Polycyclic aromatic hydrocarbons (PAHs) slurry phase bioremediation of a manufacturing gas plant (MGP) site aged soil

Bench scale tests have been carried out in order to investigate bioremediation feasibility of a Manufacturing Gas Plant site (Bovisa Gasometri - MI - I) aged soil, highly contaminated by polyaromatic hydrocarbons (PAHs) and mineral oils. Biodegradation studies were carried out at 22 degreesC in a slurry system reactor, with a solid to liquid ratio of 10% w/w. Three tests were performed, over a period of 23, 24 and 91 days respectively. In the first test, only soil and water were put into the system. In the second test, microbial activity was inhibited to evaluate the amount of abiotic losses. In the third test, macronutrients were added to the reactor; bioaugmentation was also carried out by an inoculum of autochthonous PAH-degrading microorganisms. Saturated hydrocarbons, PAHs, transformation products, heterotropic and PAH-degrading bacteria and fungi were monitored. Tests showed that high removal efficiency could be obtained following 23 days of treatment for all PAHs, including high molecular weight compounds. Abiotic losses were an important process contributing to concentration abatement in soil, especially in the first phase of the treatment. Lag time lack for all polyaromatic hydrocarbons revealed that autochthonous microorganisms were well adapted to these contaminants; bioaugmentation did not seem to speed up the process. The higher removal rate and efficiency for high molecular weight PAHs obtained in the third test suggested that nutrient addition could play an important role in the biodegradation process of these compounds, whereas it did not significantly modify total (abiotic + biotic) removal of light compounds.