ARTICLE pubs.acs.org/IECR
Effect of Membrane Filtration on Ozonation Efficiency for Removal of Atrazine from Surface Water Patricia Luis,† Mohd Saquib,† Chris Vinckier,‡ and Bart Van der Bruggen*,† †
Applied Physical Chemistry and Environmental Technology Section, Department of Chemical Engineering (CIT), K.U. Leuven, W. de Croylaan 46, B-3001, Leuven, Belgium ‡ Molecular Design and Synthesis Unit, Department of Chemistry, K.U. Leuven, Leuven, Belgium ABSTRACT: 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.
1. INTRODUCTION A large number of pesticides have been registered and marketed for pest control purposes around the world. Possible sources of pesticide contamination in drinking water sources include agricultural and urban runoffs, direct application to control aquatic insects and vegetation, domestic usage, leaching from pesticide wastes, and industrial-scale pest control operations. Because of their persistence in the aquatic environment and potential adverse health effects, the pesticide pollution of surface water and groundwater has been recognized for years as a major problem in many countries. Among pesticides, atrazine (2-chloro-4-ethylamino6-isopropylamino-s-triazine) is widely used as an herbicide13 despite having been banned in Europe and included in the priority substances list of the European Commission.4 Atrazine belongs to the group of symmetric s-triazines and is characterized by a relatively high solubility in water (0.16 mM) and persistence in the environment.5 Consequently, its concentration in surface and ground waters has been frequently detected above the maximum permissible level for drinking water (0.1 μg L1 for individual pesticides) according to the EC directives.6 Conventional drinking water treatment processes such as coagulation/flocculation, filtration, and chlorination are largely ineffective in removing atrazine.79 Thus, physical treatments based on membrane technology1019 and ozone-based advanced oxidation processes (AOPs)2029 are in the spotlight for the removal of atrazine from water. Membrane processes are suitable to remove organic matter of different sizes, from small solutes (through reverse osmosis and nanofiltration) to macromolecules (through ultrafiltration) or r 2011 American Chemical Society
suspended matter (through the use of microfiltration)30,31 obtaining a permeate that may have a sufficient quality to be reused in different applications, such as rinsing or washing in industrial processes.32,33 It is interesting to mention the work performed by M€antt€ari et al.33 where membranes and ozonation were used to increase the biodegradability of the concentrate in the paper industry, obtaining a significant removal of UV compounds that could not be retained in the membranes. The combination of membrane technology with ozonation may be a strategy to reach higher elimination levels of atrazine in the purification of surface waters by means of the removal of atrazine itself and also organic matter in order to increase the atrazine removal in the ozonation step.34 A kinetic study performed by Acero et al.35 about the atrazine degradation in pure water revealed that, at pH = 7, the relative importance of the direct reaction with ozone and the indirect path with OH radicals depends on the reaction compound fractions produced, and the presence of other substances, such as organic matter, can significantly modify the reaction rates of atrazine with hydroxyl radicals because of the competitive effect of these substances or their initiating or promoting character.36 In this study, the simultaneous removal of atrazine and organic matter was investigated by applying a membrane filtration system Received: February 23, 2011 Accepted: June 3, 2011 Revised: June 2, 2011 Published: June 03, 2011 8686
dx.doi.org/10.1021/ie200375j | Ind. Eng. Chem. Res. 2011, 50, 8686–8692
Industrial & Engineering Chemistry Research
ARTICLE
Table 1. Characteristics of the Feed Water Used in the Experiments (River Dijle, Leuven, Belgium) pH COD (mg L1)
8.0 25
TOC (mg L1)
6.7
hardness (f)a
27
absorbance of organic content (UV254)
0.099
Na (mg L1)
27
Mg (mg L1)
11
K (mg L1) Ca (mg L1)
6 117
Cd (μg L1)
