A study of selected herbicides retention by nanofiltration membranes—The role of organic fouling

Abstract

This paper reports the results from a series of experiments investigating the retention of three selected herbicides (atrazine, isoproturon and prometryn) in single solute or dissolute solutions by three typical commercial nanofiltration membranes. Based on measured permeation rates and the rejection capacity for herbicides, one of the tested nanofilters is selected in order to study the role of organic matter and calcium concentration on herbicide retention. The effect of organic fouling, caused by humic substances, on the retention of atrazine and isoproturon in dead-end nanofiltration is also examined. In the absence of other species, the retention of individually tested herbicides can be explained by the combined effect of their molecular size and dipole moment, whereas the simultaneous nanofiltration of two herbicides seems to be influenced by a competitive adsorption of solutes on the membrane surface. The extent of membrane organic fouling, depending on the nature and the relative concentration of humic substances as well as the presence of calcium, significantly affects the retention of the tested herbicides; additionally, nanofiltration of water where herbicides are present together with humic substances results in increased herbicide retention. This trend is less evident in the presence of calcium ions due to their possible interference with the humic substances–herbicides interactions.