عنوان مقاله [English]
Horizontal roughing filters (HRF) can properly remove suspended solids and microorganisms from surface waters if they operate at filtration rates below 1.5 m/h. These filters are common raw water pre-treatment before slow sand filters. This study was conducted by installing an HRF pilot system on effluent pumping station city of Qom wastewater treatment plant based on the aerated lagoon process. The pilot was a horizontal cylindrical column consisting of three compartments filled with river gravel of various sizes. Grab samples were simultaneously taken from inlet and outlet of the HRF at three filtration rates: 0.5, 1, and 1.5 m/h. Total and fecal coliforms were tested according to standard methods for water and wastewater tests. Results indicated that filtration rate had a significant effect on the amounts of total and fecal coliforms in HRF effluent. For the HRF steady-state operation, average total coliform removal efficiency for all filtration rates was higher than 87 percent.