Performance of a Three- Stage Aerobic Rbc Reactor in Dairy Waste Water Treatment

Biological treatment using attached growth in a threestage labscale rotating biological contactor (RBC) was implemented for wastewater from dairy industries. The wastewater contained high level of organic compounds due to cleaning and filling processes. Nutrients available in the wastewater enhanced the growth of microorganisms and allowed the biological treatment to be effective. The RBC consisted of 54 parallel discs rotating in reservoir and was arranged in three stages, i.e. 18 discs oriented in each stage. Effect of major operating physical variables such as hydraulic retention time (HRT), disc submergence and disc rotational speed were examined in COD removal. For duration of 5 days 96.4% BOD removal was achieved in batch experiment. BOD constant rate (k) and ultimate BOD were determined respectively, 0.8198 day-1 and 6349 mg/1 by Thomas graphical method. COD removal efficiency was increased from 85.3 to 97.4% while the HRT was increased from 8 to 32 h. The COD removal efficiency increased from 74.9 to 87.5% as the disc submergence was increased due to activation of second and third compartments. When the rotational speed was increased from 6 to 12 rpm, the COD removal efficiency was also increased from 62.7 to 93.7%.respectively. The stage COD removal efficiency was gradually decreased with an increase number of stage and about 88% of organic compounds were removed in the first stage of aerobic RBC, indicating that the single reactor may be sufficient in practical application.