Wui Seng Ang, Chemical Engineering Department, Environmental Engineering Program, Yale University, PO Box 208286, New Haven, CT 06520-828 and Menachem Elimelech, Department of Chemical Engineering, Environmental Engineering Program, Yale University, P.O.Box 208286, New Haven, CT 06520-8286.
Fouling of reverse osmosis (RO) membranes used in advanced wastewater reclamation is inevitable, especially by effluent organic matter (EfOM) found in the feed water. Many membrane fouling and cleaning studies in literature use only one type of organic foulant as the model foulant. However, in a typical wastewater effluent, the solution contains different types of organic foulants (polysaccharides, humic acids, proteins, lipids), and the proportions of the foulants will be different depending significantly on the sources of wastewater. It would be relevant to study the effect of cleaning agents on the removal of organic foulants in the fouling layer in the presence of a few types of organic foulants. In this study, model foulants : alginate, Suwannee River natural organic matter (SRNOM), bovine serum albumin (BSA), and fatty acids (octanoic acids) : were used to represent respectively polysaccharides, proteins, humic acids, and lipids in EfOM. The model foulants are fouled using different combinations of mass proportions under favorable fouling conditions. The physical and chemical aspects of cleaning of the organic-fouled RO membranes using generic cleaning agents (sodium hydroxide, disodium EDTA, and sodium dodecyl sulfate) as well as alternative “green” cleaning chemicals (iminodisuccinic acid, ethylenediaminedisuccinic acid, citric acid, enzymes, and saline solutions) were systematically studied. To further understand the mechanisms of fouling with different combinations of organic foulants and cleaning with different cleaning agents, atomic force microscopy (AFM) was used to study the foulant-foulant interactions at the molecular level. The AFM results can explain the chemical aspects of the observed fouling and cleaning behaviors and help in illuminating the fouling and cleaning mechanisms of RO membranes fouled by combined organic foulants. Preliminary results show that fouling of RO membranes by an organic foulant can be enhanced in the presence of other organic foulants in trace concentrations, and the presence of these trace organic foulants can affect the efficiencies of cleaning agents.