Photodegradation of micropollutants using V-UV/UV-C processes; Triclosan as a model compound

Alfiya Yuval; Friedler Eran; Westphal Janin; Olsson Oliver; Dubowski Yael

doi:10.1016/j.scitotenv.2017.05.172

Photodegradation of micropollutants using V-UV/UV-C processes; Triclosan as a model compound

Sci Total Environ. 2017 Dec 1:601-602:397-404. doi: 10.1016/j.scitotenv.2017.05.172. Epub 2017 May 29.

Authors

Alfiya Yuval¹, Friedler Eran¹, Westphal Janin², Olsson Oliver², Dubowski Yael³

Affiliations

¹ Faculty of Civil and Environmental Engineering, Technion, Israel Institute of Technology, Haifa, Israel.
² Institute of Sustainable and Environmental Chemistry, Leuphana University of Lüneburg, Germany.
³ Faculty of Civil and Environmental Engineering, Technion, Israel Institute of Technology, Haifa, Israel. Electronic address: yaeld@tx.technion.ac.il.

PMID: 28570974
DOI: 10.1016/j.scitotenv.2017.05.172

Abstract

Non-potable reuse of treated wastewater is becoming widespread as means to address growing water scarcity. Removal of micropollutants (MPs) from such water often requires advanced oxidation processes using OH radicals. OH can be generated in-situ via water photolysis under vacuum-UV (λ<200nm) irradiation. The aim of this study was to investigate the potential of unmasking V-UV radiation from low pressure Hg lamps (emitting at 185 and 254nm), commonly used in decentralized treatment systems, for enhancing MPs removal efficiency. Triclosan, a biocide of limited biodegradability, served as a model compound for MPs that are not very biodegradable. Its degradation kinetics and identification of intermediate products were investigated under 254nm and under combined 254/185nm irradiation both in dry thin films and in aqueous solutions. In the latter, degradation was faster under combined 254/185nm radiation, although the 185nm radiation accounted for only 4% of the total UV light intensity. In contrast, triclosan photodegradation in dry film did not show significant differences between these irradiation wavelengths, suggesting that the enhanced degradation of dissolved triclosan under combined radiation is mainly due to oxidation by OH formed via water photolysis under V-UV. This conclusion was supported by slower TCS degradation in aqueous solution when methanol was added as OH scavenger. Under both irradiation types (254, 254/185nm) three transformation products (TPs) were identified: 2,8-dichlorodibenzo-p-dioxin, 5-chloro-2-(4- or 2-chlorophenoxy)phenol, and 2-hydroxy-8-chlorodibenzodioxin. In-silico QSAR toxicity assessment predicted potential toxicity and moderate-to-low biodegradability of these TPs. Removal of these TPs was faster under 254/185nm irradiation. Considering the low cost, simple operation (i.e. no chemicals addition) and small size of such low-pressure mercury lamps, this is a promising direction. Further investigation of the process in flow-through reactors and real wastewater/greywater effluent is needed for its future implementation in small on-site systems for post-treatment of persistent pollutants.

Keywords: Advanced oxidation process; Decentralized wastewater treatment; Micropollutants; Transformation products; Triclosan; Vacuum ultra-violet.