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Title: Bubbleless Membrane Ozonation
Principal Investigator's Name(s): Dr. Drew W. Johnson
Project Sponsor: AWWA Research Foundation
Program Overview: Ozone is an ecologically friendly alternative to other disinfectants/oxidants. While ozone has found widespread use in a variety of settings, it's use in lieu of chlorine and other chemicals to reduce environmental impacts is not as wide spread as it could be because of costs associated with ozone generation and difficulties in its dissolution. Given the increased attention to disinfection by-products, alternative technologies need to be examined that will allow treatment objectives to be met in a simple and cost effective manner.
One promising alternative to conventional bubble contactors is the use of bubbleless membrane gas transfer. Hollow fiber membranes can be used to contain gasses at pressures as high as 6 atm. As a result, large driving forces are possible and the kinetics for gas dissolution are extremely rapid. Membrane gas transfer occurs by direct dissolution at the membrane surface. Transfer efficiencies can be 100 percent, no bubbles are produced and minimal amounts of volatile organic compounds (VOCs) and odors are stripped to the atmosphere. The rate of gas transfer is controlled by the transfer driving force, the membrane surface area and the water velocity past the membrane, all of which can be manipulated independently. This provides design flexibility and the capability to quickly respond to varying transfer requirements without affecting transfer efficiency.
The emphasis of the proposed research will be on developing the design information necessary to enable the design and optimization of membrane ozonation systems for a variety of applications. Results will be applicable to both disinfection and oxidation applications.
Because of the complicated nature of ozone transfer where both chemical reactions and partitioning occurs, a mathematical computer model will be required for predicting membrane ozone transfer rates in process waters. As part of the proposed research, a model will be developed and it will account for membrane length, gas pressures and velocities within the membranes, gas diffiusivity and solubility, ozone reaction rates and dissolved gas concentrations within the bulk solution. Bench scale laboratory studies will be conducted. Ozone transfer rates will be determined from the measured ozone concentrations in the inlet and outlet gases of a membrane module. Gas concentrations will be determined by the standard indigo colorimetric method. Ozone concentrations in the outlet water will be determined by the iodometric method. The experimental results will be used to verify the ozone transfer model. The model will allow for the design and optimization of a membrane ozonator.
The proposed research will develop a more efficient and cost effective ozone dissolution technology. This technology will expand ozone usage and eliminate the production of toxic byproducts and off-gasses associated with other disinfection/oxidation methods and other ozone dissolution technologies.