Production of Photo-oxidants by Dissolved Organic Matter During UV Water Treatment

Abstract

Dissolved organic matter (DOM) irradiated by sunlight generates photo-oxidants that can accelerate organic contaminant degradation in surface waters. However, the significance of this process to contaminant removal during engineered UV water treatment has not been demonstrated, partly due to a lack of suitable methods in the deep UV range. This work expands methods previously established to detect (1)O2, HO•, H2O2, and DOM triplet states ((3)DOM*) at solar wavelengths to irradiation at 254 nm, typical of UV water treatment. For transient intermediates, the methods include a photostable probe combined with selective scavengers. Quantum yields for (1)O2, (3)DOM* and H2O2 were in the same range as for solar-driven reactions but were an order of magnitude higher for HO•, which other experiments indicate is due to H2O2 reduction. With the quantum yields, the degradation of metoxuron was successfully predicted in a DOM solution irradiated at 254 nm. Further modeling showed that the contribution of DOM sensitization to organic contaminant removal during UV treatment should be significant only at high UV fluence, characteristic of advanced oxidation processes. Of the reactive species studied, (3)DOM* is predicted to have the greatest general influence on UV degradation of contaminants.

Photogeneration of reactive transient species upon irradiation of natural water samples: Formation quantum yields in different spectral intervals, and implications for the photochemistry of surface waters

“…extensive ice cover protecting CDOM from photodegradation/photobleaching). Coherently with the wavelength trend of F3 CDOM * obtained here, the quantum yield of TMP disappearance with humic substance isolates was higher under UVC than upon irradiation at l > 300 nm (Lester et al, 2013).…”

“…Comparison with results obtained under real or simulated sunlight suggests that HS quantum yields vary depending on the spectral range (Lester et al, 2013). It is also well known that the quantum yield of OH photogeneration in natural waters is higher in the UVB than in the UVA region (Mopper and Zhou, 1990;Sharpless and Blough, 2014), and variations with wavelength have been reported for the quantum yield of 1 O 2 generation by humic and fulvic substances (Sharpless, 2012).…”

A high-precision sampling scheme to assess persistence and transport characteristics of micropollutants in rivers

“…Also, the presence of humic substances may influence photodegradability. However, converse effects have been reported (Andreozzi et al, 2002;Lester et al, 2013). The mean DOC concentrations in the Steinlach during sampling were 3.5 mg L −1 at the upper and 3.4 mg L − 1 at the lower control cross-section, respectively.…”

Synthesis of core-shell structured CdS@CeO 2 and CdS@TiO 2 composites and comparison of their photocatalytic activities for the selective oxidation of benzyl alcohol to benzaldehyde

“…Semiconductor photocatalysis has attracted much attention as a promising solution to solve the worldwide environmental and energy issues [1][2][3][4][5][6]. Amongst the various semiconductor materials, TiO 2 has been widely studied because of its low-cost, nontoxicity, and high photostability [7][8][9].…”