Laboratory evaluation of crude oil biodegradation with commercial or natural microbial inocula

Experiments have been performed to screen eight microbial commercial produc ts that, according to the manufacturers, are able to degrade crude oil. Thi s study compared the crude oil biodegradation activity of commercial inocul a with that of natural inocula (activated sludge and tropical aquarium wate r). Some of the latter were previously adapted to the crude oil as the only carbon source. Nutrients and sorbents in the commercial formulations were eliminated, and each inoculum was precultured on marine yeast extract mediu m. Crude oil biodegradability tests were conducted with close initial subst rate concentration to initial bacterial concentration ratios (S0X0) of 0.94 g of crude oil/10(9) CFU, which allowed a comparison of biodegradation act ivity. The inocula oxidized the crude oil after a short lag time of less th an 3-18 days. After that time, the rate of oxidation varied between 45 and 244 mg O-2/(L.day). Crude oil biodegradation after a 28-day test was effect ive only for 10 out of 12 inocula (from 0.1 to 25% in weight). Biodegradati on mainly corresponded to the saturated fraction of the crude oil; the asph altene fraction was never significantly biodegraded. Our results led to the conclusion that natural inocula, either adapted or not adapted Co crude oi l, were the most active (from 16 to 25% of loss in crude oil weight) and on ly one commercial inoculum was able to degrade 18% of the crude oil. Other inocula had a biodegradation activity ranging from 0.1 to 14%.