Restoration of Petroleum-Contaminated Soils by Field-Scale Soil Washing System

Wan-Hyup Kang, Jun-Gyo Cheong†, Kangsuk Kim, Heehun Chae and Chung-Hee Chang

Huyundai Engineering & Construction, Yongin, 446-716, Korea

Abstract. Petroleum contaminated soil of 24,620 cubic meters, excavated from an old railroad in Daejeon, Korea, was remediated with soil washing. The contents of total petroleum hydrocarbon (TPH) and benzo(a)pyrene in the soils, presumed to originated from oil-spills and wood-preservatives, respectively, turned out to exceed the legal standards; a soil washing process was adopted to remediate the contaminated soils. A soil washing plant of 40 tons/hr capacity was installed on the site and operated for three months. The washing process successfully decreased the concentrations of contaminants enough to meet the legal standards. The water used in the washing process was reused after simple water-treatment processes, coagulation/sedimentation, which led to a zero-discharge process.

Keywords: soil washing, total petroleum hydrocarbon (TPH), benzo(a)pyrene, petroleum contaminated soil, soil restoration

1. Introduction The site of this remediation project has been used as railroad and vehicle repair workshop for over

seventy years. According to a site assessment as described in Figure 1, total petroleum hydrocarbon (TPH) and benzo(a)pyrene in the soils, presumed to originated from oil-spills and wood-preservatives, respectively, exceeded the legal standards concentrations (TPH: 2,000 mg/kg, Benzo(a)pyrene: 7 mg/kg)1,2,3). The maximum depth of contamination was about 5m and contaminants were mostly concentrated in surface to 3m below the surface vertically.1

2. Materials and Methods As shown in Figure 2, a soil washing plant with capacity of 40 tons/hr was designed to remediate the

contaminated soils. The principles of our soil washing are : (1) Pressurized water-jet removes the contaminants from the surfaces of soil grains. (2) The process of advanced particle size separation reduces the volume of contaminated soils for the

secondary treatment4,5). (3) The water used in the washing is reused after simple water treatment process that

leads to a zeo-discharge. Petroleum contaminated soil of 24,620 m3 was excavated and treated by soil washing plant. Main

equipments of the soil washing plant are presented in Figure 3. Constant amount of contaminated soils are feeded by hopper. In the contaminants desorption equipment, the soils are size-separated by hydrocyclone and contaminants are desorbed. The washing equipments clean up contaminated soils using pressurized

+ Corresponding author. Tel.: +82-31-280-7405; fax: +82-31-280-7678 E-mail address: jkjung@hdec.co.kr

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2012 International Conference on Environmental Science and Technology IPCBEE vol.30 (2012) © (2012) IACSIT Press, Singapore

water-jet. Fine soils of 0.053mm to 0.075mm settle down in the sedimentation tank and smaller suspended soils of below 0.053mm are sent to flocculation-sedimentation tank. The fine soils of 0.053mm to 0.075mm are treated by rapid mixing in the fine soil desorption tank. Highly concentrated sludge by flocculation is dewatered in the filter press. Oil and scum contained in wash water are separated and the water used in the washing process is reused after simple water-treatment like activated carbon adsorption.

Retaining wall Retaining wallExisting Platform New Platform (#5, #6)

Seoul BusanTPH concentration (Depth : 1~2m)

Retaining wall Retaining wallExisting Platform New Platform (#5, #6)

Seoul BusanBenzo(a)pyrene concentration (Depth : 1~2m)

Fig. 1: Results of site assessment on TPH and benzo(a)pyrene contamination

ContaminantsDesorption

Over SizeWashingOver Size

SeparatorFeed Hopper

Fine SoilDesorption

Sedimentation Gravel Washing

Filter PressFlocculation•Sedimentation

Flocculant

Oil/WaterSeparator

Air FloatationActivated CarbonAdsorption

> 50mm

50 ~ 3.0mm

< 0.053mm

0.075 ~ 0.053mm

Wash Water

Contaminated Soil

3.0 ~ 0.075mmSand Washing

Contaminated SoilContaminated Soil + Wash WaterTreated Wash WaterWash WaterTreated Soil

[Treated Soil]

[Treated Soil]

[Treated Soil]

[Treated Soil]

[Sludge]

Waste Treatment

(>50mm)

(<50mm)

(<50mm)

(>3mm)(<0.075±0.02mm)

(0.075~3mm)

(0.075~3mm)

(0.05~0.075~mm)

(>0.075mm)

(<0.053mm)

Fig. 2: Diagram of soil washing process

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Feeding ContaminantsDesorption

Fine SoilDesorption

SludgeConcentration

Wash-WaterStorage

Gravel & Sand Washing Sedimentation Flocculation /

Sedimentation Air Floatation Dewatering(Filter Press)

Fig. 3: Description of main equipments of soil washing plant

3. Results and Discussions A soil washing plant with capacity of 40 tons/hr was installed on the site to remediate the contaminated

soils as shown in Figure 4. The soil washing plant was successfully operated to treat excavated soils of 24,620 m3 for four months and soil washing efficiency was evaluated.

1) Hopper2) Gravel & Snad

Washing Equipment

3) ContaminantsDesorption

4) Sandy SoilWashing Equipment

5) Sedimentation

6) Fine Soil Desorption

7) Flocculation /Sedimentation

8) Sludge Concentration

9) Dissolved air flotation

10) Wash-Water Reservoir

11) Filter Press12) Sludge Cake

Fig. 4: The view of soil washing plant

Table 1 shows the concentrations of contaminants after washing. TPH concentrations showed a significant decline as much as 97% (from 65,756 mg/kg of initial maximum concentration to below 1,869 mg/kg). Benzo(a)pyrene was also successfully remediated (from 26 mg/kg of initial maximum concentration to below 7 mg/kg).

Table 1: The concentrations of contaminants after remediation by soil washing

(unit: mg/kg)

Contaminants Legal standard concentration

Initial maximum concentration

Final concentration (by washing)

Removal efficiency

Total Petroleum Hydrocarbon (TPH) < 2,000 65,736 ~ 1,869 97%

Benzo(a)pyrene < 7 26 ~ 7 73%

As shown in Table 2, total excavated soils of 24,620 m3 converted into treated soils of 18,813 m3 and waste sludge of 5,807 m3. The waste sludge was taken out for waste treatment and treated soils were reused as backfill materials in the site.

Table 2: Distribution of contaminated soil quantity by depth

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(unit: m3)

Overall Waste Sludge Treated Soil Quantity (Portion)

24,620 (100%)

5,807 (24%)

18,813 (76%)

Remarks Excavated soil Off-site waste treatment Backfill or reuse

4. Conclusion In this study, a soil washing process was adopted to reclaim the petroleum contaminated railroad soil.

We evaluated the soil washing efficiency through on-site operation of soil washing plant of 40 ton/hr capacity for four months.

The major findings in this study are : (1) The soil washing process succefully decreased the concentrations of TPH and benzo(a)pyrene

enough to meet the legal standards for railroad area. (2) Fine soils were efficiently treated by particle size separation and pressurized water-jet techniques. (3) Oil contaminants in wash water overflowed from flocculation-sedimentation tank were well removed

by air floatation and oil/water separation. (4) The soil washing is an eco-friendly remediation process that there is no discharge of water by

recycling the wash water. Finally, the soil washing process adopted here contributed to achieve efficient, rapid and cost-effective

soil remediation.

5. Acknowledgements This project is supported by Korea Ministry of Environment as “The GAIA (Geo-Advanced Innovative

Action) Project”.

6. References [1] W. Kang, J. Cheong, K. Kim, and J. Chang. Remediation of TPH-Contaminated Soils in the Railroad Area by

Using Soil Washing. Proc. Of Korea Society of Environmental Engineers. 2011, pp. 102-103.

[2] Chungnam University. Verification report of soil remediation. 2011, pp. 8-9, 24-27.

[3] W. Kang, J. Cheong, K. Kim, J. Chang and D. Kim. Remediation of Petroleum-Contaminated Railroad Soils by Soil Washing. Proc. Of International Symposium on Mine reclamation. 2011, pp. 160-161.

[4] J. M. Michael. Full-scale and pilot-scale soil washing. Journal of Hazardous Materials. 1999, 66(1-2): 119-136

[5] R. Anerson, E. Rasor, and F. V. Ryn. Particle size separation via soil washing to obtain volume reduction. Journal of Hazardous Materials. 1999, 66(1-2): 89-98.

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