Development of Electrochemical Processes for More Practical and Effective Onsite Wastewater Treatment

Citation

Kim, Seungkyeum (2022) Development of Electrochemical Processes for More Practical and Effective Onsite Wastewater Treatment. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ab1v-he77. https://resolver.caltech.edu/CaltechTHESIS:05252022-162959411

Abstract

In spite of the lack of safely managed sanitation and water supply systems, developing countries with rapid urbanization cannot afford to implement advanced treatment technologies that are highly centralized, calling for the development of practical onsite wastewater treatment. As effective yet practical solutions to the water crisis, I have developed high-performance earth-abundant electrocatalysts and an uncoupled electro-peroxone (E-peroxone) prototype reactor that can be applied in and as decentralized wastewater treatment systems. A series of conductive TiO₂ nanotube array electrodes are known to be effective for chlorine evolution reaction (CER) for wastewater treatment and oxygen evolution reaction (OER) for water splitting. In order to further enhance their electrocatalytic activities, an ultrathin layer of Al₂O₃ was deposited onto TiO₂ nanotube arrays via atomic layer deposition (ALD). Due to the facilitated formation of Ti³⁺ and oxygen vacancies by Al₂O₃ ALD, black TiO₂ nanotube arrays with 8 ALD cycles achieved up to 30% enhancement in CER and OER overpotentials in comparison to those without Al₂O₃ coating. Moreover, the ultrathin Al₂O₃ overlayer (~2 nm) reduced the charge transfer resistance and increased the electrochemical chemical surface area (ECSA) 3-fold for both reactions. Black TiO₂ nanotube arrays with 8 cycles were applied for toilet wastewater treatment and outperformed a dimensionally stable anode (DSA) in terms of chemical oxygen demand (COD) and ammonia reductions. The simplicity of the synthetic procedures and the use of inexpensive metal oxides suggest that Al₂O₃-deposited TiO₂ nanotube arrays can provide a promising approach to wastewater treatment and water splitting as practical alternatives for costly DSAs.

The uncoupled E-peroxone reactor system integrates ozonation with in situ hydrogen peroxide (H₂O₂) production to generate hydroxyl radicals for wastewater treatment. The E-peroxone process variables such as H2O2 concentration and ozone dose were optimized to maximize the treatment efficiency. Consequently, the system succeeded in reducing COD by 89%, total organic carbon (TOC) by 91%, biochemical oxygen demand (BOD) by 86%, and turbidity by 95% after 90-minute treatment of synthetic graywater. Moreover, the system reclaimed treated wastewater as an electrolyte for H₂O₂ production for subsequent treatment and maintained over 80% and 70% reductions in COD and TOC, respectively, over four consecutive treatment cycles. This system does not need any chemical additive, utilizes the energy-efficient E-peroxone process, and comprises inexpensive, accessible components. As a result, these advantages significantly reduce the system’s capital and operational costs. The promising results and cost-effectiveness show that it can provide a viable solution for the treatment of graywater and human wastewater in low-resource settings.

Thesis Files