Boiling carbon?

[mr.wilson]

Carbon is activated at a temperature of 900 C in the presence of an oxidizing gas. It can also be activated with strong acid, often leaving phosphates behind.

Anything you do in your microwave or BBQ with used carbon will only release the absorbed carbon back into your tank at a greater rate then it was originally absorbed.

There was one study done in Russia in the 50's that claimed microwaves change the molecular structure of food, but it has been discredited.