الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
In recent decades, drinking water has been cleansed of bacteria using traditional methods. The most popular of these methods was disinfection of drinking water using chlorine gas, whether in its gaseous form or as a powder (hypochlorite). But after that, several studies have shown the drawback of using chlorine to disinfect water, especially if it contains high concentrations of organic materials. where the residual chlorine in the water interacts with the organic materials, forming compounds as often as cancerous, known as disinfection by products (DBP), the most famous of which is tri-halo methane. For this reason, it was necessary to find a better way to disinfect the water from bacteria and organic materials without any side effects that might later affect the lives of the consumers of that water. One of the most important of these methods is to disinfect the water by using photocatalysis, as it depends on exposing a semiconducting material (catalyst) to light with a wavelength that has more energy than the gap between the conduction and valence bands. This process subsequently creates strong oxidizing agents in the water that can oxidize bacteria and organic materials such as hydroxyl radicals. In comparison with previous studies, many researchers disinfected water by means of photocatalysis using a catalyst suspended in water. The results gave a high efficiency, but the shortcomings were summed up by the presence of a large amount of the catalyst in the water that leads with time to increase the turbidity, which disperses the light paths and reduces the space available for the reaction, as it is not possible to return the same dose of the catalyst for several different times, which increases the cost and reduces the catalyst efficiency over time. To avoid these defects, we have tried to install the catalyst on a medium in order to reduce turbidity as much as possible, as well as the possibility of using the catalyst more than once in a row. In this work, four different nano-scale photocatalysts (Titanium dioxide TiO2 - S-TiO2 - Tungsten oxide WO3- Ru/WO3/ZrO2 composite) were fixed on aluminum plates and employed to photocatalytic sterilization of real water samples Compiled from different intakes. Bacterial inactivation was evaluated using the spreading plate technique over plate count agar medium. Raw samples of water were compiled from three different intakes of water treatment plants in Kafr El-Sheikh governorate - Egypt. The results showed high efficiency in the inactivation rate of bacterial cells during an irradiation time of 240 minutes. The inactivation efficiency using TiO2 was about 100, 99, and 97.5% for Ebshan, Elkeshla and Fowwa raw waters respectively at the first cycle. The results of re-use of TiO2 showed a removal ratio between 94 to 100% for the three sources. While the inactivation efficiency using S-TiO2 was about 86, 96, and 99.7% for raw water sources respectively at the first cycle. The results for the following three cycles ranged between 86.7 to 99.5 % for the three sources. WO3 and Ru/WO3/ZrO2 composite reveals higher photocatalytic efficiency in terms of the survival rate of bacteria which be attributed to its lower bandgap. Catalysts were reused for four continuously cycles and the results proved high stability and a good prospect of reuse. We selected ruthenium (Ru) to improve the photocatalytic activity of a WO3/ZrO2 composite but it did not give tangible results. Bacterial concentrations in the raw waters ranged 30000-500000 CFU/100 mL (CFU: colony-forming units) and different species and genus were detected including gram-negative (e.g., shigella, salmonella, vibrio parahaemolyticus, and vibrio cholera) and gram-positive bacteria (e.g., enterococcus). The Ru-based catalyst deactivated over 90% of bacteria within 120 min for most sources of drinking water. The bacterial count after 240 min of irradiation was below the detection limit for all different water sources. The synthesized Ru/WO3/ZrO2 was stable in four continuous cycles (totally 960 min) suggesting reusability potential at the commercial scale most likely for photocatalytic disinfection of point-of-use systems.