University of California Water Resources Center

The general objective of this project was to better understand the role of chemical factors in colloidal fouling of reverse osmosis membranes. The results of this research are of paramount importance for efficient operation of RO installations used in water reclamation and reuse and in potable water treatment.

Fouling experiments of thin film composite and cellulose acetate reverse osmosis membranes by aluminum oxide colloids are described. Membrane fouling was investigated at various solution chemistries under fixed hydrodynamic conditions. Results show that the fouling rate increases with an increase in the ionic strength of the solution. Fouling was significant at high ionic strengths, including in the presence of background dissolved organic matter, resulting in a gradual decrease in product water flux and salt rejection. Under the chemical conditions tested, colloidal fouling was found to be reversible, thus indicating that pore blockage is not an important mechanism in colloidal fouling of reverse osmosis membranes.

A qualitative model for the role of chemical-colloidal interactions in colloidal fouling of reverse osmosis membranes is proposed. Fouling is controlled by particle membrane and particle-retained particle interactions, which, in turn, are determined by solution chemistry, chemical properties of colloids and membranes, and the magnitude of permeation drag.