Engineering Model for Fixed-Film Bioscrubbers

Abstract

The three basic types of biological treatment systems for the control of volatile organic compounds in air streams are the following: biofilters, in which microorganisms grow on a medium, such as soil, compost, peat, or mixtures of these materials with wood chips or polystyrene particles; suspended-growth bioscrubbers, in which microorganisms are suspended in a liquid; and fixed-film bioscrubbers, in which microorganisms are attached to a packing material. Design and application of biological treatment methods for air pollution control are difficult because only limited experimental data and few theoretical models are available. This paper utilizes an engineering simulation model of a fixed-film bioscrubber to investigate the applicability, removal efficiency, operational parameters, and design requirements for gaseous waste streams. Model results indicate that the removal efficiencies can be increased by increasing the column height, decreasing the superficial gas velocity or the superficial liquid velocity, or by treating the liquid prior to recirculation to the absorber. High removal efficiencies can be obtained for compounds with relatively low values of the Henry's Law coefficient with either cocurrent or countercurrent operation. However, as the Henry's Law coefficient increases, the removal efficiency decreases and high removal efficiencies can be obtained only with cocurrent flow. Cocurrent operation is usually more efficient because stripping does not occur at the top of the column.