A novel experimental procedure to investigate the biodegradation of NAPL under unsaturated conditions |
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Authors: | Laurent Andre Monika AM Kedziorek Alain CM Bourg Frank Haeseler Denis Blanchet |
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Institution: | aInstitut Français du Pétrole, Département Biotechnologies et Chimie de la Biomasse, 1-4 Avenue de Bois Préau, 92852 Rueil Malmaison Cedex, France;bEnvironmental HydroGeochemistry, Department Geosciences, University of Pau, BP 1155, 64013 Pau Cedex, France |
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Abstract: | Soils need to be thoroughly investigated regarding their potential for the natural attenuation of non-aqueous phase liquids (NAPL). Laboratory investigations truly representative of degradation processes in field conditions are difficult to implement for porous media partially saturated with water, NAPL and air. We propose an innovative protocol to investigate degradation processes under steady-state vadose zone conditions. Experiments are carried out in glass columns filled with a sand and, as bacteria source, a soil from a diesel-fuel-polluted site. Water and NAPL (n-hexadecane diluted in heptamethylnonane (HMN)) are added to the porous medium in a two-step procedure using ceramic membranes placed at the bottom of the column. This procedure results, for appropriate experimental conditions, in a uniform distribution of the two fluids (water and NAPL) throughout the column. In a biodegradation experiment non-biodegradable HMN is used to provide NAPL mass, while keeping biodegradable n-hexadecane small enough to monitor its rapid degradation. Biodegradation is followed as a function of time by measuring oxygen consumption, using a respirometer. Degradative activity is controlled by diffusive transfers in the porous network, of oxygen from the gas phase to the water phase and of n-hexadecane from the NAPL phase to the water phase. |
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Keywords: | Unsaturated porous medium Laboratory experiments Ceramic membranes NAPL Hydrocarbon Biodegradation |
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