Abstract
Rotating drum biofilters (RDBs) could effectively remove volatile organic compounds (VOCs) from waste gas streams. A mathematical model was developed on the basis of mass transport and mass balance equations in an RDB, the two-film theory, and the Monod kinetics. This model took account of mass transfer and biodegradation of VOC in the gas-water-biofilm three-phase system in the biofilter, and could simulate variations of VOC removal efficiency with a changing specific surface area and porosity of the media due to the increasing of biofilm thickness in the biofilter. Toluene was used as a model VOC. This model was further simplified by introducing a coefficient of the gas velocity and neglecting the water phase due to the complexity of operating conditions. The equations for the biofilm phase, gas phase, and biofilm accumulation in this model were solved using colloction method, analytic method, and the Runge-Kutta method separately. A computer program was written down as MATLAB to solve this model. Results of numerical solutions showed that toluene removal efficiency in the RDB increased and reached the maximum values of 97% on day 4 after the startup, and then decreased the remained at 90% after 5 more days of operation. Toluene concentration was high at the outermost layer where more than 70% toluene was removed, and was low at the innermost layer where less than 10% toluene was removed. The dynamic removal efficiencies from this model correlated reasonably well with experimental results for toluene removal in a multi-layered RDB.