MICROFILTRATION MEMBRANE FOULING IN WATER TREATMENT: IMPACT OF CHEMICAL ATTACHMENTS
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Date
2008-01-11T19:22:42Z
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Johns Hopkins University
Abstract
Membrane fouling is the loss of membrane permeability as a result of the
accumulation of aquatic materials on membrane surfaces. It was hypothesized in this
study that the origin of MF membrane fouling is the chemical attachment of these
materials on membrane surfaces, which is variable with varying solution chemistry. This
hypothesis was tested using model simulation and experimental work.
A mathematical model was first developed based on analyses of particle
attachments in MF and a hydraulic model that relates the extent of membrane fouling to
the mass of particles attaching to different areas of the membrane. The model simulation
results indicate that depositional attachment is primarily responsible for membrane
fouling. However, increase in coagulational attachment can reduce the occurrence of pore
blocking type of fouling, thereby lowering the extent of the total fouling. Particle size has
secondary effects on membrane fouling and generally affects its extent. Particles with
radii in a range of 1/6 ~ 1/2 of membrane pore diameter cause the greatest fouling when
they are sticky to membrane surfaces. These findings were subsequently validated using
a polyvinylidene fluoride (PVDF) MF membrane and monodisperse polystyrene latex
particles with predetermined sizes and chemical stabilities.
This model was finally applied to the understanding of natural organic matter
(NOM) fouling of the PVDF membrane. The combined results from model simulation,
membrane fouling experiments, and various analytical techniques suggests that the model
NOM consists of three major components, each with different relevance to membrane
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fouling. Component A has sizes close to membrane pores and can cause substantial
fouling regardless of the solution chemistry. Component B has sizes and stabilities that
vary with varying solution chemistry, and therefore, can foul the membrane to a different
extent. Component C does not directly cause membrane fouling due to its small size.
Overall, this study established a mechanistic model useful in the understanding of
MF membrane fouling, with potential applications to other low pressure membranes. The
results suggest that particle-membrane attachment is the primary reason for irreversible
MF membrane fouling, which should be of primary concern in the research, design and
operation of MF systems.