The company that was trying to use bacteria to make fuel from water and the CO2 from the air shut down a few years ago

see my comment above ... yes, algae can take out lots of CO2 from the atmosphere,

in fact i remember reading that 50% of the global photosynthesis actually happens in the oceans.

also, the algae have the advantage that they might automatically sink to the bottom of the ocean, thus taking the carbon out of the atmosphere permanently. but i'm not sure about that, in fact. also, something similar could be achieved with wetlands, such as marsh and swamp, which bind organic material underwater. that water is oxygen-depleted, so it conserves the organic material permanently. this is how peat is created.