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Membrane Water Treatment   Volume 4, Number 1, January 2013, pages 69-81
Hypochlorite treatment of polyamide membrane for improved reverse osmosis performance
P. Shao and C.J. Kurth

Abstract     [Buy Article]
    The pH-dependent inter-conversion of the three free chlorine species (Cl2, HOCl, OCl-) present in the aqueous hypochlorite solution was theoretically investigated. Each species was found overwhelmingly present in a characteristic pH range. Hypochlorite treatment of the polyamide membrane was carried out over these pH ranges and various membrane responses were observed. As pH is less than 8, membrane tends to be N-chlorinated by Cl2 and HOCl, and N-ch lorinated membrane showed reduced water permeance and salt rejection. As pH rises to 10-12, OCl¯ appears to be the dominating chlorine species. Membrane hydrolysis was found to well interpret the improved water permeance and salt rejection. When the pH is between 8-10, both N-chlorination and hydrolysis contribute to the response of the membrane, and the treated membrane showed improved salt rejection but reduced water permeation. Excessive hydrolysis occurred while the membrane was treated at pH 13 for the much stronger alkalinity.
Key Words
    polyamide; hypochlorite treatment; reverse osmosis; salt rejection; water permeance; membrane chemistry; chlorinating species; hydrolysis; N-chlorination
P. Shao : 1Energy, Mining and Environment (EME) Portfolio, National Research Council Canada,
M12, 1200 Montreal Road, Ottawa, ON, Canada K1A 0R6, Canada
C.J. Kurth : NanoH2O Inc. 750 Lairport Street, El Segundo, CA 90245, USA

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