THE EFFECTS OF BIOFILM THICKNESS ON BIOFILM DENSITY AND SUBSTRATE CONSUMPTION RATE IN A DIFFERENTIAL FLUIDIZED-BED BIOFILM REACTOR (DFBBR)

In this study, a differential fluidized bed biofilm reactor (DFBBR-gra dientless reactor) was used to develop a biofilm of Zoogloea ramigera (NRRL 3691) on spherical activated carbon support particles. The biofi lm thickness and density and substrate consumption rates were measured and evaluated under pseudo-steady state conditions in the reactor. Ac tive biofilm thickness was estimated using a 'diffusion and reaction' model with the biofilm density depending on simultaneous effective dif fusion coefficients. The results showed that the consumption rate for each substrate increased parabolically with biofilm thickness due to t he increased amount of biomass. Meanwhile, the consumption rate increa sed with enhanced biofilm density up to a critical value, similar to 7 8 g dm(-3), and then started to decrease due to the dominating effect of diffusion. During biofilm growth, biofilm density first increased u p to a critical thickness, similar to 90 mu m, then declined slowly en abling better substrate transport to the inner regions. These experime ntal conditions facilitated homogeneous substrate concentrations and b iofilm properties for the assessment of biofilm performance which have never been experienced in literature before.