Triplet Photochemistry of Effluent and Natural Organic Matter in Whole Water and Isolates from Effluent-Receiving Rivers

Abstract

Effluent organic matter (EfOM), contained in treated municipal wastewater, differs in composition from naturally occurring dissolved organic matter (DOM). The presence of EfOM may thus alter the photochemical production of reactive intermediates in rivers that receive measurable contributions of treated municipal wastewater. Quantum yield coefficients for excited triplet-state OM (3OM*) and apparent quantum yields for singlet oxygen (1O2) were measured for both whole water samples and OM isolated by solid phase extraction from whole water samples collected upstream and downstream of municipal wastewater treatment plant discharges in three rivers receiving differing effluent contributions: Hockanum R., CT (22% (v/v) effluent flow), E. Fork Little Miami R., OH (11%), and Pomperaug R., CT (6%). While only small differences in production of these reactive intermediates were observed between upstream and downstream whole water samples collected from the same river, yields of 3OM* and 1O2 varied by 30-50% between the rivers. Apparent quantum yields of 1O2 followed similar trends to those of 3OM*, consistent with 3OM* as a precursor to 1O2 formation. Higher 3OM* reactivity was observed for whole water samples than for OM isolates of the same water, suggesting differential recoveries of photoreactive moieties by solid phase extraction. 3OM* and 1O2 yields increased with increasing E2/E3 ratio (A254 nm divided by A365 nm) and decreased with increasing electron donating capacities of the samples, thus exhibiting trends also observed for reference humic and fulvic acid isolates. Mixing experiments with EfOM and DOM isolates showed evidence of quenching of triplet DOM by EfOM when measured yields were compared to theoretical yields. Together, the results suggest that effluent contributions of up to 25% (v/v) to river systems have a negligible influence on photochemical production of 3OM* and 1O2 apparently because of quenching of triplet DOM by EfOM. Furthermore, the results highlight the importance of whole water studies for quantifying in situ photoreactivity, particularly for 3OM*.

Molecular Composition and Photochemical Reactivity of Size-Fractionated Dissolved Organic Matter

“…66 3 DOM quantum yield coefficients determined with TMP ( f TMP ) 15 and 1 O 2 quantum yields (Φ 1O2 ), 13 as well as steady-state concentrations of 3 DOM, ([ 3 DOM] ss,TMP ) and 1 O 2 ([ 1 O 2 ] ss ), measured with TMP and FFA, respectively, are calculated with previously published rate constants (Section S6). Error bars represent the standard deviation of triplicate analyses.…”

“…21,22 UV– visible spectra of DOM provide insight into the structure and photochemical reactivity of DOM. 13,15,23 For example, measurements of absorbance ratios, such as E 2 : E 3 (i.e., the ratio of absorbance at 250 nm to that at 365 nm), and exponential spectral slope terms decrease with molecular weight, 23–26 while molar absorptivity increases. 27 The specific-UV absorbance at 254 nm (SUVA 254 ) correlates with DOM aromaticity, as determined by the relative signal intensity in the aromatic region (110–160 ppm) of the 13 C NMR spectrum, and with molecular weight.…”

“…27 The specific-UV absorbance at 254 nm (SUVA 254 ) correlates with DOM aromaticity, as determined by the relative signal intensity in the aromatic region (110–160 ppm) of the 13 C NMR spectrum, and with molecular weight. 27–30 Quantum yields of 3 DOM 14,15 and 1 O 2 13–16,31 are consistently shown to increase with E 2 : E 3 , while reactive species steady-state concentrations generally increase with solution absorbance (i.e., the concentration of dissolved organic carbon; [DOC]). 17,32 …”

Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties

“…In particular, there has been growing evidence of signicant variability in the nature of 3 CDOM in DOM of terrestrial origin (e.g., surface waters with input from soil organic matter) and of microbial origin (e.g., surface waters dominated by algal DOM or wastewater effluent DOM). 134 The photochemistry of sulfa drugs serves to illustrate the point. Sulfa drugs are widespread contaminants in wastewater-impacted surface waters that have been the subject of several recent studies seeking to understand their phototransformation.…”

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

“…22 The photoreactivity of CDOM varies as a function of its chemical composition, which in turn depends on its origin and subsequent transformation by biological and chemical processes. Wastewater-derived CDOM exhibits higher production rates of PPRI compared to autochthonous CDOM; [24][25][26] however, because it is also a more efficient quencher of PPRI, the higher production rates do not necessarily result in greater PPRI concentrations in wastewater-impacted waters. 26 In addition to CDOM, nitrate and nitrite, as well as metal complexes can sensitize the formation of PPRIs in sunlit waters.…”