Biotreatment of contaminants in air streams offers an inexpensive alternative to conventional technologies such as catalytic and thermal oxidations, wet scrubbing, ozonation, and activated carbon adsorptionIn general, bioprocesses for air pollution control can be categorized into biofiltration and biotrickling systems. A biofiltration system mainly consists of a reactor packed with solid material such as compost, peat, or wood chips on which a biolayer containing a proper microbial population is formed. When a contaminated air stream passes through the reactor, the pollutants in the stream are adsorbed by the biolayer and then biodegraded by the microorganisms in the biolayer to simple molecules such as water and carbon dioxide. In a biofiltration process, the packed solid media provide the nutrient source, pH buffer, and matrix for the attachmentof microorganisms. Once the buffering capacity or nutrient source is exhausted, the packing material can be restored by adding base or nutrient salts in the irrigation water, or itcan be replaced.