Complex soil-microorganism-pollutant interactions underpinning bioremediation of hydrocarbon/heavy metal contaminated soil.
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Date
1996
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Abstract
This study evaluated the efficacy of bioremediation as a treatment option for a
hydrocarbon and heavy metal contaminated soil. Microbial degradation of
hydrocarbons under aerobic, nitrate-reducing and sulphate-reducing conditions was
examined. Nutrient supplementation with nitrogen and phosphate as well as aeration
seemed to be the most important factors for enhancing biodegradation. From initial
batch studies, a carbon: nitrogen ratio of 50: 1 was found to be optimal for
biodegradation. However, very low carbon to nitrogen ratios were undesirable since
these inhibited microbial activity. Manipulation of the pH did not seem to be beneficial
with regard to hydrocarbon biodegradation. However, low pH values induced elevated
concentrations of leachate heavy metals. Aerobic conditions provided optimal
conditions for hydrocarbon catabolism with up to 54% of the original contaminant
degraded after 2 months of treatment. Further treatment for up to 20 months did not
significantly increase hydrocarbon biodegradation. Under nitrate- and sulphatereducing
conditions, 6% and 31 % respectively of the initial contaminant was degraded
after 2 months while after a further 20 months, 50% and 42%, respectively were
degraded. The addition of soil bulking agents and the use of sparging did not
significantly increase biodegradation. Similarly, the addition of inoculum did not
influence biodegradation rates to any great degree. The presence of heavy metals up
to concentrations of 400 mgt1 Mn, 176 mgt1 Zn and 94 mgt1 Ni did not reduce microbial
activity within the soil. During the treatment phase, heavy metal and hydrocarbon
migration were limited even under water saturation and low pH conditions. A
Biodegradation Index was developed and evaluated and may, potentially, find use as
an in situ assessment technique for microbial hydrocarbon catabolism. The
iodonitrophenyltetrazolium salt assay was also found to be an effective and rapid
alternative assay for monitoring bioremediation progress.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.
Keywords
Soil pollution., Soil remediation., Hydrocarbons--Biodegradation., Soils--Heavy metal content., Sewage--Purification--Heavy metals removal., Theses--Microbiology.