The treatment of gaseous benzene by two-phase partitioning bioreactors: a high performance alternative to the use of biofilters

Abstract

A 2-l (1-l working volume) two-phase partitioning bioreactor (TPPB) was used as an integrated scrubber/bioreactor in which the removal and destruction of benzene from a gas stream was achieved by the reactor's organic/aqueous liquid contents. The organic solvent used to trap benzene was n-hexadecane, and degradation of benzene was achieved in the aqueous phase using the bacterium Alcaligenes xylosoxidans Y234. A gas stream with a benzene concentration of 340 mg l⁻¹ at a flow rate of 0.414 l h⁻¹ was delivered to the system at a loading capacity of 140 g m⁻³ h⁻¹, and an elimination capacity of 133 g m⁻³ h⁻¹ was achieved (the volume in this term is the total liquid volume of the TPPB). This elimination capacity is between 3 and 13 times greater than any benzene elimination achieved by biofiltration, a competing biological air treatment strategy. It was also determined that the evaluation of TPPB performance in terms of elimination capacity should include the cell mass present in the system, as this is a readily controllable quantity. A specific benzene utilization rate of 0.57 g benzene (g cells)⁻¹ h⁻¹ was experimentally determined in a bioreactor with a cell concentration that varied dynamically between 0.2 and 1 g l⁻¹. If it assumed that this specific benzene utilization rate (0.57 g g⁻¹ h⁻¹) is independent of cell concentration, then a TPPB operated at high cell concentrations could potentially achieve elimination capacities several hundred times greater than those obtained with biofilters.