The Egyptian Int. J. of Eng. Sci. And Technology, Vol.12, No. 1 (Jan. 2009) EIJEST INCREASE OF SELF-PURIFICATION EFFICIENCY OF WATER STREAMS USING ROTATING BIOLOGICAL CONTACTORS (RBC) Diaa S. El Monayerie*, Nabil N. Atta*, Amro. A. El Baz* and Sami A. I. Dif**(1) * Environmental Engineering Department, Faculty of Engineering, Zagazig University, Egypt ** National Authority for Potable Water and Sanitary Drainage ABSTRACT Self-purification of water streams has an important role in enhancing drain water quality. This study proposes external intervention to enhance the self-purification process. Two concrete channels were constructed on the berm of a polluted stream to investigate the effect of using rotating biological contactor (RBC) discs on the self purification efficiency of the stream. This RBC freely rotates under the effect of hydraulic discharge of water in the two channels. Changing flow rates, spacing between stages of RBC and the number of stages along the channels were considered to study their effect on the removal efficiency of chemical oxygen demand (COD), dissolved oxygen and ammonia. Experimental results indicated that, under various flow rates (20, 25, 30, 35 and 40 l/s) the highest percentage of COD was removed at a discharge value of 30 l/s. The removal efficiency of COD using this flow ranged from (39.5 – 44.35%) compared to (6.3 – 16.5) in the reference channel, with an enhancement ratio of about, 626 – 268%. Moreover the dissolved oxygen level (DO) increased from 2.1 to 3.5 mg/l compared to 2.1 mg/l in the reference channel with an enhancement ratio of about 167% and Ammonia concentration decreased from12.5 – 13.7 mg/l to 10.35 – 9.46 mg/l, compared to relatively constant for the reference channel. KEY WORDS: Aeration, Ammonia, Biofilm, COD removal, Dissolved Oxygen, Drain's water, Organic Mater, Rotating Biological Contactors (RBC), Self-Purification.