Toluene vapour removal in a laboratory-scale biofilter

A bench-scale biofilter with a 0.5-m high filter bed, inoculated with a tol uene-degrading strain of Acinetobacter sp. NCIMB 9689, was used to study to luene removal from a synthetic waste air stream. Different sets of continuo us tests were conducted at influent toluene concentrations ranging over 0.1 -4.0 g m(-3) and at superficial gas velocities ranging over 17.8-255 m h(-1 ). The maximum volumetric toluene removal rate for the biofilter (242 g m(- 3) h(-1)) was obtained at a superficial gas velocity of 127.5 m h(-1) (corr esponding to a residence time of 28 s) and a toluene inlet concentration of 4.0 g m(-3). Under these operating conditions, toluene removal efficiency was only 0.238, which suggested that effective operation required higher re sidence times. Removal efficiencies higher than 0.9 were achieved at organi c loads less than 113.7 g m(-3) h(-1). A macro-kinetic study, performed usi ng concentration profiles along the bioreactor, revealed this process was l imited by diffusion at organic loads less than 100 g m(-3) h(-1) and by bio logical reaction beyond this threshold.