Modeling of organic shock loading in a fluidized-bed bioreactor containing sorbent particles

Abstract

This work explores the behavior of a fluidized-bed bioreactor, packed with a hydrogel carrier of cyclodextrin-based polymer, under transient shock-loading events to evaluate its robustness and stability. Fourteen input rectangular pulses with different steps (6–24 times the baseline concentration) and duration (0.5–8 times the hydraulic residence time) were applied and the dynamic responses measured. A new shock-loading index is defined to quantify the combined effect of the influent concentration increase and the perturbation duration. The shock-loading index is directly proportional to the extra amount of phenol removed, to the additional oxygen consumed in the shock pulse, and to the time to return to baseline conditions. A simple model was developed to predict the effluent phenol concentration under pulsed shock-loading events. It assumes that a continuous-flow complete-mix system without diffusional mass transfer resistance in the biofilm. In addition, substrate adsorption is modeled using a simple concept based on the constant-pattern theory, while substrate biodegradation is described by the Haldane model. In spite of its conceptual simplicity, the model provides a pragmatic approach predicting a good match for data obtained during overload events (R2 = 0.9810). The best-fitting parameters obtained were μM = 0.166 ± 0.007 d–1, KS = 8.62 ± 0.46 mg/L, and KI = 95.3 ± 3.8 mg/L.