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Condom experiment #2

Last week my sister served us delicious slow roasted Jerusalem Artichokes which a few hours later put our biogas digester to shame.

Come to think of it beans have the same effect… that got me thinking – are there some veges that are better than others to use in the biogas digester?

If you recall my earlier condom experiment showed that cowdung was so much better than any kitchen wastes for biogas production.

So I borrowed 3 condoms (Trust) and used up my remaining stash of Durex)  and started grating Jerusalem artichokes, sweet potatoes, and mashing beans.

I repeated each with the same amounts of beans, Jerusalem artichokes and sweet potato mixed with some fresh cow dung. Finally I did one last condom as a control with just dung. I tied each with a dougle knot – don’t want any leakage.

I put the whole lot in a dark box and let it sit in the sun to warm up for 2 days. At night I put it in a cool box with a hot water bottle so it doesn’t get cold.

Here are the results after 48 hours

Sweet Potato, Sweet Potato+dung, Mashed beans, beans+dung, Jerusalem Artichoke, J. Artichoke+dung, Just dung

This may not be super science but it’s very very convincing. Dung and Beans Rock!

Some gas is being produced in all the condoms, but it’s astonishing how much more productive mashed beans with dung is. And that’s exactly what my stomach feels like after a meal of beans – pity they are so delicious. The Jerusalem artichokes are disappointing. So is the dung on it’s own which is very surprising.

But is this methane being produced or what? Next we need to test whether this really is methane – condom experiment #3 coming up…watch this space.

And if you want to see the latest on my amazing biogas system at home check out my latest post about a poop mobile on Afrigadget.


July 6, 2010 - Posted by | biogas | , , ,


  1. ROFL!!!

    At first I though you were posting about home made sausages!


    The Million $ Q. Is it flammable?

    Comment by Marcel | July 7, 2010 | Reply

    • Good question – experiment to test that is coming up – sausages!! what next?

      Comment by paulakahumbu | July 8, 2010 | Reply

  2. Woooiii!!My biogas is up and running at last.Thank you Dominic Wanjihia !!No problems….no smell from digester area either….cant believe it!!Wot a bargain!All I need now is someone to ask if I’ll graze their cow.
    Paula…. Try Toi market for cheap 2ndhand duvets for keeping your digester warm at night?With a plastic sheet over? (Or make your own stuffed with hay?)
    Love your experiments:) Perfectly disgusting sausages made with extreme dedication and absolutely unmarketable.
    I’m using fresh cow poo neat….so far….so good.

    Comment by roz | July 9, 2010 | Reply

  3. hi,
    Its a good idea. But the lubricant present in condom can easily affect the degradation of the organic compounds: most likely will give rise in the gas production. use of small plastic bags instead of condoms can give more accurate results. U can also measure the volume generated simply by placing it inside a leveled container containing water before and afer the experiment. and if you want to know the tentative methane and CO2 content, u can just treat a known volume of the produced gas with KOH or NaOH solution. U can simply use syringe for it.

    Comment by prakash | December 4, 2010 | Reply

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