Minimization of Multistage RBC Active Disc Area

An analytical approach to the minimization of total active disc area $\left(A_T\right)$, required for organic carbon removal [i.e., biochemical oxygen demand (BOD)] by a multistage rotating biological contactor (RBC), is presented. RBC operation is simulated using semiempirical models based on a saturation‐type (Monod) removal rate, and on a first‐order kinetics removal rate. The parameters used in the predictive equations are considered to be different from one RBC stage to the next. The minimizations of $A_T$, based in turn on each of the two semiempirical models, lead to a relationship between the optimal soluble substrate concentration of any stage and those of the immediately preceding and succeeding stages. When used in design, these relationships allow the minimum $A_T$, as well as the optimal number of stages required for carbon removal, to be obtained. For the saturation model, two parametric ratios (${\Phi }_P$ and ${\Phi }_{K_S}$) are introduced, which define the change in the model parameters with stage. Application of the relationships to the determination of the optimal number of stages and the minimum $A_T$ is included.