Evaluating the relationship between the sorption of PAHs to bacterial biomass and biodegradation

Petroleum refinery wastewater containing polynuclear aromatic hydrocarbons (PAHs) are typically treated by biological processes in the United States. PAHs are recalcitrant, hydrophobic compounds and sorption to biological sol ids may be a significant mechanism for the removal of PAHs from refinery wa stewater. The goal of this research was to investigate PAH sorption by bact erial biomass and examine the relationship between PAH biosorption and biod egradation. In this study, phenanthrene was used as a model PAH for biosorp tion studies and pyrene and fluoranthene were used as model compounds in bi odegradation studies. It was found that phenanthrene biosorption varied wit h bacterial genus and species. Bacteria with the highest sorption capacity (K-P) belong to the Nocardioforms, organisms that often cause solids separa tion problems in activated sludge plants. Consequently, blooms of these dif ficult to settle organisms in refinery treatment plants could exasperate PA H releases to the environment. The measured sorption capacities were reprod ucible and appeared to represent surface sorption, based on the apparent co mpetition between naphthalene and phenanthrene for sorption sites. Based on a comparison of K-P values, pure bacterial cultures can serve as valid mod els of biosorption by activated sludge MLSS. Finally it was found that PAH sequestration by high K-P, non-degraders has a significant impact on PAH bi odegradation. The results of this study suggest that although biosorption c an decrease the rate of PAH biodegradation in the short term, it can also r esult in the removal of PAHs from the wastewater and PAH retention in the t reatment system where it may be ultimately biodegraded. This research impro ves our understanding of processes contributing to PAH degradation in petro leum refinery wastewater treatment plants. (C) 1999 Elsevier Science Ltd. A ll rights reserved.