Surfactant enhanced bioremediation (SEB) of oil is an approach adopted to overcome the bioavailability constraints encountered in biotransformation of nonaqueous phase liquid (NAPL) pollutants. Fuel oils contain n-alkanes and other aliphatic hydrocarbons, monoaromatics, and polynuclear aromatic hydrocarbons (PAHs). Although hydrocarbon degrading cultures are abundant in nature, complete biodegradation of oil is rarely achieved even under favorable environmental conditions due to the structural complexity of oil and culture specificities. Moreover, the interaction among cultures in a consortium, substrate interaction effects during the degradation and ability of specific cultures to alter the bioavailability of oil invariably affect the process. Although SEB has the potential to increase the degradation rate of oil and its constituents, there are numerous challenges in the successful application of this technology. Success is dependent on the choice of appropriate surfactant type and dose since the surfactant-hydrocarbon-microorganism interaction may be unique to each scenario. Surfactants not only enhance the uptake of constituents through micellar solubilization and emulsification but can also alter microbial cell surface characteristics. Moreover, hydrocarbons partitioned in micelles may not be readily bioavailable depending on the microorganism-surfactant interactions. Surfactant toxicity and inherent biodegradability of surfactants may pose additional challenges as discussed in this review.

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Bioremediation approaches for the treatment of oily sludge from a refinery were evaluated using a 2(3) factorial design. The three strategies tested were bioaugmentation with indigenous microbial consortia (MO) isolated from oily sludge, biostimulation with nutrients (NP) and biostimulation with the surfactant Triton X-100 (TX). Eight experimental runs were conducted in triplicate with factor settings ± (high/low) as per the 2(3) design. The main effects and the effects of various interactions of the factors on oil degradation and microbial growth in suspension were evaluated during a 30 day study. Multifactor ANOVA could reveal the significant effects while the normal order score approach failed in this scenario. The main effect of biostimulation with nutrients in the form of nitrate and phosphate, as well as biostimulation with Triton X-100, was positive and significant when both oil degradation and microbial growth in suspension were chosen as the response variables. However, the main effect of bioaugmentation was only significant for oil degradation but was insignificant for microbial growth at a 90% confidence level. The MO-NP binary interaction and the MO-NP-TX ternary interactions were positive and significant, indicating the synergistic effect of these strategies on oil degradation and microbial growth. All other binary interactions were found to be insignificant.

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