Using Yeast to Produce Carbon Dioxide for Plants

Plants require Carbon dioxide for growth along with water and plenty of light. From photosynthesis these three things are used to produce glucose and oxygen which we end up breathing in on a regular basis and consuming when we or animals eat plants. As carbon dioxide is rather important for vigorous plant growth which in my case are aquatic plants that I intend to grow in the aquarium I am in the middle of setting up and which is also reasonably expensive to obtain in pressurised cylinders, I decided to try yeast and sugar to see how well it would work.

This is the same method that is used to produce ethanol for fuel as well as drinking although in the case of spirits, different grains and different strains of yeast are used. I’m using regular bakers yeast as its widely available and cheap.

You will need:

  • 3 1.5 litre plastic soda bottles
  • Some aquarium air tubing
  • Four plastic air valves
  • One plastic tee joiners
  • One plastic air manifold valve
  • Silicone sealant or hot glue
  • Drill for making holes in soda caps
  • CO2 diffuser or air stone
  • Couple of check valves
  • Yeast
  • Sugar
  • Water

Firstly wash out the plastic bottles with hot water to remove any residual soda. Next add 2 cups of sugar and one teaspoon yeast to two of the bottles and full to 3/4 full of warm water. Take the bottle caps and make a hole in each one and push an air valve into the hole so it fits snugly. The third bottle should have two valves with one of these having a short piece of tubing hanging down into the bottle. This is to catch any yeast/sugar should it overflow and prevent it ending up in your aquarium. Next silicone or glue the valves in place to seal any gaps and push a short length of air line onto each valve. Daisy chain the bottles using the “tee connector” as shown. A check valve should be used between the tank and the CO2 generator as well as in line with each bottle to prevent water back flowing into the generator or on to your floor.

After ensuring everything has sealed correctly, screw the caps on to the bottles and connect the outlet tube to your CO2 diffuser or air stone and wait for gas to be produced. If all is well you should see bubbles being produced after a few minutes. You will need to replace the yeast brew after around 14 days as the rising ethanol levels will eventually kill off the yeast. This can be poured down the sink or distilled to make ethanol for drinking or as a fuel or solvent.

If you have fish in your aquarium, it is highly recommended that you closely monitor the levels of oxygen and carbon dioxide in the water along with the pH of the water to ensure you don’t suffocate your fish and plants.


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