Photochemical Formation and Scavenging of Hydroxyl Radicals by Effluent Organic Matter (Efom) and the Removal of Trace Contaminants in Wastewater

Dong, Mei Mei

Graduate Thesis Or Dissertation

Photochemical Formation and Scavenging of Hydroxyl Radicals by Effluent Organic Matter (Efom) and the Removal of Trace Contaminants in Wastewater Public Deposited

Analytics

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/jd472w659

Abstract

The occurrence and fate of organic contaminants in environmental waters has raised awareness over ecological effects and potential concerns for human health. The classes of compounds that have been the focus of recent interest include endocrine disruptor compounds (EDCs), pharmaceuticals and personal care products, and pesticides. It is well documented that most of these contaminants could be removed by reaction with the hydroxyl radical (HO*). This objectives of this thesis were to: 1) investigate the effect of effluent organic matter (EfOM) on the overall scavenging of HO* in wastewater; 2) investigate the ability of EfOM to produce HO* upon photon absorption; 3) and to investigate the photochemical removal of trace organic contaminants in wastewater. The wastewater matrix scavenging is directly proportional to the second-order reaction rate constant between EfOM and HO* (kEfOM-HO*), as EfOM account for over 90% of the total scavenging of HO* from the water matrix components. The values of kEfOM-HO* for examined wastewaters measured using pulse radiolysis have shown much higher scavenging rate constants compared to the values from natural organic matter. The photochemical formation of HO* from EfOM was determined and compared to HO* formation of natural organic matter (NOM) photolysis under simulated sunlight. HO* production rates from EfOM photolysis were similar to the four NOM isolates used at similar organic matter concentration under the same photon irradiation. However, the apparent quantum yields for HO* formation in EfOM are higher than the values for NOM isolates. Because EfOM contained large amount of hydrophilic organic matter, resulting in a lower absorbance compared to NOM. In wastewaters containing low nitrate, EfOM is an important source for HO*. The study of the photodegradation of pharmaceuticals showed that the overall degradation of these pharmaceuticals was dependent on both direct and photosensitized photolysis and the contribution of each process was determined by the chemical properties of the compounds. HO* radicals are important in removing compounds that lacks of aromatic structure, and triplet state organic matter and 1O2 are as important when removing the ring containing pharmaceuticals.

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