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Effects of UV/H2O2 advanced oxidation on chemical characteristics and chlorine reactivity of surface water natural organic matter Siva Sarathy, Madjid Mohseni* Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3, Canada
article info
abstract
Article history:
The advanced oxidation process utilizing ultraviolet and hydrogen peroxide (UV/H2O2) is
Received 19 December 2009
currently applied in commercial drinking water applications for the removal of various
Received in revised form
organic pollutants. Natural organic matter (NOM) present in the source water can also be
23 April 2010
oxidized and undergo changes at the fluence and H2O2 concentrations applied in
Accepted 18 May 2010
commercial drinking water UV/H2O2 applications (fluences less than 2000 mJ cm2, initial
Available online 31 May 2010
H2O2 concentrations less than 15 mg L1). In this study, the impact of UV/H2O2 on NOM’s aromaticity, hydrophobicity, and potential to form trihalomethanes (THMs) and haloacetic
Keywords:
acids (HAAs) was investigated for raw surface water and the same water with the very
Drinking water
hydrophobic acid (VHA) fraction of NOM removed. During UV/H2O2 treatments, NOM in the
Advanced oxidation
raw surface water was partially oxidized to less aromatic and hydrophobic characteristics,
Natural organic matter
but was not mineralized, confirming findings from past research. Below fluences of
Ultraviolet and hydrogen peroxide
1500 mJ cm2 UV/H2O2 treatment of the raw water did not lead to reduction in the
Disinfection by-products
formation potential of THMs. The formation potential of HAAs was reduced at a fluence of
Fractionation
500 mJ cm2 with only small additional reductions as fluence further increased. For the water from which the VHA fraction was removed, UV/H2O2 treatment led to mineralization of NOM suggesting that, when coupled with a pre-treatment capable of removing the VHA fraction, UV/H2O2 could achieve further reductions in NOM. These subsequent reductions in NOM led to continuous reductions in the formation potentials of THMs and HAAs as fluence increased. ª 2010 Elsevier Ltd. All rights reserved.
1.
Introduction
The application of ultraviolet (UV) based advanced oxidation processes for the removal of trace contaminants from drinking water is steadily growing. Leading the way in commercial applications is the ultraviolet plus hydrogen peroxide (UV/H2O2) advanced oxidation process. There is a deep collection of literature reporting on the ability of UV/ H2O2 to treat a wide array of organic pollutants. What is
lacking though is the impact of UV/H2O2 on natural organic matter (NOM) and the types of transformations NOM may undergo when UV/H2O2 is applied for drinking water treatment. NOM is ubiquitously present in drinking water sources and plays an important role during drinking water treatment processes. Of high importance, NOM is a precursor to chlorination disinfection by-products (DBPs), including trihalomethanes (THMs) and haloacetic acids (HAAs). While the
* Corresponding author. Tel.: þ1 604 822 0047; fax: þ1 604 822 6003. E-mail address:
[email protected] (M. Mohseni). URL: http://faculty.chbe.ubc.ca/mmohseni 0043-1354/$ e see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2010.05.025
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application of UV irradiation can replace chlorine as a primary disinfectant, chlorine may still be applied as a secondary disinfectant to maintain a residual disinfectant that impedes microbial growth in distribution systems. Thus, NOM can react with chlorine in the distribution system leading to the formation of DBPs. As UV/H2O2 treatment oxidizes NOM, the formation potential of THMs (THM-FPs) and HAAs (HAA-FPs) may be affected. It has been observed that during UV/H2O2 treatment NOM was oxidized leading to (i) a reduction in aromaticity of NOM (Sarathy and Mohseni, 2007; Sarathy and Mohseni, 2009; Thomson et al., 2004; Kleiser and Frimmel, 2000; Toor and Mohseni, 2007), (ii) a shift from high molecular size NOM to smaller molecular size NOM (Sarathy and Mohseni, 2007), (iii) formation of readily biodegradable compounds (Thomson et al., 2004; Sarathy and Mohseni, 2009; Toor and Mohseni, 2007), and (iv) a decrease in the hydrophobicity of NOM (Sarathy and Mohseni, 2009). There are reports that NOM could be mineralized during UV/H2O2 (Kleiser and Frimmel, 2000; Thomson et al., 2004; Toor and Mohseni, 2007) but required irradiation times and/or H2O2 concentrations well beyond the range economically acceptable for commercial drinking water application for trace contaminant removal (fluence
