Chemical interactions between dissolved organic matter and low-molecular weight organic compounds: Impacts on membrane separation

This work considers the hypothesis that the association of trace-level hydrophobic organic compounds with dissolved organic matter (DOM), similar to macromolecular materials found in natural water systems, may influence the contaminant's ability to permeate across synthetic membranes. A batch dialysis system using semipermeable membranes in conjunction with a model lipid phase was used to explore the impact of systematic changes in solution-chemistry on the permeability of four low-molecular weight organic compounds (LMWOCs) of environmental concern: cyclonite, atrazine, naphthalene, and 2,4-dichlorophenol. Similar to previous studies, no correlation could be drawn between molecular weight and contaminant permeability across the membrane for the four LMWOCs. However, contaminant transport was observed to depend on the polarity and hydrophobicity of the LMWOCs. Moreover, the interactions between the organic compounds and DOM varied as a function of solution chemistry (i.e., pH and divalent electrolyte concentration). These results demonstrate considerable variability in the importance and the underlying mechanisms of interactions that may occur between LMWOCs and natural organic matter during membrane separations.