As a collaborative effort between MWH and Northwestern University (NWU), the objective of this research was to evaluate and optimize an innovative process called the membrane biofilm reactor (MBfR) to treat inorganic and organic oxidized contaminants. During initial testing, it was discovered that a bench-scale MBfR was effective in reducing 50 to 1000 µg/L perchlorate to below the previous California Department of Public Health Services Advisory Action Level of 18-µg/L. At pilot-scale, the objective was to evaluate the application of a pilot-scale MBfR system to biologically reduce low-concentration perchlorate-contaminated water from an active groundwater well to below the previous 4 µg/L CaDHS Action Limit. Fundamental bench-scale experiments were also performed to systematically evaluate the potential of the MBfR to remove a variety of oxidized inorganic and organic compounds (including chromium, selenium, chloroform, trichloroethene, and trichloroethane), and understand the micro-ecology behind these systems. Includes tables, figures.