The effects of biofilm thickness on biofilm density and substrate consumption rate in a differential fluidizied bed biofilm reactor (DFBBR)

Abstract

In this study, a differential fluidized bed biofilm reactor (DFBBR-gradientless reactor) was used to develop a biofilm of Zoogloea ramigera (NRRL 3691) on spherical activated carbon support particles. The biofilm thickness and density and substrate consumption rates were measured and evaluated under pseudo-steady state conditions in the reactor. Active biofilm thickness was estimated using a ‘diffusion and reaction’ model with the biofilm density depending on simultaneous effective diffusion coefficients. The results showed that the consumption rate for each substrate increased parabolically with biofilm thickness due to the increased amount of biomass. Meanwhile, the consumption rate increased with enhanced biofilm density up to a critical value, ~ 78 g dm −3, and then started to decrease due to the dominating effect of diffusion. During biofilm growth, biofilm density first increased up to a critical thickness, ~ 90 μm, then declined slowly enabling better substrate transport to the inner regions. These experimental conditions facilitated homogeneous substrate concentrations and biofilm properties for the assessment of biofilm performance which have never been experienced in literature before.