Biogas generation at Michaelhouse School
In the past few years the world has come to realise the importance of preserving our valuable energy reserves, and especially here in South Africa we have started to see the beginnings of major environmental problems. Many conventional methods of creating energy for human use rely on these swiftly depleting resources, such as coal and oil. They also pose a huge threat to our environment, in the fact that when they are burnt they release noxious gases and these are slowly degrading the state of our atmosphere. As a result of this we, a duo of pupils at Michaelhouse, in the Kwa-Zulu Natal Midlands, decided to try to develop a clean, efficient means of creating energy.
Considering the recent development of the Michaelhouse’s Oribi reserve, and the fact that cow manure is readily available, we posed the question: “Why not utilise what we have readily available on our doorstep to create energy?” So, with the help of our school environmentalist, Paul Fleischack, we decided to undertake the arduous task of producing methane by means of a biogas digester.
Biogas is a term used to describe the anaerobic respiration of organic matter in order to produce a gas, which is usually methane, which can be used as an energy source. Now seeing as methane is one of the greatest contributors to the greenhouse effect, and cows produce 15% of the world’s methane, we thought it appropriate to try and utilise the one of the by-products of these animals to produce methane- cow dung!
The “science” behind methane production from cow manure is relatively simple. The bacteria contained within the cow’s stomach anaerobically digest the cellulose contained in its diet of organic matter to produce energy. As a by-product of this process methane, amongst other gases, is produced, and this is what a digester fundamentally simulates. To make a simple digester, cow dung is collected and placed in a sealed drum with an outlet pipe that is connected to a collection vessel. It is then left and in time the digestive processes will occur. This results in methane production.
Using simple, everyday pieces of equipment we obtained through generous sponsorship from WESSA, we constructed our own digester. At first all did not go well. The wide-mouthed plastic drum purchased (with ease of filling in mind) proved to be about as air tight as a barn and no gas was collected in the inner tube attached to the drum. Another plan had to be made. The plastic drum was substituted with a metal oil drum. The delicate task of transferring the aromatic slurry of cow dung, chicken litter and water to the new drum, with an opening of only 70mm in diameter was undertaken with great care, but despite this a number of assistants needed a good shower when the task was complete.
Pic: Digester with collection tube. Unsuccessful plastic digester on left.
The necessary plumbing fittings were sourced, sealed with plumbing tape and within four days we had filled our first inner-tube with gas. Our excitement was soon dampened when this gas failed to ignite. We think it was the air in the top half of the drum which had been displaced into the tube. Not daunted we attached the second empty inner-tube which was inflated two days later. This time the Bunsen burner produced a pure blue flame – methane!
The autumn temperature in Balgowan can drop to freezing at night. This along with the small volume of our digester (200L), which will not maintain the required temperature of 38˚C for long, we have had to rely on an electrical heating system for our pilot plant. This has been provided by three confiscated electric blankets. These have been wrapped around the digester, which was then covered with insulation (old swimming pool blanket) to reduce heat loss. In a larger, sustainable system, the digester would be heated by burning some of the methane produced.
We have managed to boil 250ml water using half a tube of gas, a result which we hope to improve by scrubbing the gas emitted from the digester. Scrubbing is the removal of inflammable gases, such as carbon dioxide and hydrogen sulphide, from the gas emitted from the digester. To do this we will bubble the gas through an airtight container with water and iron filings.
This methane can be used to perform many different functions. Firstly, it is safe to burn through an everyday gas stove without any modifications. Secondly it can be used as a fuel for a petrol engine with minimal modifications. By simply replacing the fuel tank with a pressurized tank and adjusting the intake manifold and the carburettor a petrol engine is transformed into an environmentally friendly machine! This can then be used to run a generator.
Pic: Michael sitting on tube to expel gas while David measures temperature of water over flame
So far our project has been successful and a great learning experience! Further development is crucial and we look forward to the prospect of finalising an efficient method of producing energy that could hopefully be used to power parts of the school in the future. We hope to show that our simple pilot plant can be modified to a larger system which would allow the school to harvest energy from our own sewage.
By David Brill & Michael Venter (Grade 10 learners at Michaelhouse School, Midlands, KZN)
