Biogas analysis in my kitchen
I know I’m onto a great thing by running my stoves on biogas, it’s cheap, easy and good for the environment.
Here are some facts about biogas from cow dung:
Cow dung gas is 55-65% methane, 30-35% carbon dioxide, with some hydrogen, nitrogen and other traces.
One cow produces approximately 36 – 68 kg of dung per day!
About one cubic meter of biogas can be generated from 16 kg of cow manure at around 28°C. This is enough gas to cook for a few hours.
One cow produces approximately 32 kg of dung per day – enough to feed a biogas system for an entire family!
We put two massive buckets of dung into our digester and have produced about 4 cubic meters of gas over a period of 3 days. Why is it acting so slow?
There are two things I need to do to improve my biogas system.
1. Find out what inputs are optimal for biogas production – does kitchen waste help?
2. Find out whether temperature or acidity is affecting the production of methane.
I set out to ask if my biogas is really operating at optimal temperatures, and how much methane is actually in the biogas?
My condom experiment yielded gas only from the mashed beans and dung so I tested that to find out if it was producing methane and not some other noxious gas .
After scouring Nairobi’s school lab suppliers I got a thermometer (-10 deg – + 60 deg Centigrade) for a whopping 750/- (almost 10$), a measuring cylinder for Ksh 250/- or 4$ (made in China – Pyrex one was 10 x the price!). I also bought some litmus ph paper (which cost me Ksh1,150 for a reel (US 20$). I also bought a 50 ml syringe at the school shop for a whopping Ksh 150/- (2) I feel so cheated).
I’m so annoyed because you can use red cabbages to test acidity for free! (if you have red cabbages)
Determination of methane concentration
I found a website (but can’t remember where ) that provided a protocol for testing the concentration of biogas (methane) produced. Sodium hydroxide (caustic soda) reacts with carbon dioxide to produce carbonates.
1. Dissolve some caustic soda crystals in 100ml water (watch out the stuff burns – add caustic soda grains to water not the other way round and don’t make it too concentrated – it really burns (experience)
2. Fill syringe with water then squirt most out to remove all gas
3. Put syringe end into the jet of biogas and draw in about 10 – 20 cc gas. Record the amount of gas.
4. Place into the caustic soda solution and draw up another 20 cc. Shake but keep the end of the syringe in the caustic soda solution. Or use a gloved finger to seal the end. Caustic soda burns like a bitch.
5. Now calculate the volume of the gas remaining. The NaOH absorbs all the carbon dioxide so you are left with only methane (in theory).
For our biogas we had 26/30 cc of gas was methane = that is a concentration of 86.7% methane. Not bad eh?
I then took the beans/dung condom, broke it under water, trapped the gas and repeated the experiment. 14/16 cc remained – that’s 87.5% methane. No real difference.
Out door temperature
The bacteria responsible for creating methane don’t like low temperatures. They operate optimally at 20 degrees and higher to 40 degrees. Lower than 10 degrees C and will virtually stop functioning.
Well, its’ the cold season here in Nairobi and our bag is above ground so it’s taking on the air temperature, especially at night. I took 4 temperatures including waking up at at 3 am and 5 am to measure the temperature – that’s dedicated!
10 am – 20.5
4 pm – 25
3 am – 15
5 am – 11.5
The generally low temperatures and daily range of 10 degrees centigrade may be pissing our bacteria off…but its the daily fluctuations that are the real problem. The bacteria’s really don’t like temperature shifts of more than 1 degree – no wonder the biogas production has slowed down.
Now I have to find a way of raising the temperature of the biogas plant and keeping it stable. My sister suggested I cover it with hay and sprinkle with water and effective microorganisms so that they start composting and producing heat…another stinky thought to consider. Or, I could simply dig a hole and partially bury the thing……
The problem of acidity
According to people who know, methane producing bacteria prefer neutral or slightly alkaline conditions. Like us humans, they don’t tolerate acidity! To find out hat’s happening to the acidity in the biogas digester I used the super expensive Ph paper that I bought in Nairobi at a swindlers shop on Kijabe Street (if you want home lab supplies don’t go to lab supplies, go to Kijabe street there are tons of stores but avoid the industrial suppliers and head to the school suppliers near Longonot Place – they have very cheap Chinese alternatives).
Well the tests came out in favour of methanogenic bacteria – the contents of the digester are living at a healthy pH of 9 which is rather alkaline.
Or maybe I just need more dung …
To find out more about my biogas installation check out my latest condom experiment on substrates with and the super cheap and very effective flexibag system designed by Dominic Wanjihia – and the motorbike trailer he designed to get dung to my house
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