Background: Application of some materials, in order to increase raw water turbidity and to enhance the efficiency of coagulation process is usual. SFBW recycling due to its relatively high volume (4% of total water production) is usual too. In the USA usually in about 30% of water treatment plants SFBW is recycled directly to the inlet of treatment plant line. This study was achieved in order to determine the influence of SFBW recycling on coagulants reduction in Jalalieh water treatment plant.

Materials and Methods: In this study the samples were taken from raw water and filter wash water effluent. At the first step, the parameters of pH, turbidity, TDS, EC and temperature were examined for both raw water and SFBW. Then the optimum coagulant dosages for raw were determined by Jar test. The optimum coagulant dosages for raw water and the mixture of 4% SFBW and raw water were determined at the next stage. Finally the data was analyzed by SPSS software.

Results: The results of this study showed that the mean values of pH for raw water and SFBW were 8.1 and 7.73 respectively. The mean values of raw water and SFBW turbidity were 7.7 and 237 NTU respectively. The mean values of EC for these two conditions were 253.2 and 240.7 μs/cm respectively.

Conclusion: Although it was observed that by recycling 4% of filter wash water there was a 0.72 mg/l reduction in ferric chloride, but the difference was not statistically significant in the range of analyzed turbidity (3.77 25 NTU…)