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Recycling of Remediated Soil for
Effective Composting Of Diesel-
Contaminated Soil
Eui-Young Hwanga, Wan Namkoongb & Joon-Seok Parkb
a Institute of Technology, Kyong-Ho Engineering Co. Ltd., Kyonggido,
Korea
b Department of Environmental Engineering, College of Engineering,
Konkuk University, Seoul, Korea
Published online: 23 Jul 2013.
To cite this article: Eui-Young Hwang, Wan Namkoong & Joon-Seok Park (2001) Recycling of
Remediated Soil for Effective Composting Of Diesel-Contaminated Soil, Compost Science & Utilization,
9:2, 143-148, DOI: 10.1080/1065657X.2001.10702028
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Compost Science & Utilization, (2001), Vol. 9, No. 2, 143-148
Recycling of Remediated Soil for
Effective Composting Of Diesel-Contaminated Soil
Eui-Young Hwang1, Wan Namkoong2 and Joon-Seok Park2
1. Institute of Technology, Kyong-Ho Engineering Co. Ltd., Kyonggido, Korea
2. Department of Environmental Engineering, College of Engineering,
Konkuk University, Seoul, Korea
Soil contaminated with diesel oil was remediated by the addition of remediated soil.
Several mix ratios of contaminated soil to remediated soil were tested. Judging from
TPH degradation rate and biochemical parameters, the optimum mix ratio (wet
weight basis) was 1:1. In this mix ratio, the first order degradation rate constant of
diesel oil based on TPH was 0.099/day. Degradation rate of TPH and total amount of
CO2 evolved in this condition were two times larger than those of contaminated soil
without adding remediated soil. The addition of remediated soil was a very effective
treatment option to facilitate the degradation rate of diesel oil in contaminated soil.
Introduction
Recycling of remediated soil has several advantages for effective composting of
contaminated soil because the recycled soils usually have acclimated microorgan-
isms. Acclimation of microorganisms on the target contaminants can significantly af-
fect the degradation rate of contaminants in the composting process. Prior exposure
of a microbial community to hydrocarbons may result in an increase of the hydro-
carbon utilizing potential of the microbial community (Leahy and Colwell 1990).
Also, acclimation of the microbial community to hydrocarbons such as diesel may
increase the degradation rate of hydrocarbons associated with fuel oil contaminated
environments.
Bioaugmentation (the addition of commercial inocula) is occasionally employed
in the composting process, but its usefulness has yet to be proven and is currently an
issue of controversy (USEPA 1996). Bioaugmentation may be inappropriate because
introduced cultures may lack the microbial diversity that is an important factor in
decomposing contaminant mixtures in natural systems. Pearce et al. (1995) indicated
that differences in TPH (Total Petroleum Hydrocarbons) reduction capacity between
commercial and indigenous microorganisms were insignificant. They concluded that
microorganisms of indigenous microorganisms were efficient and was more cost ef-
fective compared to the commercial microorganisms for application at full scale. If
possible, recycling a portion of previously composted (remediated) soil, that once
contained the same contaminants, will ensure the presence of a large population of
microbes capable of degrading the contaminant of concern (Peramaki and Blomker
1997; USEPA 1996). The best inoculum for remediation of hydrocarbons contamina-
tion is the contaminated soil (Cookson 1995). Minna Laine and Jørgensen (1996 1997)
reported that addition of remediated soil was effective in degrading chlorophenols
and PCP (Pentachlorophenol). Namkoong and Hwang (1997) reported that recycling
of composted material was effective for nightsoil composting. Effect of remediated
soil addition on the composting of the diesel-contaminated soil, however, has not
still been reported. Also, appropriate mix ratio of contaminated soil to remediated
soil has not been discussed. Therefore, this research was carried to find out the prop-
er mix ratio of contaminated soil and remediated soil for effective composting of
diesel-contaminated soil.
Compost Science & Utilization
Spring 2001 143

Eui-Young Hwang, Wan Namkoong and Joon-Seok Park
Materials and Methods
Materials
Soil was air-dried and sieved to pass a 2mm sieve. Texture of the soil was classified
as a typical sandy loam (the portion of sand, silt, and clay in soil was 59.5%, 23.0%, and
17.5%, respectively). Organic matter content of the soil was 2.6%. Field capacity of the soil
was 26.1%, which was a typical value of sandy loam. CEC of the soil was 17.1 meq/100g
dry soil. Remediated soil was obtained from the previous experiments (not included in
this article). Organic matter content of the remediated soil was 10.4%. Field capacity and
CEC of the remediated soil was 36.3% and 24.7 meq/100g dry soil, respectively.
Experimental Apparatus
Experimental apparatus
used for this research consist-
ed of a compost reactor,
two CO2 removal traps, a hu-
midifier, and a trap for collect-
ing CO2 evolved through
biodegradation as shown in
Figure 1. Carbon dioxide was
removed from the incoming
air so that CO2 in the exiting
air was attributed entirely to
Figure 1. Schematic diagram of experimental apparatus used for this re-
search.
decomposition (Cook et al.
1994). Most of the CO2 in the
incoming air was removed by reaction with soda lime (Ba(OH)2). Any residual CO2 that
passed through the solid-phase soda lime column was efficiently removed by reacting
with 25mL sodium hydroxide (4N NaOH) in a secondary CO2 removal trap. Humidifi-
er containing 25mL distilled water was used to prevent any aspirated alkali solution
from entering the compost reactor, and to raise the moisture content of the incoming air
to nearly 100% relative humidity at room temperature. Air tight glass vessel of 3 liters
was used as reactor for this research. Carbon dioxide removed, humidified air was en-
tered into the compost reactor from the bottom through perforated stainless steel plate.
The perforated plate was covered with 5mm diameter glass beads. Volatile compounds
from the reactor were collected using a 4 mm internal diameter and 7 cm long glass tube
(SKC Cat. No. 226-01) containing 150 mg of charcoal. Charcoal tube was replaced to de-
termine volatilization rate at each sampling interval. Evolved CO2 was continuously
trapped in a solution of 4N NaOH.
Experimental Conditions
Target contaminant of this research was diesel oil, which was spiked at 10,000
mg/kg on a dry weight basis for all samples. Experimental apparatus was placed in an
incubator in which temperature was maintained at 20°C in order to minimize effect of
exterior temperature variation. Aeration rate of 100 mL/min was introduced into the re-
actor. Moisture content of sample to be treated was adjusted to 70% of field capacity. In
this research, remediated soil was mixed with fresh contaminated soil in various mix ra-
tios. The ratios of contaminated soil to remediated soil were 1:0.1, 1:0.5, and 1:1 as wet
weight bases. Composting of remediated soil-only without adding contaminated soil
144 Compost Science & Utilization
Spring 2001

Recycling of Remediated Soil for Effective Composting
Of Diesel-Contaminated Soil
was also tested to find the degradation rate of diesel oil in remediated soil as a reference.
Biocide control experiment (1:1 mix ratio) by the addition of HgCl2 of 2,000 mg/kg was
carried out to differentiate the biological and chemical degradation.
Analysis
Sample for GC analysis was extracted for 2 hr at 200 rpm at the ratio of 1 to 5 of sam-
ple to methylene chloride. Average recovery efficiency of this procedure for TPH was
98.7%. The VOCs were extracted by placing the charcoal in 8 mL screw cap vial and
adding 4 mL methylene chloride to the vial. A 1µL sample of the extract was injected
into a gas chromatograph (Hewlett Packard Model 5890 Series II) equipped with an in-
tegrator (Hewlett Packard Model 3395), a flame ionization detector and HP-1 column.
The initial temperature was kept at 50°C for 1 minute, increased at 25°C/min to a final
temperature of 300°C, and maintained at that temperature for 1 minute in order to en-
sure that the column was clean. The injection port and detector temperatures were
250°C and 300°C, respectively. Hydrogen gas and air flow rate for the flame ionization
detector was 33 mL/min and 330 mL/min, respectively. Nitrogen carrier gas was de-
livered at a rate of 28 mL/min. Carbon dioxide evolved by biological reaction was col-
lected in 4N NaOH as proposed by Stotzky (1979). An excess of barium chloride (3N
BaCl2) was added to precipitate the carbonate as BaCO3. After adding a few drops of
phenolphthalein indicator, the unneutralized alkali titrated with 1N HCl. Carbon diox-
ide-uncollected NaOH was titrated as blank. Dehydrogenase activity was used as a
broad-spectrum indicator of microbial activity in soil. Dehydrogenase activity was mea-
sured spectrophotometrically using the reduction characteristics of TTC (2,3,5-triph-
enyltetrazolium chloride) to TPF (triphenylformazan). Dehydrogenase activity was ex-
pressed in micrograms of formazan per gram of sample (µgTPF/g sample).
Results and Discussion
Volatilization-corrected TPH rapidly decreased with increasing amount of reme-
diated soil added (Figure 2). In the ratios
of 1:0.5 and 1:1 of contaminated soil to re-
mediated soil, significant decrease of
TPH was observed until 15 days. Signifi-
cantly slow decrease of TPH was moni-
tored in 1:0.1 mix ratio experiment and
soil-only experiment without adding re-
mediated soil. This means that recycling
(addition) of appropriate amount of re-
mediated soil was effective in the degra-
dation of TPH. In addition, remediated
soil-only experiment also showed a rapid
decrease of TPH. In biocide experiment,
no significant decrease of TPH was ob-
served, which means that decrease of
TPH in other experiments was primarily
due to biodegradation.
The initial TPH level in the mix ratio
Figure 2. Variation of volatilization corrected TPH and sum
of 1:1 of contaminated soil to remediated
of n-alkanes during composting (ꢀ remediated soil only,
ꢁ 1:0.1, ꢂ1:1, ꢃ 1:0.5, ꢄ biocide control, ꢅꢆ soil only).
soil was about 9,896 mg/kg. After 30 days,
Compost Science & Utilization
Spring 2001 145

Eui-Young Hwang, Wan Namkoong and Joon-Seok Park
TABLE 1.
TPH concentration decreased
to 630 mg/kg, which corre-
sponded to 93.6% degradation
of TPH (Table 1). This is simi-
lar to the TPH degradation in
remediated soil-only experi-
ment (93.3%). Based on the
first order model, degradation
rate constants of TPH were
0.105/day and 0.099/day for
remediated soil-only experi-
ment and 1:1 mix ratio experi-
ment. Degradation rate con-
stants of TPH in these
conditions was over two times
larger than that of soil-only ex-
periment (Table 2). For 1:0.1
and 1:0.5 mix ratio experi-
ments, first order degradation
rate constant of TPH was
0.046/day and 0.080/day, re-
spectively. This indicated that
the most active degradation
of TPH occurred in these ex-
perimental conditions. In case
of 1:0.5 mix ratio experiment,
TPH decreased from initial
concentration of 9,756 mg/kg
to 1,008 mg/kg during 30
days of composting, which in-
dicated that 89.6% of TPH
was degraded.
Percent removal, volatilization, and degradation of TPH
and n-alkanes during 30 days of composting
Conditions
Removal Volatilization Degradation
Contaminated soil
only (Control)
66.6
73.8
91.7
95.3
94.7
2.0
2.0
2.1
1.7
1.4
64.5
71.8
89.6
93.6
93.3
1)
1:0.1
TPH
1:0.5
1:1
Remediated soil only
Contaminated soil
only (Control)
75.3
88.3
98.7
99.9
99.9
1.4
0.3
0.4
0.3
0.7
73.9
87.7
98.4
99.5
99.5
1:0.1
2)
n-alkanes 1:0.5
1:1
Remediated soil only
1)
2)
The value implies the ratio of contaminated soil to remediated soil.
n-alkanes is the sum of individual n-alkane ranging from C10 to C20.
TABLE 2.
Estimation of degradation kinetic parameters based on
the first kinetic model
1)
k
Half-life
(day)
2)
Conditions
(1/day)
r
Contaminated soil
only (Control)
TPH
n-alkanes
TPH
n-alkanes
TPH
n-alkanes
TPH
n-alkanes
0.037
0.052
0.046
0.086
0.080
0.153
0.099
0.205
0.105
0.223
0.97
0.92
0.98
0.76
0.97
0.80
0.96
0.63
0.91
0.52
18.7
13.4
15.2
8.1
8.7
4.5
7.0
3.4
6.6
3.1
1:0.1
1:0.5
1:1
Remediated soil only TPH
n-alkanes
1)
2)
k = the first order kinetic constant. r = correlation coefficient.
Percent degradation of TPH
in the mix ratio experiment of
1:0.1 was 71.8%. This is relatively low compared to 1:0.5 and 1:1 mix ratio experiments.
That is to say, it is desirable to mix remediated soil over 0.5 part in contaminated soil of
1 part in order to obtain TPH degradation over 90%.
Minna Laine and Jørgensen (1997) reported that over 90% of the chlorophenols
were removed during six months of composting using remediated soil as inocula. Also
in a bench-scale experiment, an average of 60% mineralization of radiolabeled pen-
tachlorophenol was obtained within 4 weeks (Minna Laine and Jørgensen 1996). Re-
search on the effects of remediated soil on the degradation of diesel oil has not been
reported. Appropriate mix ratio of contaminated soil to remediated soil also was not
discussed in the literatures. In this situation, the appropriate mix ratio of contaminat-
ed soil to remediated soil that obtained from this research has a very important engi-
neering significance even though further research in pilot or full scale is necessary for
field application of this result.
Decrease of n-alkanes concentration occurred rapidly compared to TPH (Figure 2,
Table 1). In the mix ratio of 1:1, n-alkanes were degraded from the initial concentration of
2,390 mg/kg to 13 mg/kg at 30 days. This result is similar with the result of remediated
146 Compost Science & Utilization
Spring 2001

Recycling of Remediated Soil for Effective Composting
Of Diesel-Contaminated Soil
soil-only experiment (Table 1). Degra-
dation of n-alkanes for all experiments
was higher compared to the TPH
degradation. This preferential degrada-
tion of n-alkanes is in line with the liter-
atures (Chaineau et al. 1996; De Jonge et
al. 1997; Frankenberger 1992; Thomas et
al. 1992). The first order degradation
rate also indicates preferential degrada-
tion of n-alkanes (Table 2). In 1:1 mix ra-
tio experiment and remediated soil-
only experiment, for example,
degradation rates based on the first or-
der kinetics were 0.223/day and
0.205/day, which were about two times
larger than those of TPH (Table 2).
Notable decrease of individual n-
alkanes and isoprenoids was observed
during the first 4 days for the experi-
ments of high mix ratio of remediated
soil (Figure 3). Almost all the individ-
ual n-alkanes and isoprenoids were de-
graded after 30 days for 1:1 mix ratio
experiment and remediated soil-only
experiment. In case of 1:0.1 mix ratio
Figure 3. Variation of n-alkanes and isoprenoids (pristance,
phytane) during composting of 30 days (Pr: pristane, Ph:
phytane).
experiment, however, n-alkanes remained in the concentration of 8 to 51 mg/kg. Pris-
tane and phytane also remained to the concentration of 51 mg/kg and 38 mg/kg.
It is generally accepted that degradation rate of individual n-alkane compounds de-
creases with increasing of molecular weight. Degradation rate based on the first order ki-
netic model, however, indicated that no significant difference among the different mole-
cular weight individual n-alkanes was observed in remediated soil addition experiments
(data was not presented). It may be due to the effect of acclimation of microorganisms on
the n-alkanes. More research is needed
to confirm this result.
Cumulative amount of CO2
evolved had not shown significant dif-
ference among experiments until 4
days, but after 9 days rapid increase of
cumulative amount of CO2 evolved
was observed in the mix ratio 1:1 ex-
periment (Figure 4). Total amount of
CO2 evolved was 7,288 mg/kg for 1:1
mix ratio experiment, which was the
greatest among the experiments. This
means indirectly that degradation of
TPH was the most active in 1:1 mix ra-
tio experiment. The remediated soil-
only experiment showed a rather low-
er CO2 evolution (5,789 mg/kg) than
that of 1:1 mix ratio experiment. The
difference in total amount of CO2
Figure 4. Variation of cumulative amount of CO evolved and
2
dehydrogenase activity during composting (ꢀ remediated soil
only, ꢁ 1:0.1, ꢂ1:1, ꢃ 1:0.5, ꢄ biocide control, ꢅꢆ soil only).
Compost Science & Utilization
Spring 2001 147

Eui-Young Hwang, Wan Namkoong and Joon-Seok Park
evolved between 1:1 mix ratio experiment and remediated soil-only experiment was ob-
served, although the first order degradation rate of TPH and percent degradation were
almost the same. In 1:0.1 mix ratio experiment, total amount of CO2 evolved was 4,697
mg/kg, which represented the lowest among the remediated soil experiments. This val-
ue is about two times greater than that of soil-only experiment (without adding remedi-
ated soil). Dehydrogenase activity matched well with cumulative amount of CO2 evolved
(Figure 4). These results indicate that microorganisms in remediated soil are metaboli-
cally active and contribute to degradation process when added to contaminated soil.
Conclusions
The addition of remediated soil was considered as an effective treatment options for
diesel oil degradation in contaminated soil. Appropriate mix ratio (wet weight basis) was
1 part remediated soil to 1 part of contaminated soil, judging from TPH degradation rate
constant and biochemical parameters. In this mix ratio, the first order degradation rate
constant of diesel oil was 0.099/day and 94% of TPH was degraded within 30 days.
Degradation rate of TPH and total amount of CO2 evolved in this condition were two
times larger than those of soil only experiment without adding remediated soil.
Acknowledgements
This work was supported by GRANT No. 971-1202-008-1 from the Korea Science
& Engineering Foundation. Authors acknowledge Korea Science & Engineering Foun-
dation for providing an opportunity to conduct this research.
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