Doctoral Dissertations

Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Kimberly E. Carter

Committee Members

Chris D. Cox, Qiang He, Thomas A. Zawodzinski

Abstract

Electrochemically activated persulfate (EAP) is a potential point source treatment for wastewater effluents containing high pharmaceutical content. This dissertation explores the fundamental mechanisms of EAP to better understand this technology for practical application. Ciprofloxacin, a fluoroquinolone antibiotic, was chosen as the model compound to assess parameters of EAP. Ciprofloxacin was selected for its high environmental risk factor and prevalence in hospital wastewater, a potential application for EAP. During the evaluation of EAP as a point source treatment, degradation kinetics and pathways of ciprofloxacin were elucidated.In the first stage of this study, persulfate activation by solid iron with and without applied current was characterized and applied to the degradation of ciprofloxacin. It was found that persulfate activation increased with iron surface area and increased to a plateau with increasing current. Ciprofloxacin degraded via first-order kinetics; however, applied current did not affect ciprofloxacin removal.In the second part of this study, electrochemical persulfate activation without iron, using boron-doped diamond (BDD) anodes and graphite or platinum cathodes, was examined. Sulfate radical formation at a BDD anode and persulfate activation at a graphite cathode were elucidated using different electrolytes and electrochemical set-ups. In this system, ciprofloxacin degraded via first order-kinetics, with persulfate electrolyte enhancing ciprofloxacin removal over sulfate or nitrate.In the final phase of this study, parameters such as reactor configuration, electrode surface area, persulfate concentrations and the presence of a complex matrix were examined to determine their impact on contaminant removal. Due to mass transfer limitations and relative cathode sizes, a flow-through reactor was least benefited by persulfate addition while a rotating-disk electrode reactor showed enhanced ciprofloxacin removal with persulfate electrolyte. Ciprofloxacin removal from synthetic hospital effluent using electrochemically activated persulfate was found to be less than that in pure electrolyte but still followed a first-order mechanism. Considerable total organic carbon removal of ciprofloxacin and other organic components of the effluent was achieved. Similar degradation was achieved with persulfate and sulfate electrolyte in the effluent. Chlorate, chlorite and perchlorate were formed in significant amounts during the electrochemical process, with formation independent of the presence of persulfate.

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