As environmental legislation becomes ever more stringent the need for efficient and cost-effective methods for treating hazardous emissions grows. In this article Dr Derek Chitwood, DTRG Biofiltration, Tustin, California, USA, and Professor Joseph Devinny and Carol Armstrong, University of Southern California, Los Angeles, California, USA, put the case forward for the use of biofiltration systems to treat low levels of degradable contaminants in industrial waste gas. Growing public awareness of the health impacts combined with decreasing tolerance for industrial pollution has led to requirements that are more stringent. Industries are seeking to meet the ever tightening regulations, but at the lowest possible cost. Contaminants are commonly removed from industrial waste air by thermal treatment, activated carbon adsorption, or scrubbers.
Thermal treatment includes direct flaring or catalytic oxidation.
This is effective when the concentration of the organic pollutant is high enough to provide the majority of the energy required. However, it becomes too costly when concentrations are low because a secondary fuel has to provide the majority of the energy required to oxidize the contaminant. In activated carbon adsorption, compounds are adsorbed onto the surface of the carbon producing a very clean effluent. However, the amount adsorbed per unit mass of carbon is related to the concentration of the contaminant in the air. Scrubbers are effective for removing many odours and other highly soluble compounds, but suffer from very high operational costs and the production of a secondary waste stream - compounds are transferred but not destroyed.