Microbial degradation of crude oils

The microbial degradation of two crude mineral oils and one synthetic crude oil was studied under In situ estuarine conditions and in the laboratory. The three oils differed widely in composition; the Athabasca synthetic crude was a light oil with a high saturate content, conversely its parent sand tar was a heavy oil low in saturates. The North Sea Forties crude represented an intermediate between these two extremes.

A new environmental experimental system was devised to yield quantitative data on oil degradation and this was deployed in the Medway estuary under both winter and summer conditions between December 1976 and July 1978. During both winter and summer experiments oil composition had a major influence on the rate and extent of oil loss which followed the order, synthetic crude > Forties crude > sand tar. This order conforms to predictions made on the basis of the fractional composition of the oils. The saturate fraction of the Forties crude and sand tar was most extensively degraded during the second summer experiment. Temperature rather than inorganic nutrient supply appeared to limit degradation during the winter months; degradation was more rapid during the summer months. Microbial colonization of the oils was predominantly bacterial and was more rapid during the summer. The overall colonization pattern however was similar for each oil throughout both winter and summer experiments .

The laboratory experiments using supplemented media broadly confirmed the degradation patterns found during the in situ experiments. However, higher initial degradation rates for all the oils were found at 25°C in supplemented medium than those occurring in the in situ summer experiments. The laboratory- experiments also revealed the interesting phenomena of novel hydrocarbon synthesis and the occurrence of intracellular hydrocarbon inclusions during growth on the Forties crude and synthetic crude respectively.