Accumulation of inert organic solids within biofilm in a methanogenic fluidized bed was investigated by conducting a continuous feed experiment in which the influent substrate concentration was stepwise increased. The previously developed model considering accumulation of inert organic solids and biomass detachment was applied to the simulations of biofilm growth and treatment efficiency in the above-mentioned experiment.
The transient response of treatment were well explained with the model by giving the growth kinetic constants and the detachment coefficients of the responsible “active biomass”, whose concentrations were defined with the substrate consumption activities. The biofilm growth was deeply associated with the accumulation of inert organic solids, the rate of which depended on the decay coefficient and the growth yields of “active biomass” as well as the detachment coefficient. The detachment coefficient was estimated to be much smaller for decayed biomass than “active biomass” and bio-polymer. The attached biomass in the methanogenic fluidized bed contained a significant amount of bio-polymers which reached around 8 to 10% of total organic solids of biofilm. The production rate coefficient was estimated at 0.4 to 0.5 [mgCOD_Poly·mgCOD_cell^-1] with the assumed growth yield of 0.05 [mgCOD_cell·mgCOD^-1].