Typically, Cyanobacteria utilize sunlight, water, and CO2, and then "exhale" oxygen, under aerobic conditions. The source of the CO2 is of interest here. According to Joule Unlimited, the source is "waste CO2", whatever that means. References to their super secret plans are linked to from Wikipedia (#19) from when it was first patented (sorry, can't seem to paste link here).
Be careful when a loop exits to the same place from side and bottom.