Solar-driven Advanced Reduction Processes for Destroying Persistent Contaminants in Water
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Qatar has limited fresh water resources and therefore, maximizing water use efficiency and wastewater recycle/reuse and minimizing waste discharge were stated as a mandate in the Qatar National Development Strategy for Qatar National Vision 2030. Hence, it is critical to develop cost-effective water and wastewater treatment technologies that can achieve the required water quality levels for the intended use(s). Oxidation-reduction processes are the primary way for destroying contaminants in water and wastewater. A new class of treatment methods called Advanced Reduction Processes (ARP) has been developed by our research team. It is based on the strategy of combining a reducing reagent with an activating method to produce highly reactive reductant free radicals that have the ability to destroy persistent oxidized contaminants. Results of research conducted by the research team throughout previous and ongoing NPRP grants have demonstrated that ARP have the ability to destroy a wide range of oxidized contaminants. This research identified ARP that use sulfite or dithionite activated by ultraviolet light (UV) as being the most promising ARP. However, the opportunity exists to greatly reduce the cost and energy consumption of these processes by using sunlight as an activation method. Therefore, the overall goal of this project is to develop cost-effective solar-driven photocatalytic ARP (SARP) into effective treatment methods for contaminated water and wastewater. Novel photocatalysts that are based on modified titanium dioxide nanocomposites responsive to visible light will be synthesized and combined with sulfite or dithionite to produce reactive free radicals when the system is exposed to sunlight. The developed SARP will be evaluated for destroying trichloroethylene (TCE) as an example of organic contaminant and chlorate as an example of an inorganic contaminant. TCE has been detected in industrial wastewaters in Qatar and chlorate is a disinfection byproduct formed when chlorine dioxide is added to drinking water such as being planned now in Qatar. To achieve the project goal, six specific objectives will be pursued: 1) Develop analytical and experimental procedures, 2) Synthesize TiO2-based nanocomposites with novel structures and dopants and characterize them under sunlight to establish structure-property relationships, 3) Investigate photocatalytic activities of newly synthesized nanocomposites with reducing reagents under sunlight irradiation using water containing TCE or chlorate in order to determine an optimum for SARP that maximizes utilization of sunlight for production of reducing species and contaminant degradation, 4) Characterize TCE and chlorate reduction by promising SARP as affected by operating parameters and water quality, 5) Develop efficient and cost-effective methods for applying SARP in continuous flow treatment systems, and 6) Develop knowledge and problem solving capacities of researchers and practicing engineers in Qatar.