2011 Grand Prize - University Research

The Hydrogen-Based Membrane Biofilm Reactor: A Versatile Platform for Oxidized Contaminants Removal

Location: Temple, Arizona
Entrant: Arizona State University, Center for Environmental Biotechnology & School of Sustainable Engineering and the Build Environment
Engineer in Charge: Bruce E. Rittman, Ph.D., NAE, FAAAS
Media Contact: Dr. Bruce Rittman; 480-727-0434; rittmann@asu.edu

Entrant Profile

Bruce E. Rittmann: B.S. (Civil Engineering), M.S. (Environmental Engineering), Ph.D. (Environmental Engineering), Regents' Professor and Director, Center for Environmental Biotechnology, Biodesign Institute at Arizona State University. Dr. Rittmann is a member of the National Academy of Engineering and a Fellow of the American Association for the Advancement of Sciences. Dr. Rittmann was awarded the first Clarke Prize for Outstanding Achievements in Water Science and Technology from the National Water Research Institute and the Walter Huber Research Prize and the Simon Freese Award from ASCE. Dr. Rittmann is on the List of Most Highly Cited Researchers of the Institute for Scientific Information and has published over 450 journal articles, books, and book chapters. Together with Dr. Perry McCarty, Dr. Rittmann authored the textbook Environmental Biotechnology: Principles and Applications (McGraw-Hill Book Co.), which is translated into Spanish, Chinese, Korean, and Japanese. He also holds 6 patents, has co-authored 4 other books, and has mentored over 30 Ph.D. graduates. Dr. Rittmann is currently supervising 10 Ph.D, 2 M.S., 5 post-doctoral fellows, and 2 research scientists on environmental biotechnology.

Project Description

The hydrogen-based membrane biofilm reactor (MBfR) is a new water-treatment technology that combines microbiological processes with membrane technology. The MBfR delivers H₂ gas to a biofilm that naturally accumulates on the outer surface of a bubbleless membrane. Autotrophic bacteria in the biofilm oxidize the H₂ and use the electrons to reduce nitrate, nitrite, perchlorate, bromate, selenate, selenite, chromate, arsenate, trichloroethene (TCE), N-nitrosodimethylamine (NDMA), and other oxidized contaminants. Except for nitrate and nitrite, the oxidized contaminants fall into the category of emerging contaminants, which society has recognized as problems only recently. For most of these contaminants, no reliable and cost-effective treatment technology is available. Thus, society has a pressing need that is not already being met by means other than the MBfR.

The most prominent advantage of the MBfR is the way it delivers H₂. Before the MBfR, delivery of H₂ to microorganisms was impractical for two reasons. The first is that H₂ has very low water solubility: ∼ 1.6 mg H₂/L in equilibrium with 1 atmosphere of H₂. Low water solubility makes H₂ sparging inefficient. Inefficient sparging leads to the second reason: Release of H₂ off gas can create a combustible atmosphere. The MBfR overcomes the problems of sparging, because the H₂ is delivered directly to the biofilm by its diffusion through the wall of a gas-transfer membrane. Bubbleless H₂ transfer eliminates the problem of creating a combustible atmosphere. It also makes H₂ delivery nearly 100% efficient and virtually self-regulating. In essence, the bacteria in the biofilm "pull" the H₂ through the membrane wall when they consume H₂.

The first MBfR patent was awarded in 2002 and has been extensively tested at bench-, pilot-, and field-scale for many oxidized contaminants alone or in mixture. It is a versatile platform technology that can be used in many settings for waters contaminated with one or more oxidized contaminants: drinking-water sources, ground or surface waters that must be bioremediated, industrial and agricultural wastewaters, and municipal wastewater requiring advanced nutrient removal. The following sections describe these applications and summarize our experience with them.

Drinking-Water Application For Nitrate and Perchlorate

The initial application of the MBfR targeted drinking water contaminated with nitrate, perchlorate, or both. Extensive fundamental and applied research has been completed, and these applications are now moving to initial full-scale implementation.

A pilot-scale MBfR was tested at La Puente, California for both nitrate and perchlorate removal. Nitrate (∼ 25 mg N/L) and perchlorate (60 μg ClO₄^-/L) was reduced to 0.5 mg N/L and 4 μg ClO₄^-/L, respectively, at a flow rate of 4 L/d. A filed -scale MBfR was tested at Glendale, Arizona for nitrate removal. Nitrate (∼ 12 mg N/L) in the groundwater was completely removed at a flow rate of 5 L/min. An ion exchange process and a heterotrophic denitrification process were simultaneously tested and evaluated with the MBfR at Glendale. The three nitrate removal treatment processes were compared based on a multi-criteria analysis that included triple bottom line considerations of environmental, societal, and economic factors. The MBfR had the highest total benefit score (MBfR: 6.7; heterotrophic process: 6.2; ion exchange: 5.1).

Advanced Nitrogen Removal In Wastewater Treatment

Perhaps the most pervasive water-quality problem that the MBfR can address is advanced nutrient removal from wastewater. The MBfR can be directly used for advanced nitrogen removal in either of two ways: tertiary treatment or in situ augmentation. It also can be used as a stand-alone system for total-N removal.

Tertiary denitrification is the most direct approach for advanced-N removal with the MBfR, and has been tested at the bench-scale. The tertiary approach resembles how the MBfR is used for treating drinking water. Using the MBfR for tertiary denitrification overcomes two large drawbacks of the traditional tertiary denitrification that uses an organic electron donor, such as methanol. The first drawback is that over-dosing or under-dosing of the organic donor is common. Under-dosing causes the system to fail in its job of total-N removal. Over-dosing causes a breakthrough of rapidly degradable BOD. The second drawback is the high waste sludge production from the growth of heterotrophs that oxidize the added organic donor.

The alternative to tertiary denitrification is to augment the performance of a pre-denitrification system by placing MBfR modules directly in the anoxic zones of the pre-denitrification system. Thus, it is an in-situ approach that obviates the need to construct any new tanks. The in-situ approach requires that the pre-denitrification system have more than one anoxic zone, and the MBfR modules are placed in the second, third, etc. anoxic zones. The first zone is used for denitrification with influent BOD. Augmented in-situ pre-denitrification with MBfR modules overcomes the same two drawbacks of augmentation using organic donors.

Total-N removal using a stand-alone MBfR technology has been proven at the bench scale. This MBfR-only approach, called the aerobic/anoxic MBfR, couples an O₂-based MBfR that nitrifies influent NH₄⁺-level N to NO₃^- with a H₂-based MBfR for NO₃^- reduction.

Other Oxidized Contaminants

The MBfR is effective for reducing many oxidized contaminants beyond NO₃^- and ClO₄^-. Oxidized contaminants that has been tested and successfully reduced using the MBfR include nitrite (NO₂^-), chlorate (ClO₃^-), selenate (SeO₄^2-), selenite (HSeO₃^-), chromate (CrO₄^-), arsenate (AsO₃^-), bromated (BrO₃^-), tetrachloroethene (PCE), TCE, trichloroethene (TCA), chloroform (CF), dibromochloropropane (DBCP), and NDMA.

Conclusions

The MBfR is a versatile platform for reducing oxidized contaminants in many water-treatment settings: drinking water, ground water, wastewater, and agricultural drainage. Extensive bench-, pilot-, and field-scale experiments over the past ten years has proven that the MBfR can transform one or several oxidized contaminant to harmless or easily removed forms. The contaminants include inorganic oxyanions (e.g., NO₃^-, NO₂^-, ClO₄^-, ClO₃^-, SeO₄^2-, HSeO₃^-, AsO₃^-, CrO₄^-, and BrO₃^-), halogenated organics (e.g., TCE, TCA, CF, and DBCP), and nitroso organics (e.g., NDMA).