Bacterial bioavailability and biodegradability of high-molecular weight hydrocarbons from oil refinery wastes

A general problem for oil refineries is the proper disposal of production sludges generated during the processing of crude oil. Dumping of sludges leads to environmental pollution, and particularly to sediment contamination. High-molecular weight-PAHs are important constituents of refinery wastes. These are toxic and recalcitrant pollutants, several of them being known mutagens or carcinogens. Research on biodegradability of the compounds is hampered by the insolubility in aqueous media. We analysed the chemical composition of a refinery waste sludge and determined the contents of mineral oils and PAHs. In a microbial investigation of the same sludge fractions we isolated several bacterial strains having a significant potential for breakdown of mineral oils and PAHs. Many techniques have already been applied to offer these compounds as substrates for microorganisms. Linking of the water-insoluble substrates (the PAHs, fluoranthene and chrysene, or the mineral oils) to Chromosorb beads and supplying them in a fluidised bed reactor as a single carbon source to bacterial isolates, offers a practical alternative in research on biodegradation. Even, this system resembles the common soil conditions, where bio-availability is reduced by linking of the contaminants to soil particles or accumulation of the products in hydrophobic pockets. After incubation of the carrier beads in an appropriate medium, the liquid fraction from the fluidised bed reactor and the carrier beads were collected separately and analysed for longchain hydrocarbons and for PAHs. In six days of incubation in an adapted broth formulation, biodegradation amounts 60.1% for fluoranthene and 47.2% for chrysene. Heavy hydrocarbons ranging from C10 up to C40 have been utilised in a thirty-day period for 72.4%. This project is a logical extension of our previous studies on the bio-availability of PAHs in contaminated sediments. We evaluate the potential use of pure cultures as a remedial solution to enhance the solubility and biodegradation of residual PAHs due to contamination by heavy fuels.