Rotating biological contactors (RBC) have been employed for treating municipal wastewaters within the United States since 1970. The RBC process lends itself to kinetic interpretation because of the sequential stages employed in the operation. This mode of operation enables the substrate concentration to be determined after various time intervals to obtain kinetic data for interpretation. An analysis was conducted on previously published data, which contained the concentration of soluble chemical oxygen demand (COD) at various stages in the treatment train. The time intervals were calculated based on the hydraulic loading rate and the liquid volume in each stage. The data was incorporated into a number of rate equations and a second order reaction rate equation gave a good correlation for the published data. This technique was repeated with other published data on the disappearance of sCOD at different stages in the treatment train and again the data obeyed a second order rate equation. A project was initiated to obtain interstage data on soluble COD at three RBC facilities within a 100-mile radius of Cincinnati. The results again gave a strong correlation that RBC obey a second order reaction rate equation. The analytical results from nine RBC plants were compared with the predicted interstage data determined by using a second order rate equation. The results showed that second order kinetics was able to predict interstage soluble organic data at eight of the nine plants.