Role of dissolved organic macromolecules on the removal of atrazine by nanofiltration

Researchers: Erin Devitt, Frederic Ducellier

Removal of micropollutants such as atrazine is a significant concern for US and European water treatment plants. Nanofiltration has been proposed as one alternative for removing atrazine as well as divalent ions and disinfection by-product removal. This work explores the role of the raw water matrix in determining the removal of atrazine by nanofiltration membranes with emphasis on the role of natural organic matter in enhancing atrazine rejection. Significant retention of atrazine in the absence of dissolved organic matter was observed for all of the membranes with molecular weight cutoffs in the NF range. The nature and relative concentration of the organic matter, the presence of calcium and the ionic strength all notably affected atrazine rejection. Dissolved organic matter enhanced atrazine rejection in most cases and was dependent upon the relative concentrations of the organic matter and the atrazine as well as the ionic strength. Atrazine rejection was greatly enhanced in the presence of the natural organic matter surrogate, tannic acid, used in these experiments. The natural organic matter used in this work also enhanced atrazine rejection, but only at high TOC/atrazine ratios (> 3 mg/µg). Less enhancement of atrazine rejection by NOM in comparison with tannic acid is attributed to the relatively high concentrations of cations in the raw water and NOM concentrate and difference in molecular weight distribution. In experiments with tannic acid, higher ionic strengths were shown to decrease atrazine rejection. Trends in atrazine rejection as a function of recovery suggest that free atrazine rejection is controlled by mass transport limitations across the membrane while atrazine associated with organic matter is removed primarily by mechanical sieving.