Experiments were conducted in batch culture in the same conditions as 

 those described for Arabian Light Crude. The mixed culture of bacteria 

 used was the mixture of the strains Pseudomonas and Moraxella isolated 

 and purified, described in Section 1.3. By sucessive cultures in flasks 

 with the pure hydrocarbon mixture as the only carbon substrate, the 

 mixed culture was progressively adapted to grow on these ten hydrocar- 

 bon compounds. 



The culture was carried out in batch for 61 V z hours, and we observed 

 the changes in the biomass, total hydrocarbons, and each compound, and 

 also the organic substances that passed into the aqueous phase. 



Following a lag phase of about 10 hours, a growth acceleration phase 

 was observed up to the 25th hour, then a linear phase from the 25th to 

 the 35th hour, and finally the slowdown of bacterial growth. At the end 

 of the batch, the dry cell weight was 0.5 g.l -1 . The biodegradation 

 process of total hydrocarbons perfectly matched the microorganism growth 

 pattern. After 61 Y 2 hours, 82.8 % of the hydrocarbons were degraded. 



It appears that the three most volatile compounds, paracymene , decaline 

 and benzothiophene, could not be found after extraction, from the very 

 outset of the experiment. These three products must therefore disappear 

 chiefly during extract evaporation operations. However, a small propor- 

 tion passes very rapidly into the aqueous phase in the marine environ- 

 ment, because the latter contained oxidation products of p-cymene among 

 others, as well as benzothiophene. 



The two n-alkanes, n-hexadecane and octacosane, and the dodecylbenzene 

 were consumed first. For these three products, which practically 

 disappeared by the end of the batch, their respective biodegradation 

 rates after 37 Y 2 hours only of culture were 93 %, 87.5 % and 80 %. 

 Pristane only started being attacked after 24 V z hours, and was 69.2 % 

 consumed at the end of the culture. During the last 20 hours, while 

 practically no alkanes or alkylbenzene remained in the reactor, dimethyl- 

 naphtalene was biodegraded (disappearance rate 67 %) . Phenanthrene and 

 dibenzothiophene were consumed very little if at all. 



These results perfectly confirm those found with Arabian Light Crude, 

 which showed that alkanes and isoprenoids were attacked first, follo- 

 wed by mono- and di-aromatics. Similarly, it was observed that tri- 

 aromatics and sulfur-containing aromatics were only slightly sensitive 

 or insensitive to the action of microorganisms. The fact that dodecyl- 

 benzene disappeared fairly rapidly is explained by the presence of the 

 linear chain which, like the n-alkanes, is readily accessible to 

 bacteria. 



The total organic carbon concentration (TOC) measured in the medium was 

 385 mg.l -1 . After esterif ication and evaporation of the organic extract, 

 esters and some other polar compounds were found in a concentration of 

 221.5 mg.l -1 . 



We carried out analyses by gas phase chromatography and GC/MS coupling 

 in an attempt to identify these products. 



Since many products were present in trace amounts, and several of them 

 were eluted simultaneously and combined in a single peak, we encountered 

 considerable difficulty in identifying them on the mass spectrometer. 



33 



