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Does kitchen waste produce as much biogas as fresh cow dung?


I am hoping to have a very successful home biogas production system (which I wrote about here)  in about 2 weeks. But what should I feed into my system to make it really successful?

According to Dr. Anand Karve  on the ARTI website 2 kg of carbohydrate rich vegetable feedstock produces about 500 g of methane, and the reaction is completed with 24 hours. While the conventional biogas systems, using cattle dung, uses about 40 kg feedstock to produce the same quantity of methane, and requires about 40 days to complete the reaction. He won an award for this finding.

So should I switch from cow dung to kitchen wastes?  I’m not convinced – maybe Dr. Karve’s Indian cows are less flatulent and produce little biogas – I know that our Kenyan cows are super producers of gas.  But then how can I be sure?

A shitty experiment

To find out whether kitchen waste is better than cow dung, I am conducting an experiment that involved cow dung, plastic cups, condoms, water and kitchen wastes.

I added equal amounts of dung and water and mixed it and poured into a plastic cup, then covered it with a condom to enable me to see the gas forming.

The same amount of kitchen waste was similarly mixed with equal amounts of water and mixed poured into a cup and covered with a condom.

A third experiment involved a mix of dung and mashed kitchen waste, mixed with equal amounts of water, poured into a plastic cup  and covered with a condom. I conducted this experiment in my kitchen using clean disposable utensils and unused condoms (had to say that just in case you people think I’m really weird).

Results

I’ll be posting the results in pictures here

Day 0 (May 25 9 pm)

The condoms are all empty and flaccid. Sad. There was a slight emergency when one of the condoms broke as I was putting it on the cup…  I had to get more condoms purchased at 9 pm. Pharmacist was amused.

Day 2 (May 27th 9 am)

Hmmm, some biogas already being produced and poop looks like it’s slightly more than poop and veg which is more than veg alone. So far I’m putting my money on cow poop.

Day 3 May 28 10.20 pm

Watch this space for coming days and potential explosion of cow poop in my kitchen.

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May 29, 2010 - Posted by | Uncategorized | , , , , , , ,

9 Comments »

  1. […] We are on our way to northern Kenya and had to leave on Tuesday for the 2 day drive – before I left I went to check on my experiment which had gone disgusting, so I chucked it out.  Long story short – cow dung produces the most biogas, kitchen waste simply got fungus and consumed all the gas and sucked the condom into the cup – wondering what the hell I’m on about? Check out the experiment here. […]

    Pingback by Flexi-bag Biogas digester is full – Anafura kama mandazi! « Wild About Africa | June 2, 2010 | Reply

  2. […] I hope you’ll agree that’s pretty serious expansion if you compare photos of the system just a few days ago. And if it’s your first time to participate in my biogas experiment, then you must check out my condom experiment here. […]

    Pingback by Biogas bursting with Energy « Wild About Africa | June 8, 2010 | Reply

  3. Marcel Lenormand called my attention to what you are doing. It is great to see a small-scale experimental design for biogas which can be easily replicated. With my experience building digestors in Kenya as well as Egypt, Tanzania and the U.S. I thought I might share some thoughts. First, you will not get any appreciable methane from the food waste container and you are right, it will rot and consume the air (this is the sucking the condom into the cup you observed). This is because food waste contains virtually no methanogens if any at all. We did the same experiment in Cairo with a 200 liter drum filled with food waste to prove it to ourselves, just in case. One needs a source of methanogenic bacteria, and normally that is from cow or horse or pig dung (others have used goats and cows and I’ve even started a digestors using my baby’s soiled diaper). However once you have enough bacteria producing gas the kitchen waste is a superior food. In all the cases we’ve observed the dung definitely starts producing gas first because the mix of dung and food can turn too acidic, inhibiting methanogen growth. This is why Dr. Karve always recommends you start your digestor with animal dung first and WAIT until you get your first FLAMMABLE methane before adding food waste. But from then on you need only add food waste. You just have to make sure you do not add too much. Karve says (and we’ve confirmed) to start feeding slowly, about 200 grams at first and gradually building up to no more than 2 kilos a day for a 1000 liter system.
    It may be that what you are observing in your condoms is not methane at all, but CO2, for this is the first gas to be produced. Over a period of several weeks the CO2 concentration drops to about 40% and the methane concentration increases to about 60% and that is when it starts burning. So don’t let the gas production you see at first be the indicator of how well your system is doing. What you are trying to do is grow a stable and large colony of methanogenic bacteria. Once you have done that, you can start feeding the food waste and you will not have to feed animal wastes again (though you are always welcome to — it is a good thing to add fresh bacteria through new dung introductions but if it gets to be a hassle you don’t have to put more in.) Among the Masai at the Boma we recommend putting any waste cabbage leaves and potato skins and ugale that fell on the floor and mix in any cow dung that is convenient. The addition of the food wastes improves output. Hope that helps!

    Comment by T.H. Culhane | June 13, 2010 | Reply

  4. […] If you recall my earlier condom experiment showed that cowdung was so much better than any kitchen wastes for biogas producti…. […]

    Pingback by Condom experiment #2 « Wild About Africa | July 6, 2010 | Reply

  5. That interesting I have had this thought/idea of making bio gas but it always fizzles away when I think of the space and cow dung shit that’s needed but then again you did put the spark in me again .I need to get funds and put this together esp. at my rural area where its needed most can someone help me out with step by step construction steps on how to do a bio gas plant.

    Regards
    Edwin

    Comment by Edwin Kidambu | July 14, 2010 | Reply

    • Edwin we can help you get a biogas system in place – it costs 28-30k – that’s it! Let me know if you need more information.

      Comment by paulakahumbu | July 15, 2010 | Reply

      • Hi
        can you tell me where I can buy this type of balloon digester in Nairobi?
        Is the bag UV resistant? How long will it last?
        Ingo

        Comment by Ingo | February 14, 2011

      • Pls contact Dominic Wanjihia 0722700530

        Comment by paulakahumbu | March 1, 2011


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