Studies of biodegradation of phenanthrene controlled by absorption in cell membrane

A mathematical model based on the structure of a bacterial cell was derived to describe the biodegradation of polycyclic aromatic hydrocarbons (PAHs). Phenanthrene was used as a model compound in this study. It was hypothesized that cell membrane is a highly hydrophobic compartment capable of absorbing phenanthrene. This biosorption decreased the concentration of phenanthrene degradable by enzymes in the cytoplasm. The structured biosorption-biodegradation model incorporates the mechanisms of biosorption, cell decay, release of membrane-bound phenanthrene, and the degradation of phenanthrene.; Batch experiments were conducted using an acclimated culture capable of degrading phenanthrene. The disappearance of phenanthrene and the production of carbon dioxide were monitored over time. The experimental, results show two different stages in the change of phenanthrene that can be explained by the biosorption and biodegradation mechanisms. Biosorption occurred mainly in the cell membrane due to the hydrophobicity of phenanthrene. The biosorption process reduced the bioavailability of phenanthrene and the subsequent biodegradation was limited. The results of batch biometer test verified the structured biosorption-biodegradation model developed in this study.; One key finding of this study was that there were two mechanisms, diffusion-and-degradation and decay-and-release, occurring simultaneously to either decrease or increase the concentration of phenanthrene in the liquid solution. Dead cells released phenanthrene previously absorbed in the membrane to the liquid solution. As a result, the concentration of phenanthrene in the bulk aqueous phase was increased, even though the degradation of phenanthrene was always going on.; The biosorption-biodegradation model has a capability to explain PAH biodegradation processes which incorporated with biosorption mechanism. The model predicted phenanthrene concentration in the liquid solution closely. Deviation between model prediction and experimental results of carbon dioxide production was decreased when initial phenanthrene concentration was decreased. It clearly shows that phenanthrene was mineralized very efficiently without a significant accumulation of intermediates at low initial phenanthrene concentration.