Scale-up dynamics for the photocatalytic treatment of textile effluent

Abstract

Enhancing the efficiency of large scale photocatalytic systems has been a concern for decades. Engineering design and modelling for the successful application of laboratory-scale techniques to large scale is obligatory. Among the many fields of research in heterogeneous photocatalysis, photocatalytic reaction engineering can initiate improvement and application of conservative equations for the design and scale-up of photocatalytic reactors. Various reactor configurations were considered, and the geometry of choice was the annular shape. Theory supports the view that annular geometry, in the presence of constant transport flow properties, monochromatic light, and an incompressible flow, will allow a system to respect the law of conservation of mass. The degradation of a simulated dye, methyl orange (MO), by titanium dioxide (TiO2) with a simulated solar light (halogen lamp) in a continuous recirculating batch photoreactor (CRBPR) was studied. A response surface methodology (RSM) based on central composite design (CCD) was applied to study interaction terms and individual terms and the role they play in the photocatalytic degradation of MO. The studied terms were volume (L), TiO2 (g), 2 (mL), and initial dye concentration (mg/L), to optimize these parameters and to obtain their mutual interaction during a photocatalytic process, a 24 full-factorial CCD and RSM with an alpha set to 1.5 were employed. The polynomial models obtained for the chosen responses (% degradation and reaction rate constant, k) were shown to have a good externally studentized vs normal percentage probability fit with R2 values of 0.69 and 0.77 respectively. The two responses had a common significant interaction term which was the H2O2 initial dye concentration term. The optimum degradation that was obtained in this study was a volume of 20 L, TiO2 of 10 g, H2O2 of 200 mL and the initial dye concentration of 5 mg/L which yielded 64.6% and a reaction rate constant of 0.0020 min-1. The model of percentage degradation was validated on a yield of 50% and 80% over a series of set volumes and the model validation was successful.