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1999Survey 8

Survey of Technology for Remediation of Oil-Contaminated Soil in Kuwait

1. Introduction More than nine years have passed since the Gulf War shocked the world in 1991. In Kuwait, rehabilitation has proceeded steadily and urban areas have been quickly restored to their pre-war status. However, in the outlying desert areas, large-scale environmental pollution – the result of crude oil spilling from more than 700 wells destroyed during the war – remains a grave issue.

Millions of barrels of crude oil gushed freely from these wells, creating oil lakes in low-lying areas of the desert. Lakes were formed at more than 500 different locations, covering a total area initially estimated at 49 km2. While the Kuwait Oil Company (KOC) has recovered 22.5 million barrels of the spilled crude; the remaining amount, is considered unrecoverable by standard methods. An estimated 22.7 million m3 of contaminated soil remains, threatening pollution of precious groundwater resources (Table 1).

Figure 1 Satellite photo of oil lake

(Burgan oil field)

Figure 2 Aerial photo of oil lake (Burgan oil field)

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In Kuwait, the remediation of this enormous quantity of oil-contaminated soil to prevent such groundwater pollution and to restore the surface biota, has been a critical issue. Japan Petroleum Energy Center (PEC) has been undertaking joint research with the Kuwait Institute for Scientific Research (KISR) for the remediation of oil-contaminated soil, since 1993. The purposes of this joint research are to establish effective remediation technologies, both physical/chemical and biological (bioremediation) methods, through field-testing; and to develop a suitable action plan for rehabilitating all such contaminated soil in Kuwait.

During Phase I (FY 1993), possible remediation technologies were investigated through site surveys and laboratory testing. During Phase II (FY 1994 to 96), physical/chemical remediation technology, heated solvent/water washing, was field tested through the operation of a pilot plant. The effectiveness of three typical bioremediation methods was also confirmed through field-testing. During Phase III (FY 1997 to 99), large-scale operations were conducted, to more accurately assess the requirements for the actual implementation of full-scale remediation. 2500 tons of oily-sludge were processed by heated solvent/water washing, and 5,000m3 of light and moderately contaminated soil were treated by bioremediation. The effectiveness of both remediation technologies was confirmed.

Table 1 Estimates of oil-polluted land areas and soil volumes in Kuwait

Oil field region Oil-polluted area (km2)

Oil-polluted soil volume (m2)

Total

2. Pre-survey (FY 1993) 2.1 Oil lakes Prior to an investigation of possible oil lake remediation technologies, the status of pollution in the Burgan oil field was surveyed. As most of the lighter fraction of oil had either been recovered by vacuum tanker, or had been vaporized by intense summer temperature exceeding 50°C, only heavy components of oil remained in the oil lakes.

Oil had penetrated into the soil to a one-meter depth on average, of which the top 30 cm was oily-sludge of oil concentrations greater than 40% or more by TPH (Total Petroleum Hydrocarbon). (Similarly indicated by TPH hereinafter.) Below this sludge layer, was contaminated soil with oil concentration at 20% or less. Additionally, large quantities of salt were present where seawater had been used to extinguish well fires. Table 2, presents oil content, salt content, etc., of contaminated soil by depth. Also, oil components were transformed (oxidized) by weathering due to direct exposure to intense sunlight over several years.

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Table 2 Results of Analysis of Oil-Polluted Soils

Sample source Solvent extraction method (TEM %)*

Infrared spectroscopic

analysis (I.R. &)Ignition loss

(%)

Electroconductivity rate (µS/cm)

Ground surface area

0 to 20 cm deep

20 to 40 cm deep

40 to 60 cm deep

60 to 80 cm deep

* TEM (Total Extractable Matter) = TPH: freon extraction oil (weight %)

2.2 Investigation of remediation technologies applicable to oil-contaminated soil Different methods of remediation of various contaminated parent material, i.e., soil, water, have been proposed and put to practical application around the world. Of these technologies, those applicable to oil contamination are summarized in Figure 3. Each of these remediation technologies has its advantages and disadvantages. Therefor, the optimum technologies were selected to match site conditions, and in consideration of such factors as pollutant concentration, its components, and cost.

In the present study, physical/chemical remediation technologies were identified as best for contaminated soil containing more than 40% oil, and bioremediation technologies for soil containing less than 5% oil. Accordingly, physical/chemical remediation was required to treat contaminated soil containing more than 40% oil to less than 5%, the level at which bioremediation becomes possible. The specific physical/chemical method adopted, was heated solvent/water washing, which allows for recovery of oil, as well as remediation of contaminated soil.

Soil treatment technology

In-situ

Not in-situ

Other

Physical/chemical treatment

Heating treatment

Bio-treatment

Physical/chemical treatment

Heating treatment

Bio-treatment

Natural purification

Land fill treatment

Soil aeration method

Heating, vaporization and extraction method

Land farming

In-situ bio-treatment

Bio-reactor (solid)

Bio-venting

Melting and solidifying

Soil remediation

Incineration

Solvent extraction

High-temperature heating for desorption

Low-temperature heating for desorption

Bio-reactor (slurry)

Figure 3 Oil-polluted soil treatment technologies

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3. On-site verification testing 3.1 Soil samples One hectare (133m x 75m) of Oil Lake No. 102, was excavated to an average depth of one meter. First, a large-scale grader was used to remove approximately 30 cm of oily-sludge from the surface. Then, a Kuwait Ministry of Defense explosive ordnance removal team checked for landmines and unexploded bombs, after which, front loaders were used to excavate the remaining oil-contaminated soil. The excavated oil sludge

(3,000 m3) was utilized for field-testing of physical/chemical remediation technology. Oil ingots of 40 mm or more were removed by rotary type screening machine from the oil contaminated soil (7,000 m3), after which it was classified into heavily contaminated soil (20% oil concentration), moderately contaminated soil (4%) and lightly contaminated soil (2%), on the basis of external appearance, hand feel, etc. Each of the soil classifications were independently well-homogenized, and the moderately and lightly contaminated soils were utilized for field-testing of bioremediation.

3.2 Physical/chemical remediation technology (heated solvent/water washing method) 3.2.1 Oil sludge purification method The targets of oily-sludge remediation by the heated solvent/water washing method, were reduction of oil concentration to less than 5%, and reduction of salt concentration less than 3% - the levels at which bioremediation becomes possible.

Even at 70°C, the viscosity of oily-sludge is 10Pa · s, which is extremely high, and cannot be transported by regular pumps. Therefore, addition of solvent, kerosene, is necessary as well. Initially, oily-sludge is placed in a solvent washing tank, where 15-50% kerosene is pre-heated to 70°C. The sludge and heated kerosene are then mixed, reducing the viscosity to 2 to 3 x 10-2Pa · s, so that transportation by pump becomes possible. After sufficient mixing, the mixture is allowed to settle, the kerosene-washed soil is separated from the oil. With this procedure, the oil concentration in soil is lowered to 12% or less.

In the second stage, 100 to 200% water and 0.1 to 0.2% surface-active agent are added to the separated kerosene-washed soil, and heated to 70°C, again followed by mixing and settling. After settling, the water, oil and water-washed soil are separated. This procedure lowers both the oil and salt concentrations in soil below as 3%, well below the treatment targets. Figure 4 presents an overview of the solvent/water washing method and the results of treatment of 2,500 tons of oily-sludge (batch treatment by pilot plant, capacity 38 tons per day). Typical oil and salt reduction by the washing processes are given in Figure 5.

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Sludge:2,500 tons

Sludge pond

Solvent:500 tons

Surface active agentWater: 1,500 tons

Solvent purification

Water purification

Mixing

Separation

Mixing

Separation

SWashed soil:1,400 tons

Bioremediation

Bioremediation

Waste water: 1,100 tons(sludge from water washing 1,000 tons)

800 tons Separated oilSeparated oil

Refining of separated oil (salt removal) Water treatment

2,000tons

Figure 4 Oily-Sludge Washing Process

Oil component wt%Salt component wt%

Before washing After solvent washing

After water washing

Figure 5 Purification of oil and salt components in the washing process

3.2.2 Refinement of separated oil discharged in the washing process Contained in the separated oil discharged by the oily-sludge purification process are large concentrations of salt, ranging from 5 to 15%, and methods for efficiently removing salt from separated oil were studied to allow recovery of reusable oil (Figure 6).

solvent washing process

Separated oil from

WaterEmulsion breaker

Sludge

Solid-liquid separation

Heating/mixing tank

Waste water

Liquid-liquid separation

Refinedoil

Figure 6 Separated oil Refining Process

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The bulk of the salt found in separated oil consists of crystalline granules 10µm or less in diameter. Standard centrifugal separation and water washing were considered as methods for the removal of such salt. Laboratory tests confirmed that for using separated oil as fuel, centrifugal separation alone is inadequate, and water washing is essential. However, water washing alone is also inadequate, as the oil contained in oily-sludge has been transformed due to direct exposure to intense sunlight for many years. It is believed that the sludge consists largely of oxidaized, hydrophilic substances and salt. Thus, once such oil is mixed with water, an emulsion is formed, and oil and water separation becomes problematic. Therefor, both centrifugation and water washing are required in conjunction . Initially, most of the fine hydrophilic particles of sludge and some of the salt, is removed from the separated oil by centrifugation. Then, the oil is washed with heated water to dissolve the remaining salt from the oil into the water. Finally, an organic emulsion breaker is added, and the oil and saline water are successfully separated by a centrifugation.

Oil derived from the oily-sludge purification process undergoes initial centrifugal separation at a centrifugal force of 2,100 to 3,100 G of 15 rpm and a differential speed. By this process, the salt concentration of the separated oil drops to about 5%. After adding an equivalent volume of heated water to the separated oil and mixing adequately, and then, adding emulsion breaker of 0.1 to 1% and mixing further, the oil and saline water are separated by a second centrifugation. By this refining process, the salt concentration of the separated oil can be reduced to as low as 0.3% (Figure 7).

API value Salt content (TDS) wt%

Figure 7 Salt Concentration and API Value in Separated Oil Refinement Process

3.3 Bioremediation 3.3.1 Overview of on-site verification testing In laboratory tests conducted prior to on-site verification testing, it was confirmed that oil-degrading microorganisms exist in the oil-contaminated soil in Kuwait (Figure 8, Figure 9).

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Figure 8 Example of Petroleum

Degrading Microorganism (Nocardia SP.)

Figure 9 Example of Petroleum Degrading Microorganism(Psewdomonas SP.)

In verification testing, wood chips, compost and nutrients (nitrogen, phosphoric acid fertilizer) were added to the oil-contaminated soil (5% of cubic capacity) and mixed so as to increase the activity of oil-decomposing microorganisms in the soil by improving the water retention of the soil and by providing the microorganisms with nutrients or habitats. Using this soil mixture, treatment areas were created and verification testing was performed on three typical modes of bioremediation: 1) land farming mode; 2) windrow composting soil pile mode, and 3) static bio-venting soil pile mode (Figure 10).

Monitoring took place over 15 months from June of 1995 to September of 1996. In the land farming area, samples of treated soil were taken at a depth of 10 cm and 30 cm from each of 30 locations equidistant within one area (H 30m x L 40m x D 0.3m). In each soil pile area (W 3m x H 1.5m x L 20m), samples were taken at depths of 10 cm, 30 cm and 70 cm each from a total of 20 locations on both sides of the pile. After the soils were mixed adequately, the status of oil degradation and other parameters were analyzed. Monitoring frequencies were as follows. Aside from automatic measurements, the temperature and moisture content of soils were checked daily; analysis of inorganic ingredients and of oil volumes contained in soil was performed once per month, and detailed analysis of petroleum (fraction) was performed once every three months.

Excavation and removal of mine

Soil excavation

Screening and mixing with supporting materials (amendments, fertilizer) Oil lake residue and

surrounding area

Windrow composting soil pile

Bio-venting staticsoil pile

Landfarming

Figure 10 Schematic Diagram of On-site Verification Testing

Procedure for Bioremediation

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3.3.2 Results of on-site verification testing The results of on-site verification testing of the bioremediation are summarized in Table 3.

(1) Degradation behavior of oil ingredients

A look at the temporal changes of TPH in the three modes reveals that degradation speed is faster in the landfarming mode than in the soil pile modes; after nine months, 75% of the initial TPH degrades, and over 85% degrades after 15 months. With the soil pile modes, on the other hand, over 75% degrades after 15 months.

As a result of differential quantification of TEM (Total Extractable Matter), it was learned that of the oil ingredients in oil-contaminated soil (for example, saturated aliphatic component, aromatic component, asphalten or other ingredient, each making up 1/3 of the soil), the saturated aliphatic and aromatic components degrade but the resin and asphalten components hardly degrade at all. In the land farming area, where degradation was most advanced, approximately 80% of the aliphatic component, and 50% of the aromatic component, degraded after nine months, and after 15 months, approximately 90% or more of the aliphatic and 60% or more of the aromatic component degraded. In both soil pile areas, degradation of the aromatic component tended to be slightly lower than in the landfarming area (Figure 11).

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Table 3 Comparison of three modes of bioremediation

Mode Landfarming mode Windrow composting pile mode

Static bio-venting pile mode

Schematic drawing

Executed with medium contaminated soil (TPH: 4%) or light contaminated soil (TPH: 2%)

Executed with medium contaminated soil

Executed with light contaminated soil

Supply mode

Water

Air

Rotary irrigation system

Mixing by tractor and tiller

Supply from leaky pipe and from soil top

Overturning once per week using front loader

Supply from leaky pipe and from soil top

Forced ventilation from floor using compressor

Temporal change in TPH Moderately-contaminated soil

(treatment area) Moderately-contaminated soil (control area) Lightly-contaminated soil (treatment area) Lightly-contaminated soil (control area) Land farming

Soil pileWindrow pile (treatment area)Windrow pile (control area)Static pile (treatment area)Static pile (control area)

Elapsed time (month) Elapsed time (month)

Extent reached after 12 months

Over 80% of TPH degrades, to 0.7% with medium contaminated soil and to 0.3% with light contaminated soil. 80% of aliphatic fraction and 40 to 50% of aromatic group degrades.

Over 70% of TPH degrades to 0.95%. 80% of aliphatic fraction and 40% of aromatic fraction degrades.

Over 70% of TPH degrades to 0.46%. 80% of aliphatic fraction and 50% of aromatic fraction degrades.

Average water supply volume

Summer

Autumn, winter and spring

Total result

17 to 20 l/m3 · day (5 to 6 mm/day)

5 l/m3 · day (15mm/day)

6 m3/m3 · oil-polluted soil

4 to 7 l/m3 · day

1 l/day

1.4 m3/m3 oil-contaminated soil

4 to 8 l/m3 · day

1 l/day

1.6 m3/m3

oil-contaminated soil

Equipment necessary for maintenance and control

Tractor, tiller, irrigation system

Front loader, leaky pipe Compressor, leak pipe

Evaluation (concerning medium contaminated soil)

Initial degradation speed

Speed reached after 12 months

Water supply volume

It was found that in the aliphatic fraction, degradation of the saturated aliphatic fraction of low carbon number is advanced. As for the aromatic fraction, the degradation behavior of 16 toxic aromatic compounds designated by the EPA was traced, and it was found that after six months, compounds of low ring number down to three rings, including phenanthrene, anthracene, fluoranthene and pyrene, degraded almost completely, but 15 months was required for degradation of aromatic compounds of greater ring number.

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Landfarming Moderately-contaminated soil treatment area

Aliphatic fraction

Aromatic fraction

Resin

Asphalten fraction

In soluble residue

Elapsed time (month) Elapsed time (month) Elapsed time (month) Elapsed time (month)

LandfarmingLightly-contaminated soil treatment area

Windrow pileModerately-contaminated soil treatment area

Static pile Lightly-contaminated soil treatment area

Figure 11 Results of Differential Quantification of TEM Conversion and Petroleum Ingredients

(2) Water spray volume

In order to preserve the activity of oil decomposing microorganisms, each area was sprayed with water so as to maintain a water content rate of 8 to 10% in the soil. The land farming areas required 2 to 2.5 times more spray water than the soil pile areas.

(3) Mutagenicity tests

Among petroleum ingredients, it is said that there are large quantities of substances which have, or are suspected of having, mutagenicity. Accordingly, the pattern of change in the mutagenicity of contaminated soil with bioremediation was traced.

The Salmonella Typhimurium TA98 strain was used for testing. Contaminated soil samples exhibited mutagenicity at the start of testing. In the control area, which was left untreated for 15 months, mutagenicity was assessed as being positive. On the other hand, in the bioremediation treated area, mutagenicity dropped after 3 months, and it is believed that strong mutagenicity was broken down within a relatively early period. Over the period from 3 to 15 months, the treated areas were not assessed again as positive in mutagenicity.

It was determined that the mutagenicity of contaminated soil can be lowered by bioremediation.

(4) Comparison of 3 modes

Of the three modes, it was in the land-farming mode that degradation was most advanced. This technology can be implemented in a short time period, but the amount of water it requires for maintaining a suitable water content ratio is two to three times greater than with the other modes, so it is not economical. In the windrow composting soil pile mode, the amount of water required is slight but a long time is required for treatment and overturning by front loader incurs considerable costs. The cost of the static bio-venting soil pile mode is relatively low, but a long time is required for treatment and the level of purification reached is inadequate.

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In view of the aforementioned, the ideal method of treatment in bioremediation of oil-polluted soil in Kuwait is one in which the low water volume required by the windrow composting soil pile mode is satisfied while stirring takes place adequately, as in the land farming mode. It was concluded that the most ideal mode of treatment for satisfying these conditions is the windrow composting soil pile mode by means of pile turner, which is used for overturning in making compost, etc. This mode is currently undergoing verification testing on a practical scale (5,000m3) (Figure 12).

In areas where oil contamination is relatively shallow, it is believed that the land-farming mode can be effective in-situ.

Figure 12 Overview of maintenance and control by pile turner mode

(5) Bioremediation of soil washed by kerosene

The effects of bioremediation on kerosene-washed soil, produced by physical/chemical purification of oil sludge, were investigated.

Shown in Figure 13 are the results of treatment by land farming of kerosene-washed soil after the soil has been stirred and mixed adequately by front loader, then homogenized and laid out at a thickness of 30 cm. The figure clearly indicates that degradation of the oil in kerosene-washed soil progresses smoothly as a result of bioremediation treatment. Nevertheless, although there are hardly any microorganisms in kerosene-washed soil, no differences in degradation behavior could be noted whether microbial strains were added or not. This is ascribed to the fact that indigenous strains in the desert soil get mixed into the kerosene-washed soil.

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Control area (nutrients present) Control area (nutrients absent) Stirring only Addition of nutrients and strains Addition of nutrients

Elapsed time (month) Figure 13 Degradation of kerosene-washed soil by land farming

4. Confirmation of remediation of oil-contaminated soil by bioremediation (vegetation experiments)

4.1 Test overview To confirm remediation of oil-contaminated soil by bioremediation, the status of contaminated soil restored by planting was confirmed, and the possibilities for using treated soil as plant growth material were investigated. Used as soil samples were bioremediated soil, which was treated over 15 months by the various modes, untreated soil and desert natural soil, as indicated in Table 4. The plants used were alfalfa, Bermuda grass, broad beans, and barley.

The first test phase was performed over a three-month period from February of 1997. The second test phase was performed over a five-month period from November of the same year. Over this interim the growth of plants was analyzed (plant length and weight of above-ground portion), weather conditions were monitored and soil was analyzed.

Table 4 Properties of soil provided for planting experiments

All treated soils were treated for 15 months.

Landfarming moderately-contaminated soil Landfarming lightly-contaminated soil Windrow pile moderately-contaminated soil Static pile lightly-contaminated soil

Untreated moderately-contaminated soil

Natural desert soil

Chloride ion

4.2 Test results and Discussion In untreated contaminated soil, no germination of any of the four types of plants provided as samples for cultivation testing could be noted, but in treated soil, the germination of three types of plants (alfalfa, Bermuda grass, barley) was about the same as in natural desert soil. The effectiveness of bioremediation was thus made clearly evident. As for broad beans, water supply was inadequate because of improper pile formation so that germination and growth were inadequate in all areas, and investigations are currently being made again.

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Measurements of Bermuda grass and alfalfa harvests, taken by reaping aboveground portions, are presented in Figure 14.

Alfalfa (4/16) (second phase)Bermuda grass (5/17) (first phase)

Fres

h w

eigh

t (g/

m2 )

Fres

h w

eigh

t (g/

m2 )

Landfarming moderately-contaminated soil

Land farming lightly-contaminated soil

Windrow pile moderately-contaminated soil

Static pile lightly-contaminated soil

Untreated soil

Native desert soil

Landfarming moderately-contaminated soil

Land farming lightly-contaminated soil

Windrow pile moderately-contaminated soil

Static pile lightly-contaminated soil

Untreated soil

Native desert soil

Figure 14 Harvest volumes

As for Bermuda grass, from phase 1, except for the soil of the untreated area, a level of growth equivalent to or greater than that in natural desert soil was noted. In the area of lightly-contaminated soil, however, a tendency for growth to exceed the level in the area of moderately-contaminated soil could be noted, and it was found that there are differences in growth due to level of purification. Bermuda grass and barley exhibited the same trend. With alfalfa, on the other hand, although growth was favorable in the area of lightly-contaminated soil in phase 1, growth in the area of medium contaminated soil was inferior to the level in natural desert soil. Nevertheless, in phase 2 growth was favorable in both lightly-contaminated and moderately-contaminated soils. This is believed to be related to both the oil and salt components included in treated soil.

The results of the above tests confirmed that remediation of oil-contaminated soil by bioremediation is possible within the range of normal plant growth. On the basis of laboratory test results, it can be affirmed that when TPH is 1% or less, fertility is rehabilitated within the range of normal plant growth potential. In on-site bioremediation efforts, however, salt concentration in the soil drops together with irrigation. It appears that there is a close relationship between this drop in salt concentration and improvement of growth by treatment. Studies are scheduled to be made for clarifying this point in the future.

In addition to the aforesaid planting experiments, a garden measuring approximately 3000m2

was made from bioremediated soil, over 20 types of desert plants were planted in it and growths were monitored. As shown in Figure 15, soil contaminated by flowing crude oil could be adequately used as material for plant growth thanks to bioremediation.

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Figure 15 Garden created with bioremediated soil

5. Synopsis 5.1 Physical/chemical purification technology By combining kerosene solvent washing with warm water washing, the oil content in oil sludge could be reduced from 50% to 2%. A treatment rate of 30 tons per day was reached at a pilot plant, and 2,500 tons of oil sludge was treated. The effectiveness of the solvent/warm water two-stage purification method could thus be verified. In addition, the large salt content in separated oil could be reduced to as low as 0.3% and initial targets could be reached.

5.2 Bioremediation technology (1) The unique characteristics of three typical modes of bioremediation were determined, and

the conditions under which oil concentration (TPH) could be reduced to 1% or less by each mode were clarified. As a result, it was found that for bioremediation of oil-contaminated soil a method of treatment must be developed in which the low water volume required by the windrow composting soil pile mode is satisfied while stirring takes place adequately, as in the landfarming mode. It was concluded that the most ideal mode of treatment for satisfying these conditions is the windrow composting soil pile mode by means of pile turner, which is used for overturning in making compost, etc. This mode is currently undergoing verification testing on a practical scale.

(2) It was confirmed that soil of 3% oil concentration and 3% salt concentration treated by physical/chemical means (kerosene-washed soil) could be purified still further through bioremediation.

(3) It was verified that a combination of physical/chemical purification technology and bioremediation technology is effective in purifying oil-polluted soil in Kuwait.

5.3 Vegetation experiments using treated soil On-site cultivation experiments were performed using various types of soil subjected to bioremediation over a period of 15 months. It was confirmed that germination and growth could be adequately realized with bioremediated soil.

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6. Future schedules (1) A number of effective strains will be selected which can degrade ingredients separated

from oil-contaminated soil in Kuwait or beaches, etc. For more effective bioremediation, on-site application of these strains for bioaugmentation will be studied.

(2) Bioremediated soil will be evaluated for safety and for plant growth potential. Specifically, treated soil will be used in plant cultivation experiments conducted on a scale of 2 hectares in the city of Ahmadi, Kuwait.

7. Acknowledgement For this study, which yielded extensive results as indicated above, development of physical/chemical purification technology was consigned to the Shimizu Corporation and development of bioremediation technology was consigned to the Obayashi Corporation. We wish to express appreciation to these consignees for their efforts. We also want to take this opportunity to express special gratitude to the following professors for their advice and assistance over many years: Professors Matsumoto and Oyaizu, Graduate School of Agriculture and Life Science, the University of Tokyo; Professor Mino, Faculty of Frontier Sciences, the University of Tokyo; Professor Omori of the Biotechnology Research Center, the University of Tokyo.

Copyright 1999 Petroleum Energy Center all rights reserved.