The scientific research area which will be investigated for the development of the greywater treatment reactors is called heterogenous photocatalysis. Photocatalysis refers to the use of light to increase the rate of a reaction. In this particular application, the reaction leads to the decomposition of pollutants in water. The photocatalyst is the materials being developed will when irradiated by a source of light generates species that degrade pollutants of both a chemical and biological nature. A successful photocatalyst is one which converts complex molecules to simpler ones such as carbon dioxide (CO2) and water (H2O). It is important that the pollutants are broken down completely as intermediate products of the photocatalytic reaction can be just as harmful as the parent contaminant.
Photocatalytic materials used for water treatment are mainly semiconductor metal oxides. One of the materials which has garnered much interest in photocatalysis is titanium dioxide (TiO2). This material is inexpensive, chemically stable, non-toxic and most importantly an excellent photocatalyst when used in a nanometric form. TiO2 nanoparticles in the form of suspensions or slurries have been successfully employed in water purification for a number of years. One drawback of TiO2 nano particles is the difficulty and the laborious process required to separate the nanoparticles from the purified water. Whilst deemed non-toxic, the effect of nanoparticles on the human body is still not known. The MicroWatTs team aims to produce photocatalysts on solid substrates thus eliminating the use of nano particles and their associated problems.
Regrettably, TiO2 is only photocatalytic when exposed to UV light. Sunlight a free and infinite resource but it only contains about 5% UV light. In order to fully exploit the photocatalytic process in an environmentally sustainable manner, the partners in MicrowatTS seek to develop photocatalytic surfaces that can also be activated by the visible light spectrum. This will greatly expand the potential of greywater reactors being developed.