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Gas from the Past: Biogas 101

Most people who follow renewable energy have heard of biogas by now, yet the origins and uses of biogas remain mysterious to many. Biogas is unusual in that its use predates the use of fossil fuels. In fact, it is older than fossil fuels completely. The microorganisms that create biogas are among the oldest life forms on earth, over three billion years older than the plants and animals that became today's fossil fuels. Biogas not only provides excellent, clean-burning energy that can replace fossil fuels in the future, but in many places it already is.

Often confused with liquid biofuels, biogas has also been called swamp gas or sewer gas. It is a mixture of gases composed largely of methane (CH4) produced during the natural decomposition of organic material in an airtight environment. This methane is the same flammable component found in natural gas derived from fossils, only instead of taking 65 million years to make, biogas can be generated in 48 to 72 hours.

The ancient Assyrians used biogas to heat their baths in 3,000 BC, and considering it is easier to make a fire with biogas than it is with wood, human use of biogas may extend into the Neolithic Age. The famous gas lamps of Victorian England were fueled with biogas from city sewers.

Hydrogen may look simpler on the Period Table, however, it is nowhere near as simple to manufacture. Biogas can be generated in your own back yard using ordinary household waste with no special equipment or chemicals whatsoever. It can be -- and is -- generated in an ordinary kitchen trash bag with table scraps in it.

One popular misconception is that biogas can only be made from cattle manure, in reality all organic matter can be used as a feedstock to make biogas. Ordinary lawn clippings yield one of the highest volumes of biogas per ton. So, yes, one could very easily run a lawn mower with the grass clippings from the previous mowing.

Unlike liquid biofuels, biogas does not compete with food, as it does not require dedicated crops and can use non-edible parts of plants. Biogas yields 2-5 times more fuel per acre than any liquid biofuels and runs cooler, quieter and cleaner in machines.

Today China leads the world in the number of biogas plants with an estimated 50 million households using biogas.  These are mostly small, home and village-scale plants. The torch at the 2008 Beijing Olympics was fueled with biogas. India is estimated to have over four million biogas plants. Many European cities, especially in Sweden, use biogas as vehicle fuel and feed it into natural gas pipelines.

The biogas process, called anaerobic digestion, is particularly aggressive against pathogens and parasites and has historically been used in wastewater treatment as an inexpensive, natural alternative to chemical treatment. The World Health Organization estimates there to be 80 million cases of dysentery (Shigella flexneri) each year, of which 700,000 cases will be fatal. A simple, low or no-cost anaerobic digester will kill dysentery bacteria in 30 hours.

The liquid byproduct that results from the anaerobic digestion process is a high-quality, nitrogen-rich fertilizer and soil amendment for urban farming or local agriculture. Where the nitrogen in ordinary compost is largely volatilized into the atmosphere, anaerobic digestion not only traps and retains that nitrogen, but also converts it to ammonia, which is more readily absorbed by plants.  

Biogas slurry is a liquid and can be applied on a commercial scale with existing farm equipment, which is impractical with compost. The biogas process also takes less time, normally 10-20 days to decompose organic matter, allowing much higher volumes of waste to be processed compared to compost piles.  

When people learn 30-50% of biogas is carbon dioxide (CO2) and see the “C” in CH4, they often think that biogas contributes to global warming. This is not the case. The carbon in biogas is called biogenic carbon. Unlike fossil fuels, which release carbon from a long past geological era into the present atmosphere, biogenic carbon is part of the natural biosphere. The same amount of carbon would be released if the organic matter were left to decompose naturally in the environment. We exhale biogenic carbon every few seconds. 

With the many advantages of biogas, one might ask why biogas remains largely underutilized in the West. It could be said biogas has too many advantages for its own good. The energy, waste management, pathogen elimination and agricultural aspects of an effective biogas program are inseparably interrelated and modern Westerners are not used to thinking so systemically. Effective biogas programs, like those in Sweden and China, require a level of interagency cooperation between utilities, municipalities and local agriculture that does not exist in the United States and other developed countries with large fossil fuel reserves and no incentive for different organizations to cooperate with each other to achieve a more efficient result.   

The barriers to biogas use are not physical; they are man-made. A well-planned biogas program is possible at any latitude in any habitable environment in any cost range, using 100% natural, annually renewable organic waste. The process is self-regulating by the seasonal availability of locally-available wet waste.  Because wet waste is too heavy and expensive to transport great distances distributed plants are more efficient.

As biogas is a flammable gas, it can be used to fuel engines and boilers and the waste heat from these machines can provide heating and hot water, a system that the German agricultural village of Jühnde began implementing in 2009. The odor control and clean-burning properties of the biogas process allow it to be used in the densest urban environments, meaning the largest cities could be broken down into smaller bio-villages.

Biogas democratizes energy with its low cost and simplicity by making it available to everyone, regardless of economic status. Where modern renewable energies tend to focus on electricity or vehicle fuel, biogas also provides clean-burning heating and cooking energy as well as irreplaceable benefits to human health and agriculture. This ancient renewable energy is indeed a modern marvel. 

For details on the biogas program in Sweden, play the video below.


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Manufacturer of 2 cu.m. residential biogas digesters and home CHP generators operating off biogas and syngas from thermal gasification.


Volume 18, Issue 3


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