Rates of microbial degradation of petroleum components as determined by computerized capillary gas chromatography and computerized mass spectrometry

The biodegradation rates of Arabian light crude oil components under the action of a marine mixed microbial culture were monitored in a quasicontinuous culture during a 60 day experiment. The saturated hydrocarbons were degraded more rapidly and extensively (74%) than the aromatics (50%), whereas the biodegradation of asphaltenes (30%) and of resins (< 5%) was very low. The joint use of computerized high-resolution chromatography and of computerized mass spectrometry permitted classification of the petroleum constituents according to their biodegradability: (i) highly susceptible, − and iso-alkanes; (ii) susceptible, 6, 1, 5 and 2 ring alkanes, 1 ring and sulphur aromatics; (iii) moderately susceptible, 3 and 4 ring alkanes, 2 and 3 ring aromatics; (iv) resistant, tetra-aromatics, steranes, triterpanes, naphtheno-aromatics; and (v) highly resistent, penta-aromatics, asphaltenes and resins. Unlike saturates, aromatics were degraded at a rate that was in relation to the number of rings of the molecules. The microbial activity leads to the formation of a residue which can be considered as a form of stable organic matter. The biodegradation potential of a mixed microflora is much more elevated in continuous culture systems than in batch cultures.