Addressing biofilter limitations: a two-phase partitioning bioreactor process for the treatment of benzene and toluene contaminated gas streams.

A two-phase partitioning bioreactor (TPPB) achieved simultaneous and continuous removal and degradation of benzene and toluene from an air stream. The aqueous- organic system utilized n-hexadecane as the organic phase, and the organism Alcaligenes xylosoxidans Y234 in the aqueous phase to achieve the degradation of benzene and toluene. The system, which operates as a well-mixed dispersion and is therefore resistant to substrate surges, was first shown to be capable of utilizing toluene while operating at a loading capacity of 235 g m(-3) h(-1) with an elimination capacity of 233 g m(-3) h(-1). It was also determined that to characterize TPPB performance in terms of elimination capacity the definition of elimination capacity must be extended to include the cell mass present, a readily controllable variable given the nature of the system. Based on this criterion, it was estimated that for a cell concentration of 1 g l(-1) present in the TPPB, the potential maximum toluene elimination capacity is 1290 g m(-3) h(-1) which is substantially higher than any toluene elimination capacity achieved by biofilters at a high removal efficiency. If no other factor were to limit the system, elimination capacities could be many times higher still, and are dependent on maintaining desired cell concentrations above 1 g l(-1). The TPPB was then operated at nominal loading capacities of 63 g m(-3) h(-1) (benzene) and 51 g m(-3) h(-1) (toluene) at a removal efficiency greater than 99% to demonstrated the applicability of this system in dealing with two chemical species simultaneously. TPPB systems therefore have been shown to be effective at removing gaseous organic contaminants at high removal efficiencies while also possessing desirable operating features, such as providing and maintaining high cell concentrations throughout the reactor, and a capacity to effectively deal with high contaminant loadings.