[Digestion] young scientist project

[Duncan Martin]

Stephen

Many methods have been tried but I know of nothing SIMPLE and CHEAP that 
works really well.

A lot depends on what you want to store biogas for. Usually, at this scale, 
it's to measure it.

First, check that your digester and collection system are 100% gas-tight, by 
a static pressure test.

I'd avoid the standard lab method of collection in a vessel inverted over 
water (or whatever*). It's likely to lose its seal due to evaporation over 
months of observation, unless you are unusually vigilant about topping it 
up - and never take any holidays. Also the water will become foul unless 
changed from time to time.

(*Acidified brine is better - but more awkward to work with. Bear in mind 
that even sparingly soluble gases can dissolve and gradually escape when 
stored over water for many weeks.)

Bear in mind too that a digester can suck gas back at times**, so you need 
to make sure that it has "access" to gas to suck back - or it will pull in 
water (or air).

(**Various reasons but you can have long periods especially at first, with 
essentially zero biogas production - I assume you plan a batch process. 
There might be a few days of rapid CO2 production but then nothing for many 
weeks - which isn't great for a Young Scientist project! One 10L digester of 
mine only began to produce biogas after a TWO YEAR lag - but then 
accelerated to almost 10L/day. During such a long lag period, suck-back can 
be caused by all sorts of things, including small changes in temp or atm 
pressure.)

One method I found worked quite well was to use the kind of foil balloons 
sold in party shops etc. You can often get old stock quite cheaply (eg 
Valentine's Day ones in March!). Liberally grease the outside of a small 
piece of rigid plastic or metal tubing and push it up the nozzle and into 
the balloon. This opens the flap valve in the neck and holds it open, so 
that gas can flow in - and (when you want it) out again, by disconnecting 
the tube from the digester briefly.

This collects gas at zero back-pressure - until the balloon is almost full - 
and you should empty it as soon as it gets to that stage. You could meter 
the gas as it flows out if you want accuracy - but "balloonfuls" might be a 
good enough measure.

NB As I hinted above, time-scale might be a problem for a Young Scientist 
project, unless you plan to become an Old Scientist in the process!! What do 
you plan to digest and what to seed it with?

Good luck!

Best regards

Duncan

================================
CONTACT DETAILS
Duncan J Martin, PhD, CEng, CSci, MIEI, MCIWM, MIChemE
24 Townsfield, Cloughjordan, N Tipperary, Ireland
Home: +353 505 42087
Mobile: +353 86 8377 906
Email: duncanjmartin at eircom.net
================================
----- Original Message ----- 
From: "stephen cullinan" <stephencullinan at gmail.com>
To: <digestion at listserv.repp.org>
Sent: Friday, August 03, 2007 1:28 PM
Subject: [Digestion] young scientist project


>I have developed a mini anaerobic digester. It consists of a plastic can
> about 30cm by 30cm by 90cm.I have cut a hole in the lid of the can. In 
> this
> lid I placed a mini agitator which contained a pipe leading from the top 
> of
> the inside of the plastic can to the outside transporting any gas
> produced.Iplaced three of these in a plastic
> box.I placed a small immersion heater into the box and filled the box with
> water. However this is where I am stuck. I need some help in thinking up 
> of
> a way of trapping the gas
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> Beginner's Guide to Biogas
> http://www.adelaide.edu.au/biogas/
> http://info.bioenergylists.org
>
>
>
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