(580b) The Time Evolution of Fouling Development upon Design Aspects of Direct-Flow Filtration

Key words:
hollow fibre membrane, direct-flow filtration, packing density, membrane
fouling, filtration resistance

Current
membrane manufactures are prone to particle removal and membrane cleaning
technologies because of the very challenge fouling issue that they are trying
to address. It is that fouling decreases the filtration flux over time during
constant pressure filtration and contrastively increases the transmembrane
pressure difference (TMP) during constant flux filtration, which both restrain
the productivity of the filtration process. In literature, most fouling studies
have been directed to the constant pressure cross-flow filtration performances,
however filtration operations with constant fluxes are more preferred in
practice. This study explores the time evolution of fouling development upon
design parameters of constant flux direct-flow filtration (DFF), which permits
the use of smaller diameter fibres and generates less tangential flow compared
with classical cross-flow filtration (CFF). DFF is usually achieved by capping
one end of a CFF hollow fibre module to maintain no outlet flow from the
module.

Fouling
formation and its effect on filtration are influenced by various parameters,
such as filtration resistance, backwash cleaning frequencies and module design parameters,
out of which resistance is mostly emphasised. As reported in the literature,
the rate of change of resistance is proportional to the instantaneous
filtration resistance raised to a power, which varies from filtration to
filtration. Hence, our investigation started with a DFF model developed by
dividing the module into thousands of sections along the axial distance, which
allows us to adapt a positional-changing resistance for each filtration circle.
The model was validated by comparing the results with the mathematical model
resulting from solution of the Navier-Stokes equations, and one group of
results are given in Fig.1, Fig.2 and Fig.3. Whilst there is little evolution
in the TMP profiles (Fig.1), the evolution of the resistance profile (Fig.2)
results in the changing profiles of local fluxes (Fig.3). These results reflect
a particular fouling model and will be contrasted with two other fouling models
in the presentation. The models will be manipulated with module design
parameters aiming to explain the fouling mechanism and approach for
optimization of DFF.

Fig. 1. The transmembrane pressure differences (TMP) upon the operating circles versus
axial distance at constant flux 70
LMH. The module had a length of 1.6m
and 55% packing density
of 1.3mm outer diameter fibres. 

Fig. 2. The local resistance in log
scale upon the operating circles versus axial distance at constant flux 70 LMH. The module had a length
of 1.6m and 55% packing density of 1.3mm
outer diameter fibres. 

Fig. 3. The local flux upon the
operating circles versus axial distance at constant flux 70 LMH. The module had a length
of 1.6m and 55% packing density of 1.3mm
outer diameter fibres.