Analysis of immobilized cell responses to substrate impulses

The responses of immobilized cells cultivated in a steady-state continuous-flow, completely-mixed fluidized bed reactor (FBR) to a range of monoethylamine (MEA) impulses are evaluated. Responses due to bacterial activities and physical flows are separately estimated using mass balance calculations. The experimental data show that the impulse response, in terms of combined total organic carbon (TOC) utilization and nitrification, spreads over a time period that includes an initial lag phase without bacterial activities, followed by a biodegradation phase that can be MEA-inhibited. The pattern of TOC utilization responses is similar to that according to Andrews kinetics, and MEA inhibition is evident at the loadings >0.12 mg TOC/mg volatile solids (VSs). By comparison, nitrifying bacterial cells are more susceptible to MEA impulses than their heterotrophic counterparts, and nitrification activities are impeded at loadings as low as 0.03 mg TOC/mg VS. The ability of the FBR to retain high immobilized biomass inventories is pivotal to its recovery from MEA impulses, in spite of the low cell activities resulted from the cultivation conditions adopted.