Simulation of FBR-Fenton/GAC process for recalcitrant industrial wastewater treatment with a computational fluid dynamics-kinetic model framework

Abstract

An integrated computational fluid dynamics (CFD)-kinetic model framework was developed to numerically describe the hydrodynamic and kinetic phenomena in a liquid-solid two phases Fluidized-bed reactor Fenton/granular activated carbon (FBR-Fenton/GAC) system. The model obtained excellent accuracy for predicting chemical oxygen demand (COD) removal in reverse osmosis concentrate (ROC) treatment under different operation conditions. Hydrodynamic evaluation demonstrated that under the quasi-steady state, the GAC particles were uniformly circulated in the bed region with two pairs of counter-rotating recirculation cells, and a clear interface layer formed between the solid and the liquid phases. Superficial liquid velocity highly affected the fluidized bed expansion and solid volume fraction, while its impact on the overall COD removal efficiency was negligible. Chemical evaluation revealed that GAC/H2O2 catalytic reaction enhanced the •OH production in FBR-Fenton/GAC process by 2.7 folds as compared to homogenous Fenton process. Fenton reaction mainly occurred in the upper liquid region and its kinetics for •OH generation significantly diminished by 75% within the first 10 min. GAC/H2O2 reaction took place in the fluidized bed region for continuous •OH generation with a relatively stable rate from 1.21 × 10−6 to 0.60 × 10−6 M/s. Along the ROC treatment with FBR-Fenton/GAC process, the simulated COD degradation rate decreased along the reaction time with 2.05 × 10−6 M/s and 2.93 × 10−7 M/s at 2 min and 60 min, respectively. Faster COD removal was attained in the fluidized bed region due to combining effects of •OH oxidation and GAC adsorption. The overall predicted COD concentration reduced from 122 to 35 mg/L, •OH oxidation and GAC adsorption contributed 59% and 41%, respectively, to the total COD removal.