| Summary: | Slow Sand Filters are as a proper technology for pre-treatment of raw water, with a fine and medium trubidity in small communities in developing countries. Thus, with a minimum operation cost and minimum need for expest bodies have the maximum efficiency. The purpose of this research is carried out to evaluate the efficiency of two processes of horizontal flow roughing filter and vertical flow roughing filter, in order to remove the trubidity and parasite egg from water. For this purpose, two series of pilots are used, each pilot has 3 sections, which consists of granular particles of 4-25 mm. First section of each filter is filed with the granuls of 12-18 mm in diameters. Second section of each filter also contains with sand of 8-12 mm in diameters and the third section of each filter also contains with the sand of 4-8 mm in diameters. The head sections 1, 2 and 3 were 1 meter in down flow roughing filter, respectively. Samples of turbid water, which were made artificially (silty soil + water) and sample waters with different turbidities were injected into two systems and since on of the other goals of research was to study the efficiency of these filters, in removal of parasitic egg from water, therefore from the total concentrates which were prepared from parasitic eggs; such as:Ascaris, Fasicola hepatica and Trichosephal and water was added to them. These samples were finally passed through filters. The outcomes of the study, indicate that accelerating the filteration process, leads to declined efficiency of both filters. Horizontal flow roughing filters also have a higher efficiency compared with medium and fine media filters, in removing trubidities, in such manner that these filters are able to treat and refine waters with turbidities of 500-1000 NTU which vertical flow roughing filters, are only able to receive waters with turbidities up to 150 NTU.
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