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Advanced Membrane Fouling Characterization 109
quantitatively related to the fouling indices. Therefore, SDI and related indices cannot be
used as a rigorous parameter in process design. Pilot tests usually have to be conducted for
observation of fouling development in the full-scale RO processes to generate the needed
design parameters in fouling mitigation and control. The duration of pilot test may take
months or over a year to obtain the meaningful information. However, because pilot tests are
usually costly and time consuming, only limited scenarios can be tested and evaluated.
Hence, the information obtained for fouling characterization is quite limited and incomplete.
A quick, cost-effective, and reliable method for fouling characterization is therefore the key
to a successful fouling control.
3. QUANTIFICATION OF FOULING POTENTIAL OF FEED WATER
3.1. Desirable Attributes for Fouling Potential Parameter
A more effective index or indicator for fouling potential of feed water is needed for a better
characterization. It is preferred that the water fouling potential is determined with RO
membrane and preferably under the conditions similar to the designed working conditions
for the full-scale RO processes. Because of the use of RO membrane, all possible foulants in
the feed water are considered in the measurements. In this way, the fouling index determined
is “inclusive,” which is a big advantage over most existing indices for fouling potential
measurement of feed water.
Another desirable attribute of fouling index is that it is indicative to membrane fouling in
full-scale RO processes. A quantitative relationship between the index and fouling development
in the full-scale RO processes can be effectively and accurately established with a
simulation model. When the fouling index of feed water with different pretreatments is
determined, the fouling behavior of the water in the can be immediately simulated and
assessed. The effectiveness of a pretreatment alternative can be evaluated in a few hours or at
most a few days. It becomes possible to evaluate more pretreatment methods and operating
conditions compared to conventional pilot testing. The need for pilot tests will be significantly
reduced or eliminated with the new fouling characterization and modeling method
developed (see Fig. 3.3).
In Sect. 3.2, an inclusive parameter for water fouling potential will be introduced. In Sect. 4,
the associated mathematical model for the linkage of the parameter to fouling development in
the full-scale RO processes will be introduced.
3.2. An Inclusive Parameter for Fouling Potential
Under the driving pressure, permeate flux moves perpendicularly to the membrane surface
from the bulk solution and passes through the membrane. The foulants containing in the water
will be retained on the membrane surface. The foulant deposition rate onto the RO membrane
surface induced by the permeate flow is
j ¼ vcf0; (2Þ