S. Guha et Pr. Jaffe, BIOAVAILABILITY OF HYDROPHOBIC COMPOUNDS PARTITIONED INTO THE MICELLAR PHASE OF NONIONIC SURFACTANTS, Environmental science & technology, 30(4), 1996, pp. 1382-1391
The apparent solubility of polycyclic aromatic hydrocarbon compounds s
uch as phenanthrene can be increased in the presence of surfactants ab
ove their critical micelle concentration. A fraction of the phenanthre
ne partitioned into the micellar phase of some nonionic surfactants ca
n be directly bioavailable to phenanthrene-degrading microorganisms. A
model describing the biodegradation of the directly bioavailable mice
llar-phase substrate is presented. The hypothesis on which the model i
s based considers the following steps: (a)the contaminant is transport
ed by filled micelles from the bulk solution to the proximity of the c
ells; (b) the exchange of the filled micelle with the hemimicellar lay
er around the cell delivers the contaminant to the cell; (c) the conta
minant diffuses into the cell and is biodegraded. The biodegradation k
inetics were explained in terms of a series of mass-transfer processes
, which lead to a similar equation as the Monod kinetics. The theoreti
cally derived expression, describing the micellar-phase substrate that
is directly bioavailable, includes a series of surfactant dynamics an
d mass transfer rate parameters that are not readily available or easi
ly determined. A simplified formulation, which can be used to estimate
the direct bioavailability of the micellar-phase substrate was theref
ore obtained and was used to explain experimental observations. The bi
oavailable fraction of the micellar-phase substrate was independent of
the biomass concentration and was a function of the surfactant concen
tration, the polyoxyethylene chain length of the surfactant, and the b
iomass surface characteristics.