Air emission controls using biotechnology is a new focus area for publicly owned treatment works (POTWs), especially now with many Federal, State, and Local air quality laws and regulations that often require significant air emission reductions for a new plant or collection system source to be permitted. CH2M HILL and others have collected biotechnology-based odor and air emissions control performance data over the last 4 years to track performance of various biofilters and biotowers as those technologies have evolved and emerged over time. Specifically, odor removal performance data have been collected from soil, organic, and inorganic media biofilters and inert inorganic media biotowers. Results indicate that biotechnology-based odor control is a viable and reliable technology capable of achieving high removal performance for hydrogen sulfide (H2S) as well as various other broad spectrum odor-causing compounds. While control of other air emissions such as overall volatile organic compounds (VOC) and hazardous air pollutants (HAP) is feasible, typically removal efficiencies of VOC and HAP are lower than those observed for typical odorous compounds such as H2S. In many cases, a biotechnology device is removing odors at very high levels while the same device has relatively lower removals of other air emissions. Properly designed biofilters evaluated during the testing showed high levels of removal for both H2S and overall odor if sufficient contact time is provided. Biotower systems tested also provide high removal rates for H2S at substantially reduced contact times compared to biofilters, but they show overall lower removal rates for other odor-causing compounds. Some lessons learned and rule of thumbs on the differences among types of biofiltration units, is also provided. (c) 2005 Elsevier B.V. All rights reserved.