(245f) Relation between Organic Matter Optical Parameters and Photodegradation of Emerging Contaminants

Emerging contaminants are susceptible to degradation by reaction with Reactive Intermediates (RIs) - such as triplet-state organic matter (³DOM^*), singlet oxygen (¹O₂), and hydroxyl radical (^•OH) - produced when organic matter present in water is exposed to light. It has been shown that contaminant degradation kinetics strongly depend on the organic matter composition and characteristics.

Organic matter present in water bodies may be naturally derived - natural organic matter (NOM) - or come from wastewater treatment effluent - effluent organic matter (EfOM) -. The generation of RIs has been shown to differ between EfOM and NOM, affecting the photodegradation of emerging contaminants in the aquatic environment, especially when effluent is released to the environment. Therefore, it is important to understand the differences between EfOM and NOM in terms of photodegradation of contaminants. However, characterizing organic matter can be expensive and complex.

Several optical parameters have been defined to extract information from UV-Vis and fluorescence spectroscopy about organic matter’s composition and properties. For instance, SUVA₂₅₄, HIX, FI, S_275-295, and E2:E3 have been used as indicators of DOM characteristics such as molecular weight, aromaticity, and light absorbance. Because of this, optical parameters of organic matter may provide insight on the reactivity of organic matter. In this work, we aim to correlate optical properties of EfOM and NOM to degradation kinetics of emerging contaminants.

Here, p-cresol was used as a surrogate for other phenolic emerging contaminants, which are persistent in nature and among the most toxic chemicals. p-Cresol photodegradation experiments were carried out in seven different EfOM samples and four different NOM samples to investigate contaminant photodegradation kinetics. EfOM samples consist of wastewater effluent obtained from a variety of wastewater treatment processes. NOM samples were standards obtained from the International Humic Substances Society. Fluorescence and UV-Vis spectroscopy was performed to characterize different fractions in the various organic matter samples. Optical parameters such as SUVA₂₅₄, HIX, FI, S_275-295, and E2:E3 were determined to indicate organic matter characteristics such as molecular weight and aromaticity. EfOM and NOM solutions were spiked with p-cresol and exposed to light in an AMETEK SUNTEST XLS+ sunlight simulator. The concentration of p-cresol was measured by an Alliance HPLC instrument every 30 minutes for four hours. Degradation kinetic parameters were determined, including quantum yields, RIs steady-state concentrations, and p-cresol degradation rate constants. Finally, Pearson correlations were determined among optical parameters and p-cresol degradation rate in both EfOM and NOM samples.

This work will provide a report on trends in p-cresol photodegradation in both NOM and EfOM samples. Moreover, the relation of p-cresol photodegradation kinetic parameters to optical parameters will be evaluated. It will also discuss the p-cresol degradation mechanism work in different aquatic matrices. The effect of organic matter composition on emerging contaminants degradation will be presented. These findings will benefit future studies by providing correlations to predict the degradation of emerging contaminants in NOM and EfOM.