Is this even remotely possible anywhere with current technology? Can we even make completely self-sufficient colonies on Earth (like the technologically advanced kind we want to make in space, not just people living in the woods.)
A new planetary economy would certainly have to be very tightly circumscribed in terms of materials and techniques, and even then I think it would be dismayingly huge, though modern techniques like 3D printing would help. It would be a worthwhile exercise just to plan such a thing on paper. Might make an interesting if overly-complicated game with sort of a Dwarf Fortress feel.
(Of course most parts of space are much more hostile than an Earth desert)
A short ton (907.2 kg) of oxygen is 635 cubic meters or 24160 cubic feet as a gas and 794.5 liters as a liquid ( http://www.uigi.com/o2_conv.html ) so they would have needed 5 tons to raise the O2 levels by 2%. For what it's worth, the concrete depleted the O2 levels from 21% to 15%, so about 30 tons would have been need to fully restore the O2 levels.
800,000 mL/ton means that it was not the case that it needed "a few millilitres of liquid oxygen injected every 6 months or so." More like a few thousand liters every 6 months.
(A similar example, some submarines use electrolysis for oxygen)
http://www.defenseindustrydaily.com/treadwell-supplies-oxyge...
Citation urgently needed.