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Environmental Engineering Graduate Seminar

Lathika Varanasi, PhD Candidate, Department of Civil & Environmental Engineering

Abstract:

Photolysis with ultraviolet (UV) light is an established technology for disinfection of pathogens and potential oxidation of chemical contaminants in water and wastewater treatment processes. UV-based advanced oxidation processes (AOPs) such as UV/hydrogen peroxide, UV/chlorine, and UV/persulfate are promising technologies to destroy a wide variety of organic compounds due to the formation of reactive radical species such as hydroxyl radicals (HO•), chlorine radicals (Cl•), and sulfate radicals (SO₄^•-).  The presence of dissolved organic matter (DOM) can affect the performance of UV photolysis and UV-based AOPs.  Photons emitted by UV lamps are absorbed and the radical species are scavenged by DOM, consequently reducing the efficiency of photolysis and oxidation in engineered UV photolysis and UV-based AOPs. 

This study aims to understand the molecular level DOM transformation induced by UV irradiation and reactive radical species in UV-AOPs. It is hypothesized that the different reactivity of photons (excitation) and radical species (abstraction, addition and electron-transfer) can cause the different patterns of DOM transformation. As a start, we used Suwannee River Fulvic Acid as DOM standard surrogate.  The sample solution containing approximately 10 mgC/L of DOC was irradiated by UV light in the absence or presence of hydrogen peroxide, free chlorine, or persulfate by using a 25 W low pressure UV-lamp.  Hydroxyl radicals, chlorine radicals, and sulfate radicals were quantified by using probe compounds (e.g., para-chlorobenzoic acid).  Concentrations of singlet oxygen with furfuryl alcohol and excited triplet state of DOM with 2,4,6 trimethylphenol were also measured.  We used a Thermo Scientific Orbitrap Elite Hybrid Ion Trap Mass Spectrometer in negative-ion mode to determine the elemental compositions of DOM. 

Lathika Varanasi¹, Erica Coscarelli¹, David Perram¹, Maryam Khaksari², Lynn Mazzoleni² and Daisuke Minakata¹

1. Department of Civil and Environmental Engineering, Michigan Technological University

2.Department of Chemistry, Michigan Technological University