Effects of natural organic matter and the raw water matrix on the rejection of atrazine by pressure-driven membranes

This work explores the role of the raw water matrix, particularly natural organic matter (NOM), in determining the removal of atrazine by nanofiltration membranes. The nature and relative concentration of NOM, the presence of calcium and ionic strength affected atrazine rejection. Dissolved organic matter (DOM) enhanced atrazine rejection in most cases and was dependent upon the relative concentrations of the DOM and the atrazine and the ionic strength. Atrazine rejection was greatly enhanced in the presence of the NOM surrogate, tannic acid. Less enhancement of atrazine rejection by NOM in comparison with tannic acid is attributed to relatively high concentrations of cations in the raw water and NOM concentrate and difference in molecular weight distribution. Higher ionic strengths decreased atrazine rejection. Trends in atrazine rejection as a function of recovery suggest that free atrazine rejection is mass transport-limited. Atrazine associated with DOM is removed by mechanical sieving.