MINIMIZATION OF MULTISTAGE RBC ACTIVE DISC AREA

An analytical approach to the minimization of total active disc area (A(T)), 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.