Application of advanced oxidation processes for organic compound removal from saline water

Freshwater scarcity and emerging organic (micro)pollutants in the water bodies create challenges for the ecosystem. In addition, the development of the industrial sector enhances freshwater consumption enormously. Closing the water cycle by reusing the treated wastewater is essential to meet several sustainable goals. Cooling towers in the industries are one of the largest freshwater consumers and discharge large volumes of saline wastewater as cooling tower blowdown water (CTBD). Reuse of the CTBD could reduce freshwater footprint and enable them to become an eco-efficient and sustainable industry. The CTBD contains a complex mixture of salts and organic compounds. The research project described in this thesis was designed to study advanced oxidation processes (AOPs) to remove the organic compounds (OCs) in this saline condition. In this research, four different AOPs, namely- electrooxidation, photocatalytic degradation, heat-activated persulfate oxidation, UVC/vacuum UV process, have been studied. A special focus has been given on the effectiveness of removing the OCs and the influence of chloride ions. The thesis has eight chapters, including six experiment chapters, a general introduction, and a general discussion. Chapter one gives a general introduction about freshwater water consumption, pollutants, the necessity of treatment, principles of AOPs. Chapter two presents the possibilities and limitations of electrochemical oxidation to removed OCs in the presence of chloride. Chapters three and four focused on strategies to minimize the bottleneck of electrochemical oxidation in the presence of chloride ions. Chapters five and six focused on the influences of chloride ions on photocatalytic degradation, heat-activated persulfate oxidation, and UVC/vacuum UV AOPs. Chapter seven described a complete technology train to treat the CTBD. The train includes wasteland, nanofiltration, reverse osmosis, and electrochemical oxidation. A comprehensive overview of chloride chemistry in all state-of-the-art AOPs has been summarised in chapter eight to guide the end-user to select appropriate AOPs in saline conditions.