In this study, biological methods (biostimulation
and bioaugmentation) were used to treat oil tank bottom
sludge contaminated soils to total petroleum
hydrocarbon (TPH) levels suitable for landfill disposal. The
sludge’s hydrocarbon-degrading microbial capacities were
initially compared to those from other contaminated environments
using culture-based methods. Results indicated
that a fungus,
Scedosporium
dominated the sludge microbial
community. Its application in a nutrient formulation
resulted in greater reduction in oil tank bottom sludge
viscosity (44 %) and residual soil hydrocarbon compared
to hydrocarbonoclastic microorganisms from other sources
(26.7 % reduction in viscosity). Subsequent field-based
experiments showed greater TPH reduction (54 %) in
fungal-nutrient-treated sludge–waste soils than in naturally
attenuated controls (22 %) over 49 days. 16S ribosomal
ribonucleic acid and internal transcribed spacer regionbased
polymerase chain reactions and denaturing gradient
gel electrophoresis analyses showed minimal effects on the
microbial communities during this time. TPH reduction to
landfill disposal levels occurred at a slower rate after this,
falling below the 10,000 mg kg
-1 legislated TPH disposal
threshold earlier in amended samples (91.2 %;
9,500 mg kg
-1) compared to the control (82 %;
17,000 mg kg
-1) in 182 days. The results show that the
intrinsic hydrocarbon-degrading microbial capacities in
sludge are better suited for sludge degradation than those
from other sources. The substantial TPH reduction
observed in control samples demonstrates the beneficial
effects of natural attenuation with waste soils for oil tank
sludge treatment. Microbial capacities in sludge and treated
waste soils can therefore be successfully employed for
treating oil tank bottom sludge.
