The Mathematical Modeling of Biofilter Performance in Hydrogen Sulfide Removal from AirStreams

Biofiltration is one of the most effective methods for pollutant removal from a gas stream. An accurate mathematical model to predict removal efficiency can be applied in design and optimization of such equipment and also in investigating biofiltration process.The objective of this study was to develop a mathematical model for predicting biofiltration process performance in hydrogen sulfide removal from a gas stream and also examining the influence of several main parameters such as biofilm diffusivity and biofilm thickness on the predicted results. In order to achieve the goals, the governing equations expressing mass conservation for a differential control volume in both gas and biofilm phases were solved. Hydrogen sulfide concentration distributions in gas and biofilm phases were determined by solving these equations. The presented model is capable of predicting the variation of biofilm thickness through time due to bacteria growth and biofilm surface abrasion. The results from the expanded mathematical model were well in agreement with empirical data. The results revealed that hydrogen sulfide removal efficiency increases by increments in packing specific surface area and biofilm diffusivity along with decreasing entering gas velocity. In addition, the results of the model showed that increasing biofilm thickness tends to raise the removal efficiency for biofilm thickness of less than 5 micrometer. This fact reveals that the reaction rate is the rate-controlling step for lower biofilm thickness and the biofilm-diffusion resistance does not affect mass transfer rate significantly. However, further increasing biofilm thickness (to more than 20 micrometers) causes hydrogen sulfide removal efficiency to decrease. It can be attributed to magnifying the influence of biofilm diffusion on mass transfer rate.