title: Bench-scale evaluation of water disinfection by visible-to-UVC upconversion under high-intensity irradiation.
abstract: The feasibility of applying visible-to-UVC upconversion (UC) luminescence to enhance the kinetics of solar water disinfection was evaluated using Lu7O5F9:Pr(3+) ceramics incorporated into a solar reactor containing E. coli suspensions. Inactivation was assessed in batch conditions using both laser and lens-concentrated sunlight excitation conditions. Under 840-mW argon laser excitation, the UC efficiency was estimated to be 1 order of magnitude greater than previously reported under lamp excitation and UVC emitted by the reactors resulted in 3.6-log inactivation in 20 min. However, experiments using ~1500 mW of concentrated natural sunlight showed no additional inactivation that could be attributed to UC within the timescale studied. Due to the fundamental and practical limitations of solar focusing, the optical concentration ratio employed herein prevented the excitation beam from achieving the power densities required to attain UC efficiencies comparable to the laser experiments. We also observed that the high intensity of both the laser and sunlight induced rapid photoreactivation by the bacteria, which detracted from net disinfection performance. The results suggest that current UC materials perform inadequately for environmental application; nonetheless, valuable qualitative and quantitative insight was gained that more explicitly defines materials development goals and considerations for application of UC to environmental technology.
authors.affiliation: Department of Environmental Engineering & Earth Sciences, College of Engineering and Science, Clemson University, 342 Computer Ct, Anderson, SC 29625, United States.
authors.forename: Ezra L
authors.initials: EL
authors.lastname: Cates
authors.affiliation: Department of Chemical & Environmental Engineering, School of Engineering & Applied Science, Yale University, 9 Hillhouse Ave, New Haven, CT 06511, United States. Electronic address: jaehong.kim@yale.edu.
authors.forename: Jae-Hong
authors.initials: JH
authors.lastname: Kim
mesh_terms: D004203:Disinfection / Q000379:methods*; D004926:Escherichia coli / Q000528:radiation effects*; D054020:Lasers, Gas; D050296:Microbial Viability / Q000528:radiation effects; D013472:Sunlight; D014466:Ultraviolet Rays; D014871:Water Microbiology
keywords: Disinfection; Photoreactivation; Praseodymium; Solar; UVC; Upconversion