Hayley Todesco, 17, Canada
When bitumen is mined from tar sands to be refined into oil, tailings containing toxic naphthenic acids are left behind. These nasty acids present an environmental challenge, as millions of cubic meters of tailings pool up in ponds. Hayley Todesco constructed filters using sand and bacteria in IV bags. These filters essentially serve as bioreactors. The tailings seep through a layer of bacteria first, then sand, and, in the process, the naphthenic acids decompose 14 times faster than they would in tailing ponds.
Update: Todesco won the 17-18 category.