Residence time distribution studies and modeling of rotating biological contactor reactor for decolorization of congo red from synthetic dye wastewater

A continuous study in a rotating biological contactor (RBC) reactor was carried out using polyurethane foam (PU) surface-immobilized live fungal biomass of Neurospora crassa with wheat bran adsorbent/substrate for the removal of Congo red (CR) color from aqueous solutions. Residence time distribution studies were conducted at various flow rates of water (1–6.5 mL min^–1) using pulse input of tracer to explore the performance of mixing and type of flow behavior inside the reactor. It was found that the value of dispersion number at various flow rates of water such as 1, 3, and 6.5 mL min^–1 was 4.36, 7.89, and 13.65, respectively, which indicates that the RBC reactor can be modeled as a mixed flow reactor. A model for a single stage RBC reactor for the decolorization of CR from synthetic dye wastewater has been developed using the principles of conservation of mass. Using the developed mathematical model and experimental data, the model parameters such as maximum specific growth rate of the attached active biomass (μ_max ), Monod kinetic constant (K_s ), rate constant for pseudo-second-order biosorption (K₂ ), and effluent dye concentration at equilibrium (S_e ) were estimated. The system of non-linear first-order ordinary differential mass balance equation was solved by the fourth-order Runge–Kutta method and the model parameters were evaluated using the Solver tool in Excel. The predicted and experimental values of effluent dye concentrations are then compared. The predicted values of effluent concentrations found from the theoretical model developed fitted well to the experimental data, suggests that the proposed model is valid for CR dye decolorization. The results reveal that the live fungal biomass of N. crassa with wheat bran is a suitable dual adsorbent for decolorization of CR from synthetic effluents using RBC reactor and it can be used effectively in wastewater treatment.