Effects of natural organic matters on bioavailability of petroleum hydrocarbons in soil-water environments

The bioremediation efficiency of petroleum hydrocarbons in natural soil-water systems is regulated by active microbial populations and other system parameters. Relevant factors include the transfer rate of petroleum contaminants from a medium into microorganisms, the partitioning behavior of contaminants from water into the soil organic matter (SOM), and the influence of the dissolved organic matter (DOM) on the contaminant level in water. The objectives of this study was aimed to determine the correlation among bioavailability of petroleum hydrocarbons, SOM content, and DOM level in soil-water systems. Heptadecane, pristane, and decylcyclohexane were selected as model hydrocarbon contaminants. The bioavailability of target contaminants in soil was examined using soils of different SOM contents (2% and 20%) in slurry bioreactors. In addition, the contaminant bioavailability as affected by various DOM levels (0–100 mgC/L) was also examined. The results showed that the SOM content affected the degrading rate of hydrocarbons significantly, where the rate constant was 4 times higher in 2% SOM microcosm than in the 20% SOM bioreactor for heptadecane degradation. Similarly, the pristane degrading efficiency after 240 h operation was 95% for the 2% SOM microcosm and only 38% for the 20% SOM microcosm. The hydrocarbon degradation rates in water phase were found to be enhanced by the added DOM level. A positive correlation existed between the contaminant bioavailability and the contaminant level in water as impacted by the SOM content in soil and the DOM level in water.