Effect of Dispersants on Oil Biodegradation Under Simulated Marine Conditions

Abstract

ABSTRACT A study was undertaken on the dispersion, microbial colonisation and biodegradation of chemically-dispersed weathered Forties crude oil under simulated marine conditions in laboratory microcosms. The measurements of droplet size, number and microbial colonisation were made using new techniques developed by the project team. Rapid growth of indigenous micro-organisms capable of degrading both crude oil and dispersants was observed in the presence of chemically-dispersed oil. These organisms colonised the dispersed oil and biodegraded the aliphatic and aromatic hydrocarbons. These processes was stimulated by the addition of inorganic nutrients. Some colonised droplets agglomerated into neutrally-buoyant “clusters” (100 µm- 2 mm diameter) consisting of oil, bacteria, protozoa, and nematodes. After substantial hydrocarbon biodegradation these clusters sank to the bottom of the microcosms. No biodegradation or cluster formation was noted in “killed” controls in which biological activity had been inhibited. Different dispersants promoted microbial growth to differing extents. These results suggest that the addition of dispersants can increase the rate of oil biodegradation under natural conditions by promoting the growth of indigenous hydrocarbon-degrading bacteria, as well as increasing the surface area of oil available for microbial colonisation.