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Abstract
a) ahmoudia canal, the source of water to water purification plants in Alexandria Govemorate, is exposed to contamination by agricultural as well as industrial wastes. In Alexandria, there are six water purification plants were installed. One of these plants is EI-Manshia water purification plant. The average daily production of treated water is approximately 500,000 m3/day. The water purification. process consists of coagulation using alum, flocculation, sedimentation and filtration followed by disinfection using chlorine. Also chlorine is applied to raw water before coagulation in EI-Manshia water purification plant, Le. prechlorination with the aim of improving the water purification process. However, prechlorination were reported to result in the production of disinfectant by-products such as trihalomethanes which are accused of being carcinogenic. There are three types of rapid sand filters exist in EI-Manshia water purification plant. These filters are Italba, Degremont and Czech filters. . The present study was performed in EI-Manshia water purification plant form March 2003 to December 2004, aimed to improve the quality and increase productivity of the existing water purification. This study was accomplished by using a survey of the design parameters of the existing rapid sand filters and the filtered water quality and a pilot filter was designed with Granular Activated Carbon (GAC)-Sand as a filter media. This study aimed to: . Determine the effect of using GAC with Sand as a dual filtering media with different ratio to improve water quality and choose the optimum GAC depth that should be used. . Compare the performance of GAC-Sand dual media filter as a model with that of existing conventional rapid sand filter for improving the water quality. . Investigate the feasibility economic and cost effectiveness of adding GAC to the existing filter unit. . Design a numerical plant model to simulate multi media for purification plant. The present study was carried to evaluate the performance of GAC-Sand dual media filter. For each filter run the following parameters were measured and recorded: filtered water turbidity, head loss, filtration rate and filter run time. To compare the effectiveness of filtered water for GAC-Sand dual media filter with that of existing rapid sand filter, it was necessary to determine parameters for evaluating filtered water quality. Samples of influent and effluent water for both pilot filter and field filter were collected during each filter run. These samples were analyzed for turbidity, residual chlorine, free ammonia, total trihalomethanes, bacteria and algae count. The data collected in the survey study showed that, the filtration rate of Czech filter of 6 mIh was the lowest filtration rate compared to Degremont and Italba filters, controlled by constant rate controller which was not working. Moreover, the Czech filter produced the lowest water quality compared to the other two filters. The Czech filter was chosen in this study in order to improve its water quality and quantity. , The results of the present study showed that the pilot filter, GAC-Sand dual media filter of depth: 30 cm GAC and 90 cm sand had the greatest effect on improving water quality and costs 0.04 piaster/m3 of filtered water. However, at filtration rate of 6 m/h, the optimum depth of GAC was 40 cm. The initial filtration rate of the pilot filte