AWWA ACE95077

The objectives of this study were to assess the biomass growth and distribution in a biofilter, modify the homgeneous biofiltration model to a more representative heterogenous biofiltration model and validate the heterogeneous model by comparing the model predictions with experimental results. Monod-type kinetics were used to model the utilization of the quickly-biodegradable NOM, and first-order kinetics were used to model the utilization rate of the slowly-biodegradable NOM. The model assumes that the utilization rate of each NOM fraction varied with filter depth due to the distribution of biomass. Biomass growth and distribution in the biofilters at different organic carbon loading rates, i.e. different filter velocities and similar DOC concentrations, was evaluated. The results showed that the biomass growth rate was high at the top of the biofilters and decreased as the filter depth increased. Also, the growth rate was higher at a higher organic carbon loading rate at the same filter depth, suggesting that the amount of NOM was the limiting factor for biomass growth in this study. Additionally, the results showed that most of the biomass growth occurred in the first few minutes of empty bed contact time (EBCT), indicating a relationship between the utilization of the quickly-biodegradable NOM and biomass growth. After the biomass distribution profile was fully developed, most of the biomass was distributed at the top of the biofilters. The results showed that the biomass distribution was independent of filter velocity, but was a function of EBCT for a given influent water quality.