Microfiltration with Rapid-Backpulsing and Surface-Modified Membranes

University of Colorado, Boulder CO.
December 1999

Report #58 - Executive Summary -

A combined method of backpulsing and membrane surface modification was used for the reduction of membrane fouling in water treatment applications. A novel photoinduced grafting method was used to render membranes hydrophilic with neutral, positively- or negatively-charged surfaces formed by grafting monomers of poly(ethylene glycol 200) monomethacrylate (PEG200MA), dimethyl aminoethyl methacrylate (DMAEMA), or acrylic acid (AA), respectively, onto a variety of substrates, including polypropylene (PP) and cellulose acetate (CA). Both unmodified and modified PP membranes, as well as commerical CA membranes, were evaluated in a crossflow microfiltration system with and without backpulsing in the presence of Escherichia coli bacterial suspensions. The grafting processes on the surfaces studies was found to be controllable and reproducible. The process was modeled successfully and can be used to graft a variety of monomers with independent control of the graft density, chain length, and total amount

For membrane studies it was found that without backpulsing the resulting permeate volume is nearly unchanged for a variety of different membranes. With backpulsing, however, the permeate volume for one hour of filtration with 0.14 g/L E. coli using the unmodified PP membanre is almost two times that without backpulsing, and is significantly higher for the modified membranes. The optimal membrane process was found to be one which involved both backpulsing and modification with a neutral, hydrophilic surface graft. The permeate volume for such a PP membrane is almost three times that of the base case. Additionally, after cleaning, the recovered clean water flux of the modified membranes is twice as high as those for the unmodified membranes and even more improved when compared to unmodified membranes with backpulsing.