* The basis of this peer-reviewed paper is a presentation at the 9th FECS Conference on Chemistry and Environment, 29 August to 1 September 2004, Bordeaux, France.
Scope and Background. Contamination of soils, aquifers and groundwater by nonaqueous phase liquid (NAPL) pollutants constitutes a major environmental issue of concern, worldwide. The residual (biodegradation-resistant) hydrophobic fuel hydrocarbons entrapped in the soil porous matrix, possess a particular bioremediation challenge due to their becoming virtually immobile, nor desorbable, or water dispersible. Consequently, they are not available as substrates to the micro-organism-based biodegradation.
Materials and Methods. Our research involves the development of economically feasible, surfactant/surfactant-nutrient mix (SSNM) – enhanced bioremediation methodologies for sustainable, in situ bioremediation of fuel-contaminated aquifers. This required, methodologically, (a) the optimization, via in vitro flow (columns) lab experiments and screening processes, of an effective mixture for the intended SSNM-enhanced bioremediation; and (b) the study of the combined effect of the optimized SSNM on the solubilization/mobilization and biodegradation of NAPL (fuel) in in vitro site/aquifer – simulated bioremediation.
Results and Discussion. The essence of our findings: (1) kerosenes maximum enhanced mobilization – f = 3.6, compared with that of deionized water, was achieved with an SSNM having the composition of linear alkylbenzene sulfonate (LABS): coco-amphodiacetate (containing N): surfactant-nutrient X (containing both N and P) = 0.15: 0.15: 0.05 g/L, respectively; (2) 62-64% of the initial amount of kerosene in the initially saturated soil matrix, packed in a column, has been eluted from it during ~30 days, compared with 68% of kerosene biodegradation in vessel settings, in 21 days.
Conclusions. (1) The indigenous microorganisms present in the vadose zones of fuel-contaminated sandy soil aquifers are potentially capable of unassisted removal of ~80% of the initially contained fuel (kerosene), during a period of about 42 days; (2) the major effects of the SSNM addition are (a) enhanced mobilization of the bulky NAPL; and (b) enhanced desorbtion/ solubilization/dispersion of the entrapped NAPL which, in turn, facilitate their enhanced biodegradation.
Recommendations and Perspectives. Our findings suggest that pre-optimized, biodegradable SSNM is essential for surfactants-based bioremediation of NAPL-contaminated aquifers, in order to make this in-situ methodology both technologically and economically feasible. |
