The rotating biological contactor process offers the specific advantages of a biofilm system in treatment of wastewater for removal of soluble organic substances. It is a unique adaptation of the moving-medium biofilm system which facilitates easy and effective oxygen transfer. Two steel channels were constructed on the concrete sump of primary treated wastewater in El-Asloagy WWTP with self-rotating discs in order to investigate the performance of self-rotating discs in wastewater treatment. These discs were freely rotate under the effect of hydraulic discharge of water in the channel without any mechanical power. The effect of flow rates and number of stages of self-rotating discs with the variation of organic loads were assessed, COD removal ratio and DO were assessments tools. Self-rotating disc 230 mm in diameter and five numbers of discs per stage applied in the present study with 35% of disc submergence, with UPVC as a structural disc’s material. Flow rates ranged (5.5, 6.35, 7.23 and 8.16 l/s) were studied. The highest percentage of COD removal ratio achieved at discharge 8.16 l/s. different number of stages were studied in addition to a front disc at the dropping point of the channel weir. Highest value of COD removal ratio achieved (54.44%) at five stages. Results indicated that, COD removal rate increased from 28.22 to 43.2 kg /m2.d when COD loading rate increased from 51.85 to 259.25 kg/m2.d, while COD removal ratio decreased from 54,44% to 16.66 % at the same COD loading rate. Moreover, the dissolved oxygen level (DO) increased from (zero, 0.9 mg/l) to (1.5, 2.0 mg/l) respectively. The determination of the number of stages necessary to accomplish a required degree of treatment, as well as determining the effect of each stage on the total treatment scheme, however, requires a stage-by-stage analysis of the RBC. Experimental results of the present study were used for adaptation of RBC mathematical model. Kinetic coefficients constant was estimated. The determinations of the amount of substrate removed per day per unit surface area of each disc which referred to the area capacity constant (P) and the amount of substrate removed per unit surface area of each disc which defined as the removal coefficient (R) were made.