Simple prediction of oxygen penetration depth in biofilms for wastewater treatment

The distribution of oxygen in a biofilm is very important in oxidation processes such as simultaneous carbon oxidization and nitrification using a fluidized bed biofilm reactor. In this study, attention was paid to biofilm thickness and biofilm density which significantly affect the oxygen distribution in biofilms. Using an oxygen microelectrode that we fabricated, the oxygen distribution in biofilms of different thicknesses was measured, and subsequently oxygen penetration depth and ratio were determined. As a result, oxygen penetration ratio decreased gradually with increasing biofilm thickness. Moreover, the kinetic parameters of a Monod-type reaction and the effective diffusion coefficient were computed based on the oxygen distribution in the biofilms. Using the obtained biofilm dry density, kinetic parameters and effective diffusion coefficient, the oxygen distribution in biofilms was successfully fitted to the results of a microelectrode analysis. The oxygen distribution was simulated by the finite difference method using the kinetic parameters and effective diffusion coefficient. Therefore, oxygen penetration ratio can be predicted at various biofilm thicknesses and oxygen concentrations in a bulk solution.