The central aim of this study was to determine if indigenous fungi of an oil-contaminated
soil could be effectively used in a low-cost bioremediation of the soil. Since some of the
contaminant had been present at the site for over two decades, the indigenous microbial
species had been subjected to specific selection pressures for a protracted period, thus
facilitating key enzymatic capabilities for hydrocarbon degradation. Analysis of the
pertinent influential parameters of soil bioremediation indicated that an ex situ technique,
utilising the catabolic activities of the indigenous soil fungi, was a feasible low-cost option.
Fungi were isolated from the contaminated soil through a variety of techniques. The
abilities of these isolates to degrade the contaminant oil and a range of representative
hydrocarbon molecules was evaluated by a systematic screening programme. Sixty-two
isolates were initially examined for their growth potential on hydrocarbon-supplemented
agar. A bioassay, utilising hydrocarbon-impregnated filter paper discs, was then used to
examine the abilities of 17 selected isolates to catabolise three representative hydrocarbon
molecules (hexadecane, phenanthrene and pristane) in different concentrations. In the same
bioassay, the influence of a co-metabolite (glucose) on growth potential was also examined.
Eight fungal species: Trichophyton sp.; Mucor sp.; Penicillium sp.; Graphium sp.;
Acremoniwn sp.; Chaetomium sp.; Chrysosporium sp.; and an unidentified basidiomycete
were then selected. Liquid batch cultures with a hydrocarbon mixture of hexadecane,
phenanthrene, pristane and naphthalene facilitated quantitative analysis (HPLC) of the
hydrocarbon catabolic abilities of the selected isolates.
Ex situ bioremediation was evaluated at laboratory-scale by both bioaugmentation and
biostimulation in soil microcosm trials. During the course of the study, total petroleum
hydrocarbon (TPH) concentration (U.S. EPA Method 418.1) was used as a simple and
inexpensive parameter to monitor hydrocarbon disappearance in response to soil
treatments. Soil microbial activities were estimated by use of a fluorescein diacetate
hydrolysis bioassay. This was found to be a reliable and sensitive method to measure the activity of respiring heterotrophs as compared with the unreliable data provided by plate
counts.
In the bioaugmentation trial, the eight selected isolates were individually used to inoculate
(30% v/v) the contaminated soil. The highest rate of biodegradation (50.5% > than the
non-sterile control) was effected by an Acremonium species after 50 days incubation
(25°C). The second highest rate of biodegradation (47% > than the non-sterile control)
was achieved with a soil treatment of sterile barley/beer waste only. Comparable rates of
hydrocarbon degradation were achieved in simple biostimulation trials. Thus, due to its
lower cost, biostimulation was the preferred remediation strategy and was selected for
further laboratory investigation. Common agricultural or industrial lignocellulosic wastes
such as: wood chips; straw; manure; beer brewery waste; mushroom compost; and spent
mushroom substrate were used as soil treatments, either alone or in combination. The
effect of the addition of a standard agricultural fertiliser was also examined. The highest
level of biodegradation (54.4% > the non-sterile control) was recorded in a microcosm
supplemented (40% v/v) with chicken manure.
Finally, an ex situ bioremediation technique was examined in a pilot-scale field trial. Wood
chips and chicken manure were co-composted with the contaminated soil in a low-cost,
low-maintenance bioremediation system know as passive thermal bio venting. Extensive
monitoring of the thermal environment within the biopile was made as an indirect measure
of microbial activity. These data were then used to optimise the composting process.
Three-dimensional graphical representations of the internal temperatures, in time and
space, were constructed. From these graphs, it was determined that an inner core region of
approximately 500 cm3 provided a realistic simulation of conditions within a full-scale
biopile. During this trial a TPH reduction of 68% was achieved in 130 days.
The findings of this research suggested that the utilisation of fungal catabolism is applicable
to soils contaminated with a wide range of hydrocarbon contaminants. Passive thermal
bioventing offers a bioremediation strategy which is highly suitable for South African
conditions in terms of its low level of technological sophistication, low maintenance design and, most importantly, its relatively low cost. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5421 |
| Date | January 1997 |
| Creators | McGugan, Brandon Ross. |
| Contributors | Senior, Eric. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
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