Onlooker, I agree with P, with the exception of Biochar, that all of these schemes require vast amounts of energy making them impractical, uneconomical, and probably environmentally degrading.
Even Biochar is not economical on a large scale mass produced bases. Transportation of the feedstock's to the production facilities, processing, and then shipping back out to be buried would require a lot of ever dwindling energy. Good biochar has to be produced at certain temps and quickly cooled. This all adds to the price of biochar, making it a rather expensive soil amendment. Still, all hope is not gone.
Biochar is easier to implement at the local level, using local feedstock's, local construction materials, and local use of the biochar. By applying some permaculture principles the process can be profitable and regenerative. Lots of experimentation is going on with biochar on the small scale (village on down to the individual).
The smallest application is the use of cook stoves in poor countries that make biochar while producing heat for cooking. once the meal is cooked the biochar is cooled and put out in the garden. The stoves use less wood than the traditional cook fires while at the same time producing a soil amendment, (among other uses), that will also reduce the amount of water and nutrients needed for the soil to produce food. Local businesses have already been set up in several countries to produce and sell these stoves.
On a little larger scale, you can build a "TLUD" Biochar maker fairly inexpensively to make your own biochar pretty easily. You can check this out on You Tube.
Scale up a little and you can use the heat produced to dry your feedstock or heat your greenhouse. Throw your biochar into your active air compost tea mixture and you have a super inoculant that restores life to your soil requiring less and less inputs as the years go by.
Bottom line, I don't think you can do biochar in a centralized massive way, but you can do it with a massive number of little projects. Plus it would be good for the earth, good for people, and good for the future. Basically following the three Permaculture ethics.