Abstract:
The removal of natural organic matter (NOM) is a key requirement of many processes
in potable water treatment. Conventionally, removal of NOM and colloidal material has
been achieved by coagulation with inorganic coagulants followed by either direct rapid
gravity filtration alone or clarification (sedimentation or flotation) followed by at least
one stage of rapid gravity filtration.
An alternative to conventional processes is to combine membrane microfiltration (MF)
with coagulation for NOM removal. The advantages of MF technology over traditional
sand filters is the maintenance of an absolute barrier throughout the filtration process,
thereby enhancing the physical separation process by presenting an absolute barrier to
suspended materials. This thesis presents the results from such a system.
A 9.6m2 hollow fibre hydrophilic polysulphone MF membrane system was used in
combination with ferric sulphate under controlled pH conditions. The system was
operated under constant flow condition and the coagulant concentration varied to assess
performance. Coagulation conditions which promoted rapid aggregation of particles was
found to give best performance with respect to pressure development, this coincided
with a zeta potential at or near zero. Also, a pre-flocculation time of 20 seconds was
found to be sufficient to allow complete removal of material associated with the
coagulation process. Comparison with other workers showed similar results for the
specific cake resistance despite considerable differences in both the scale and type of
system used.
