Biodegradable atmospheric pollutants, released at low to moderate concentrations, can be removed by bicifiltration. In this work, a laboratory-scale compost-based biofilter has been evaluated for the removal of high levels of toluene in air (- 4.0 g.m(-3)). By applying a variable nitrogen input in the irrigation solution, it was shown that the biodegradation extent can be controlled through the nutrient supply. The maximum elimination capacity achieved was 135 g.m(-3).h(-1), for a N-concentration of 3.0 g of N.L-1. A quantitative analysis of the bioreaction aspects (stoichiometry temperature) led to the determination of the water flow rates associated with the toluene oxidation. Thus, it was estimated that some 530 to 800 g of water.day(-1) were lost at the bioreactor outlet, but were balanced by the irrigation system.