Picture of Build a fermentation fueled water pump
The  pump will work using the pressure built up by the gas released from any fermentation process.   I expect that yeast and lactic acid fermentation will work well. The "fuel" can be kitchen waste or garden waste. 
I think these pumps will be used to slowly recirculate water and compost tea to plants in pots and to soil blocks and various stuff like that.   Plant spirals could be built with a water reservoir at the bottom and this pump could keep a steady slow stream of water going.  It might also be used in the windowfarm project.  I see that it might have potentials for keeping compost heaps moist too.
I have uploaded a video of the same thing powered by an aquarium air pump.
http://www.youtube.com/watch?v=G6pfE_IxVgQ  I think it is worth a look because you can clearly see the pump and refill cycles in that video.  These cycles take much longer when it is biofueled (especially in winter).
Brrr, cold and yucky in my little shed!

Step 1: The digester

Picture of The digester
This is the container that produces the bubbles.  I used a 2 liter pop bottle and yeast and sugar for the first one.    It worked.  Next I decided to use kitchen waste in a large water container.  It is about 5 gallon in size and it has a fairly big "mouth"  I had to buy an oversize cork for it.
1tri2god2 years ago
maybe I'm off here, but doesn't this produce methane more than CO2?
gaiatechnician (author)  1tri2god2 years ago
First 4 to 14 days it is CO2. Then it would stop because the acid and alcohol that is produced prevents further decomposition. (Like silage or sauerkraut). My thinking after that is just to add it to the compost to continue to breakdown aerobically.