The Collaborative International Dictionary of English v.0.48:

bioremediation \bi`o*re*me*di*a"tion\, n.
   the branch of biotechnology that uses biological processes to
   overcome environmental problems.
   [WordNet 1.6]

WordNet (r) 3.0 (2006):

bioremediation
    n 1: the branch of biotechnology that uses biological process to
         overcome environmental problems
    2: the act of treating waste or pollutants by the use of
       microorganisms (as bacteria) that can break down the
       undesirable substances