ENGINEERING MODEL FOR FIXED-FILM BIOSCRUBBERS

The three basic types of biological treatment systems for the control of volatile organic compounds in air streams are the following: biofil ters, in which microorganisms grow on a medium, such as soil, compost, peat, or mixtures of these materials with wood chips or polystyrene p articles; suspended-growth bioscrubbers, in which microorganisms are s uspended in a liquid; and fixed-film bioscrubbers, in which microorgan isms are attached to a packing material. Design and application of bio logical treatment methods for air pollution control are difficult beca use only limited experimental data and few theoretical models are avai lable. 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 str eams. Model results indicate that the removal efficiencies can be incr eased 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 L aw coefficient with either cocurrent or countercurrent operation. Howe ver, as the Henry's Law coefficient increases, the removal efficiency decreases and high removal efficiencies can be obtained only with cocu rrent flow. Cocurrent operation is usually more efficient because stri pping does not occur at the top of the column.