Issue 65 / September - October 2008
Biogas as a Clean Energy
Recent years have witnessed rapid industrialization and population growth, along with profligate consumption of energy. This in turn has triggered enormous increase in energy production based on non-renewable energy resources such as oil, coal, and natural gas. In order to break the dependence on fossil fuels, much research is underway to find new and efficient ways of energy production from renewable energy sources. Wind power and solar energy are two widely known examples of such alternatives.
According to a recent report by the UN, factors like climate change and high demand for energy are the main reasons for switching to alternative sources, among which biogas is an essential one. The same report also indicates that increasingly higher shares of budgets are spent on biogas, solar and wind energy research.
What is Biogas?
Biogas is a mixture that is produced by microorganisms during the decomposition of vegetable and animal wastes in an oxygen-free environment. It consists of methane (60â70%), carbon dioxide (30â40%) and hydrogen-sulfide (0â2%). For its production, plant seeds that are rich in oil (e.g. sunflower), vegetables rich in carbohydrates (e.g. potato, wheat, corn, beet), fiber-rich plants (e.g. flax), other plant and tree remains (e.g. branches, hay, roots, bark), and animal remains can be utilized as raw material. Municipal and industrial waste can also be utilized on the condition that they are purified from inorganic materials like plastic and glass.
Biogas is an environmentally friendly energy source that is easy to produce almost anywhere. Biogas production capacity is directly proportional to the agricultural level of a country. Its ease of production and relatively higher efficiency compared to other renewable energy sources make it particularly important for countries which are not self-sufficient in energy production.
Biogas production in reactors
Biogas is produced by two main methods. In one case, the amount of biogas that can be extracted from the available organic waste is calculated. Then reactor tanks are designed according to the rate of production. In the other case, the energy requirement of a certain system (in terms of biogas energy) is calculated first, and then the reactors are built accordingly. The main concern in both designs is of course achieving the maximum efficiency and ease with minimum cost.
We can list the parameters in the design of a reactor tank as follows:
- Type and amount of organic material
- Type and amount of raw material
- Meeting the heat requirement of the chemical process
- Mixing various materials in appropriate proportions
Currently, reactors that are fed with raw materials on a daily basis are widely used in rural areas. This type of reactor is known as a continuous reactor. In cases where daily feeding is not possible, semi-continuous reactors are used instead. In this second type, re-feeding of the reactor is not necessary till the end of the first production cycle, but at the end of each cycle, the reactors have to be emptied and cleaned for the next cycle.
Keeping the temperature of the medium at the correct level is crucial. Solar energy can be used to manage this. It can help heat the liquid mixture up to the desired temperature and prevent the heat loss in certain designs by providing the green-house effect.
implementing in daily use
How to implement biogas as an alternative source of energy in real life is surely an important subject. Currently, energy production from biogas is carried out either by direct burning or enriching and converting it into other forms of fuel to be used in industry.
One may wonder how good biogas really is compared to current energy sources. In terms of biogas production capacity, 440 lbs of food waste is equivalent to the daily manure production from 5 cows. From this much food waste or manure, 88 ft of biogas can be obtained. In terms of energy, this is equivalent to 9 lbs of wood, or 3 lbs of charcoal or 0.16 gallons of coal oil, 1.5 lbs of gasoline and finally 56.50 ft of natural gas. What can we really do with this much energy? Here is a small list of things we can do:
- cook 3 meals a day for a normal size family for 3 days
- run a 2-horsepower engine for an hour
- keep a 60â100 Watt lamp on for six hours, which is approximately 1.25kWh electrical energy
- heat two bedrooms daily
Although when the western developed countries are considered, biogas is an excellent way of making use of waste food and other organic remains, it still calls for global thinking. In western countries, cutting food waste and turning it into useable energy is an advantage of biogas. Whether that energy is really needed is another issue to think about. People need to evaluate honestly how much energy they really need; they must consider the lights that are left on for no purpose, the heating and cooling systems that are over-used for extreme comfort, the excess of food they leave on plates and the pots of food dumped in the trashâ¦ Besides, in much of the rest of the world, there is malnutrition and a shortage of food. So, a straightforward question is, âIs it fair to consume edibles to make energy that we do not necessarily need, while there are people suffering from hunger?â
Biogas clearly holds promise to resolve both the energy problem and the environmental crisis of our modern days. However, will it ever be possible to find resources that can satisfy the consumption needs of a humanity that lacks virtues such as contentment and the desire to share?
Bekir MugayitoÃ°lu is an environmental engineer. He lives in West Virginia, USA.