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Background & Aims of the Study: Spent filter backwash water (SFBW) consists of 1-5% of the total treated water typically and it has a high turbidity. Because of the scarcity of water resources and in order to prevent the environmental contamination, effluent treatment of rapid sand filter backwashing is unavoidable. One of the new technologies for removal of turbidity from the effluent is ElectroCoagulation (EC) processes. This study aimed to examine the efficiency of continuous electrocoagulation in turbidity removal from spent filter backwash water.

Materials & Methods: This study was non-continuous experiment. A rectangular cube electrocoagulation tank in 24 cm×17 cm×18 cm dimensions from Plexiglas with the volume of 7.35 liter was made. In this tank there were 4 metal plates (electrode) (15× 22× 0.1cm); two electrodes as cathode and anode which were made of aluminum and iron, respectively. All of the tests were done in continuous flow. According to the study criteria (Time, Turbidity and pH), 126 sample got with the turbidity 320, 350, 400 NTU from rapid sand filter backwashing water, so they were tested in current density; 1, 1.4, 1.8, 2, 2.4, 2.8 and 3.2 ampere in 3 selected detention times (10, 20 and 30 min). Each experiment was repeated two times. In this research the space of electrode and pH is fixed at 1.5 cm and 8.2.

Results: In this case the highest turbidity removal for Al electrode from rapid sand filter backwashing occurred in the current density 3.2 ampere, 30 min detention time and 320 NTU turbidity. The percent of removal for Al was 95.12. The highest removal for Fe electrode from rapid sand filter backwashing occur in the current density 3.2 ampere, 30 min detention time and 320 NTU turbidity. The percent of removal for Fe was 87.40.