Background & Objectives: Rapid sand filter backwashing water typically consists of 2-5% of the total treated water and it has high turbidity. Therefore, effluent treatment of rapid sand filter backwashing is essential. This research aimed to survey turbidity removal from filtration effluent of Tehranpars water treatment plant using Electrocoagulation (EC)/Electroflotation (EF) process.

Methods: This practical study was done in a continuous system at laboratory scale. An electrocoagulation tank with the dimensions of 24×17×18 cm and volume of 7.35 l from plexiglass was used in this work. Inside the tank 4 Al or Fe plates (15×22×0.1cm) were used as cathode and anode. Each electrode was immersed up to 16 cm in effluent of electrocoagulation tank. 126 samples with turbidities of 320, 350, and 400 NTU were taken from effluent of rapid sand filter backwashing and the removal efficiency was tested at current densities of 4.16, 5.83, 7.5, 10, 11.66, and 13.33 mA cm^-2 in detention times ranging from10 to 30 min. The space of electrodes is fixed at 1.5cm and pH at 8.2.  Data analyzed by excel software.

Results: The optimum pH of 8.2 was determined for this process. The optimum current density and detention time for both electrodes were the same and equal to 13.33 mA cm^-2 and 30 min, respectively. At optimum conditions the respective highest turbidity removal by Al and Fe electrodes were 95.13 and 4.87%.

Conclusion: Regarding the results, using electro coagulation-electro floatation processes has an appropriate efficiency in turbidity removal. One can say that aluminum electrode has higher efficiency than iron electrode to remove turbidity.