Wow, holey thread resurrection Batman!
As for the idea, no I never gave it a go... I only had a small tank at the time and never really thought it worth doing.
However as luck wouht have it I got involved with a yeast + algae research project at uni earlier this year, this involved amongst other things bubbling air through a yeast culture then into a separate algae culture (same principle really).
We didn't attempt to quantify the CO2
conc in the outlet stream from the yeast culture, but what we did find was a marked increase in the growth rate of the algae attached to the aerobic fermenter. This surprised us as the resulting yeast effluent stream would still only be a low conc. of CO2
, but apparently it's enough to give a boos to the algae.
We used a yeast media with 10g/L glucose as the carbon source, 5g/L Bacto Peptone, and 3g/L of yeast extract and malt extract, and had each experiment running for about 2 weeks.
What I guess is that if you were to set up a similar system at home you could operate it as a fed batch. Just keep topping up the sugar every few weeks as it's used up.
As it happens I've now got a much larger planted tank set up with a classic DIY yeast fermenter up and running. I used a 5L water bottle as the fermenter, about 300-500g of sugar (didn't bother measuring), 1 heaped teaspoon of marmite, tip of a teaspoon of bicarbonate of soda, and 1 crushed aspirin. It's been running for about 2 weeks now, with daily top ups of sugar (about 1 tsb).
Another way of getting some indication of the CO2
conc. in a mixed air stream would be to use the pH. Since you'd only expect the CO2
to be fairly low conc coming out of the aerobic fermenter you could bubble the air through a water solution (ideally some known buffer standard, 4dKH for example) with a few drops of bromethyle blue (the pH indicator solution in the API master test kit). The more CO2
in the air stream the more yellow the water will go, the less CO2
the more blue. Without any sort of calibration data though you couldn't use this method quantitatively, just an easy visual indicator of production rate.
You've got me thinking about it again now! I may have to dip back into this idea.