Simultaneous biodegradation of benzene, toluene, and p-xylene in a two-phase partitioning bioreactor: Concept demonstration and practical application

In this work, a mixture of benzene, toluene, and p-xylene was simultaneousl y biodegraded by Pseudomonas sp. ATCC 55595 in a two-phase partitioning bio reactor. This bioreactor consisted of a l-L cell-containing aqueous medium phase and a 500-mL immiscible organic phase. The organic solvent systematic ally selected for use in the bioreactor was Adol 85 NF, an industrial-grade , biocompatible solvent. In the first of three experiments, the organic pha se was loaded with 2.0 g of benzene, 10.15 g of toluene, and 2.1 g of p-xyl ene, which partitioned into the aqueous phase at concentrations of 25, 50, and 8 mg/L, respectively. The system ultimately biodegraded all of the subs trates within 144 h. During the rapid growth phase of this fermentation, th e cells were oxygen-limited. This fermentation was therefore repeated using an enriched air supply to remove the oxygen limitation. The use of enriche d air ultimately reduced the length of the fermentation to 108 h, thereby i mproving the overall volumetric consumption rates. Finally, 500 mt of Adol were used to recover 2.0 g of benzene, 10.15 g of toluene, and 2.1 g of p-x ylene from silica sand that was contaminated as part of a simulated soil "s pill". The solvent washing procedure was able to recover greater than 99% o f each compound from the contaminated soil. The Adol was then transferred t o the two-phase bioreactor to permit biological treatment of the BTX contam inants. This process was repeated when the initial BTX load had been consum ed almost to exhaustion, and the solvent was able to recover the contaminan ts at greater than 99% efficiency once again. The system was ultimately abl e to degrade 4.0 g of benzene, 20.2 g of toluene, and 4.2 g of p-xylene wit hin 144 h. These results represent an unprecedented level of BTX degradatio n and illustrate a potential practical application for this novel biotechno logy.