Even though methyl tertiary butyl ether (MTBE) is banned as a gasoline additive in half the states in the U.S., past spills and underground storage tank leaks continue to impair groundwater quality. Environmental Resolutions Inc., Petaluma, CA, is trying to address this problem with quiet and odor-free bioreactors, which are being used at dozens of locations. The company says naturally occurring micro-organisms concentrated in state-of-the-art bioreactors can clean contaminated groundwater sites. Joe O'Connell, company president, says water industry officials are embracing bioreactors as a treatment tool because they clean both MTBE and related chemicals such as tertiary butyl alcohol and other gasoline components. Environmental Resolutions Inc. worked with Drs. Edward Schroeder, Daniel Chang and Kate Scow at the University of California at Davis to develop its bioreactor technology. Bioreactor-based water treatment involves pumping groundwater out of the ground, mixing it with active micro-organisms in a bioreactor system and discharging the newly treated water. The discharge is sent back into the ground, to a municipal sewer system or into surface water.