The fossil fuels that we rely on for most of our energy needs don’t just cause pollution, in addition, they are also limited. In the near future, these would become scarce and expensive. Therefore, to tackle our needs we would have to rely on renewable sources. According to experts, solar energy might become mainstream in the future. However, to extract it we have to use silicon, which is expensive. Moreover, we can’t generate it when the sun is down. So, it is necessary that we look for other alternatives as well. In this situation, biogas plants might be what we are looking for.
What exactly are biogas plants?
Biogas plants are a great way to reduce environmental pollution. Why is that? Well, a biogas power plant is an anaerobic digestion system which is designed specially for the purpose of generating energy.
You must be wondering when anaerobic digestion takes place. When there is biological degradation of organic material (like manure, municipal solid waste and biodegradable waste) in the absence of air, then this is know as anaerobic digestion.
Biogas (which is primarily composed of methane and CO2) is the byproduct of anaerobic digestion. This biogas can be used very effectively for generating electricity and even used as a vehicle fuel. It can also be burned directly for lighting, cooking and heating.
One of the major reasons for the popularity of biogas production by anaerobic digestion is because it is a great way to destroy disease-causing pathogens and reducing the volume of disposed waste products.
Are you aware why the harvesting of biogas is an important part of waste management? This is because methane is a greenhouse gas which is even more harmful to the environment than carbon dioxide. Nevertheless, we can use it for beneficial purposes too.
In order to become more eco-friendly many developed countries are building biogas plants. In fact the Ministry of Energy, Thailand has set a target of building 1,540, 100 MW bio-gas plants by 2011, many of them fuelled by solid waste and polluted water.
I hope more countries all over the world build anaerobic digestion systems; because it is not only good for the environment it is great for business too.
How to make a biogas digester
The anaeorbic decomposition process carried out in these plants gives a source of energy that not only reduces green house emissions but improves sanitation as well. Moreover, one also gets a high-quality organic fertilizer in the end (as a waste). The article below gives a simple description of how to carry out a construction of Biogas Digester plant.
Based on usage, scale and complexity of building a plant, one can classify the different types of Digesters in following categories.
a. Easy: (For first-timers. Anyone can do it)
This requires two plastic drums of 1 cubic meter and 0.75 cubic meter capacity. Unlike other plants one does not require cement construction for installing this unit.
b. Moderate: (Requires basic knowledge)
The bigger biogas digester plants with 4 to 6 cubic metre capacity will require 25 to 35 kg of dung on daily basis. Moreover, one should have basic knowledge about plumbing, construction and stone masonry to carry out construction of these units.
c. Moderately Challenging: (May require expertise in few areas)
These are bigger plants with 8 to 15 cubic meter of capacity. A group of skilled and unskilled labor might be needed for installation of these units.
d. Challenging: (Requires considerable experience and expertise)
Installing plats with 20 cubic meter of capacity is a quite a complex job and one should take professional help for design and installation of such units.
The article below will give details about the easiest type of biogas digester. It relies on plastic drums instead of cement construction. The unit could be erected easily in three hours. Furthermore, it should not take more than ten hours, even if some issue arises. It becomes productive in less than two weeks.
The cost at very liberal estimates involving the 2 plastic water tanks, flexible pipe, stable horizontal base, a frame to stop the gas tank rise and inlet and outlet fittings should not cross $ 100.
The plant works on the principle of biomethanisation. It is a process in which anaerobic digestion of organic material is carried out by the bacteria. These bacteria decompose organic material (Feedstock) to release methane and carbon dioxide.
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- Select two plastic water tanks (1 and 0.75 cubic meter) so that one could be fitted into another, when there tops are cut open. Out of these two tanks, the bigger tank is the main digester which holds the Feedstock and water mix (Slurry). Smaller tank is placed in an ‘upside down position’ inside the chamber and serves as a gas holder.
- An inlet flexible pipe about 300 mm diameter and slightly longer than the height of the tank is needed to be fitted at the bottom side of the bigger tank. This will require minor plumbing and fitting skills. At the top end of this pipe a funnel could be fixed as it serves as an entrance for the feedstock material in the chamber. Make sure that this arrangement is kept loose and not permanent, so that it can act as a purge if required.
- The effluent outlet is supposed to be built at the upper part of the bigger tank with similar type of pipe. It determines the maximum level mix that can be maintained in the tank.
- The gas outlet requires a tightly secured fitting at the top of smaller gas tank, and it connects the unit to the gas stove inside the homes.
- A frame structure has to be built for preventing the gas tank form falling apart in case it is overfilled. One can also put additional weight on upper tank to increase gas pressure build up.
- Special burners which have a valve arrangement for mixing air with methane are required so that flame remains blue.
- For starting operation, a slurry of about 20 kg of cattle dung, waste flour or starch and water is required to be feed in via inlet pipe.
Frequently asked questions
Are there any special additives or bacteria required for production?
No, it is the bacterial growth inside the tank due to presence of cattle dung which is responsible for Biomethanisation of organic material into methane and carbon dioxide. In less than two weeks the upper tank will raise, indicating the gas build up. If initial tests show that the gas is combustible, one can start adding the high calorie material.
How much of feedstock is required on daily basis?
In the above capacity, 1 to 1.5 kg of mashed feedstock mixed with 10 to 15 liters of water is required to be put in, twice a day.
Apart from using cattle dung and waste flour what else could be used as a feedstock?
People can use vegetable residues, waste food, fruit peelings and rotten fruit pulps as feedstock. One can also use rhizomes of banana, non-edible seeds and spoilt grain as a possible feedstock material.
What is the output of such a digester?
A steady supply of gas of around 250 grams per kg of (dry matter) of feed could be achieved with this digester.
It is advisable to break down the larger lumps of waste into a uniform mix before feeding it into the tank, as larger lumps don’t decompose easily and would lower the efficiency of the entire plant. For better yield the system should be installed at a warmer place (32 to 37 degree Celsius).
Things to watch out for
Methan along with air forms an explosive mix. So all fire safety norms sould be adhered to, while using this system.The digester area needs to be well ventilated (ideally an open space) to minimize the risks of fire/explosion and asphyxiation.