Enhancement of Remediation Technologies with Biosurfactants - Biosurfactants: Research Trends and Applications - page 240

Soil or sediment particle surface
properties and characteristics
important in pollutant retention

Physically constrained
bioaccessible pollutants
adsorbed at soil particles'
surfaces

Enhanced bioavailability for
microorganisms due to
presence of biosurfactants
compounds

Microorganisms

FIGURE 10.5

Enhancement of the bioavailability of pollutants by biosurfactants.

Noordman et al. (2002) determined that the biosurfactant from Pseudomonas
aeruginosa could enhance biodegradation if the process is rate-limited, such as in
the case of small soil pore sizes (6 nm), the hexadecane is entrapped and of limited
availability. The rhamnolipid can enhance release of entrapped substrates and uptake
by cells (if the substrate is available). This could then stimulate bacterial degradation
under in situ conditions. Al-Awadhi et al. (1994) showed that during in situ studies on
oil-contaminated desert sands, up to 82.5% reduction of total petroleum hydrocar-
bons and 90.5% reduction of total alkanes could be achieved in 12 months.
Rahman et al. (2003) examined the bioremediation of n-alkanes in a petroleum
sludge. The sludge contained an oil and grease content of 87.4%. The addition of
a bacterial consortium, nutrients, and the rhamnolipids to 10% sludge led to the
degradation of 100% of the C8-C11 alkanes, 83%-98% of the C12-C21 fraction,
80%-85% of the C22-C31 and 57%-73% of the C32-C40. Lower rates of biodeg-
radation occurred as the chain length increased but were still significant even for
C32-C40 compounds that are of low solubility.
The feasibility of biosurfactant production to bioremediate a soil contaminated with
a mixture of petroleum hydrocarbons and heavy metals was evaluated using batch
experiments (Jalali and Mulligan, 2007). After 50 days, the activity of the indigenous
soil microorganisms was enhanced, enabling reduction of total petroleum hydrocarbon
(TPH) by 36%. The biosurfactant concentration during this period reached three times
the critical micelle concentration, which increases the average concentration of TPH and
metals in the filtrate from 2.1% and 2.2% to 8.3% and 4.4%, respectively. The results indi-
cate that biosurfactant production can enhance bioremediation of cocontaminated soils.
Li et al. (2006) isolated six diesel oil degrading bacteria from an oil-contaminated
soil. One of the isolates produced a rhamnolipid biosurfactant with a CMC of the
biosurfactant of 65 mg/L in water and 185 mg/L in soil. The difference in the soil
was due to sorption on to the soil. This biosurfactant at concentrations of 0.01% and
0.02% was then evaluated for enhancement of diesel oil biodegradation in water and
soil. Rhamnolipid improved both the extent and rate of biodegradation when the
concentrations were higher than the CMC.