In this work, a laboratory biofilter was operated as a CSTR using internal recycle to expose all the packing material (compost and soil) to a uniform toluene concentration in air. The reactor was combined with water content control using the suction cell principle and traditional inlet concentration, temperature and humidity control. This novel type of reactor configuration allows a much higher degree of manipulation and control then a traditional plug flow reactor system for research purposes.

Nitrogen and other nutrients were added to investigate their influence on the elimination capacity (volumetric degradation rate) of toluene. In addition, the effect of temperature on the elimination capacity was investigated between 14 and 60 °C. Maximal removal rates were found between 25 and 55 °C. The EC decreased by 90% going from 55 to 60 °C.

Without any extra nitrogen added to the media, the EC averaged around 10 g m^-3 h^-1 for compost and 30 g m^-3 h^-1 for soil. When NH4Cl (1 g l^-1) was added to the reactor, the EC increased to 65 g m^-3 h^-1 in the case of compost. After removing the nitrogen, the EC remained at this level. Other macronutrients tested like phosphate, sulphate, magnesium, calcium and iron did not increase the EC.

The EC was dependent on the residual toluene concentration. The EC increased with increasing toluene concentration until reaching a critical concentration. Above this concentration, 100 – 300 ppm depending on biofilm thickness and area of coverage, the EC was constant.