Author

Amir Ahmadi

Date of Award

2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Committee Chair

Tingting Wu

Committee Member

Michael Anderson

Committee Member

Ashraf Al-Hamdan

Committee Member

Guangsheng Zhang

Committee Member

Robert Peters

Subject(s)

Sewage--Purification--Cost effectiveness., Water--Purification--Cost effectiveness., Titanium dioxide., Nanostructured materials., Oxidation-reduction reaction.

Abstract

Electrochemical redox processes have emerged as a viable option for water and wastewater treatment as they offer several advantages such as capable of degrading a wide range of contaminants, small footprint, capability to adjust to influent fluctuation, and less waste generation. In electrochemical treatment applications, the electrode material largely determines the efficiency of the treatment processes. However, electrodes commonly used for water treatment may either suffer low reactivity and/or stability (e.g. metal and mixed metal oxides such as SnO2, PbO2, IrO2, RuO2, and IrO2/RuO2 electrodes) or be subject to limited applications due to high cost and the scarcity of the materials (e.g. Pd, Pt, Boron Doped Diamond (BDD), and Au). Therefore, efficient, inexpensive, and stable electrode materials are the key to viable electrochemical treatment systems. Titanium dioxide (TiO2) have been studied for many environmental applications specifically photocatalysis owing to their outstanding properties such as strong photoreactivity, superhydrophilicity, chemical stability, nontoxicity, and low cost. However, TiO2 as a semiconductor material has intrinsically low electrical conductivity and electrocatalytic activity. Therefore, the overarching goal of this study was focused on engineered modifications of the main structure parameters including the crystallinity, shape, size, surface structure and defects to improve the electrochemical functionalities of TiO2 so that different water contaminations can be treated with high efficiency and low energy consumption. In this Ph.D. study, four specific objectives are pursued to comprehensively evaluate the developed TiO2 nanotube array (NTA) electrodes for different water/wastewater treatment applications so to achieve the overall research goal. The application of electrochemical technology for water/wastewater disinfection studied in chapter II. The most common method of electrochemical disinfection is the use of electro-generated oxidants, such as reactive chlorine species (RCS) and reactive oxygen species (ROS), as disinfectants. TiO2 NTA anode can effectively inactivate E. coli by generating RCS and ROS especially hydroxyl radical in different kinds of electrolyte as well as real water samples. In chapters III and IV, the electrochemical oxidation and reduction of water pollutants explored, respectively. Results from electrochemical oxidation (chapter III) demonstrate that Meropenem, a representative recalcitrant antibiotic that is widely present in wastewater, can be effectively removed from environmental matrices (e.g. secondary effluent and RO concentrate) using TiO2 NTA based anode material. Moreover, Co-doping Co/Bi has proved to be a viable approach to enhancing the lifetime and promoting ROS generation of TiO2 NTA electrodes. In chapter IV, Nitrobenzene was successfully removed from synthetic electrolytes through the electrochemical reduction process using TiO2 NTA cathode material with different morphological and crystallographic characteristics. Results indicate that the performance of TiO2 NTA electrodes was enhanced with the {001}-exposed facet and increases in the nanotube length and diameter. In all last three chapters, the electrochemical treatment of water pollutants was investigated through either anodic oxidation or cathodic reduction processes, where only half of the cell potential is utilized for pollutant removal, resulting in a low energy efficiency. In chapter V, several coupled anodic oxidation and cathodic reduction processes (e.g. sequential and simultaneous) using TiO2 NTA electrode as both anode and cathode were examined to utilize the full cell potential for the elimination of a widely-used antibiotic, Meropenem, from environmental matrices. Compared to the sequential oxidation/reduction process, simultaneous oxidation & reduction with regular polarity switching appeared to be the preferred treatment scheme for environmental matrices with simpler setup and higher energy efficiency. Overall, TiO2 NTA electrode material with excellent anodic and cathode performance for the elimination of different water pollutants, high chemical and electrochemical stability, and the low cost and environmental friendliness can be served as novel electrode materials for different electrochemical water and wastewater treatment applications.

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