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 oxi- 

 dized 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 absolu- 

 tely 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 satu- 

 rates, 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 sulfu- 

 compounds and other aromatics. 



Apart from those with a rough formula C n H2 n -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 biodegra- 

 dation, 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 sub- 

 tances. 



30 



