4 Raw material (cow dun) Kg (per day) 25 50 75 100 For cooking (number of people) 3-4 4-7 7-10 10-12 The number of lamps that can be burnt 2 3 6 8
Sri Lankan biogas digester
This is a novel method identified by the Sri Lanka National Engineering and Research Institute. It also won the silver medal at the International New Developers contest held in Geneva, Switzerland, 1996. As shown in the picture the cylinder is made using brick and cement. The cambers used to collect the biogas are made of low-cost 45 gallon barrels, which can be bought from a normal market. As shown in the picture these barrels are kept separately and connected with air pipes. The raw material (hay, grass, seaweed, waste from the markets etc) is added and waste is collected by removing the cap on the top. Connecting pipe
G.I Pipe Gas release pipe
Dome Concrete ring
Gas collecting chambers
Brick base and walls Concrete ring Concrete bottom
The special advantages of the Sri Lankan bio-digester When filled, biogas can be obtained for about 5-6 months. Therefore there is no need to add the raw material daily The main raw material is hay, which is abundant in Sri Lanka and is commonly burnt. Additionally, waste vegetables from markets (market waste), aquatic plants and other grass can be used. Even some factory waste can be used. The remaining waste is organic manure full of nitrogen. This is an environmentally friendly method of generating energy and helps in the process of recycling waste that is otherwise a threat to the environment.
By Sanjeevani Munasinghe, Published by Practical Action South Asia on 02/02/02
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