I thought of a neat idea for purifying a world without having to do a stuffton of work.
Probably done before but w/e
The clentaminator has a range of roughly 61 blocks so if you were do build a horizontal tunnel `60 blocks down straight across your map that was 5 blocks (I think that's the range you need to keep a biome from spreading) high than spray the clentaminator upwards, you would safely have a purified surface without having to deal with the whole underground.