Modeling of organic shock loading in a fluidized-bed bioreactor containing sorbent particles
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 (R-2 = 0.9810). The best-fitting parameters obtained were mu(M) = 0.166 +/- 0.007 d(-1), K-S = 8.62 +/- 0.46 mg/L, and K-I = 95.3 +/- 3.8 mg/L.