Note: Descriptions are shown in the official language in which they were submitted.
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A SOIL DECONTAMINATION METHOD
Technical Field
The present invention relates to the treatment of
soil or groundwater contaminated with organic compounds.
More specifically, the invention relates to a method of
reducing or eliminating contaminants in soil or ground-
water, in which a solid particles of an oxidation agent
are supplied to said soil or groundwater and dissolved
in water, said oxidation agent being allowed to react
with said contaminants under controlled release conditions.
The invention also refers to_the use of solid par-
ticles of an oxidation agent as an active component for
reducing or eliminating contaminants in soil or ground-
water.
Background of the Invention
The removal of hazardous substances from soil and
ground water is a major problem in the industrialised
world. Contaminants from earlier generations as well as
present industrial operations, leakages and accidents can
result in the dispersal of hazardous chemicals in soils,
ground water and surface water. A large number of sites are
now contaminated as a result of earlier disposal of
hazardous waste. Old landfills containing hazardous waste,
industrial sites contaminated with hazardous chemicals,
polluted sediments in fjords, harbours, rivers and lakes,
and areas contaminated by discharges from abandoned mines
constitute a risk of serious acute and long-term contamina-
tion. At some sites, such a pollution may be a direct
health risk, cause irreversible environmental damage, or
mean that land is unusable for some purposes. In environ-
mental terms, the most serious problems are the risk of
further dispersal of hazardous chemicals and the risk that
they may enter food chains.
Soils contaminated with hydrocarbons is one of the
major problems facing companies and government agencies
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today since the discharged substances largely comprise
aromatic and aliphatic organic compounds refined from
petroleum hydrocarbons. The chemical content in petroleum
products generally comprises hundreds of thousands of
different organic substances. The composition may vary
depending on the conditions of production, the additives
used etc. The solubility of the chemical substances in
water is limited, but varies considerably for each specific
contaminating chemical substance. The volatility is usually
estimated as high, but for certain fractions the volatility
is very low. The substances have a long lifespan under
anaerobic conditions in the ground and are very slowly
transported away with the groundwater. However, the energy
content in these substances is high, which easily allow
15.. most of the substances to react with arid.be decomposed by
an oxidation agent, such as hydrogen peroxide'. Contaminat-
ing halogenated organic substances and solvents also repre-
sent a significant carcinogenic risk. The contaminating
substances are often present at the surface soil matrix,
but can migrate to great depths beneath the surface of the
soil, and are difficult to dispose off.
Examples of released substances into the soil and
groundwater include, but are not limited to gasoline, fuel
oil, motor oil, polychlorinated biphenyl (PCB), benzene,
toluene, ethyl benzene and xylene.
Costs for cleanup are high and going higher. Results
are slow, sometimes years are needed to see if the invest-
ment in time and money will correct the problem.
The need to identify, control and treat these release
sites in a timely, cost effective and environmentally sound
manner is a matter of concern throughout the world. Once a
release is identified and the source of the contamination
(e.g. leaking tank, broken fuel transfer line, etc.) is
corrected, a remediation technology that could rapidly
oxidise the gasoline components would be a very useful
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tool. Second only to prevention of fuel releases, rapid
source treatment is the most effective way to prevent
adverse, long-term impacts to groundwater resources.
When groundwater is decontaminated, it is usually
pumped from underground to the surface where it is treated.
The processed groundwater is then returned underground.
Such a procedure is usually expensive and can require years
to perform.
More recently in situ chemical oxidation techniques
have been employed for the treatment organic environmental
contaminants. These techniques are less costly than the ex-
situ methods. Strong oxidising agents, such as sodium and
potassium permanganate, oxygen, ozone, and hydrogen per-
oxide, are used for treating chemicals in process streams
and for decontaminate sites affected by various organic
chemicals. The ability of these chemicals to reduce conta-
minants in a matter of minutes, days and weeks as opposed
to months or years for other technologies has generated
interest in studying the effectiveness and impacts of their
use.
For example, in US 6,102,621 contaminants in soil and
groundwater are treated by providing inorganic oxidative
chemicals in granular form and adding a carrier fluid
comprising a fine-grained inorganic hydrophilic material.
The oxidative inorganic chemicals remain in the granular
form until applied by injection through an injection well
into subsurface soils. The small granular size of the
particulate oxidative chemicals allows the particles to
remain as a slurry of solids suspended in the carrier
fluid. The method is intended to deliver a mixture of
granular reactive chemicals, suspended within a carrier
fluid to an in situ area of contaminated soil and ground-
water without significant dissolution of the reactive
granules before injection into the subsurface.
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In US 5,525,008 organic contaminants in soil and
ground-water are treated by injecting calculated amounts of
a metallic salt solution with hydrogen peroxide under
pressure.
US 6,268,205 discloses a method for treatment of
decontaminated soil and/or groundwater by injection of a
slurry, immediately after mixing, of water and a powdered
mixture of metallic peroxides into the soil. Decomposition
rate modifiers, which are not specified, can be included in
the powder mixture for controlling the reaction rate of
peroxide with water.
The hydrogen peroxide is converted to a powerful
oxidant (a hydroxyl radical), which in turn reacts with and
oxidises the organic carbon in the treated media and the
reaction chemistry is well documented for many types of
contaminants. The reaction products obtained from the
hydrogen peroxide reaction process are only carbon dioxide
and water.
However, in an aqueous solution hydrogen peroxide is
a very strong oxidation agent which is rapidly decomposed.
The decomposition is catalyzed by wide variety of sub-
stances. Several transition metals and compounds thereof as
well as organic substances are especially active. The same
effect is obtained with substances having a large contact
surface. Such a surface catalyzed decomposition of hydrogen
peroxide may in a subsurface environment result in oxygen
formation and potentially to an abiotic oxidation of or-
ganic contaminants. Thus, in practice such a use of aqueous
solutions of hydrogen peroxide is prevented by the decom-
position taking place before the actual decontamination
effect of hydrogen peroxide can be utilized. The hydrogen
peroxide will directly start to rapidly decompose when
contacting the surface of the soil material and the oxid-
ising effect will be considerably reduced.
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It is also known that in highly contaminated systems
(where the potential for unproductive side-reactions are
great), H202 efficiently is improved by performing the
oxidation either in a step wise fashion or, optimally, in a
5 slow, continuous mode - as opposed to adding the aqueous
solution of H202 all at the same time.
Summary of the Invention
The purpose of the invention is to provide a new
method of reducing or eliminating contaminants in soil or
groundwater by means of an oxidising agent, said oxidation
agent is allowed to react with said contaminants under
controlled release conditions, said controlled release
conditions are obtained by controlling the dissolution of
at least one inorganic and/or organic coating applied onto
said oxidation agent., whereby the above-mentioned problems
are eliminated.
Another purpose of the invention is to provide
such a method, whereby the decomposition of the
oxidising agent does not result in the formation of
toxic substances.
Still another purpose is to provide such a method,
whereby the oxidising agent can be homogeneously distri-
buted in the soil before the actual oxidation reaction of
the contaminants therein takes place.
Still further another purpose is to provide such a
method, whereby the oxidation agent is applied directly
with the same result as in a stepwise mode or in a slow,
continuous mode.
These and other objects are accomplished by the
method and use as claimed in claim 1 and 21, respectively.
Detailed Description of the Invention
According to the invention a method of in situ or ex
situ reducing or eliminating contaminants in soil or
groundwater is provided, in which solid particles of an
oxidation agent are supplied to said soil or groundwater
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and dissolved in water, said oxidation agent is allowed to
react with said contaminants under controlled release
conditions, said controlled release conditions are obtained
by controlling the dissolution of at least one inorganic
and/or organic coating applied onto said oxidation agent.
The oxidation agent is preferably crystalline sodium
carbonate peroxyhydrate.
Sodium carbonate peroxyhydrate is a so-called
addition product, in which the hydrogen peroxide is quite
loosely bonded, and this addition structure is partly
responsible for its instability. It does not comprise any
group, which corresponds to the structure of actual per-
compounds, as do, for example, sodium perborate, sodium
monopersulfate, or alkali persulfates. Sodium carbonate
peroxyhydrate is also known b,y the names sodium
percarbonate, sodium carbonate sesqui(peroxyhydrate), and
sodium carbonate peroxide. It is considered environmentally
friendly since its decomposition products do not pollute
the environment.
Sodium percarbonate is well-known a bleaching or
oxidising agent which has been used for bleaching, textile,
pulp and paper, dental, cosmetic, hair, or medicinal pur-
poses. It has mainly been used as the bleaching component
in washing, bleaching and cleaning agents in powder form.
It is highly soluble in water and is characterized by a
rapid liberation of hydrogen peroxide.
The controlled release conditions can be obtained in
that the dissolution is controlled by adjusting the crystal
size and/or the crystal form of the crystalline sodium
carbonate peroxyhydrate, the solid particles being an
agglomerate of crystals.
The form of the crystalline sodium carbonate peroxy-
hydrate can be a monocrystal in the form of a hexagonal
prism with a density of between 0.9 and 1 g/cm3, a mono-
crystal in the form of a regular rhombohedral, a hollow
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granule with an apparent density of about 0.4 g/cm3 and
with an average diameter of about 480 um, or in the form
of a compact grain with an average particle size of about
450 um.
Preferably, the crystal size is between about 1 um
and about 100 um, most preferred between about 5 um and
about 20 Vim.
The solid particles, as agglomerates of crystals
to be coated according to the invention, should have a
particle size from about 150 ~m to about 1500 um, prefer-
ably from about 450 um to about 1000 um, most preferred
from about 600 um to about 800 um. Such particles should
have an apparent density of more than about 0.6 g/cm3, pre-
ferably from about 0.75 g/cm3 to about 1.1 g/cm3. Coated as
well as non-coated particles should have an average bulk
density between 0.5 and 0.6 g/cm3.
The average diameter of the sodium carbonate peroxy-
hydrate particles to b'e coated is generally 100 to 2000 um,
preferably 200 to 1500 um and in particular 250 to 1000 um.
Commercial preparations are available with an average par-
ticle size of about 500 um.
The active oxygen content of the crystalline sodium
carbonate peroxyhydrate particles should be as close to the
theoretical active oxygen content of 15.28 weighto as pos-
Bible, such as between 13.5 and 14.50 by weight. However,
lower amounts of available oxygen may be an advantage in
especial applications.
The coatings can comprise various additives in a wide
range of proportions and in accordance with known teachings
and/or practice. Such additives include, amongst others,
persalt stabilisers, crystal habit modifiers and salting
out agents.
The inorganic coating can be an alkali metal salt, an
alkaline earth metal salt or another non-heavy metal salt
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of an organic or inorganic acid, alone or a combination
thereof.
The least one inorganic coating is an alkali metal
salt, an alkaline earth metal salt or another non-heavy
metal salt of an organic or inorganic acid, alone or a
combination thereof.
Examples of inorganic coatings are sodium carbonate,
sodium bicarbonate, sodium sulphate, silicates, borates,
perborates, boric acids, silicate-silicofluoride mixtures,
and alkaline earth metal salts, etc.
Suitable coatings are alkali metal silicates, for
example potassium silicate, sodium silicate, sodium meta-
silicate, sodium orthosilicate, sodium sesquisilicate and
mixtures of two or more thereof.
The coating can also comprise a borate, such as
dehydrated sodium perborate, dehydrated sodium perborate
and sodium silicate, a borate-silicate mixture; a mixture
of boric acid or borate and a water repellent agent, a
borate-magnesium compound mixture. The borate is preferably
a sodium salt of boric acid, such as sodium tetraborate
decahydrate (or borax), sodium tetraborate pentahydrate,
sodium tetraborate tetrahydrate, sodium tetraborate
anhydrate, sodium octaborate tetrahydrate, sodium penta-
borate pentahydrate, sodium metaborate tetrahydrate and
sodium metaborate dehydrate, especially preferably sodium
metaborate dehydrate or sodium metaborate tetrahydrate.
Combinations of alkali metal silicates and borates
also increase the mechanical strength of the coating.
Salts of phosphoric acids, such as orthophosphoric,
pyrophosphoric, tripolyphosphoric, metaphosphoric,
hexametaphosphoric or phytic acid, can also be used.
Other examples of coatings are salts of phosphonic
acids, such as ethane-1,1-diphosphonic, ethane-1,2-tri-
phosphonic, or ethane-1-hydroxy-1,1-diphosphonic acid and
derivatives thereof, ethane-hydroxy-1,1,2-triphosphonic,
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ethane-1,2-dicarboxy-1,2-diphosphonic, or methane-hydroxy-
phosphonic acid, as well as salts of phosphonocarboxylic
acids, such as 2-phosphonobutane-1,2-dicarboxylic, 1-
phosphonobutane-2,3,4-tricarboxylic and a-methylphosphono-
succinic acid, or salts of amino acids, such as aspartic or
glutamic acid, or a silicate-glycine mixture.
Examples of inorganic coatings are salts of organic
acids, such as diglycolic, hydroxydiglycolic, carboxy-
methyloxysuccinic, cyclopentane-1,2,3,4-tetracarboxylic,
tetrahydrofuran-1,2,3,4-tetracarboxylic, tetrahydrofuran-
2,2,5,5-tetracarboxylic, citric, lactic or tartaric acid,
carboxymethylated products of sucrose, lactose or raffi-
nose, carboxymethylated pentaerythritol, carboxymethylated
gluconic acid, condensates of polyhydric alcohols or sugars
with malefic or succinic anhydride, condensates of hydroxy-
carboxylic acids with malefic or succinic anhydride, ben-
zenepolycarboxylic acids such as mellitic acid, ethane-
1,1,2,2-tetracarboxylic, ethene-1,1,2,2-tetracarboxylic,
butane-1,2,3,4-tetracarboxylic, propane-1,2,3-tricarbox-
ylic, butane-1,4-dicarboxylic, oxalic, sulfosuccinic,
decane-1,10-dicarboxylic, sulfotricarbollylic, sulfo-
itaconic, malic, hydroxydisuccinic or gluconic acid.
Other organic and/or polymer compounds are waxs, a
latexes, paraffins, polyols, vinyl resins, polyethylene
glycols, polyvinyl alcohols, and polyvinylpyrrolidone.
Suitgable coatings are polyacrylic acid, polyaconitic acid,
polyitaconic acid, polycitraconic acid, polyfumaric acid,
polymaleic acid, polymesaconic acid, poly-a-hydroxyacrylic
acid, polyvinylphosphonic acid, sulfonated polymaleic acid,
malefic anhydride/diisobutylene polymers, malefic
anhydride/styrene polymers, malefic anhydride/methyl vinyl
ether polymers, malefic anhydride/ethylene polymers, malefic
anhydride/ethylene cross-linked polymers, malefic
anhydride/vinyl acetate polymers, malefic
anhydride/acrylonitrile polymers, malefic anhydride/a~crylate
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polymers, malefic anhydride/butadiene polymers, malefic
anhydride/isoprene polymers, poly-(3-ketocarboxylic acid
derived from malefic anhydride and carbon monoxide, itaconic
acid/ethylene polymers, itaconic acid/aconitic acid
5 polymers, itaconic acid/maleic acid polymers, itaconic
acid/acrylic acid polymers, malonic acid/methylene
polymers, mesaconic acid/fumaric acid polymers, ethylene
glycol/ethylene terephthalate polymers, vinylpyrroli-
done/vinyl acetate polymers, 1-butene-2,3,4-tricarboxylic
10 acid/itaconic acid/acrylic acid polymers, polyester
polyaldehyde carboxylic acid containing a quaternary
ammonium group, cis-isomer of epoxysuccinic acid, poly[N,N-
bis(carboxymethyl)acrylamide], poly(oxycarboxylic acids),
starch succinate, maleate or terephthalate, starch
phosphate, dicarboxystarch, dicarboxymethylstarch and
cellulose succinate.
The controlled release conditions can be improved by
including a controlled release retarder in the at least one
coating and/or by adding the same together with the solid
particles to the soil or groundwater. The controlled
release retarder can be a metal chelating agent, or an
antioxidant, alone or a combination thereof.
Examples of suitable retarders are salts of amino-
polyacetic acids, such as nitrilotriacetic, ethylenedi-
aminetetraacetic or diethylenetriaminepentaacetic acid,
nitrilotriacetate and the phosphate, and ascorbic acid.
Likewise, the controlled release conditions can be
improved in that the dissolution of the least one coating
is controlled by including a controlled release accelerator
in the at least one coating and/or by adding the same
together with the solid particles to the soil or
groundwater. The controlled release accelerator can be a a
transition element or another non-heavy metal, or a
peroxidase, alone or a combination thereof.
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The controlled release conditions can also be
improved in that the dissolution of the at least one
coating is controlled by adjusting the thickness of the at
least one coating. The thickness of the coating depends on
the specific application and should under normal circum-
stances have a thickness between 5 ~m and 30 um.
The solid particles of crystalline sodium carbonate
peroxyhydrate can be used in situ as well as ex situ.
When used in situ, solid particles are added the soil
via a dosage pipe which can be installed by means of guid-
able horizontal drilling. In this way tubes etc can be in-
stalled in order to reach far contaminants below deposits,
buildings, parking places, lakes, rivers, etc, without the
normal activity being disturbed. Preferably, the solid
particles are injected in situ to the soil by the same or a
similar process as when lime-cement columns are installed,
a common. method in Scandinavia of deep stabilization of
cohesive soils, the soils being reinforced with lime or
lime/cement columns. In this way the particles can be
delivered at the required depth by means of vertical
drilling and ejecting the same by using air pressure.
The water required for dissolution and transport of
the solid particles comprising crystalline sodium carbonate
peroxyhydrate to the contanimants is either existing and
running ground water or machanically injected water.
When added ex situ to the soil, mechanical mixing can
be used. Alternatively, the solid particles are added by
means of sprinkling onto the soil on for example a con-
veyor. In this way a homogenous distribution of the solid
crystalline sodium carbonate peroxyhydrate particles can be
obtained prior to the chemical oxidation reaction. The soil
can be deposited in heaps for reaction and subsequent ana-
lysis.
In either case, the controlled release conditions are
further obtained in that the dissolution of the at least
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one coating is controlled by mechanically injecting or
spraying additional water into or onto the soil, respec-
tively.
Likewise, the release conditions can be further con-
s trolled in that the dissolution of the at least one coating
by heating the soil or groundwater and/or the solid parti-
cles while adding the same. Both the oxidizing reaction and
the reaction in which the salt is dissolved are exothermic,
which further controls the release conditions.
Tests have been made on the possible difference in
efficiency between sequential and direct application of the
solid particles comprising crystalline sodium carbonate
peroxyhydrate, and the results show that no such difference
exists.
The dosage of the oxidation agen in the inventive
method, for degradation of contaminants in soil is mostly
based on experience. Theoretically, the consumption of the
oxidation agent can be calculated, but in practice a lot of
factors affect this consumption. For example, the level of
catalytic metals (iron, copper and others) have a big in-
fluence on the course of events in soil.
For contaminants the unit -CH2- can be used as
average formula. In this case a reaction with hydrogen
peroxide is
Reaction: CHZ + 3 H202 =_> COZ + 4 H20
MW, g/mol: 14.03 34.01
Thus 14.03 g contaminant consumes 3*34.01 = 102.03 g H202,
which corresponds to a theoretical consumption of 7.27 g
H202 per 1 g of contaminant. The level (which can be
controlled during manufacturing of the solid particles) of
HzOz produced by the oxidation agent should for example be
between 10 and 80 weight o, preferably between 15 and 65
weight o, more preferably between 20 and 55 weight °s, most
preferably between 25 and 40 weight o. For example, an
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amount of 30 weight ~ corresponds to 1 g of a contaminant,
which demands 24.23 g of a H202 producing oxidation agent.
EXAMPLES
The invention will now be further described and
illustrated by reference to the following examples. It
should be noted, however, that these examples should not be
construed as limiting the invention in any way.
EXAMPLE 1
The utility of the invention method was evaluated by
measuring the decomposition of hydrogen peroxide from solid
particles of sodium carbonate peroxyhydrate crystals having
a coating of sodium sulphate thereon. The thickness of the
coating was about 0.02 mm and the total diameter of the
particles was about 1.5 mm. These particles were mixed
(50:50 by weight) with zeolite, Wessalith P (4A), which was
used as a substitute for soil. The dry mixture was stored
in a climate chamber with a temperature of 30 .°C and a
relative humidity of 70 0. After 0, 1, 2, 4, 6, 8 and 12
weeks, samples of 5 g were removed and the hydrogen
peroxide content was analysed by titration with potassium
permanganate according to LPU-Ol.
Fig. 1 shows a diagram of the decomposition (y-axis),
in o, of solid particles with (W) and without (WO) coating,
50 o sodium carbonate peroxyhydrate + 50 % zeolite, temp.
30 °C, 70 o R.H., wherein time (x-axis) is in weeks.
The low decomposition rate of particles, having a
coating thereon provides a longer active oxygen treatment
in the soil. This is a benefit compared with a rapid active
oxygen release, when all the active oxygen does not have
time to react with contaminants in the soil.
EXAMPLE 2
Two approaches of mixing were investigated, each
comprising 20 kg of soil material (see Table 1) and the
same amount of the oxidation agent particles. The solid
particles used were the same as in example 1.
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A petroleum contaminated soil from an industrial site
was used as a matrix material in tests, which comprised
sand and 0.5%( dry weight) organic substances, analyzed as
loss on ignition (LOI) at 550 OC.
Half of the organic content was estimated to consist
of petroleum products, with enhanced levels of non-polar
aliphatic compounds of a quality indicating diesel oil
contamination. The remaining part of the organic content in
the soil we considered to be naturally occurring substan-
ces. Table 1 below shows the main parameters studied and
their levels, as determined by means of the method used.
Table 1
Parameter Method Number of Levels*
samples
Soil Visual 5 Sand -
judgement
DM1~ SS 028113 5 88 % by weight
TOC2~ Calculated 5 0.5 0 of DM
from LOI
Total non-polar SS 028145-4 2 3119 mg/kg DM
alifatics
Benzene GC-MS 2 <0.05 mg/kg DM
Toluen GC-MS 2 <0.05 mg/kg DM
Ethyl benzene GC-MS 2 <0.05 mg/kg DM
Total xylenes GC-MS 2 <0.05 mg/kg DM
Alifatics GC-MS 2 <10 mg/kg DM
(>C5-C8)
Alifatics GC-MS 2 <10 mg/kg DM
(>C8-C10)
Alifatics GC-FID 2 410 mg/kg DM
(>C10-C12)
Alifatics GC-FID 2 1689 mg/kg DM
(>C12-C15)
Alifatics GC-FID 2 2353 mg/kg DM
(>C16-C35)
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*) Average
1) Dry matter
2) Total organic content
Intermixing of the oxidation agent of the present in-
s vention in one of the approaches (A) was performed momen-
tary at one occasion and under mixing. The intermixing of
the oxidation agent of the present invention in the second
approach (B) was performed at four repeated occasions, in a
three day interval. At every intermixing occasion (B) one
10 fourth of total volume of the oxidation agent in the pre-
sent invention was added. A mixed sample is taken out from
each of the two different approaches on day 1, 3, 6, 10,
and 12, and is analyzed with regard to the total amount of
non-polar alifatic substances. In one fraction (Reference)
15 no oxidation agent of the present invention is added and
the fraction (Reference) is handled in the same way, with
repeated intermixing, as the fractions with the oxidation
agent of the present invention. The results are shown in
Table 2 below, which shows the reduction of total non-polar
alifatics (in o).
Table 2
Experiment Day 1 Day 3 Day 6 Day 10 Day 12
Reference - 10 24 33 32
A 58 71 - - -
B - 51 58 62 71
EXAMPLE 3
The study comprises a volume of 150 tons soil materi
al in total, where the dosage of the oxidation agent of the
present invention was made in a mixing barrel. During in
termixing, water was also added to get as close as possible
to the optimal moisture level in the soil. It appeared that
the physically most suitable level of moisture for slow
dissolution of the oxidation agent in the method of the
present invention should be about 85 o DM. After dosage of
the oxidation agent, samples were taken from the soil
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material, which were analyzed with respect to non-polar
alifatics and aromatics. Results are shown in Table 3
below.
Table 3
Parameter Samp- Level Dev.z Unit Reduc- Dev.2Unit
les tionl
Tot. non-pol. 10 951 +/-97 mg/kg DM 69 +/-4
Alifatics
Benzene 2 <0.05 - mg/kg DM - - -
Toluene 2 <0.05 - mg/kg DM - - -
Ethyl Benzene 2 <0.05 - mg/kg DM - - -
Tot. Xylenes 2 <0.05 - mg/kg DM -- - -
Alifatics 2 <10 - mg/kg DM - - -
(>C5-C8)
Alifatics 2 <10 - mg/kg DM - - -
(>C8-C10)
Alifatics 2 180(1 - mg/kg DM 56 - o
(>C10-C12) 30)3
Alifatics 2 605(4 - mg/kg DM 64 - o
(>C12-C16) 60)3
Alifatics 2 850(6 - mg/kg DM 64 -
(>C16-C35) 90)3
1) Average
2) 95o confidence interval
3) 2 months after dosage
The chemical oxidation with hydrogen peroxide is
an exoterm reaction and brings about an increase in
temperature in surrounding material. Furthermore, the
increase in temperature can even be correlated with the
physical process that take place when salts of sodium
carbonate take up water (crystal water). Accordingly, the
increase in temperature is accordingly a measure of that
the oxidation agent in the inventive method is dissolved
and that hydrogen peroxide is liberated. The temperature
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was studied during and after the application of the oxida-
tion agent. The results are shown in Table 4 below.
To prevent leavage of hydrogen carbons to the atmos-
phere, the surface of the laid out, ready-mixed soil was
covered with a thin layer of wood bark, which acts as a
absorbant. The relative amount of hydrogen carbons, which
may be formed during the treatment and liberated to the
environment, was monitored consecutively with a portable
equipment, a photo ionization detector - PID, for determi-
nation of volatile hydrogen carbons. The results are shown
in Table 4 below.
Table 4
Time/h Time/ Temp. PID/ Comment
days C ppm*
0.00 0.00 20 350 Temperature at start
0.25 0.01 25 -
1.00 0.04 38 400
1.75 0.07 53 300
2.50 0.10 59 360
2.67 0.11 60 367 Maximum temperature
3.00 0.13 56 -
3.50 0.15 56 -
4.00 0.17 56 -
13.25 0.55 37 - 1/2 max. temp. after 1/2 day
37.25 1.55 29 -
61.25 2.55 20 - Back to start temp. after 2.5 days
* The measurement was made at constant temperature
Originally 450 kg contaminants were present in the
soil and after treatment 310 kg of them was eliminated,
which corresponds to a level of reduction of 69 +/- 40. The
result from the laboratory experiment show that a further
degradation of alifatics is obtained with an elevated
dosage of the oxidation agent in the method of the present
invention.
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Volatile contamination from stored piles of petroleum
contaminated soil was minimized by covering the piles with
an absorbent (bark) directly after mixing.
Furthermore, it can be established that the levels of
short alifatic fractions (defined by the analysis methods
GC-FID/MS, IR SS028145-4) do not increase after degrada-
tion, and that the value from PID measurement of volatile
organic substances does not increase. The chemical process
does therefore not contribute to any substantial degree to
the liberation of contaminants to the environment. Those
alifatics which react with hydrogen peroxide are probably
completely degraded and do consequently result in water and
carbon dioxide.
The optimal moisture content in the soil was deter-
mined in order to obtain an effective dissolution of the
oxidation agent in the inventive method. The moisture con-
tent does not only affect how.fast the oxidation agent in
the present invention is dissolved, but also the mobility
of the hydrogen peroxide released. This study shows that 85
o DM is an optimal level. If the moisture content was
altered to 80 and 90 o DM, respectively, the reduction of
contaminants was decreased by approximately 30 0.
The degradation of contaminants does mainly occur
during the first couple of days, and during this process an
increase of temperature in the material is denoted. Conse-
quently, during dosage of hydrogen peroxide, the monitoring
of the temperature constitute an easy control parameter for
the chemical oxidation of contaminants in soil. This para-
meter can be used to continuously control and optimize the
chemical degradation process.
In summary the method according to the present inven-
tion acts satisfactory for oxidation of petroleum constitu-
ents in tested piles. The method is easy to apply in field
and the chemical process is fast. Handling of contaminated
soil, from an environmental and health point of view, may
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be minimized. Since the contaminants are degraded fast and
are eliminated, in course of time, a long and hazardous
handling of harmful piles of soil may be avoided. The de-
contaminated soil has not been recontaminated by additional
additives, which is a positive characteristic, from an.
environmental and health point of view.
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