Effect of Membrane Filtration on Ozonation Efficiency for Removal of Atrazine from Surface Water

The kinetics of the decay rate of atrazine from surface water by ozonation was studied at pH 3, 7, and 9 without and with pretreatment with several pressure-driven membrane filtration methods: ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), in order to determine the influence of the feedwater quality on the chemical oxidation of atrazine. First, the atrazine decay rate was determined in surface water (without pretreatment with membranes) in the presence of natural organic matter (NOM). An increase in the atrazine decay rate is observed at pH 3 and 7 in surface water, which can be attributed to the presence of NOM since it acts as OH radicals promoter. However, at pH = 9, the NOM effect vanishes since at this high pH, the advanced oxidation process (AOP) effect becomes far dominant. The efficiency of combining membrane filtration techniques with a subsequent ozonation step for removing atrazine from surface water mainly depends on the pH and the molecular weight fraction of the NOM. Under acidic conditions only UF enhances the atrazine decay rate since this technique does not retain the low molecular weight fraction of the NOM, which acts as OH radical promoter, while removing the high molecular weight fraction of the NOM which acts as a radical scavenger. At pH = 7, the presence of carbonate/bicarbonate ions as OH radical scavengers starts to prevail over the NOM effect. Because RO is the most efficient technique to decrease the carbonate/bicarbonate content, RO enhances the atrazine decay by more than 50%. At pH = 9, the AOP effect becomes by far dominant and annuls the NOM and carbonate/bicarbonate effect. The efficiency of membrane filtration techniques becomes doubtful in view of their marginal effect on the atrazine removal rate and the low statistical confidence levels of the measured kinetic constants under alkaline conditions.