A two-phase organic-aqueous system was studied as an alternative, due to the low cost associated used to degrade phenol in both batch and fed-batch culwith this option, as well as the possibility of complete ture. The solvent, which contained the phenol and partimineralization of the xenobiotic (Singleton, 1994). Howtioned it into the aqueous phase, was systematically seever, in the past, biodegradation has been considered lected based on volatility, solubility in the aqueous phase, too slow for practical applications, and the limitations partition coefficient for phenol, biocompatibility, and cost. The two-phase partitioning bioreactor used 500 mL associated with biological degradation of an inhibitory of 2-undecanone loaded with high concentrations of phecompound have been impossible to overcome to the nol to deliver the xenobiotic to Pseudomonas putida extent necessary.
ATCC 11172 in the 1-L aqueous phase, at subinhibitory Microorganisms that can degrade phenol were isolevels. The initial concentrations of phenol selected for lated as early as 1908 (Evans, 1947). Current technology the aqueous phase were predicted using the experimentally determined partition coefficient for this ternary syspermits the use of these microorganisms in batch and tem of 47.6. This system was initially observed to degrade continuous processes, using either suspended or immo-4 g of phenol in just over 48 h in batch culture. Further bilized cultures. The difficulty associated with batch reloading of the organic phase in subsequent experiments actors is that the initial substrate concentration must be demonstrated that the system was capable of degrading 10 g of phenol to completion in approximately 72 h. The lower than the value at which the organisms are inhibhigher levels of phenol in the system caused a modest ited, which, for most xenobiotics, results in a very low increase in the duration of the lag phase, but did not lead concentration of xenobiotic being degraded in a relato complete inhibition or cell death. The use of a fed-batch tively long period of time. Increasing the initial substrate approach allowed the system to ultimately consume 28 concentration in a batch reactor simply prolongs the g of phenol in approximately 165 h, without experiencing substrate toxicity. In this system, phenol delivery to the process, by increasing the duration of the lag phase aqueous phase is demand based, and is directly related (Andrews, 1968).
to the metabolic activity of the cells. This system permits In continuous culture, low dilution rates are necessary high loading of phenol without the corresponding subto avoid process instability or low conversion (Pawlowstrate inhibition commonly seen in conventional bioreactors.