Here is one of the options I mentioned earlier, this system claims to reduce the waste of a standard 75gpd system by half.
http://www.bulkreefsupply.com/brs-15...grade-kit.html
Some people claim to re charge activated carbon by baking it. But from what I've read that doesn't work. Apparently the true process requires pressure, steam and heat.
GFO can however be recharged with some harsh chemicals.