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A Guide to Biogas

written by: Charles M Bowen•edited by: Lamar Stonecypher•updated: 9/24/2014

Biogas is a fuel generated from common and renewable biological sources, including from garbage and biological wastes. It is highly advantageous as biogas can power equipment designed to run on non-renewable natural gas.

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    Why Produce Biogas?

    Shifting away from petroleum-based energy sources has one crucial and often overlooked issue: an abrupt shift from petroleum fuels to another medium of propulsion will make every existing power plant, generator, car, truck, ship, and airplane obsolete. The cost of replacing all of this hardware with models designed to run based on another technology is too great for even the wealthiest nations to bear. Another benefit of exploiting biogas is that it keeps human-produced methane, a far more powerful greenhouse gas than CO2, from entering the atmosphere.

    When methane is burned, the emissions are relatively harmless compared to the effects of free-floating methane in the atmosphere. Methane is the primary component of natural gas, which is widely used to heat homes, generate electricity, and even run vehicles. Biogas is therefore a renewable energy source which can be used by all the technology that currently runs off on non-renewable geological natural gas. Biogas solutions allow common agricultural waste products to be processed into fuel that can run a power plant, a cooking stove, and even a modified gasoline or diesel engine. When one considers that some power plants and generators have the potential to be used for over a century, a biogas supply ensures that this equipment will continue to operate even if the original fuels are no longer economically viable.

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    The Science and Infrastructure Behind it

    Biogas plant sketch 

    While biogas emissions are plentiful, harvesting it poses a bit of a challenge. For example, the methane produced by cows could power whole countries, yet it escapes into the atmosphere as there is no viable way to harvest it from cows out in the fields. Since it isn't possible to take the biogas plant to the cows, we need to take what the cows produce that generates the methane, their dung, to the bio-gas generator. Since the cost of transporting the feedstock over distances can add up, most existing biogas plants are built in remote agricultural areas near large herds of cattle.

    This is a good thing so far as it keeps the unavoidable noxious odor of the process away from the population, but it does pose the challenge of getting the biogas to consumers. At the biogas plant, the dung is concentrated, and mixed with water and other materials that decompose in a similar way, creating a slurry. The slurry is then left to ferment in a digestion chamber. The gas can then be easily collected through a pipe at the top of the domed digestion chamber.

    Biogas plants require very little energy to produce the unrefined biogas. It is therefore a very cheap fuel to produce. Technology is only part of the equation of getting biogas production up and running; the greatest idea in the world will never get off the ground without a little seed money. Fortunately for alternative energy producers, many countries have generous subsidies in place for entrepreneurs interested in cashing in on alternative energy.

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    Fuel from Your Rubbish Bin?

    Next time you drive past your local Mount Trashmore, think about how much potential energy is going to waste. Even though cow dung is currently the most exploited source, biogas can be extracted from any form of organic garbage. Food and vegetable waste like banana peels, even dry forest leaves, will all emit biogas while they decompose, as long as the right conditions are created. Even biological pests like the water hyacinth can be harvested and converted into a fuel source thanks to biogas extraction technology. Rather than burying these resources and leaving them to the worms, it is far more worthwhile to harvest this gas.

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    Refining and Applications

    Raw biogas contains too much CO2 to burn efficiently. Thus there are many methods for refining the biogas to suit different purposes. There is a challenge to the economic feasibility of biogas in this area. The cost of refining can offset the low-cost of producing the raw gas, making non-renewable alternatives a cheaper and more economically feasible option for gas-powered technology.

    Yet refined biogas can be used for anything in which natural gas is currently used. There is even a method for converting automobile engines to run off of cleaner, more efficient gas. Biogas in a less purely refined state could easily replace propane as the preferred outdoor cooking fuel source. A new method of producing pure biogas uncontaminated by CO2 and sulfides from wind and solar sources in being developed which may even allow biogas to start finding its way into applications currently running on only the purest natural gas.

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    Drawbacks and Criticisms

    Despite the promise already shown, biogas carries its share of problems and liabilities. In order to be pure enough to be used by current motors, or handled by the existing transportation networks, it must go through a complex refining process. The level of refining necessary to make biogas pure enough to operate a car, for example, means that oil prices will need to go much higher before biogas can be considered an economically viable fuel source for vehicles. In addition, while biogas has all the benefits of natural gas, it possesses the same drawbacks too. Then there is the problem of the smell. Dealing with this by locating the processing plants far away from populated areas will add to the operation costs of biogas as it would have to be transported over long distances. Its most promising application, replacing propane and butane as the cooking gas of choice, is hampered by the need to refine the biogas before it can be transported and used, or put into existing pipeline networks. In addition to technical limitations, the conversion of farmland production from food crops to producing biomass for energy can increase the cost of food, hurting the world's poor.