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Title: Bubbleless Membrane Oxygen Transfer in Membrane Bioreactor Applications
Principal Investigator's Name(s): Dr. Drew Johnson
Project Sponsor: U.S. Army Research Office
Program Overview: Membrane Bioreactors (MBRs) are compact wastewater treatment systems and the US Navy has expressed an interest in using MBRs for treating shipboard wastewater. As with most biological waste treatment systems, MBRs require oxygen addition to function properly. Treatment effectiveness of MBRs are often limited by the ability to deliver oxygen at a rate fast enough to satisfy process demand.
Objective of the Project: The intent of the proposed research is to improve MBR performance by developing an improved oxygen delivery system based upon bubbleless membrane gas transfer. Bubbleless membrane gas transfer is a novel membrane process where a membrane provides a discrete barrier between the gas and liquid phases. Hollow fiber membranes can be used to contain pure oxygen at high pressures. As a result, the rate of gas transfer is extremely rapid and hollow fiber membranes are ideal for supplying oxygen to compact treatment systems. While membrane oxygen transfer provides for the ability to transfer oxygen both rapidly and efficiently, a drawback is that the membranes are susceptible to biofouling. Biofouling retards the rate of oxygen transfer and must be minimized if one wants to ensure adequate oxygen delivery. Biofouling can be controlled by operating the membranes at oxygen pressures that are toxic to the microorganisms and/or by creating high water velocities past the membranes to shear off the biofouling layers.
The proposed research will investigate the use of hollow fiber membranes for membrane bioreactor oxygenation. Research will include plate count studies to investigate the effects of oxygen toxicity. Laboratory scale reactor studies will be conducted to investigate how hydrodynamic shear and oxygen toxicity influence the makeup and thickness of biofouling layers in MBR treatment systems. An economic analysis incorporating the costs of membrane will be completed and comparisons will be done between membrane oxygen transfer and other gas dissolution technologies. This will be the first study to demonstrate the use of membrane oxygenation in membrane bioreactor applications.