Gigaton scale carbon capture using algae

As I understand it, there are some problems with this kind of approach. The first is separating the algae from the water for its disposal (if you just let it free, it dies and releases the CO2 when it decomposes.) This is apparently a very hard problem that has stymied attempts to use algae to make synfuels. The second is that it is limited by mass transfer of CO2 to the water. If it's only using the carbon that was already dissolved in the water, enormous amounts of water will have to be pumped. The concentration of bicarbonate ion (which is 90% of dissolved carbon) in seawater is about 2 millimoles per kg.

I'd suggest looking for algae that grow in very alkaline water, in soda lakes. There are some in Africa, for example. Very alkaline water can contain much larger amounts of carbon, and one might be able to directly extract CO2 from air by spraying that alkaline solution upward to make fine droplets for large surface area air contact.

I find this an excellent doable and logical approach. There are huge areas of suitable desert land, in addition, the algae also generates cellular fatty acids - which can be gene tailored and have the prospect of eliminating many of the old oil industries, like palm oil. As far as I can see, the same genes used in palm trees can serve (there will be work to do - of course, to expand the repertoire to many other fats as well as many petroleum based oils. Each pond can yield a different oil, as well as many other chemicals and drugs. In truth, this is done in vats now with yeast. bacteria etc.