Photocatalytic ozonation under visible radiation for the remediation of Masdar City's grey water

Abstract

The accessibility to drinking water and sanitation is still strongly restrained in many areas of the world, slowing down economic development and being a threat for the public health of these regions. As a matter of fact, the UN has designated it as one of its 17 Sustainable Development Goals for the 21st century to be achieved by 2030 worldwide. The scientific community has done a great effort over the last decades to develop new technologies to overcome this issue. Different advanced oxidation processes (AOP) have been developed, being very effective for wastewater treatment. Photocatalysis is among the most successful AOP studied so far. One of the many uses of photocatalysis is the treatment of wastewater in a sustainable way using only solar radiation, an abundant resource in the UAE. The use of TiO2 as a photocatalyst has brought the attention of many researchers due to its high oxidation potential. However, photocatalysis with pure TiO2 is only feasible under UV radiation, which represents only 5% of the total radiation reaching the Earth's surface. The degradation of 4-nitrophenol is achieved in the presence of oxygen and ozone, achieving a decrease in the total organic carbon content of the solution of 51% and 82% respectively after 7 hours of treatment. This thesis focuses on the study of photocatalysis for wastewater treatment under visible radiation using nitrogen doped TiO2 photocatalysts in the presence of ozone, which has no precedent on the literature. The photocatalytic treatment of the effluent of an electrochemical membrane bioreactor (eMBR) was achieved in the presence of ozone and oxygen under visible radiation reaching 60 and 75% TOC decrease after 5 hours of treatment. The photocatalytic treatment of urban grey water using this catalyst is achieved in the presence of oxygen and ozone achieving up to 48% and 55% of TOC decrease after 32 hours of treatment. In some cases a kinetic study of the photocatalytic reaction is performed following Langmuir-Hinshelwood model for heterogeneous photocatalysis. The better performance of ozone must be ascribed to its electrophilic character which is stronger compared to the one of oxygen, allowing a faster formation of reactive radicals upon interaction with electrons formed on the photocatalysts. It is worth noting that the achievement of photocatalytic ozonation under visible radiation for real wastewater effluents has no precedent in the scientific publications.

Date of Award	May 2017
Original language	American English