Date of Award

January 2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

First Advisor

Feng Xiao

Abstract

Per- and poly-fluoroalkyl substances (per- and poly-PFASs) are emerging contaminants that have raised great concern in recent years. Two anionic per-PFASs in particular, perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), has received worldwide attention for their persistence in the natural environment, resistance to typical environmental degradation, bioaccumulation potential, and adverse health effects in humans. The stable chemical characteristics have enabled these chemicals to be used in many industrial and consumer products over the past 50 years. They have been detected all over the world in various environmental matrices.

The water treatment removal of per-PFASs has been well documented, but the full classification of PFASs has yet to be determined and new compounds are being discovered and tested. Recent studies have identified numerous cationic and zwitterionic poly-PFASs whose fate and removal during drinking-water and municipal wastewater treatment remain unclear. However, there is limited knowledge on the fate of these emerging PFASs in water treatment processes. Studies on the removal mechanisms of cationic and zwitterionic poly-PFASs are needed to select the efficient treatment approaches while limiting the secondary formation of PFOS and PFOA. Furthermore, a few recently manufactured poly-PFASs as PFOS/PFOA alternatives have been found in drinking water and environmental samples. As the use of certain PFASs are being phased out of major manufacturers to reduce emissions, alternative PFAS compounds may start to become more detected in aquatic environments, which creates many unknowns for removal methods.

The goal of this project is to examine the removal of PFOS/PFOA alternatives and precursors and to model cationic and zwitterionic poly-PFAS compounds during conventional, enhanced, and advanced drinking-water treatment systems. Various water treatment technologies were investigated with regard to the removal and transformation of cationic and zwitterionic PFASs and PFOS/PFOA alternative compounds, including, enhanced coagulation, filtration, advanced carbon adsorption, chlorination, and ozone treatment to determine removal possibilities. These cationic and zwitterionic poly-PFASs have similar chemical structures as PFOS and PFOA, and our data as shown below indicate that certain cationic and zwitterionic poly-PFASs can convert to PFOS and PFOA during water disinfection processes with chlorine or ozone. The results of this work will shed light on the overall contribution of precursor compounds to the formation of PFOS and PFOA in engineered environmental systems.

It was determined that the removal of the target PFASs during conventional techniques, coagulation, and sand filtration was low. As for filtration by activated carbon, the concentrations immediately were almost below detectable ranges proving its wide known effectiveness against the removal of longer chained PFASs. Disinfection technique, chlorination, was found to be effective for the removal of PFOAB and PFOAAmS. Alternatively, ozone was found to be more effective at removing PFOSB and PFOSAmS at high ozone concentrations. Remarkably, in certain experiments, we observed the generation of PFOA and PFOS from cationic and zwitterionic precursor PFAS compounds during disinfection with either chlorine or ozone. Supported by some of the results, it was concluded that PFOAB and PFOAAmS degrade to form PFOA and, PFOSB and PFOSAmS degrade to form PFOS. PFOA was generated as high >4000% of their initial concentrations under certain conditions. These results will shed light on the degradation and removal behaviors of emerging PFASs during engineered systems and their contribution to the secondary formation of PFOS and PFOA.

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