Characterisation and removal of natural organic matter in drinking water treatment

Abstract

In this thesis, NOM removal by coagulation, advanced oxidation and adsorption process (with advanced oxidation for regeneration) were studied with the ultimate aim to improve water treatment technologies and treatment trains. The work starts with the development of novel PACl-chitosan composite coagulant for removal of NOM from water. It was confirmed that there is an intermolecular interaction between Al species and chitosan molecules as shown by the presence of Al-NH2 bonds in the composite coagulant. Improvement in the removal of NOM from synthetic water was observed at lower Al dosage when PACl-chitosan composite coagulant is used compared to PACl coagulant. However, a slight improvement in the removal of UV254 absorbing components of NOM was observed when natural water was treated with PACl-chitosan. Using UV-visible spectroscopy analysis, it is observed that PACl-chitosan is more effective than PACl for treating water containing higher levels of activated polyhydroxyaromatic moieties. The second part of the thesis focused on the study of the organic matter transformation as a result of oxidation process using titanium dioxide (TiO2). The degradation rate in the UVA/TiO2 process varied depending on the pH of the reaction, with faster removal rate at lower pHs. It was found that humic substances and building blocks are two of the components that contributed to the formation of THM. Short period of UV irradiation leads to high trihalomethanes formation potential (THMFP) levels for waters at neutral and basic pHs, while lower THMFP values were observed for water at acidic condition. The last part of the thesis focuses on the design of a magnetic photocatalyst (Fe3O4@SiO2@TiO2) to rapidly remove NOM from water by adsorption and thereafter can be effectively regenerated by light irradiation in a post treatment process. NOM adsorption on magnetic TiO2 was found to rapidly reach equilibration, with a majority of the organic matters adsorbed within 5 min. The THMFP after treatment was either within the range or lower than the acceptable Australian limit (250 μg.L-1) and these levels were sustained throughout the five adsorption-regeneration cycles. Significant enhancements in the organic removal as well as THMFP values were observed for adsorption at lower pH.