Date of Award

Spring 2022

Project Type

Thesis

Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

James P Malley

Second Advisor

Anyin Li

Abstract

Most nutrients and contaminants within municipal wastewaters are removed through physical, chemical, and biological treatment methods. Per- and polyfluoroalkyl substances (PFAS) are a class of contaminants of emerging concern (CECs) that are concentrated in wastewater treatment facilities (WWTFs) from municipal, industrial, and commercial sources in communities. PFAS are poorly removed in conventional municipal wastewater treatment because these facilities are generally not designed for treatment of low-level CECs. Some PFAS leave WWTFs through aqueous effluent, while others partition to solids and are handled in sludges due to properties based on the degree of fluorination, chain length, and headgroup. As the last step of the treatment train, wastewater disinfection is achieved with UV light, ozonation, or chlorination and dechlorination. Research over the last decade has shown the potential for PFAS to be transformed through advanced reduction processes (ARPs) that are also used for disinfection. Processes and technologies already familiar to facility operators, such as UV light and sulfite addition for dechlorination, can be used in combination to create conditions for advanced reduction. UV light activates sulfite, the reductive agent, to generate highly reactive radicals with the goal of transforming perfluorooctanesulfonic acid (PFOS) to shorter chain compounds. These radicals, known as hydrated electrons, have a reduction potential of -2.9 V. By cleaving C-F bonds, hydrated electrons defluorinate PFOS in a stepwise manner, releasing fluoride to the treated water. Previous research has explored the UV/sulfite ARP under unrealistic operating conditions with part per million PFAS concentrations, higher than typically found in WWTFs. This research explores the effectiveness of the treatment option when applied to actual wastewater at more realistic PFOS concentrations and a lower UV dose, without raising the pH, altering the dissolved oxygen, or controlling temperature. The conditions in this applied engineering study included a sulfite concentration of 7.5 mM (945 mg/L Na2SO3) and a target initial PFOS concentration of 354 ng/L (ppt). A delivered UV dose of 1000 mJ/cm2 was achieved by using a low pressure high output lamp at 254 nm, and was corrected for reflection, refraction, and absorption of photons by the system. Decreased PFOS concentrations were observed under these conditions when the UV/sulfite ARP was applied to ultra-pure lab water. The application to wastewater yielded no indication of PFOS transformation to other metabolites or mineralization to basic elements and was therefore deemed unsuccessful. The UV/sulfite ARP is a promising treatment technology for PFAS transformation under ideal laboratory conditions, but further research is needed to optimize the treatment under realistic conditions for implementation in wastewater treatment facilities.

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