Date of Award
2-7-2025
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Population growth, urban densification and climate change are increasing the water pollution and water shortage problems. To achieve more sustainable water management, wastewater reuse, both for non-potable and potable reuse purposes, appears to be an attractive option. In wastewater treatment and water reuse processes, oxidation treatment processes and membrane technologies are commonly applied by water utilities to remove recalcitrant contaminants and ensure the safety of the treated effluent. However, these processes are facing challenges including requirements of chemical reagents storage and transport, issues of membrane fouling and formation of toxic byproducts. Electrochemical technology presents a promising chemical-free approach with its potential to be applied in wastewater treatment and water reuse processes. This research aims to advance electrochemically assisted wastewater treatment and reuse processes, by developing chemical-free processes for oxidative wastewater treatment, understating the byproduct formation mechanisms, and proposing potential strategies for membrane fouling control and byproduct removal in wastewater reuse processes. A systematic literature analysis on byproduct formation and control in electrochemical oxidation revealed that wastewater parameters and types have significant effects of organic byproduct formation. The types of electrode materials such as nonactive and active would largely influence inorganic byproduct formation. Byproduct formation may be controlled through the optimization of key operating parameters. Using free chlorine quenchers and developing chlorine-inert anode would minimize byproduct formation. Post-treatment of byproducts such as electrochemical reduction or microbial reduction technology could also be applied. The degradation of organic contaminants and formation of byproducts were revealed in electrochemical oxidation treatment of phenolic wastewater. Multiple electrochemical cells were constructed to treat the recalcitrant wastewater. Formation of both the carbonaceous and nitrogenous byproducts were rigorously investigated through the electrochemical processes. Critical intermediates for byproduct formation and the potential byproduct formation pathways/mechanisms were identified and revealed. The effects of key water parameters and operating conditions were investigated. The removal and detoxification of halogenated byproducts by electrochemical reduction was elucidated in batch and continuous experiments. A granular activated carbon (GAC) – based cathode electrode was developed to enhance byproduct removal through integrated adsorption and reductive degradation. The analysis of degradation products demonstrated the detoxification of the byproducts via reductive dehalogenation. The continuous experiments indicated the consistent and sustainable byproduct treatment performance of the GAC-based cathode electrode. To achieve non-potable reuse of domestic wastewater, a microbial electrochemical system (MES) assisted UV/H2O2 process was developed. MES achieved organic compounds removal through bioanode degradation, while simultaneously generated H2O2 by the air diffusion cathode through oxygen reduction. The MES effluent containing H2O2 was further treated by an UV/H2O2 process to removal recalcitrant contaminants such as pharmaceuticals and personal care products (PPCPs) and pathogenic bacteria. The developed process achieved wastewater treatment without any chemical/water input, and the treated effluent meets the non-potable reuse guidelines of different countries. The feasibility of electrochemical softening and chlorination for potable reuse processes was tested in batch and continuous experiments using real secondary effluent. Through electrochemical processes, the OH--containing catholyte was used to achieve water softening through hardness precipitation. The H+- and chlor(am)ine-containing anolyte was applied to adjust pH and add disinfectants. Electrochemical treatment could help mitigate membrane fouling issues and supply disinfectants for water disinfection and distribution. This dissertation concludes with identifying future research opportunities in trade-off between contaminant removal and byproduct control in oxidation water treatment processes, scaling up of the lab scale systems and exploring more scenarios for application of electrochemically assisted water reuse systems, and utilizing renewable energy for the electrochemical techniques.
Language
English (en)
Chair
Zhen He
Committee Members
Daniel Giammar; Kevin Moeller; Kimberly Parker; Young-Shin Jun