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The saturated hydrocarbons were most rapidly biodegraded.
At the end of the culture, the disappearance of aromatic compounds is
accompanied by an enrichment of the aqueous phase in organic carbon,
the concentration of which may reach 250 mg.l - -'-. This observation
tends to show that a large part of the aromatics are only partly oxidized
before passing into the aqueous phase.
The resins were only slightly attacked if at all, and the asphaltene
concentrations at the start and end of the batch culture were absolutely
comparable, demonstrating total insensitivity of these substances
to biochemical processes.
The determination of n-alkanes (C14-C35) and detectable isoprenoids
(C15-C23) by gas phase chromatography showed that these compounds
disappeared almost totally by the end of the culture.
The mass spectrometry analysis of the "saturates" fraction showed that
the alkanes were mainly biodegraded, as 88.9 % disappeared at the end
of the culture. This enables us to postulate that, in addition to the
n-alkanes and isoprenoids, which only account for 14.8 % of the
"saturates" fraction, the bulk of the iso-alkanes present in the crude
oil was consumed by microorganisms.
Among the naphtenic compounds, the 1- and 2-cycle naphtenes were mainly
consumed, with respective biodegradation rates of 44 and 47 %.
Proton NMR analyses giving the CH3/CH2 ratio, conducted on the saturates,
failed to indicate any significant difference between the start
and end of the batch culture.
With respect to the "aromatics" fraction, the action of microorganisms
mainly affected the mono- and di-aromatic compounds. At the end of the
culture, all the mono- and di-aromatics with a number of carbons less
than 16 had disappeared.
Among the mono-aromatics , the substances most sensitive to microbial
action were the alkylbenzenes, of which 67.7 % disappeared at the end
of the culture, and the benzocycloparaf f ins , with a consumption rate
of 46.2 %. The differences measured for benzodicycloparaf f ins were not
sufficiently wide to be meaningful.
As for di-aromatic compounds, the microorganisms displayed a very clear
effect on the residual concentration of naphtalenes, of which 50 %
disappeared after 48 hours of culture.
Through a second experiment, we investigated the changes in composition
of the aromatics fraction, by drawing a distinction between sulfucompounds
and other aromatics.
Apart from those with a rough formula C n H2n-10S, the sulfur-containing
compounds were not attacked by bacteria. The aromatics/sulfur-compounds
ratio of 0.98 before biodegradation decreased to 0.82 after biodegradation,
showing that it was mainly the non-sulfur-containing aromatics
(mono- and di-) that disappeared. In addition, the weight percentage of
sulfur in the aromatics fraction increased with time from 4.05 to 4.15,
confirming the enrichment of this fraction in sulfur-containing subtances.
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