Sulfate radical based advanced oxidation processes coupled with ceramic membranes for water purification

• Main Author: Bao, Yueping
• Other Authors: Hu Xiao
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Environmental engineering
• Online Access: https://hdl.handle.net/10356/136891
• Institution: Nanyang Technological University

The intensive use of antibiotics for human, veterinary and agricultural purposes results in their continuous release into the environment, which causes the concern in relation to the development of antibiotic resistance genes and bacteria. Sulfate radical based advanced oxidation processes (SR-AOPs) have been recognized as an effective alternative method to the destruction of recalcitrant organics in wastewater, in which highly-reactive sulfate radical was generated and utilized to oxidize organic contaminants to innocuous CO2 and H2O. However, most of the catalysts used in SR-AOPs are suspended in water during usage and therefore need a further separation process. On the other hand, membrane separation has been proved to be a promising technology for water purification in recent decades because of the high yield of production and low energy consumption. However, the membrane fouling caused by the accumulation of a broad range of foulants on top of membrane surface / inside the membrane pores results in a substantial decrease in their water permeability, which leads to a high permeability loss and energy consumption. Meanwhile, the separation principle for microfiltration (MF) is based on size exclusion, which means that it cannot remove many kinds of organic micro-pollutants during the physical separation process, resulting in the effluent discharge with potential hazard. The aim of this thesis work is to overcome these drawbacks by integrating MF with SR-AOPs in the water purification system to remove antibiotics, in which sulfamethoxazole (SMX) works as the target pollutant. Firstly, a Co3O4 surface functionalized ceramic membrane (CoFCM) was synthesized via a novel ZIF-67 induced surface nucleated heterogeneous growth method (Chapter 3). The CoFCM showed an enhanced performance in SMX removal in a semi-batch experiment. In chapter 4, a Co3O4 impregnated ceramic membrane (CoCM) was developed via an in-situ self-scarified template method. With this method, Co3O4 was isotropically impregnated into the whole membrane while did not affect the pore size of the membranes. Due to the advantages of mix-metal oxides on PMS activation, a cobalt ferrite (CoFe2O4) impregnated ceramic membrane was developed via a one-step urea combustion method (Chapter 5). Results showed that CoFe2O4 was impregnated into the membrane pores as well as the membrane surface. With increasing of repeating times, the catalyst loading amount increased while the pure water permeability decreased, which means the catalyst would form a dense catalytic layer on the membrane surface due to the aggregation during the combustion process. The membrane performance was evaluated in a home-made dead-end membrane filtration mode, and results showed the robust membrane can function well during a wide pH range as well as the existence of NOM and anions. Finally, to have a better understanding on the SMX transformation via PMS in the presence of nano-bimetallic Co/Fe oxides, a systematic study was conducted in Chapter 6. The influencing factors (pH, NOM, catalyst loading and PMS dosage) were investigated and the radical generation as well as PMS activation mechanism were explored. The SMX transformation pathway including both non-radical and radical pathways was proposed.