Ultrafiltration of Natural Organic Matter
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Date
2001Author
Aoustin, E.
Schäfer, Andrea
Fane, Anthony G.
Waite, T. D.
Metadata
Abstract
Increasingly stringent regulations for drinking water quality have stimulated the application of
ultrafiltration to water treatment. In addition to removing particulate materials from water
(including microorganisms, bacteria and viruses), the use of membrane treatment also meets
purification requirements. However, irreversible fouling curtails the economic viability of such a
process.
Experiments in stirred-cells were conducted to evaluate the effects of surface water composition on
rejection and fouling of two ultrafiltration membranes with different molecular weight cut-offs
(10kDa and 100kDa). Experimental solutions consisted of natural organic matter or humic
substances in a background electrolyte.
The effect of calcium concentration decreased rejection of humic acid under certain circumstances.
This is believed due to reduced molecular size with an initial increase in calcium concentration.
However, at about 2.5mM CaCl2, IHSS humic acid aggregates. This aggregation increased
rejection, and also caused irreversible fouling of the 100kDa membrane, presumably as a result of
pore size reduction due to internal deposition of aggregates. This was confirmed by blocking law
analysis. The variation of transmembrane pressure indicated the importance of a ‘critical flux’
effect.
The organics and their various fractions showed differences both in rejection and flux decline. The
larger and more UV-absorbing fraction of humic acid was shown to be responsible for irreversible
pore adsorption and plugging. The fulvic acid and the hydrophilic fraction showed a smaller and
mostly reversible flux decline.