In a 5 litre beaker containing 4 litres of a medium suitable for biodegradation, around 5 grams of crude oil are added together with micro-organisms capable of degrading oil (seeding from a few grains of sand taken from Cedre's beach and containing less than 1 mg of oil).
The medium is prepared according to the recommendations laid out in AFNOR standard NFT 90-347 on "Water trials - Dispersant products - Assessment of the inhibitory action of biodegradability on oil in an aqueous environment". This standard is applied as part of the dispersant approval process and aims to assess the biodegradation of the dispersed oil.
The experiment lasts one month and, following this period, the remaining oil is extracted using dichloromethane, dried on magnesium sulphate then analysed.
The biodegraded samples extracted after the one-month trial are analysed by high temperature gas phase chromatography coupled with flame ionisation detection (HTGC-FID).
This method enables a global analysis of the oil, from the lightest fractions (around 10 carbon atoms) to the equivalent of vacuum distillation residues (90 to 100 carbon atoms). The oil is analysed before and after biodegradation, and the two analytical responses are standardised using the C50-C90 fraction, assumed to be stable as it resists biodegradation.
By comparing the calculated quantities of oil, the maximum biodegradation or biodegradability rate can be estimated.