Trihalomethane treatment using gamma irradiation: kinetic modeling of single solute and mixtures
Introduction
It is well known that use of chlorine for disinfection of drinking water leads to formation of several by products that are potentially harmful for human beings. Among these disinfection by-products (DBP) the four trihalomethanes (THMs), chloroform (CHCl3), bromodichloromethane (CHCl2Br), chlorodibromomethane (CHClBr2) and bromoform (CHBr3), which exhibit potentially cancerous activity have been investigated most (Rook, 1974). They are formed as a result of hypochlorous acid (HOCl) reactions with natural organic matter in water in presence or absence of bromide (Gallard and von Gunten, 2002).
Advanced oxidation processes have not been used to any great extent for THM control because of their low reactivity towards the 
OH, and because of the efficiency of aeration stripping and carbon adsorption. The gamma rays or electron beam process, containing both oxidizing and reducing species, may in selected cases be an economically viable option for halogenated compounds (Bolton et al., 1998; Tobien et al., 2000), in particular when other disinfection by-products or contaminants are present (e.g. chloroacetones, (Williams et al., 2002)). For example, MTBE is primarily removed via oxidative pathways (Mezyk et al., 2004) while THMs by reductive processes (Tobien et al., 2000) and it is possible that some drinking water supplies may contain all of these compounds. Therefore, this study was undertaken to examine the effectiveness of γ-irradiation on the destruction of these compounds singly and in mixtures.
There have been a number of studies examining the radiolytic destruction of the THMs (e.g. Cooper et al., 1993; Mak et al (1996), Mak et al (1997); Tobien et al., 2000). Kinetic modeling of individual solutes has achieved reasonably good results in describing the destruction of these solutes at large scale (0.45 m3/min) (Mak et al (1996), Mak et al (1997); Tobien et al., 2000). However, no detailed laboratory studies have been conducted where mixtures of these compounds have been modeled. This study was designed to investigate the removal of the four THMs from distilled water, individually and as mixtures. We have applied our kinetic model to individual compounds and to mixtures and compared the experimental and model data.
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Radiation source
A Cobalt –60 gamma rays radiation source was used for irradiations. This Gamma cell 220 radiation source (Nordion, Canada) was calibrated using aqueous ferrous sulfate solution (Fricke dosimetry) (Sehested, 1970). Typical dose rate was 104 Gy/min and transit dose was estimated to be 9 Gy.
Gas chromatography
A Shimadzu model GC-17A gas chromatograph with a Restek, Rtx®- 1 F&F capillary column (30 m long, 0.25 mm ID, 0.25 μm film thickness) together with an Electron Capture Detector (ECD) was used for determination of
Irradiation of individual solutes
When irradiated by gamma ray, each individual THMs (100, 200 and 1000 μg l−1) in water undergoes destruction. With increasing radiation dose (absorbed energy), the concentration of each contaminant in water decreases for all solutes. A measure of the efficiency of the irradiation process is given by the G value (as defined in Eq (2)). Table 3 summarizes these results; i.e. absorbed dose and corresponding percent reduction and the G-values for CHCl3, CHCl2Br, CHClBr2 and CHBr3. In all cases we
Acknowledgements
The authors would like to acknowledge the support of King Abdulaziz City for Science and Technology (KACST) for funding this project. In addition, we would like to acknowledge Prof. William J. Cooper, University of North Carolina at Wilmington for his advice and support in planning and implementation of this project with travel support from the International Atomic Energy Agency (IAEA).
References (20)
- et al.
OH reactions with aliphatic alcoholsevaluation of kinetics by direct optical absorption measurement. A pulse radiolysis study
Radiat. Phys. Chem
(2003) - et al.
Figures-of-merit for advanced oxidation processes—a comparison of homogeneous UV/H2O2, heterogeneous TIO2 and electron beam processes
J. Adv. Ox. Technol
(1998) - et al.
Critical review of rate constants for reactions of hydrated electrons, hydrogen atom and hydroxyl radicals (
OH/O−) in aqueous solutionsJ. Phys. Chem. Ref. Data
(1988) - Carver, M.B., Hanley, D.V., Chapin, K.R., 1979. MAKSIMA-CHEMIST, a program for mass action kinetic simulated...
- et al.
Removing THMS from drinking water using high-energy electron-beam irradiation
J. Am. Water Works Assoc
(1993) - et al.
Kinetic modeling of the destruction of methyl tert-Butyl Ether (MTBE)
Radiat. Phys. Chem
(2003) - et al.
Chlorination of natural organic matterkinetics of chlorination and of THM formation
Water Res
(2002) Automatic integration of ordinary differential equations
Comm. ACM
(1971)- et al.
Rate constants for reactions of hydroxyl radicals with several drinking water contaminants
Environ. Sci. Technol
(1992) - et al.
Decomposition of aqueous solutions of phenol using high energy electron beam irradiation—a large scale study
Appl. Radiat. Isotopes
(1995)
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Present address: Radiation Chemistry Laboratory, National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar 25120, Pakistan.