The treepods contain an alkaline resin (a base.) When air is filtered through this resin, the CO₂ (an acid) reacts with the the resin, storing it. This resin can hold the CO₂ until it reacts with water, releasing the CO₂. Thus, the envisioned usage would be to take CO₂ from the air using the resin, then release it into some type of storage tank. As of now, humans are unable to convert CO₂ to usable energy, but there are many scientist trying to figure out how to do just that. However, as of right now, I don't think there is a good answer for what to do with the CO₂.