Hollow fiber membrane degassing in ultrapure water and microbiocontamination

To eliminate bacterial contamination in the production of ultrapure water (UPW), an advanced oxidation process (AOP) destroys bacteria via the use of H₂O₂, O₃ and/or UV light. To remove the AOP byproducts like CO₂, O₂, etc. from the treated water, membrane degasification is utilized to achieve near complete removal of dissolved gases, CO₂, O₂, from deionized water. A small and compact membrane module, commercially available as a blood oxygenator and made out of porous hydrophobic polypropylene (PP) hollow fibers, has yielded excellent degasification. Feed water was in crossflow on the shell side; a vacuum was used on the tube side. To protect the fibers against residual/trace oxidative agents in water, the hollow fibers were coated on the outside with an ultrathin coating of PDD-TFE (perfluorodimethyldioxole-tetrafluoroethylene). Two N₂-consuming bacterial strains were grown on a flat porous PP membrane (Celgard 2400) as well as on the PDD-TFE coated hollow fibers. Bacterial adhesion lowered the degassing capabilities of the flat membrane as well as the coated hollow fibers. The mass transfer coefficient in the hollow fiber module has been characterized vis-a-vis the flow rate dependence.