Above: Drying cow dung for fuel (Peretz Partensky)

Did you know? Cows don’t have four stomachs; they have one stomach with four compartments.

The ongoing search for new sources of energy may lead to something most of us don’t want to look at, much less touch: cow dung. But nature has found wonderful uses for this foul-smelling resource. For example, dung beetles and flies use poop not only as food source, but also as a home for their offspring. Thankfully, you can still benefit from cow dung while keeping it off your dinner plate and out of your home. It might sound like a load of bull, but cow manure has heaps of potential as an energy source.

Unlike humans, ruminants such as cattle have evolved unique digestive systems to deal with complex, fibrous plant material such as cellulose. Cattle famously have four different stomach compartments. Our bovine friends also depend on special rumen microorganisms in their stomachs to do most of the work involved in breaking down and fermenting tough plant materials, which are converted into more usable energy sources.

Did you know? Cow dung has been studied as a potential shield against radioactivity.

However, not all of the energy sources converted in this way get used by the animal. Certain products of digestion, such as volatile fatty acids (acetic acid, proprionic acid, and butyric acid) provide about 70% of a cow’s energy needs. But others aren’t metabolized because cows don’t have the enzymes and proteins required to process them. Instead, these other products of digestion get deposited into feces or released into the atmosphere.

As a result, there is still a good deal of usable energy left in cow excrement. For example, cow dung contains methane (CH4). Although cows don’t have use for it, methane is a major component of natural gas and an easily combustible energy source.

The simplest way to extract energy from the methane in animal dung is to burn it. Since fresh excrement is too moist to be combustible, most of the water needs to be removed by drying the dung before it can be burned. In many parts of the world such as India, Egypt, and Mongolia, this method has been used for thousands of years to provide fuel for heating and cooking.

Did you know? A single cow can produce up to 500 litres of methane every day.

Granted, burning cow poop to cook Thanksgiving dinner probably won’t catch on anytime soon. One alternative to burning cow patties is to extract biogas from them instead. Cow dung, already rich in methane-producing bacteria, can be mixed with other organic waste products and injected into bioreactors, which are large tanks that contain active microorganisms. In this way, any undigested material in the cow dung is completely fermented, producing (thankfully) odourless methane gas that can be used as a fuel.

Methane is a great fuel, but it is also the second most prevalent greenhouse gas and a major contributor to global warming. So it’s a much better idea to burn methane than to release it directly. Combustion converts methane into water and carbon dioxide. By weight, carbon dioxide has 20 times less impact on climate change than methane.

So the next time you happen upon manure, don’t turn away in disgust. Cow poop might just be the environmentally friendly, renewable energy source you’ve been looking for.

References

General information

Animal Facts: Ruminant (Animal Planet) Cow dung a good nuclear shield? (Times of India) Nutrient Absorption and Utilization in Ruminants (R. Bowen, Colorado State University) Overview of Greenhouse Gases (US Environmental Protections Agency)

Scholarly publications

Bergman E. 1990. Energy contributions of volatile fatty acids from the gastrointestinal tract in various species. Physiological Reviews. 70(2):567-590. Johnson KA, Johnson DE. 1995. Methane emission from cattle. Journal of Animal Science. 73:2483-92. Sweeten JM et al. 1986. Combustion of cattle feedlot manure for energy-production. Energy in Agriculture. 5(1):55-72. Tauseef S et al. 2013. Methane capture from livestock manure. Journal of Environmental Management. 117:187-207.

Sam Au

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