Hydraulics of bench-scale rotating biological contactor

Abstract

The hydraulic characteristics of a four-stage bench-scale rotating biological contactor (RBC) were studied using its three major operating parameters: (i) liquid flow rate, (ii) rotational speed of disc and (iii) degree of submergence. The liquid flow rate and the degree of submergence have been combined to obtain the dimensionless parameter Reynolds number ( Re), whereas the liquid flow rate and the rotational speed have been grouped together, leading to another dimensionless parameter, Modified Froude number ( Fr). Moreover, the different stages of RBC have been expressed in terms of dimensionless length ( L R ). The overall dispersion number ( d = D UL , where D is the dispersion coefficient, U is the velocity of liquid and L is the length of liquid flow path) of the flow regime in the RBC has been formulated by a hydraulic model based on multiple linear regression analysis through a package of 96 observations on tracer response data in the RBC operating at flow rates of 0.04–21.90 m 3/day, rotational speeds of 1–15 rpm and degrees of submergence of 32–60%, resulting in Re values in the range of 51–2500 and Fr values in the range of 5.61 × 10 −6 to 1.26 × 10 −3. The overall value of d has reduced significantly, by 76%, from the first stage (2.48) to the fourth and final stage (0.60). It increased with the increase of Re and Fr values. The range (0.048-8.24) of the observed values of d shows insignificant deviation from the corresponding values predicted by the following proposed hydraulic model for a multi-stage RBC reactor. The model with a multiple correlation coefficient value of 95% is d p = D UL = 0.32(Fr) 0.57(Re) 0.75 (L R 1.1