Mathematical Modeling for Gas Removal in a Fixed-film Bio-scrubber Process

Abstract

Bio-scrubbers include fixed-film or suspended microorganisms and can be used to remove gas and liquid contaminants. They often require reliable modeling due to their highly complex mechanisms. However, only a few studies have conducted mathematical modeling for bio-scrubbing processes, particularly, gas treatment using fixed-film microorganisms in bio-scrubbers. This study applied a simple mathematical model to predicting the removal efficiencies of ammonia, formaldehyde, toluene, butanol, acetone, and ethylene gases. The model presumed a steady-state condition and combined various physicochemical and microbial factors to obtain a series of closed-form solutions from equations. In the model, the gaseous compounds were absorbed into liquid phase and degraded by fixed-film microbes attached to the scrubber media. As a result, removals of strongly hydrophilic or hydrophobic gases were relatively invariant along the media depth. The gas and water flow rates highly affected scrubber performances for the gaseous compounds with moderate or low water solubility. In contrast, the removals of the highly soluble gaseous compounds, that is, formaldehyde and butanol, were not sensitive to variations in gas or water flow rates. Water flow at under 100 L/h produced limited wetting efficiencies (<20%) of the scrubber media (600 m2/m3). Henry constants and microbial parameters of maximum microbial degradation rates and half saturation coefficients had significant effects on gas removal, while media properties, such as specific surface areas and surface tensions, had less significant effects.