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What’s that smell?

Posted Thursday 19th September 2013, 9:00am
What's that smell?

Here's a little science fact for you. The average human fart has the following basic gas composition: oxygen, nitrogen, carbon dioxide, hydrogen sulfide and methane:

  • Nitrogen: 20-90%
  • Hydrogen: 0-50%
  • Carbon dioxide: 10-30%
  • Oxygen: 0-10%
  • Methane: 0-10%

This is very variable (e.g. due to diet) but as you can see Nitrogen is the primary gas released. But it's the Methane and Hydrogen, the lesser components, which are flammable. If sufficient amounts of these gases are present, it's possible to light a fart on fire - we have all seen the YouTube clips. Keep in mind, not all farts are flammable as only about half us have the bacteria in our bodies that are necessary to produce methane. Sound familiar?

But why the interest in farts? A common question asked of us is if the gas produced by the biogeneration of dog waste will smell. Biogas is a mix of methane, carbon dioxide and other trace gases including hydrogen sulphide. Biogas and farts have a number of gases in common but it's the hydrogen sulphide that causes the smell of both. It is often referred to a pungent 'rotten egg' smell and the science experiment to produce this gas has been replicated across school labs around the world.

So it's the hydrogen sulphide and not the feces to blame, but H2S is corrosive so we need to remove this trace gas before we use it to generate the lights for your parks. This can be done a number of ways and with its removal, biogas production efficiency is increased and maintenance costs are greatly decreased.

Now, wouldn't it be interesting to do a scientific investigation on the diet of dogs for optimal methane and minimal hydrogen sulphide production?

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