Date of Graduation
Doctor of Philosophy in Engineering (PhD)
Julian L. Fairey
Second Committee Member
Justin R. Chimka
Third Committee Member
Carbon nanotube, Disinfection byproduct precursors, Fluorescence, N-nitrosamines, X-ray photoelectron spectroscopy
As drinking water sources become increasingly impaired with nutrients and wastewater treatment plant (WWTP) effluent, formation of disinfection byproducts (DBPs) – such as trihalomethanes (THMs), dihaloacetonitriles (DHANs), and N-nitrosamines – during water treatment may also increase. N-nitrosamines may comprise the bulk of the chronic toxicity in treated drinking waters despite forming at low ng/L levels. This research seeks to elucidate physicochemical properties of carbon nanotubes (CNTs) for removal of DBP precursors, with an emphasis on total N-nitrosamines (TONO).
Batch experiments with CNTs were completed to assess adsorption of THM, DHAN, and TONO precursors; physiochemical properties of CNTs were quantified through gas adsorption isotherms and x-ray photoelectron spectroscopy. Numerical modeling was used to elucidate characteristics of CNTs controlling DBP precursor adsorption. Multivariate models developed with unmodified CNTs revealed that surface carboxyl groups and, for TONO precursors, cumulative pore volume (CPV), controlled DBP precursor adsorption. Models developed with modified CNTs revealed that specific surface area controlled adsorption of THM and DHAN precursors while CPV and surface oxygen content were significant for adsorption of TONO precursors.
While surrogates of THM and DHAN precursors leverage metrics from UV absorbance and fluorescence spectroscopy, a TONO precursor surrogate has proved elusive. This is important as measurements of TONO formation potential (TONOFP) require large sample volumes and long processing times, which impairs development of treatment processes. TONO precursor surrogates were developed using samples that had undergone oxidative or sorption treatments. Precursors were analyzed with asymmetric flow field-flow fractionation (AF4) with inline fluorescence detection (FLD) and whole water fluorescence excitation-emission matrices (EEMs). TONO precursor surrogates were discovered, capable of predicting changes in TONOFP in WWTP samples that have undergone oxidation (R2 = 0.996) and sorption (R2 = 0.576). Importantly, both surrogates only require just 2 mL of sample volume to measure and take only 1 hour. Application of the sorption precursor surrogate revealed that DBP precursor adsorption was feasible with freeform CNT microstructures with various dimensions and surface chemistries, establishing a framework for development of this novel CNT application for drinking water treatment.
Needham, E. (2017). Total N-nitrosamine Precursor Adsorption with Carbon Nanotubes: Elucidating Controlling Physiochemical Properties and Developing a Size-Resolved Precursor Surrogate. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/1993