| Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are often present together at contaminated sites. These sites are considered difficult to clean-up using bioremediation technologies because of the toxicity of heavy metals to microorganisms. Laboratory experiments were conducted to verify if biodegradation of a model PAH, naphthalene, could be sustained over a long time-period (weeks) in the presence of a common heavy metal contaminant, Cr (VI). Complete reduction of Cr (VI) at concentrations up to 6.3 mg/L was achieved by Pseudomonas putida ATCC 17484 in the presence of naphthalene that was continuously released from an immiscible organic liquid, 2,2,4,4,6,8,8-heptamethylnonane (HMN). The presence of Cr (VI) inhibited bacterial growth and reduced naphthalene biodegradation rates. Despite this the microorganisms were able to degrade significant masses of naphthalene, quantities much greater than those reported in earlier studies. The addition of 1,2-Naphthoquinone, a possible by-product of naphthalene degradation and an oxidizing agent, resulted in improved naphthalene biodegradation rates in the presence of Cr (VI). |
