Solar Powered Photoreactor for Water Treatment

The access to clean water is a pressing issue across the world today, which for the decade ahead is of greater concern than climate change, food crises and social instability. Globally, close to one in ten people are without access to a clean drinking water source. Developing nations in tropical climates will be disproportionally affected by the water crisis as these regions have the largest populations without access to clean water. There are different methods available for the treatment of water which includes industrial water treatment plants that purifies water through stages. These steps in the industrial treatment process are broken into primary, secondary and tertiary stages. These water treatment processes include methods such as slow sand filtration, activated sludge or photocatalytic systems.

For developing regions, a lack of funds and infrastructure can result in conventional water treatment plants not being a possibility. This has led to investigations into reusing wastewater as it can be cheaper, require minimal infrastructure and the impact on major water sources is reduced. Water from different sources will have distinct water quality that can impact which is ideal for reuse.

The objective of this project is the development of a solar powered photocatalytic reactor for water treatment, specifically disinfection. The photocatalytic process would ideally be activated by solar light instead of an artificial source as this would reduce costs and simplify the system. After initial treatment, water would enter a photocatalytic reactor where light reaching the reactor would activate a catalyst that would photodegrade organic compounds and photoinactivate pathogens. The photocatalytic breakdown is a result of reactive oxygen species (ROS) being produced which go on to interact with the pollutants and pathogens present in water. Determining which ROS are responsible for the breakdown of the main pollutants and pathogens will allow for these ROS to be optimised to favour the degradation rate.

The catalyst selected is required to be inert, stable and cheap, TiO2 is considered to fit these requirements as an ideal photocatalyst. TiO2 exists in three different crystalline forms, anatase, brookite and rutile which is the abundant. However, anatase is the most active form for photocatalysis due to the superior mobility of the electron-hole pairs in its structure. TiO2 can also be immobilised onto a media to remove the need for filtration after a photocatalytic reaction has been completed in the reactor. The photocatalytic capabilities of TiO2 are often optimised through doping the catalyst with metal particles. This results in less chance of election-hole recombination and therefore efficient separation and desired photocatalytic reactions due to the metal's lower Fermi levels.

For research into the ROS produced in photocatalysis to breakdown pollutants and pathogens, models of each most be selected that ideally have been widely used in literature. 17-beta estradiol and Escherichia coli have been investigated heavily within literature as a model emerging pollutant and pathogen respectively.