RO Membrane Fouling by Low Molecular Weight Organics: Models and Experimental Results

D. Bhattacharyya and M. E. Williams, Dept. of Chemical Engineering,

University of Kentucky, Lexington, KY 40506

Polymer - membrane interactions play an important role in reverse osmosis separation of organics from aqueous systems. Various organics (chloro- and nitro-phenols) showed substantial water flux drop (even in dilute solutions) during RO separation with cross-linked, aromatic polyamide membranes. For example, organic sorption on membranes caused about 50% flux drop with 2,4,6-trichlorophenol (TCP) as a solute. It is proposed that the number of hydrophilic sites of the polymer is reduced by specific interactions which involve hydrogen bonding of the phenolics to the carbonyl groups of the polyamide membrane. For the cases involving non-specific adsorption (such as, benzene), very little flux drop was observed. RO transport models were formulated to describe water flux and separations for dilute organic systems. The diffusion - adsorption (DA) and modified finely porous - adsorption (MFPA) model equations were solved numerically for selected organic systems. The models gave very good fit of water flux (typically within 5%) for benzene, chloro-, and nitro-phenols. The unsteady state trends in cumulative permeate concentration were similar to that observed experimentally. XPS analysis of the membrane containing adsorbed organic (TCP) showed the presence of TCP through all the sections of the membrane barrier layer. Pre-Ozonation of feed solutions resulted in dramatic reduction in fouling problems.