A lab-scale three-stage RBC was fabricated with a thick acrylic plastic transparent sheet. The schematic experimental setup is shown in Fig. 1. The RBC had total volume of 96 l and working volume of 60 l. The dimensions of the RBC reactor were 80 cm long, 40 cm width and 30 cm depth, which consisted of three stages. Each stage was separated by fixed baffle plates with 18 discs in each compartment. Lightweight clear plastic discs with 35 cm diameter were mounted on a galvanized hollow metal shaft (o.d. 2 cm) and interspacing of 7 mm. The available surface area for biofilm growth was about 10 m2. The shaft passes through the center of each disc and was mounted on bearing attached to each end of the wastewater container. The disc spacing along the length of the shaft was minimized while maintaining enough space for wastewater to circulate between discs. The shaft and attached discs were rotated by a variable speed drive motor. Flow through discs was parallel to the shaft. The substrate feed rate was controlled by a variable speed peristaltic pump.The variables in the rotating biological contactors were hydraulic retention time, disc submergence level in the wastewater, rotational speeds, pH control, supplementary nutrients and volumetric flow rate of the wastewater. The influent was taken at volumetric flow rate of 30, 36, 45 and 60 l/day. The samples were taken for analysis for each volumetric flow rate after two times of corresponding retention time, based on steady state assumption.