Abstract
Seeking economic solutions for the pre-treatment of polluted waters is at the forefront of current reverse osmosis (RO) desalination research. The modern trend is to remove the polluting species by various UF/MF membrane pretreatment schemes. This paper describes progress in an ongoing project aiming to improve membrane pre-treatment processes by placing dynamic membranes in front of the UF/MF unit so as to relieve the load on the downstream processing. Dynamic membranes (DM), a class of membranes that has not yet found general industrial application, are formed in situ by colloid deposition on a porous support. They are an attractive method to relieve the load on the downstream pre-treatment membranes because, once fouled, they can be removed and reformed in place. This research has shown that DM formation conditions for organic foulant retention are not necessarily those suggested in the literature for other applications. The membranes tested were formed by dead end filtration of a hydrous zirconium oxide colloidal suspension on inexpensive nondashwoven flat sheet supports and post-treated by a poly(acrylic acid) solution. The quality of a DM membrane was characterized by measurements of permeate flux and retention of ovalbumin, used as a model contaminant. The properties of dynamic membranes are known to depend on a large number of variables. Results are described showing the effect of parameters found to exert a significant influence on membrane properties. They include the zirconium oxide colloid concentration, the tightness of the support fabric, the pH level of the colloidal suspension and the poly(acrylic acid) post-treatment. The best dynamic membrane achieved exhibited 85% ovalbumin retention at a concentration of 1000 ppm and over 95% retention at a concentration of 50 ppm. Permeation rates were in the range of UF fluxes (10–50 l/m2·h·bar). The work carried out to date has yielded encouraging results that are being currently extended.
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