The concentration of toxic materials and infectious microorganism in the natural resources of drinking water is constantly increasing causing severe environmental pollution. Availability of safe drinking water to people in developing countries has become a serious challenge. The traditional chemical methods for the disinfection of drinking water have limitations due to their costs for the undeveloped nations. Furthermore, generation of harmful disinfection byproducts associated with the chemical disinfection processes like chlorination is a source of rising concern among the masses. Hence, there is an urgent need to work out some more reliable alternate techniques for the purpose. Heterogeneous photocatalysis, being considered as a promising technique to control environmental pollution has attracted the interest of researchers during the last couple of decades. The method is not only free of generation of harmful byproducts, but could also be cost effective and environmental friendly by utilizing ambient solar light. We present an overview of photocatalytic inactivation of water borne microbial pathogens. We focus here on various factors involved in the disinfection processes and discuss how different researchers have addressed them to improve the overall efficiency of photocatalytic inactivation of microbes. Research reports on the subject show that heterogeneous photocatalysis degrades wide range of microbial pathogens including bacteria, molds, fungi, and virus. Titanium dioxide (TiO2) has been found as an efficient photocatalyst to produce hydroxyl (OH•) radicals under ultraviolet irradiation. The nanoparticulate photocatalyst has been observed to adsorb at the surface of the microbe and perforate the cell envelop through redox reaction leading not only to complete disintegration/mineralization of the cell. There exists an optimum catalyst loading while the inactivation rate increases with intensity of the incident light. For enhancement of the microbial inactivation efficiency under solar light, the photocatalyst has been modified in different ways which include doping and coupling with other materials, dye sensitization, and application of voltage. Suspended particles and ions have been observed to suppress the photocatalytic inactivation rate. Furthermore, water under the photocatalytic treatment has been seen to change spontaneously from basic into acidic, while, decreasing pH of suspension from 7 to 4 during the course of photocatalytic treatment increases the inactivation rate. The photocatalytic microbial inactivation has been seen to follow Langmuir-Hinshelwood kinetic model.
Springer Berlin/Heidelberg, 2012. Vol. 2, 511-541 p.