BioGas

What is biogas?

Biogas is a byproduct of the decomposition of organic matter by anaerobic bacteria.

Biogas is typically composed of 60% methane and 40% CO2. It is similar to natural gas which is composed of 99% methane.

Biogas is a clean and renewable energy that may be substituted to natural gas for cooking, to produce vapor, hot water or to generate electricity.

At room pressure and temperature biogas is in gaseous form, not liquid like LPG (propane). Bottling biogas is an very expensive process.

How does it work?

Organic waste is put into a sealed tank called a digester (or bioreactor) where it is heated and agitated. In the absence of oxygen anaerobic bacteria consume the organic matter to multiply and produce biogas.

What type of waste produces biogas?

Any organic waste has the ability to produce biogas: human excreta, manure, animal slurry, fruit and vegetable waste, slaughter house waste, meat packing waste, dairy factory waste, brewery and distillery waste, etc…

Fiber rich waste like wood, leafs, etc. are difficult to digest and make poor feedstock for digesters.

How much biogas can I get out of my waste?

The amount of biogas you can extract from your waste depends on the waste itself and the design of the digester system.

Some digesters can yield 20 m3 of biogas per ton of waste while others can yield as much as 800 m3 per ton.

It all depends on waste quality, digester design and proper operation of the system.

Where is biogas produced?

Biogas is naturally produced in nature by the anaerobic degradation of organic waste in soil, marshes, ocean, etc.

Biogas is also produced in landfills where organic food waste degrades in anaerobic conditions.

Biogas can be produced in anaerobic digesters. These are equipment (tanks) providing full control of the process and ensuring full biogas recovery.

Since methane is a potent green house gas, isn’t it stupid to produce biogas?

Methane has a green house gas (GHG) heating factor 21 times higher than CO2.

Combustion of biogas converts methane into CO2 and reduces the GHG impact by over 20 times.

By extracting methane out of waste and using it to produce heat and/or electricity we ensure that the waste will not degrade in an open environment therefore reducing direct methane atmospheric emissions. Moreover, the energy provided by the biogas is likely to displace fossil fuel which is the main contributor to GHG emissions.

Biogas energy is considered carbon neutral, since carbon emitted by its combustion comes from carbon fixed by plants (natural carbon cycle).

How much energy is in biogas?

Each cubic meter (m3) of biogas contains the equivalent of 6 kWh of calorific energy.

However when we convert biogas to electricity, in a biogas powered electric generator, we get about 2 kWh of useable electricity, the rest turns into heat which can also be used for heating applications.

2 kWh is enough energy to power a 100 W light bulb for 20 hours or a 2000W hair dryer for 1 hour.

What happens to the waste after digestion?

Despite popular belief, the amount of waste going in the digester is almost equal to the amount coming out. However the quality of the waste is altered for the better (less smell, better fertilizer, organic load reduced, less polluting)

Waste coming out of the digester can be separated (solid/liquid) to compost the solid part and use the liquid part as fertilizing irrigation or to be treated further for rejection in nature.

So why make biogas?

It always costs money to get rid of waste. If it doesn’t cost anything, you are probably creating an environmental hazard.

By putting a digester in your waste treatment chain you introduce a potential revenue center. For example:

On a farm the manure is not considered to be a waste but a fertilizer. By installing a digester the farmer can profit from the biogas by reducing odors and enhancing the fertilizing value of the manure.

In an agro-food industry the digester can be used as a primary waste treatment unit where the biogas is used to offset some energy cost in the plant and reduce the size of the secondary waste treatment.

How much does it cost and how much can I make?

Biogas plants can take various shape and form.

30 m cubic biogas disgester for schools costs anything between 1500-2000 euro depending on the materials and the labour costs.

Biogas systems are significant capital investments that require careful planning to maximize the chances of success.

If you feel exposed to energy price fluctuation and you have an environmental conscience about your waste then a biogas plant could be a sustainable solution for you.

Can I make a biogas plant myself?

Yes, if you have time and money you can surely make one. You will have to educate yourself on the intricacies of a biogas plant.

How long does it take to build a biogas plant?

For schools it takes approximately 3 weeks then another 2 weeks for the for the biogas production to peak after filling with 28 tonnes of cowdung.

How difficult is it to run a biogas plant?

A biogas plant is like an animal. You must feed it every day and feed it the right stuff in the right amount. Just like an animal if you don’t take good care of it, it will become ill and will yield poor yields.

Related Links!

http://www.biogas.co.uk/carbon.htm learn about carbon credits here.

http://www.biogas-info.co.uk/ more on going green.a case study from UK

http://shalinry.org/blog/about/ volunteer in Kenya on green matters