The Hydrogen-Based Membrane Biofilm Reactor for Reducing Oxidized Contaminants

Water contaminants that are chemically oxidized present a serious challenge for water and wastewater treatment. While nitrate and nitrite are well-known oxidized pollutants, many oxidized pollutants fall into the category of “emerging”: e.g., perchlorate, selenate, hexavalent chromium, and chlorinated solvents. The challenge is serious and widespread, because these contaminants are commonly found in groundwater, surface water, industrial wastewater, and municipal wastewater. In most cases, reliable and cost-effective treatment is not yet available for the emerging contaminants.In almost every case, microbiological reduction of oxidized contaminants leads to innocuous products: nitrate to N2 gas, perchlorate to H2O and Cl− ion, selenate to elemental selenium (Se°), hexavalent chromium to Cr(OH)3(s), and the chlorinated solvent trichloroethene (TCE) to Cl− ion and ethene. A microbiological treatment process able to reduce all of the oxidized pollutants is the hydrogen-based Membrane Biofilm Reactor (MBfR). Hydrogen gas (H2) delivered to the inside of hollow fibers diffuses through the fiber wall and is oxidized by bacteria that live as a biofilm on the fibers' exterior surface. These H2-oxidizing bacteria use the electrons to reduce one or more of the oxidized pollutants, which become the bacteria's electron-acceptor substrate.Over about ten years, my team has carried out extensive studies to evaluate the fundamentals and applications of the MBfR for reduction of nitrate, perchlorate, selenate, chromate, TCE, and several other oxidized contaminants. This work included fundamental laboratory research and field pilot testing. Almost all of this work has been documented in peer-reviewed papers, and a representative list is provided in the REFERENCES section.This presentation introduces the conceptual basis for the MBfR, highlights advantages of using H2 with the MBfR, and reviews key examples of our experience reducing nitrate, perchlorate, and other oxidized contaminants in drinking water and wastewater.