[Digestion] Methane measurement

[Zietsman, Rex]

What a wonderful low tech idea! Well done to Paul if he is the inventor.


Rex


Frank, Hi

I tried Paul Harris's very simple idea recently. Fill a disposable
plastic 
syringe with gas, up to about 80% i.e. a 50 ml syringe should be filled
to 
40 ml. Then draw in a solution of a hydroxide so the plunger comes to
the 
maximum reading (50 ml means drawing in 10 ml of solution). Sodium 
hydroxide is probably the best, but lime water, calcium hydroxide, will
do. 
Close the end of the syringe. There are rubber caps that are available
for 
this. Using a finger tip means that you get corrosive hydroxide on it. 
Shake the syringe, so the carbon dioxide dissolves in the solution and
the 
syringe plunger is pulled in. You can press gently on the plunger to 
overcome friction, but not so hard as to push the solution out. The new 
volume reading is the volume of biogas less that of carbon dioxide 
(probably mainly methane).

The group in India to whom I showed this idea were very pleased. They
now 
have a low tech method of measuring methane content of the gas.

I normally use a methane analyser that I bought second hand when British

Gas were replacing their old ones. It has a thermal conductivity cell. 
Methane will transfer heat more easily than air or carbon dioxide. It
was 
calibrated on methane/air mixes, but it should be OK for methane/carbon 
dioxide mixes, if not completely accurate.

Cheers,

David