The rendering process consists of crushing and heating animal remains to produce by-products. The U.S. produces approximately 30 billion pounds of inedible animal by-products annually, exporting a market value of US$ 1.5 billion. Benefits of the rendering process include reducing total waste material, and helping the livestock industry stay competitive over vegetable protein manufacturers. However, the rendering process can have a negative effect on the environment through the emission of nuisance odorous compounds such as hydrogen sulfide, reduced sulfur compounds, ammonia, various fatty acids, ketones and aldehydes. Several strategies are currently used to combat odor in rendering facilities. In recent years, rendering facilities are increasingly selecting bioliltration for combating nuisance odor. This work describes modeling and design strategies used in building large-scale biofilter systems of up to 250,000cfm (cubic feet per minute) capacity. The models facilitated in the design and evaluation of operating conditions and capital investment. This work demonstrates that models play an important role in the design of large-scale odor control systems that deliver predicted performance. (c) 2005 Elsevier B.V. All rights reserved.