Among the most challenging water pollutants are those whose common characteristic is that they are chemically oxidized. The "classic" oxidized pollutants are nitrate and nitrite, and emerging oxidized pollutants include perchlorate, selenate, chromate, radionuclides, and precious metals. For all of the oxidized contaminants, microbiological reduction leads to innocuous products. A novel biological treatment process able to reduce all of the oxidized pollutants is the hydrogen-based Membrane Biofilm Reactor (MBfR). Hydrogen gas (H2) is fed to the interior of hollow fiber membranes, diffuses through the membrane wall, and is then consumed by biofilm bacteria that use it as their electron-donor substrate while reducing one or more of the oxidized pollutants as their electron-acceptor substrate. We have carried out extensive studies to evaluate the fundamentals and the application of the MBfR for reduction of nitrate, perchlorate, selenate, and metals. This presentation addresses the conceptual basis for the MBfR, advantages of using H2, our vast experience reducing nitrate and perchlorate, our recent successes reducing selenate and palladium, and an update on the status of field testing and commercialization.