Science Buddies: "Ask an Expert"

I am growing algae in two liter plastic soda bottles. Using valves, tubing, sealant, fertilizer, and a paintball CO2 tank, I created a sealed environment in each bottle with purely CO2, a fertilizer-water-algae solution, and neutral pressure. However, the bottles collapse inward, even if the bottle contains only CO2 and pure water, so the water must be absorbing CO2 and creating a vacuum. How can I overcome this? Can I saturate the water with CO2 until it absorbs no more? Would glass bottles implode if I decided to use them? Are there any other simple solutions?

Hi,

If you keep the pH in the bottles less than about 6 the liquid will tend not to absorb much Carbon dioxide. However the other reason your bottles could be collapsing is because the algae are consuming the Carbon dioxide. Glass containers are fairly strong, so would be unlikely to implode under the slight vacuum you are talking about.. An alternative would be not to seal the containers, but allow them to suck in carbon dioxide as needed. Are you really saturating the liquid in the bottles with carbon dioxide before sealing them? Carbon dioxide ould just be dissolving in the liquid and creating the vacuum if not.

Hope these idas help!

Best regards,

Barrett L. Tomlinson