That's food grade, I have no idea about industrial grade.
I've never thought about it before but if I had I would would have just thought they extract it from air but that is only 400 ppm so maybe not so easy. There are CO2 wells, like oil wells I guess, but not many of them. There is/was one in SA, maybe it has shut down.
I'm a little pissed because there is no home brand lemon, lime & bitters on the shelves. Beer drinkers may want to put in a store because they pasteurise beer, killing the yeast, and then carbonate it like soft drink.
