Physical and chemical conditions for microbial oil degradation

Oil residues arising from the Christos–Bitas spillage were found to contain 28% of oil extractable by carbon tetrachloride; the remainder comprised water and undefined solids. When incubated in 8‐L rectangular tanks with a mixed population of mainly bacteria to which diammonium hydrogen phosphate was added, ca. 97% of the Christos‐Bitas oil fraction was degraded. When the same substrate was degraded by only three isolated Pseudomonas strains in 1‐L cylindrical tanks, degradation was only ca. 56%. Raising the temperature from 20 to 50°C brought about a visible loss in cell viability with only ca. 38% of the substrate degraded. Oil degradation proceeded in direct proportion to increases in cell attachment to the dispersed oil. The aliphatic fraction of Kuwait crude oil up to n C 25 measured by gas liquid chromatography (GLC) was oxidized within 48 h. Using this substrate the three pseudomonads together brought about a more complete degradation (87%) than a single Bacillus isolate. The Bacillus strain was capable of deggrading between 50 and 65% of the crude, depending on whether diammonium hydrogen phosphate supplemented a peptone‐based medium. The preferential biodgradability of fractions was the following aliphatics > aromatics > asphalts, as has been widely reported.