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Abstract
Macromolecular components, including protein and polysaccharides, are viewed as one type of major foulants in the
complex feed membrane filtration systems such as membrane bioreactor (MBR). In this thesis, the mechanisms of
macromolecular fouling including protein and polysaccharide in the complex feed solution are explored by using
Bovine serum albumin (BSA) and alginate as model solution.
During the filtration of BSA and washed yeast with 0.22 ¥ìm PVDF membrane, it was found that the critical flux of
mixture solution was controlled by washed yeast concentration while the existence of BSA significantly changed the
cake reversibility of much larger particles.
The fouling mechanisms of alginate, as a model polysaccharide solution, were investigated both in dead end and
crossflow membrane filtration. In the dead end experiments, it was found that the cake model appears to fit the entire
range of the ultrafiltration data while the consecutive standard pore blocking model and cake model are more
applicable to microfiltration membranes. The alginate was featured with high specific cake resistance and low
compressibility despite some variations between different membranes. The specific cake resistance ( c
) is similar to
c
of BSA and actual extracellular polymer substance (EPS) in MBR systems reported in the literature, and higher
than that of many colloidal particles. In a system contained alginate-particles mixture, it was found that the existence
of alginate dramatically increased the cake specific resistance and decreased the cake compressibility.
The fouling mechanism of alginate was also studied using long term cross flow filtration under subcritical flux. A
two-stage TMP profile similar to that typically observed in MBR was obtained, confirming the important role of EPS
during membrane fouling in MBR. In addition to adsorption, trace deposition of alginate also contributed to the initial
slow TMP increase during the subcritical filtration. TMP increase during the long-term filtration was found not only
due to the increase of the amount of deposition, but also the increase of specific cake resistance. A combined standard
pore blocking and cake filtration model, using a critical pore size for the transition time determination, was developed
and fit the experimental results well.