Biomass accumulation and clogging in biotrickling filters for waste gas treatment. Evaluation of a dynamic model using dichloromethane as a model pollutant

A dynamic model is developed that describes the degradation of volatile aci difying pollutants in biotrickling filters (BTFs) for waste gas purificatio n. Dynamic modelling enables the engineer to predict the clogging rate of a filter bed and the time it takes the BTF to adapt to changes in its inlet concentration. The most important mechanisms that govern the behaviour of t he BTF are incorporated in the model. The time scale of the accumulation of biomass in a filter is investigated, and an approach is presented that can be used to estimate how long a BTF can be operated before its packing has to be cleaned. A three-month experiment was carried out to validate the mod el, using dichloromethane (DCM) as a model acidifying pollutant. Valuable e xperimental data about biomass accumulation and liquid hold-up in the react or were obtained with an experimental set-up that allows the continuous reg istration of the weight of the BTF. The results show that in BTFs eliminati ng DCM from a waste gas, clogging is not to be expected up to concentration s of several g/m(3). Model calculations based on the measurements also sugg est that the maximum carbon load that can safely be applied per unit void p acking volume should not exceed 0.5-1.6 C mol/(m(3) . h), depending on the density of the biofilm formed. The model is a good predictor of the elimina tion of the pollutant in the system, the axial gas and liquid concentration profiles, the axial biomass distribution, and the response of the system u pon a stepwise increase in the DCM inlet concentration. The influence of th e buffer concentrations in the liquid phase upon the performance of the BTF is investigated. (C) 1999 John Wiley & Sons, Inc.