we never seize to learn, here is something for the weekend.
Currently, there is no doubt anymore that biogas systems all over the world are functioning under a variety of climatic conditions. They respond successfully to needs of poor rural populations, urban communities and industrial estates. However, a widespread acceptance and dissemination of biogas technology has not yet materialized in many countries. One main reason, often mentioned, is the required high investment capital. But often the reasons for failure were the unrealistically high expectations of potential users. Biogas technology cannot solve every problem of a farm, a village or a big animal production unit. If disappointment is to be avoided, the limitations of biogas technology should be clearly spelt out.
In the Introduction to Biogas blog I spoke greatly at this concept of methane production from biodegradable waste. Such an easy concept of collecting biodegradable waste and placing it in sealed anaerobic digester has really not taken off as we all anticipated due to a lot of misconceptions that I will highlight in this blog, if you feel I left out any reason as to why you or any other person would not opt for biogas, please feel free to comment below or write me an email and I will surely respond to you. The challenge I personally believe can be in 3 parts viz;
- In some sectors of life, cow and human waste is traditionally unacceptable especially the human one;
- The people are used for decades to use wood-fuel and other biomass sources and trying to convince them otherwise is a mammoth task;
- A lack of passion or general ignorance in acquiring knowledge of this awesome technology;
- Firstly, dung collection proved more problematic than anticipated particularly for farmers who did not keep their livestock penned in one location.
- Secondly, small-scale farmers with small herds were not able to get sufficient feedstock to feed the biodigester unit and ensure a steady generation for lighting and cooking.
- After heavy rains, there is a possibility of flooding in the digester and therefore care must be taken in the design phase to ensure that no unwanted material can enter;
- It can be hard to collect animal dung from grazing animals, especially if they cover a large area. In several cultures dung is seen as low value and a fuel only to be used when no other fuels are available.
With careful planning all these can be avoided as they simply are issues that have solutions and mechanisms to defeat/neutralize their effects.
- Cost of even the smallest biogas unit proved prohibitive for most poor African rural households.
- It is a technology whose main thrust is to add value to waste and may only cater for cooking and possibly lighting. In many instances people will think it will cater for a lot of their power demands.
- There is a requirement for consistent maintenance to clean the pipework, digester components to avoid gas leakage and explosions.
Even if small biogas plants are considered to be a cheap source of energy they are still coupled with an initial investment that can be hard to afford for poor communities and households. Calculations have shown that without any subsidies the payback time for a farmer scale Chinese type fix dome biogas digester would be around 3.6 to 5.8 years. This depends on how the biogas digester is used, what substrates, size, price on firewood etc. (Woods et al 2006)
Though evidence from many African countries is still limited, the general consensus is that the larger combined septic tank/biogas units that are run by institutions such as schools and hospitals are more viable than small-scale biogas digesters. I must say these are some of the basic challenges characterized in this biogas technology, and the benefits far outweigh the challenges and therefore is a reason to still believe in going for a renewable source of energy.
There i’am pictured with my colleague Shumirai Mukamba doing some experimental work on household digesters
After the successful publishing of The Introduction to Biogas, a friend of mine who is into Agricultural Engineering wrote me an email commenting on the article. He emphasized that I had left out the digestion process that takes place anaerobically in the digester, we discussed it over and how I felt it was too technical and all but at the end of the day I compromised and hence I just thought of giving you the basics of the digestion process and I realized that it wasn’t that hard writing about it.
THE BIOLOGICAL PROCESS
The biological conversion of organic material under anaerobic conditions can be described by the following four stages:
The first step involves the extra cellular enzyme-mediated transformation of higher molecular -mass organic polymers and lipids into basic structural building blocks such as fatty acids, monosaccharide, amino acids, and related compounds which are suitable for use as a source of energy and cell tissue.
The fermentative bacteria degrade the soluble organic monomers of sugars and amino acids, producing volatile fatty acids (propionic, butyric and valeric acids), acetate, H2 and CO2. Ammonia is also produced by the degradation of amino acids.
Both long chain fatty acids and volatile fatty acids (VFA) are degraded generating acetate, carbon dioxide and hydrogen.
The fourth and last step involves the bacterial conversion of hydrogen and acetic acid formed by the acid formers to methane gas and carbon dioxide. The bacteria responsible for this conversion are strict anaerobes, called methanogenic. Due to their very slow growth rates, their metabolism is usually considered rate-limiting in the anaerobic treatment of organic waste (Mata-Alvarez, 2003).
The article on the challenges of this technology are still on their way, the manager of the blog is yet reviewing and therefore expect it soon.
For your view and comments about these and any other energy related issues, the author can be contacted on firstname.lastname@example.org