Solar disinfection of water by photocatalytic processes : physico-chemical and biological aspects

Chlorine, widely used as a disinfectant for drinking water production, is known to interact with organic matter to yield disinfection by-products (DBPs). Some of these compounds, as the trihalomethanes, are highly toxic for human health. Alternative disinfection methods are thus currently being developed, especially in industrialized and wealthy countries. Methods such as ozone and ultraviolet light are equally effective and less toxic. However, these techniques are expensive and often technically difficult to apply in less favorable conditions. In this context, solar disinfection could become promising to potabilize waters in developing countries with high availability of solar irradiation. The main objective of this research is to evaluate the solar photocatalytic treatment of water as: a) an alternative to bacterial inactivation by chlorination; b) a complement by assessing the influence of the process on the disinfection by-products precursors (DBPPs). In the proposed system a physical, chemical or biological technology can be used as pretreatment, preceding the solar photocatalytic. This thesis is organized in 6 chapters in which the link is the solar treatment applied to disinfect and decontaminate water. In the first chapter a review of the disinfection of water by solar and photocatalytic treatments is presented. Particular enfaces is made on the mode of action of TiO2 upon bacteria. Chapter 2 focuses on the study of physico-chemical and catalytical aspects of water disinfection by photocatalysis. Physico-chemical parameters related either to the operative system or the intrinsic properties or phototreated water influences the processes. The increase of some parameters such as light intensity, extend of continuous irradiation and catalyst concentration has a positive effect on disinfection. TiO2 immobilized on Nafion membranes inactivates E. coli K12 with efficiencies close to those observed for bacterial suspension containing the same concentration of suspended TiO2. TiO2 immobilized on glass flask, showed lower effectiveness than suspended catalyst. Chapter 3 focuses on the influence of biological aspects on the effectiveness of photocatalytic disinfection. To illustrate these aspects, synthetic and real waters were used as a model of study. In the first case, deionized water was contaminated by E. coli; in the second case, wastewater was taken at the outlet of a biological treatment plant located in Switzerland. The influence of initial bacterial concentration, physiological state of bacteria, and bacterial transfert in the culture are presented using pure culture of E. coli. The response of different Gram (+) and Gram (-) bacteria such as Enterococcus sp, and Fecal coliform, present in the effluents of urban treatment plants is discussed. The behavior of the bacterial suspension during the subsequent dark period was extensively discussed in order to estimate the potential of using the photocatalytic treatment process in a real water d