Biogas: Biogas Plant, Working and Benefits

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Biogas is a renewable source of energy.

 

Need I say more? This single line is enough to motivate a person to set up a biogas plant at home.

It is very simple to set up and whatever cost you incur to build this up, will all be paid back to you by this plant that too with 1000% interest rate.

 

What is Biogas?

 

Biogas is a gas which is generated when the anaerobic decomposition of organic matter(like cow dung, vegetable waste, sewage, etc.) takes place.

Methane is the main component of Biogas which is flammable and it is a good fuel. The composition of this gas includes carbon monoxide, hydrogen sulphide and a few other components.

 

Anaerobic Decomposition:

 

Anaerobic decomposition is the degradation process which happens without the presence of oxygen. This decomposition produces methane. A vast variety of materials can be decomposed this way.

 

Biogas Plant Design and Working:

The primary idea of a biogas plant is to decompose the organic material and collect biogas. Every design and structure of the plant revolves around this idea. There are many designs of a biogas plant but, the basic idea behind each and every one of them is the same. Here, I have mentioned the two most efficient and popular designs of biogas plant.

 

Here are two ways to design a Biogas plant:

 

  1. The first way to design the plant is by including a partition in the biogas digestor and dividing it into two chambers as shown in the figure.
Biogas plant with partition
Biogas plant with partition

 

When the first chamber gets full, the excess organic material which is at the top of the first chamber falls down in the second chamber. This top layer is already decomposed as it has been in the first chamber for a few days.

In the second chamber, there is still a chance for the organic material to decompose further. When the second chamber is full, the decomposed organic material goes out of the pipe and accumulates in a separate tank dedicated exclusively to collect this slurry.

From this slurry tank, we can recover this decomposed material to use it as an organic fertilizer.

The floating drum at the top of the digester collects methane. After which we can use this gas by connecting a pipe to the outlet of the drum at the top of it.

2. The second way of designing the plant is by not building the partition in the biogas digester.

Here, the inlet is at the bottom of the digester as shown in the figure. The outlet is at the top of the digester on the opposite side.

Biogas plant without partition
Biogas plant without partition

The material gets decomposed and comes up whenever new organic material enters the biogas digester. Slowly, when it reaches the top it comes out of the outlet and it is collected in a different tank.

We can use this material as a fertilizer. The floating drum collects the methane and we can use the gas directly from this drum. A valve at the top of the drum regulates the flow of gas.

 

Dimensions  and Construction of a Biogas plant:

 

Well, deciding the dimensions of the biogas plant is completely up to you but, here, I’ll describe the most common design of the plant. The most important part of the biogas plant is the digester.

The depth of the digester should be 10 feet and the diameter should be 5 feet. The sides and the floor of the digester are made from concrete.

The floating drum has a diameter of 4 feet and it is 5 millimetres thick. When the sludge is decomposed, the biogas comes up and accumulates in the drum. The drum has a concave top surface, so as to collect the gas and direct the flow of the gas towards the biogas outlet at the top.

A 2×2 feet concrete sludge tank is built beside the digester to feed the digester with the organic material. This tank is 3 feet deep.

All the slurry coming out of the digester is then collected in the pit. The pit is dug on the ground such that the outlet of the digester is at the top of the pit, so that, the slurry will fall right off in the pit. The pit is 4 feet deep. The length of the pit is 5 feet and breadth is also 5 feet.

Again, these dimensions are for a generic model, you can decide the dimensions according to your needs.

The proper way to feed the digester:

To boost up the process of decomposition, the organic material should be mixed with water. First of all, mix the feed with some water in the sludge tank. The feed and the water should be mixed in a 1:1 ratio. For every kg of the feed, you need 1 litre of water.

To give you a better picture, the viscosity of the sludge should be like curd. The sludge decomposes quickly if it’s consistency is like curd.

 

What feeds can be fed into the biogas plant?

 

Cow dung:

Many farmers rear cows and cattle. So, their dung alone can produce enough biogas to fulfil all farmer’s needs.

Food waste:

Food waste is also a good option as it is generated daily.

Human waste:

Drainage pipes can directly be connected to the plant.

Agricultural waste:

All the organic agricultural waste can be directly put in the digester to decompose it.

Slaughterhouse waste:

If you have access to slaughterhouse waste, then you can directly put this waste in the digester, however, these materials decompose slowly and take a longer time to generate biogas.

Vegetable leftovers:

Vegetable leftovers decompose very fast and provide biogas quickly.

Plant materials:

If you have a garden, consider putting plant waste in the digester.

Wastewater sludge:

Wastewater from houses, gardens and farms can also be used. One thing to keep in mind here is that the wastewater should be free of hazardous chemicals.

Fallen tree leaves:

If it is autumn, then you are in luck, as many trees shed leaves in this season. You can directly put these leaves in the plant.

 

Other Benefits:

 

Cooking Food:

Methane produced from the biogas plant can also be compressed. We can then store it in cylinders. This is a good substitute for LPG cylinders which are used for cooking food.

Fuel for vehicles:

Methane is a good substitute for petrol. We can then power our vehicles with methane by compressing it in cylinders.

Electricity generation:

In some instances, people have used methane to power generators and fulfil their electricity-related needs.

Fertilizer:

We can use the slurry from the biogas plant as an organic fertilizer. We can then spread it all over our farm and get some really good yield. Also, we can sell the remaining manure in the markets at a good price.

Hot water production:

If you somehow implement the Jean Pain setup with the biogas plant, you can even get hot water for your lifetime. I have already discussed Jean pain technique in the blog.

 

Safety Measures:

 

  • Methane is a flammable gas. So, we need to make sure that the biogas plant is away from the fire.
  • Build proper barricades around the slurry tank so that, no one would go near it. This tank is similar to a bog, once stuck in it, it is difficult to get out of it.
  • Don’t let anyone stand or walk on the floating drum.
  • Keep children away from the plant.
  • It is advisable to maintain a particular level of gas in the drum.
  • However, these factors are not very serious but as we all know, precaution is better than cure.

Household Biogas Plant:

 

Biogas is an excellent topic for the researchers to work on. They have developed new techniques to implement a biogas plant.

Generating Biogas has now become a profitable business. Huge industries are now setting up just to produce and sell biogas.

We can also use small-scale biogas digesters made from a plastic drum. Their size is so small that we can accommodate them in our homes. We can then put leftover vegetables and other organic materials in it to reap its benefits.

It will cost you around ₹25,000. If you don’t want to spend even this much money, you can make them by yourself using a plastic drum.

 

As we can see, there are a lot of benefits of a biogas plant. We can recover the full cost of the plant in around 3 years. After 3 years, it will pay us back good returns.

The government also provides various subsidy schemes for building biogas plants. You can get even 50% subsidy in some regions, you just have to look for whatever schemes are applicable in your respective regions.

While a lot of farmers are running towards solar power, I personally think that biogas is a perfect substitute for this. I agree that solar power generating machines require very less maintenance but they are very expensive. Biogas is almost free.

 

Note:

 

Gobar gas is the same as Biogas, the only difference is that, in Gobar gas plant, we only use cow dung and in Biogas, we use any organic material.

Many a time, people build covered biogas digester. The digesters have a solid concrete dome. Well, it doesn’t matter which type of dome you use. It is, however, easy to handle some problem occurring inside the digester if we use the floating drum.

 

 

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