BIOREMEDIATION OF AN OIL DEPOSIT IN A RELEVANT GEOLOGICAL MATRIX

摘要

The main scope of the work was to perform the clean up of the contaminated soil after the dismantling of an old oil deposit based on a hill close to the city of Genoa, Italy. The contaminants namely consisted of medium and heavy hydrocarbons diffused in the soil during the plant’s lifetime from various sources, I.e. Tanks/pipes leakage, loading and unloading spills, etc. According to a preliminary test report, biopiling was selected as the most appropriate technology. The concentration of the contaminants varied greatly from point to point within the whole site, depending on the particular geological structure of the soil, basically consisting of shale strongly interfering with the natural diffusion, so as highly polluted spots were intercalated with relatively clean zones. Soil excavation was therefore performed very carefully according to a fine mapping of small lots supported by a very precise and detailed analytical campaign, whilst contaminated soil to be submitted to the pile was previously pre-treated through a screening step and stored before piling. Parameters of the biopiling process were continuously monitored and maintained to the right values in compliance with the relevant soil nature (I.e. pile humidity had to help the biological process but had to be maintained at quite low levels in order to prevent from the natural shale mudding). No bulking agent and/or nutrients were used. The average concentration of the pile contaminants was about 800 ppm as total hydrocarbons (up to C25) and 7,000 ppm as mineral oils, whilst the after treatment value was ranging between 250 and 300 ppm of total hydrocarbons and 3,500 ppm of mineral oils, with a removal efficiency of about 66 and 50% respectively. This result was achieved in about six months of actual biopiling, while the rest of the time was devoted to civil works, excavation and contaminated soil preparation. Over one year of treatment, total hydrocarbons mass was degraded up to 80 – 90 ppm and mineral oils up to 850 ppm, reaching a global effectiveness around 85 – 90%. The above described experience shows that biopiling can be considered a successful and flexible technology even in the case of a very hard matrix, provided that the process is properly operated and monitored.