Assessing the potential of fluorescence spectroscopy to monitor contaminants in source waters and water reuse systems

Abstract

It is of ongoing interest to evaluate real-time instruments for monitoring water contaminants for source water control and water reuse system performance applications. Portable fluorescence sensors have the potential to provide instantaneous measurements of fluorescent organic compounds present in chemical and biological pollutants. Comparisons between one-dimensional fluorescence data from portable sensors and data obtained from higher sensitivity benchtop fluorometers, capable of three dimensional spectral acquisition, are needed to evaluate the performance of portable instruments. We tracked fluorescence intensities in titration experiments with diverse pollutants, including two volatile organic compounds (diesel, gasoline), three pharmaceuticals (ibuprofen, caffeine, lopinavir), and a pesticide (isoxathion), added to creek water, tertiary treated wastewater, and water from different treatment stages at a water reuse facility. Our results indicated that optical filters with wavelength bands in the tryptophan-like and tyrosine-like peak regions were able to track the peaks of most organic chemicals studied. Fluorescence intensities measured with both portable and benchtop instruments were highly correlated for all samples and all contaminants (R² > 0.90). In the final product water of the water reuse facility, both portable and benchtop fluorometers displayed high sensitivity, being able to discern contaminants from the background at concentrations as low as 0.2 ppb. However, in creek water, post-ozone water, and tertiary effluent, pollutant detection limits were much higher for both portable and benchtop fluorometers. Therefore, in waters with substantial background fluorescence, fluorescence-based sensors may be best suited for tracking higher concentrations of organic contaminants, such as those found in chemical spills in source waters.