Green Chemistry and Biosurfactant Research - Biosurfactants: Research Trends and Applications - page 11

The increasing environmental concern about chemical surfactants triggers attention
to microbial-derived surface-active compounds essentially due to their low toxicity
and biodegradable nature. At present, BSs are predominantly used in remediation of
pollutants; however, they show potential applications in many sectors of food indus-
try. Potential applications of microbial surfactants in food industry and other areas
are discussed.

BIOSURFACTANT-ENHANCED BIOREMEDIATION

o il B ioremeDiation
Petroleum bioremediation is carried out by microorganisms capable of utiliz-
ing hydrocarbons as a source of energy and carbon (Reisfeld et al., 1972). MEOR,
exploiting microbial activities and metabolites, is at present gaining increased atten-
tion due to some advantages such as the following:

• Natural products are generally harmless and less detrimental to the

environment.

• Microbial processes do not require high temperatures and thus there are

low energy requirements.

• Costs of microbial products are not affected by the crude oil price and can

be produced using inexpensive raw substrates or even waste materials.

• Microbial products/activities can be stimulated in situ within the reservoir,

potentially allowing both tailor-made and cost-effective treatments.

Several metabolites are of interest for applications in MEOR including gas
(e.g., carbon dioxide, methane, and hydrogen), acids (e.g., acetate and butyrate),
solvents (e.g., acetone, n -butanol, and ethanol), biomass for selective plug-
ging, and BSs/biopolymers. BSs in particular have several benefits enhancing
oil displacement and movement through oil-bearing rocks by means of three
main mechanisms:

1. Reduction of interfacial tension between oil rocks and oil brine

2. Modification of the wettability of porous media

3. Emulsification of crude oil

In addition, BS production contributes to the metabolism of viscous oils by micro-
organisms that release lighter hydrocarbon fractions, thus making the oil even more
fluid. The strategies investigated so far for MEOR involving BSs include the following:

• Injection of ex situ produced BSs into the reservoirs

• Injection of laboratory-selected BS-producing microorganisms into the

reservoirs

• Stimulation of indigenous microbial population to produce BSs in situ

through supplying suitable nutrients