2. INTRODUCTION
M icrobial degradation of petroleum products in soil, either via naturally
occurring or facilitated methods, is used to reduce soil concentrations
of these products to acceptable levels (Atlas, 1988; Rhodes et al., 1994; Rhodes et
al., 1994b). Microorganisms found in soils include naturally occurring populations
that possess the ability to degrade petroleum products. Important soil factors that
affect biodegradation processes, which apply to petroleum hydrocarbon and other
organic contaminants, include (1) an energy source, (2) favorable soil pH, (3) soil
temperature, (4) availability of soil moisture, (5) availability of essential macro and
micro-nutrients, (6) the nature and bioavailability of the pollutants, and (7) aera-
tion. The potential biodegradability of petroleum hydrocarbons can generally be
estimated based on the structure of the chemicals comprising the source hydrocar-
bon product causing the pollution. For example, branching structures typical of
asphaltenes, generally reduce the biodegradation rate, and aromatic compounds are
degraded more slowly than alkanes (Huesemann, 1997).
A number of engineered treatment systems are available for bioremediation of
petroleum products in soil. The selection of a bioremediation system should be
based on the physical/chemical/biological properties of the product, site con-
straints, cleanup criteria, and state or local regulatory requirements (Guerin, 1996).
Land treatment, generally referred to as landfarming, has been widely used for
treatment of petroleum products, both in liquid and solid waste forms. Land
treatment is a bioremediation technique in which the petroleum product (liquid,
solid, or contaminated soil) is spread on soil, mixed with nutrients, and biode-
graded by soil microbes (either naturally occurring or amended to the soil). Land
treatment is a relatively uncontrolled method of reducing petroleum hydrocarbons
because volatilization is usually not prevented. Land treatment is now not gener-
ally recognized as an industry best practice for treatment of petroleum hydrocar-
bon-contaminated soils and wastes. A modification of land treatment that also
utilizes microbial degradation is the biopile (which can be static or aerated).
Composting is the addition of a soil amendment to contaminated soil to (1) supply
energy for microbial growth and biodegradation of petroleum products as well as
(2) a bulking agent to allow for enhanced microbial activity in the contaminated
soil (Rhodes et al., 1994a; Rhodes et al., 1994b). Soil composting, or co-composting,
an emerging bioremediation technology, relies on the actions of microorganisms
to degrade organic pollutants, resulting in the formation of heat and inorganic and
organic compounds (Semple et al., 2001). With changes in temperature, the
structure of the microbial community changes, and this encourages a diversity of
degradation reactions. Both aerobic and anaerobic processes can occur in windrow
composting, depending on the frequency and extent of soil and organic matter
mixing.
Soil composting is now becoming widely recognized and adopted for the
remediation of soils contaminated with recalcitrant organic compounds (Guerin,
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3. 2000). It has particular application to soils and sludges that have a large proportion
of nonvolatile petroleum hydrocarbons that are not readily degraded using conven-
tional land treatment (Prado-Jatar et al., 1993) or bioventing processes. Semple
(2001) provides an up-to-date overview of the application of soil composting and
readers are referred to this for further details on soil composting. In summary, for
recalcitrant petroleum hydrocarbons, soil composting is quicker; more controlled,
results in lower pollutant endpoints, and requires less space than land treatment.
There have been numerous reports on the effectiveness of composting processes
for the remediation of petroleum hydrocarbons. Weathered, hydrocarbon-contami-
nated soil containing 17,000 mg/kg oil and grease (O&G) of which 40% (w/w) was
aliphatic, 32% (w/w) polar, and 28% (w/w) aromatic was composted with maple
leaves and lucerne (Medicago sativa) in a laboratory-scale reactor. During this
period the compost temperature had risen from ambient to 53°C (day 2) and
subsequently, gradually returned to room temperature. The maximum rate of O&G
degradation (600 mg/kg/day) occurred at the beginning of the experiment. Soxhlet
extraction indicated that 50% of the O&G of soil origin was degraded in the first
105 days. O&G fractionation demonstrated that 60% of the aliphatics, 54% of the
aromatics, and 83% of the polars were degraded during the first 180 days of co-
composting. After 287 days, at least 73% of O&G of soil origin had been degraded
(Beaudin et al., 1996). Previous research has shown, however, that static windrows
can be as effective as turned windows in soil composting processes. Static and
windrow composting techniques were compared with respect to their efficiency in
the degradation of petroleum hydrocarbons. Static and windrow compost piles
were constructed from diesel fuel-contaminated soil with a TPH of 11,000 mg/kg.
Static aerated pile composting provided more effective treatment than windrow
composting (Wong et al., 1993), which involved turning of the soil compost mix.
In other studies, composting of horse manure was used as a means of degrading
two oil wastes; oil sludge from petrol stations and petroleum residues from a
refinery. Oil wastes decomposed to 78 to 93% during 4.5 months of composting.
No difference was found between the two types of oil wastes concerning their
decomposition. At the end of the experiment, most of the PAH compounds had
been degraded except pyrene, chrysene, and dibenz(ah)anthracene. Gaseous losses
of oil compounds through volatilization from composts were found not to be
significant (Kirchmann and Ewnetu, 1998).
In the current study, a site investigation was conducted at a fire fighting training
facility. This site investigation identified several areas of soil contamination requir-
ing remediation. The results of these investigations were then used to develop and
evaluate remedial options. The remediation process was conducted in two stages.
The excavation, validation, and reinstatement of two contaminated areas was con-
ducted first, followed by development of a composting treatment process. The
overall goal of the remedial works at the site was to enable the upgrade of the
Flammable Liquid Pad (FLP)/Fuel Mix Areas (FMA) facilities, to provide better
management of liquid fuels and hydrocarbon contaminated effluents and so prevent
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4. further soil and water contamination from the fire training activities. The specific
objective was to remove and treat the petroleum hydrocarbon contaminated soils on
the site to <1000 mg/kg for the C10-C36 n-alkane hydrocarbon fractions (Victorian
EPA Guidelines for low level contaminated soil). This study reports the results of a
composting treatment process implemented to remediate this contamination.
SITE BACKGROUND
Location
The site is located in southeastern Australia. The site (~150 ha) is in a rural pasture
setting and currently is used as a training area for fire and emergency services
personnel from various organisations. This principally involves fire fighting exer-
cises at a number of “props”, using both gas and liquid fuels. The site has been used
for such training for ~20 years. Prior to this few buildings existed on the site. The
main areas of the site comprise a FLP and FMA used for fire training, bulk fuel
storage area, light industrial facilities, including stores, workshops, and under-
ground diesel storage tanks. All of the industrial facilities are located in the central
part of the site where the contamination is present.
Topography, Drainage, and Subsurface
The site is located on a flat to gently undulating plateau, with lakes and wetlands
formed in local depressions. A small lake is situated immediately southwest of the
contaminated area and a central north-south ridge forms a break in the site drain-
age. The site drains to two creeks surrounding the facility.
Subsurface Conditions
The site lies over quaternary olivine basalt bedrock. Surface soils are residual silts
and clays, generally no more than 2 to 3 m deep, overlying very stiff, high plasticity
residual clays, grading to variably weathered basalt. Shallow fill, comprising
gravel or road base, is found on parts of the site, particularly in the area of the
Flammable Liquids Pad. A summary of the site stratigraphy is given in Table 1.
Eight bores (four deep bores to 20 m, and four shallow to 2 m) were installed.
Groundwater was encountered in only two of these bores. The basalts are generally
dense and unjointed without significant primary or secondary porosity to enable
groundwater flow. The residual clays are also of low water bearing potential. As
a result, the occurrence of any significant groundwater is precluded, and the
potential for contaminant migration via groundwater is very limited.
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5. TABLE 1
Generalized Subsurface Profile
Soil Depth to Top of Thickness Description
Unit Layer (m) (m)
1 0 0.1 - 0.8 Fill: fine to coarse grained sandy gravel, silty
clay or medium plasticity red clay.
2 0.2 - 1.0 0.1 - 0.2 Residual silty clay: medium plasticity, grey to
grey-brown, may comprise rounded buckshot
gravel (2-5mm) with clay.
3 0.3 - 1.2 0.5 - 1.8 Silty clay: high plasticity, yellow-grey to yellow-
brown, mottled orange-yellow. Residual clay
formed on basalt.
4 0.8 - 2 14 - 18 Basalt
5 16 - 18.8 3.2 - 6.0 Volcanic ash
Nature of Soil Contamination
Soil and sediment contamination was present on the site, predominantly as petro-
leum hydrocarbons, with lower concentrations of benzene, toluene, ethyl benzene,
and xylenes (BTEX), phenols, and lead. This contamination principally resulted
from storage and handling of fuels, use of liquid fuels in fire training activities, and
disposal of fuel residues such as sludges. The petroleum hydrocarbons were
generally medium to heavier fractions (C15-C36), as expected from the nature of the
activities on the site with concentrations up to 20,000 mg/kg. Light hydrocarbons
(C6-C9 and C10-C14), including BTEX constituents, were present in a drum burial
area with concentrations up to 2000 mg/kg. This area also contained elevated
concentrations of phenols. One sample from the old Fire Training Pits (FTP)
contained elevated concentrations of lead. No significant concentrations of poly-
cyclic aromatic hydrocarbons or other heavy metals were found at the site. No
organochlorine pesticides or PCBs were detected in any samples tested in soil from
the site.
Extent of Soil Contamination
Two areas of soil contamination were identified requiring remediation, as part of
development plans for the site, as follows: (1) FLP. This large area contained
obvious and unsightly superficial soil contamination with fuel residues from fire
training activities. Crushed rock fill was contaminated with petroleum hydrocar-
bons at depths of 0.1 to 0.5 m, but generally no deeper than 0.8 m. Total petroleum
hydrocarbon concentrations ranged up to 1600 mg/kg; (2) Old FTP. Two decom-
missioned fire training pits, east of the FLP contained a thin layer (less than 10 cm
thick) of black petroleum hydrocarbon sludge, at a depth of 0.1 to 0.6 m. The
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6. sludge was covered by a 0.1- to 0.8-m-thick layer of surface fill comprising silty
clay, silt and gravel. High concentrations of total petroleum hydrocarbons (TPH),
up to 88,000 mg/kg, were found in the sludge layer and in soil from 0.6 to 1.0 m.
Phenols were present at concentrations up to 50 mg/kg. The average initial phenol
concentration in the segregated, uncomposted, material was 2.5 mg/kg and the
maximum was 9.3 mg/kg. In the soil that was actually composted (not stockpiled
only), the initial average phenol concentration was even lower, at 1.6 mg/kg, with
a maximum 4.1 mg/kg. No post-composting analysis were conducted to determine
phenol in the current study. A guideline is provided by the Dutch soil intervention
value of 40 mg/kg (RIVM, 1994). The current Australian risk-based health inves-
tigation levels for phenol are higher still (i.e., 8500 mg/kg for a residential, i.e., a
sensitive setting) (NEPC, 1999). Given the current land use at the site, and the
absence of any significant groundwater or surface water resource, the maximum
phenol concentrations of the treated soil do not represent a significant risk to
human health or the environment. Elevated lead (710 mg/kg) was found in one
sample. The TPH, BTEX, phenol, and lead contamination was distributed within
the top 1 to 1.5 m of the soil profile.
MATERIALS AND METHODS
Excavation Criteria
Remediation of the soil contamination involved excavation of all soil exceeding
specified criteria for organic contaminants and lead, and transport to a treatment
area constructed elsewhere on the site. The criteria adopted for the excavation work
were the relevant guidelines for off site disposal of contaminated soil as clean fill:
total petroleum hydrocarbons (TPH) ([C9) 100 mg/kg; total petroleum hydrocar-
bons (TPH) (C10-C36) 1000 mg/kg; phenols 1 mg/kg; BTEX 7 mg/kg; lead 300 mg/
kg.
Soil Treatment
The excavated contaminated soil was treated by on site composting. Given the
contaminants were predominantly medium-heavy hydrocarbons, the aim of the
treatment was to stabilize the soil so that it could be reused on site as fill material,
for example, under a new training pad. Two criteria were proposed. Either the
average concentration of TPH should fall below 1000 mg/kg (C10-C36) or the
composting process should reach completion.
The selection of an environmentally acceptable endpoint for treatment of petro-
leum hydrocarbons in soil is a complex process involving numerous factors (Linz
and Nakles, 1997). A plateauing of biodegradation activity was considered to
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7. represent a natural, or environmentally acceptable endpoint for the composting
process and was used to assess the status of the soil remediation process. At this
stage, the residual petroleum hydrocarbons can be considered to be ‘biostabilized’,
effectively immobile and unavailable for further uptake and biodegradation, and
thus unlikely to adversely affect the quality of the soil or water with which it may
come into contact’(Huesemann, 1995; Huesemann, 1997). Changes in the tem-
perature regime were not used as an indicator of biostabilization since other
factors, such as soil mixing, could reactivate the biodegradation reaction and again
decrease the residual petroleum hydrocarbons. The temperature was measured (see
section “Monitoring and Maintenance) in order to assess whether a mesophilic or
thermophilic process was occurring in the windrows.
Construction of Treatment Area
The facility consisted of a bunded area with final dimensions of 200 m × 40 m. The
area was scraped and graded, before stockpiling and processing the contaminated
soil. The 500 mm bunds were constructed of compacted local clay soil. Surface
drainage external to the treatment facility, was diverted around the facility via a
perimeter drain. Any run-off within the facility area was collected and pumped to
the nearby dam. This dam was a retention pond and retained any leachate on site.
This was achieved with a shallow drain within the bund wall, draining to a deeper
sump (500 to 600 mm) at the low southern end of the treatment area. Though no
data were collected, only very small volumes of leachate were actually generated
during the composting process because of judicious application of water to the
windrows. Once operational, access to the site was controlled by site personnel, so
that only machinery directly involved in the process would contact contaminated
soil. Trucks, excavators, and other machinery were washed down after handling
contaminated soil and compost, and before these machines were allowed to leave
the site. This wash down water, which was of a low volume (no data collected), was
colleted in the on site retention pond.
Establishment of Compost Windrows
Soil was excavated from the FLP (including the FMA) and the FTP, and stockpiled
in 7 rows in the bunded treatment area. The total volume of soil excavated was
~6000 m3. This material was sampled to determine TPH contamination. Any soil
that was determined at >1000 mg/kg TPH (C10-C36) was segregated and designated
for treatment by soil composting. Excavated soil determined at <1000 mg/kg TPH
was set aside. As well as low concentrations of TPH, this material was found to
contain low concentrations of total phenol compounds (up to 9 mg/kg). These low
concentrations were not considered to represent any unacceptable risk to health or
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8. environmental receptors at the site since these concentrations fell within the
regulatory guidelines of 10 mg/kg for low-level contaminated soil at the facility.
Additionally, it was decided that biodegradation would be stimulated through
aeration and mixing during excavation and placement, resulting in a further reduc-
tion in the concentration of phenols and TPH. In total, 4300 m3 of soil was
designated for soil composting.
Hydrocarbon contaminated soil was then stockpiled in four windrows (~1000 m3
each). The approximate dimensions of the windrows were that of rectangles of 200
m long × 5 m wide × 1 m high. To each soil stockpile a mixture of freshly shredded
green tree waste (-20 mm fraction), cow manure, gypsum, and nutrients (MaxBac,
Scotts, Sydney) were added. Approximately 35% by volume of raw materials were
added to the soil to initiate composting. Table 2 provides details for the volumes
of soil and raw materials used. The shredded green tree waste provided necessary
bulking agent into the soil mix, which in turn allowed for improved aeration by
diffusion if only contaminated soil was in the windrows. Cow manure also contrib-
uted as a bulking agent. The shredded green tree waste and cow manure also
contributed an energy source to the soil mixture that allowed microbial populations
to flourish. Gypsum was added at ~4% (v/v) and has previously been shown to
enhance soil properties in bioremediation processes (Rhodes and Guerin, 1996;
Guerin, 2000). The MaxBac, a proprietary mixture of slow release micro nutrients
only, was added at the recommended rates of 50 g/m3 of contaminated soil.
Monitoring and Maintenance
For the first 2 months of composting, the internal temperature of the compost
windrows was monitored using thermocouples linked to a field datalogger (Datataker
Model DT50). The soil compost windrows were kept moist (20 to 25% w/w)
during the dry summer months with regular watering. No other maintenance on the
windrows was performed. The windrows were therefore static for the remainder of
the trial.
Sampling Protocol
General. Once the composting process was initiated, the windrows were sampled
after 2 months, and followed up with a second round of sampling after 6 months
composting. The samples were collected by taking multiple composite samples
from the loader bucket. In order to determine the variation associated with this
sampling technique a set of 20 separate samples were taken from one bulldozer
bucket and analyzed. Each bucket load was taken as a cross section through the
short length of each windrow. Each sampling event introduced oxygen into the
windrow, at least in the adjoining 1 to 2 m of windrow length.
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9. 340306.pgs
TABLE 2
Composition of Soil Compost Windrows
Compost Green Cow Gypsum Total Raw Contaminated Total Initial
667
Windrow Tree Waste Manure (m3) Materials Soil Volume
(m3) (m3) (m3) (m3) (m3)
1 270 75 50 395 940 1335
2 280 75 50 405 1035 1440
3 265 75 60 400 1185 1585
4 280 75 50 405 1180 1585
Total 1,605 4,340 5,945
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10. Sampling After 2 Months. Four windrows were established in the composting
process. From windrow 1, samples were taken at seven locations along the wind-
row, and at three different depths (top, middle, and bottom). Additionally, in order
to determine the variation associated with sampling, additional samples were taken
from this windrow. Field duplicate samples were taken 0.5 m from the original
samples. This resulted in a total of 42 samples being collected from Windrow 1.
From each of the other three windrows, samples were taken from the middle depth
and at three locations along each windrow.
Sampling After 6 Months. Samples were taken at seven intervals along each
windrow, again at three different depths. This resulted in a total number of 84
samples.
Analytical Protocols
Solvent extraction of the total petroleum hydrocarbons was conducted using DCM
(dichloromethane):acetone (3:1) as the same method as previously described (Guerin,
1999c). Total phenols were analyzed using APHA 5530C (Anon., 1992). Soil pH
(1:5 soil water extract) was also monitored during the process. Soil pH, soil lead,
PCBs, organochlorine pesticides, and TPH analyses were taken from standard US
EPA protocols as described elsewhere (USEPA, 1983; USEPA, 1996).
RESULTS AND DISCUSSION
The initial average concentration of TPH (C10-C36) in the excavated contaminated
soil was 3075 mg/kg, ranging between 1000 to 7900 mg/kg. After 2 months of
composting, the second sample set indicated that the average TPH concentration
for the four windrows had been reduced to 900 mg/kg.
There was variation in the TPH concentrations between the four windrows, and
also within the windrows. This variation was analysed statistically and the total
error was found to be ± 40%, that is, the TPH concentration overall was 900 ± 370
mg/kg (Table 3).
While the average TPH concentration was below the target of 1000 mg/kg
C10-36 TPH after 2 months, the 95% upper CI for the total compost mass for this
sampling program was 1270 mg/kg. A third sampling program was performed
6 months after the windrows were established. At this time, the average TPH
concentration was 730 mg/kg (Table 3). Error analysis was again performed
that also indicated a total error of ±40%, as found in the initial error analysis.
While the upper 95% CI for windrows 1 and 2 exceed 1000 mg/kg TPH (1500
and 1100, respectively), the average TPH concentration across the 4 windrows
after 6 months of treatment was below the clean fill criterion of 1000 mg/kg
C10-36 TPH.
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11. TABLE 3
TPH Concentrations in Soil Compost
TPH concentration
Compost (mg/kg total dry mattera)
Windrow
Average Average Average Upper 95% CI at 6
Initial 2 Months 6 Months monthsb
1 2,800 1,200 1,080 1,510
2 4,500 850 810 1,130
3 3,400 780 530 740
4 1,800 770 510 710
mean 3,100 ± 1,270 900 ± 370 730 ± 300 1,020
a All data are given to 2 significant figures. Concentrations are not adjusted for dilution from added organic
matter. The TPH reported here is in the range of C10-C36.
b 95% Upper Confidence Interval (CI) = Average Concentration + 40%.
There were no other contaminants of significance in the composted soil. For
example, there were no volatile petroleum hydrocarbons (C6-C9) present in the
soil-composting mix in the windrows, prior to treatment. Elevated lead concentra-
tions were identified in one sample taken from the FTP, which represents ~30% of
the total material in the compost windrows. However, the rest of the compost
windrows consist of material sourced from the FLP and the FMA which reported
acceptable concentrations of lead. After mixing the material it was expected that
the lead “hotspot” would have been dispersed and diluted. Results of the lead
analysis (at T = 6 months) showed that the average lead concentration of all the
material was 55 mg/kg, which is well below the 300 mg/kg clean fill criteria for
lead. All of the samples assayed were below these guidelines (Table 4). In the lead
sampling program, 20 replicate samples were analyzed (the same samples were
used as those used for TPH analysis at 6 months). This found that the subsampling
and analytical error for the lead analysis was 13%.
There are several important soil factors that affect the biodegradation processes,
which also apply to composting or co-composting of petroleum hydrocarbon-
contaminated soil. These are an energy source, favorable soil pH, soil temperature,
availability of soil moisture, availability of essential macro and micro-nutrients,
bioavailability of the pollutants, and aeration. These are discussed as follows:
• Energy Source. In the current study, the energy source was provided through
the added organic matter and the TPH contaminants.
• Mixture pH. The pH of soil/OM mixture remained within the range of 6.5
to 7.5 throughout the process.
• Windrow Temperature. There was only a relatively small increase in the
temperature profile in the soil composting mix during the 6 month treatment
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12. TABLE 4
Extent of Lead Contamination in Compost Windrows
Compost Lead Concentration (mg/kg)
Windrow
Average Minimum Maximum
1 60(a) 42 69
2 38 20 82
3 48 22 82
4 55 33 97
a One sample from windrow 1 assayed at ~360 mg/kg lead. Another sub-sample was taken and assayed, this
yielded a result of 60 mg/kg lead. The first assay is considered an outlier, and has been omitted from the
statistical analysis.
period (Table 5). This is unlike other studies of the composting of soil (also
referred to as co-composting in the literature), where composting tempera-
tures have increased to >40°C (Guerin 1999a). Typically composting reac-
tions cause windrow temperatures to increase to as high as 45 to 65°C
(Semple et al., 2001). These lower temperatures recorded in the current
study may be a reflection of lower levels of aerobic microbial activity.
• Windrow Moisture. Moisture content of the soil/OM mix in each windrow
was kept within the target moisture content of 20 to 25%. The soil-compost
mixture was also shown to have a strong water absorbing capacity as there
was only very small volumes of leachate released after each water period.
Furthermore, after heavy rainfall, only small amounts of rain water re-
mained free within the bunded treatment area.
• Bioavailability. No specific tests were conducted to evaluate this property
of the TPH compounds in the soil composting mixtures. However, from the
6 month composting data, it was likely that the composting process may
have increased the bioavailability of the TPH in the soil as this contamina-
tion had been present for periods of up to 30 to 40 years.
• Windrow Aeration. Given that the windrows were only mixed during the
initial stages of the process, it is likely that there would have been anaerobic
processes in the windrows. Therefore, even under conditions where oxygen
was likely to be limiting, petroleum hydrocarbon degradation still occurred,
attaining the target criteria of <1000 mg/kg C10-36 TPH. Further research
would be needed to determine to what extent anaerobic and aerobic pro-
cesses were occurring in the windrows.
After 6 months, the composting was considered to be complete, with the soil-
compost mix posing no unacceptable risks to human or environmental health. It is
expected that without further maintenance of the compost windrows (i.e., watering,
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13. 340306.pgs
TABLE 5
Temperature Changes in Compost Windrows (°C)
Days Windrow Mean Windrow Maximum Ambient Maximum Variation(a)
671
0 16 16 14 2
3 28 32 14 4
5 28 32 13 4
10 27 30 13 6
20 24 27 12 5
40 22 25 11 5
80 16 17 10 4
a variation across 4 treatment windrows
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14. aeration) contaminant degradation will continue, albeit slowly. Grasses colonised
the compost (90 to 100% surface coverage) in the 6 month period immediately
after the end of the processing. This growth will stimulate phytoremediation
processes that will further promote contaminant degradation (Chang and
Corapcioglu, 1998). The bund walls will be maintained, until the compost wind-
rows are sufficiently vegetated, to prevent potential run-off of sediment-laden
water.
CONCLUSIONS/IMPLICATIONS
The composting process was successful in reaching its primary objective of reduc-
ing TPH concentrations to acceptable clean fill criteria of <1000 mg/kg C10-36 TPH.
The process observed is best described as mesophilic because high temperatures
(i.e., >45°C) were not achieved. The composted soil remaining from the composting
process was used to rehabilitate the treatment area, leveling the soil and compost
windrows within the bund walls, and allowing revegetation to take place. Co-
Composting, with minimal windrow turning (i.e., aeration), can be effective in
bioremediatin in long-chain, nonvolatile n-alkanes in clay soil.
ACKNOWLEDGMENTS
The contributions of my colleagues in Rio Tinto Technical Services (Sydney and
Melbourne, Australia) are gratefully acknowledged, in particular Stuart Rhodes.
The information and opinions expressed in this paper are those of the author and
do not necessarily reflect those of Shell Engineering
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