Disinfection of greywater by heterogeneous photocatalysis

ABSTRACT

Proper disinfection of greywater is needed to ensure the safety of its reuse, especially in applications with potential for human exposure. Various advanced oxidation processes have been used in recent years for the degradation of organic contaminants, as well as for disinfection of water and wastewater. The purpose of this study was to test TiO₂ supported in microtubes to disinfect greywater by photocatalysis in order to reuse it in sanitary bowl. The greywater used in the experiments was collected after passing through a treatment system consisting of an evapotranspiration tank followed by constructed wetland with horizontal flow. Batch tests were conducted using a cylindrical photochemical reactor of 1.0 L (total volume of the reactor), filled with small glass Pyrex cylinders with supported TiO2. For disinfection tests, the processes UV, H₂O₂, UV/TiO₂, UV/H₂O₂ and UV/TiO₂/H₂O₂ were used. It was possible to obtain a homogeneous layer of TiO₂ deposited in small Pyrex glass tubes with an average thickness of 35.3 µm; this layer was able to promote an increase in the greywater disinfection. However, even with a greater disinfection power of TiO₂ compared with photolysis (UV), the processes with hydrogen peroxide was much more efficient in disinfection (total inactivation of total coliforms, enterococci and Pseudomonas aeruginosa) and in the removal of organic matter in terms of chemical oxygen demand (around 60%). Samples stored at a room temperature and wrapped in plastic dark showed no bacterial regrowth after 24 hours of storage after the experiments, thus showing the viability of treated greywater for domestic reuse.

Keywords:
greywater; titanium dioxide; advanced oxidation processes