Laboratory scale biological trickling filters and three-phase airlift bioreactors have been studied for the elimination of methylene chloride (or dichloromethane) vapors from waste air, and the results used herein for the design of small industrial-scale reactors. The conditions chosen for scale-up were an air flow rate of 100 m3 h-1, a methylene chloride inlet concentration of 2 g m-3, and a target removal of 99.5%. The scale-up procedure, design, and cost analysis are discussed. The full-scale biotrickling filter appears to be the most cost-effective reactor, with global costs of about $62 per 1,000 m3 treated. Treatment in the airlift reactor was estimated to be twice as expensive and catalytic oxidation 5 times as expensive. Biological waste air treatment offers economical alternatives to conventional techniques for waste air treatment. © 1997 Air & Waste Management Association.