SOIL TREATMENT
in-situ chemical oxidation of contaminated soils
(using hydrogen peroxide)
Introduction
Soils contaminated with hydrocarbons (petroleum residues, solvents, pesticides, wood
preservatives, etc.) present one of the more difficult challenges for remediation specialists. This
is particularly true when the contamination has spread deep below the surface, making
excavation costly or impractical. The technologies currently in use all have serious shortcomings.
Technology Option
Major Shortcomings
Soil washing
Produces an aqueous effluent needing treatment/disposal
Not effective for DNAPL뭩
Vapor extraction
Requires treatment of the extracted vapors
Not effective for DNAPL뭩
Biotreatment
Lengthy process (years)
Difficult to monitor and control
Inconsistent results associated with toxicity, biodegradability,
solubility, and nutrient availability
Landfilling
Decreasing availability of suitable disposal sites
Increasing transportation and disposal costs
Incineration
Lengthy and difficult permitting process
High capital costs
The use of H2O2 to chemically oxidize the contaminants into mineralized products (CO2 , salts,
and readily biodegradable organic fragments) offers a number of advantages over these current
treatment methods.
Benefits of Soil Decontamination by Chemical Oxidation:

The reagent used (H2O2) is inexpensive, readily available, and has as its
reaction products water and oxygen;
1

The chemistry of the process (Fenton뭩 Reagent) has been known for over 50
years and its applicability to a wide variety of contaminants is well documented;

The process is easily applied and controlled;

The treatment occurs rapidly, lasting from a few hours to a few weeks;

The process produces no by-product wastestreams, and can be tuned for the
degree of contaminant removal desired. This allows it to be used synergistically
with other technologies such as biotreatment or soil washing.
Background/ Principles
The basis of the process involves Fenton 뭩 Reagent, whereby the transition metal catalyst is
either provided by iron oxides within soil or added separately as a solubilized iron salt. The
oxidation occurs both at the soil interface (in the case of DNAPL 뭩) and within the interstitial
groundwater (in the case of desorbed organics). The process is related to UV photolysis
methods used in groundwater remediation in that both processes are considered Advanced
Oxidation Technologies (AOTs). By definition, AOT 뭩 generate highly reactive, short-lived
hydroxyl radicals (.OH) which degrade even the most recalcitrant organics.
The application of chemical oxidation technologies for degrading toxic, inhibitory or biorefractory
organics has also been well studied of late. These properties are highly correlated to aromatic
ring structures and non-polarity (low water solubility). Chemical digestion of these substances
by AOT 뭩 results in ring cleavage and insertion of oxygen into the digested fragments. This
reduces their toxicity and increases their water solubility, thereby facilitating their degradation in
the natural environment.
Discussion
The following is an overview of the variables which affect the technology 뭩 application.
1. Effect of H2O2 : contaminant dose ratio
This parameter is closely related to the efficiency of treatment since H2O2 is generally
the primary cost component in the application. And because of the complexity of soil
matrices, the process is inherently less efficient than that in aqueous reactions. This
results in effective weight ratios of 5-50:1 for soil treatments versus 1-5:1 for aqueous
treatments. Typical of most chemical reactions, efficiency increases with higher
contaminant concentrations and decreases as target treatment levels become more
stringent.
2
2. Effect of H2O2 concentration
Unlike aqueous applications of Fenton 뭩 Reagent where the strength of the H2O2
feed solution has no effect, in soil applications the amount of water present in the
reaction mix (termed liquid:soil ratio) is critical. This aspect was characterized for the
treatment of PAH-contaminated soils by Richard Watts at Washington State University.
Two systems were studied: 1) a low (water) volume/high (solids) concentration, which
used 25-50% H2O2; and 2) a high volume/low concentration, which used 0.5 - 2%
H2O2. It was observed that the lower water volume (higher H2O2 concentration)
provided faster reaction times (hours versus days/weeks) but less efficient H2O2 use. A
second important finding was that the lower water volume (higher H2O2 concentration)
provided significantly greater removal of DNAPL-type contaminants. The following
general guidelines were produced for applying the process in an ex-situ mode.
High volume/low concentration system
Initial TPH Conc. (mg/Kg) H2O2 Conc. H2O2 Volume (gallons / ton of soil)
300 - 800
0.5%
800
800 -1300
1%
2000
1300 -1800
1%
2400
1800 -2300
1%
3200
Low volume/high concentration system
Contaminant
Initial TPH Conc. (mg/Kg) H2O2 Conc. H2O2 Volume (gallons / ton of soil)
Gasoline/diesel
200 - 1000
25%
48
Gasoline/diesel
1000 - 2000
35%
48
Motor/Hydraulic oils 200 - 1000
50%
96
Motor/Hydraulic oils 1000 - 2000
50%
192
3. Effect of soil type
The type of soil affects the process in many ways, the most obvious being the
availability of iron. Various studies have shown that crystalline soils (especially those
3
containing goethite and hematite iron oxides) effectively catalyze the reaction. Silica
sand was even used in one study. Amorphous soils (e.g., clays) are less effective. If
supplemental iron is needed, application rates of 0.5 - 2 gms-Fe2+ per Kg-soil are
indicated.
A second effect of soil type relates to its buffering capacity (carbonate alkalinity). This
has two effects: 1) Fenton reactions perform best at pH 2-4 and not at all at > pH 7-8
(except if certain chelated iron complexes are used); and 2) carbonate ions are strong
free radical scavengers and effectively retard Fenton reactions. Thus, highly alkaline
soils (e.g., those containing limestone) may require mineral acid to be added to the
zone of contamination in order to bring the pH into the optimal range. Such pH
adjustment is not needed for low alkalinity soils since the desired pH is quickly obtained
by the organic acid fragments once the reaction gets underway.
A third effect of soil type relates to its organic carbon (humus) content. Since the
hydroxyl radical is relatively non-selective in its reactions, we should expect competition
between the natural background organics and the hydrocarbon contaminants. As the
ratio of background-to-contaminate organics increases, so will the required H2O2 :
contaminate dose ratio. However, Watts, et.al. observed no significant effect with
contaminant levels of 500 - 2000 mg/Kg against background organic carbon contents of
0.1 - 1.3%.
4. Effect of reaction time
Theoretically, applications of Fenton Reagent follow a first-order rate equation (i.e.,
contaminant removal is a linear relationship to H2O2 dose). However, there are a
couple of factors which cause results to deviate from the model. The first is the
concentration of iron catalyst. In most cases, supplemental iron addition to the soil will
provide savings in both H2O2 efficiency and project length. The second factor relates to
the polarity of the organic contaminants. There is evidence that reaction times may
depend on the desorption of adsorbed organics from the soil particles into the aqueous
phase. This is consistent with the known properties of Fenton 뭩 Reagent, and explains
why, all things being equal, DNAPL-type organics react more slowly than light
hydrocarbons (weeks versus hours). However, as discussed above, this can be
compensated for by lowering the liquid:soil ratio (increasing the feed concentration of
H2O2). Incidentally, this work suggested that other (non-Fenton-type, heterogenous)
reaction mechanisms may be partially responsible for the oxidation of such non-polar
contaminants.
In summary, the following factors may be used to reduce the reaction times: higher
H2O2 : contaminant dose ratios, higher iron catalyst doses, and lower liquid:soil ratios
(higher H2O2 feed concentrations).
4
5. Effect of contaminant type.
Soil decontamination with H2O2 has been demonstrated on the following types of
organics:
Contaminants Treated

Chlorinated solvents (TCE, PCE)

Munitions (TNT, RDX)

Pesticides (chlorophenoxy, atrazine, pendimethalin)

Petroleum residues (BTEX, PAH, TPH, MTBE, diesel fuel)

Wood preservatives (PCP, creosote)

Misc. (PCB뭩, phenolics)
6. Effect of other parameters
Although much work remains to identify and characterize these other variables, we can
gain some insight from aqueous reactions of Fenton 뭩 Reagent. For example, the
optimal pH is 2-4, and the optimal temperature is 10-20 deg-C. We also know that in
highly contaminated systems (where the potential for unproductive side-reactions are
great), H2O2 efficiency is improved by performing the oxidation either in a stepwise
fashion or (optimally) in a slow, continuous mode ?as opposed to adding the H2O2 all
at once.
Practical considerations
Although soil decontamination with H2O2 is relatively easy to employ, for the following reasons
the process is rather complex to evaluate:

The major cost component (H2O2 requirement) is not a linear function of contaminate
levels. As discussed above, there are a number of parameters to consider -- soil type,
liquid:soil ratios, contaminant type, and reaction times. Profiling these variables requires
carefully designed column studies (using multivariable, multilevel factorial design
experiments).

The costs incurred as a result of project length, H2O2 use, and special site constraints
will inevitably present trade-offs. These must be carefully evaluated to develop the
process parameters which provide the most benefit at the least cost.

Given the diminishing returns in treating to ppb levels of residual contaminant, there
may be synergy in combining this technology with other technologies more suitable to
removing trace levels of organics. Examples of complementary technologies include
5
biotreatment, soil washing, and UV photolysis (of the groundwater). Choosing an
appropriate combination and determining the optimal transition point requires careful
study.

Site constraints, especially geohydraulic considerations, will impact how the technology
is applied. In-situ applications (treating the soil in place using sprayers, sprinklers or
nozzle injectors) have the advantages of less exposure of workers, less impact of site
constraints, and typically less cost. Ex-situ applications (excavating the soil and treating
it batchwise in a surface mixer, leach pile, etc.) have the advantages of greater process
control and reduced risk of leaching contaminants or degradation products into the
groundwater. NB. To reduce these risks, known subsurface process delivery and control
methods have been adapted for this technology. These include: vertical/horizontal
sparging, recirculation wells, permeable treatment walls, hydraulic fracturing, enhanced
soil mixing, and injection/permeation dispersal. Choosing and applying the best
method(s) requires the services of a geohydrologist specializing in the field.
Another practical consideration relates to the safety of applying concentrated H2O2 solutions to
soils. The reaction can be vigorous, with the rapid evolution of oxygen, steam and carbon
dioxide. Allowances should be made to ensure adequate venting of these gases. If possible, the
H2O2 should be added stepwise or in a slow, controlled continuous fashion.
Conclusions
Adaptation of Fenton 뭩 Reagent from treating aqueous wastes to treating contaminated soils
has been successfully demonstrated for number hydrocarbons, and the primary variables
affecting its performance have been identified and characterized. The technology has been
shown to remove organic contaminants adsorbed onto soils and degrade them to CO2 or more
polar compounds which are amenable to subsequent treatments. Compared to currently used
technologies, the process offers advantages related to simplicity, cost, and range of
effectiveness.
Literature References
Greenberg, Richard S. and Richard Watts, "In-Situ Fenton's Like Oxidation of Volatile Organics:
Laboratory Pilot and Full-Scale Demonstration", presented at WEFTEC Workshop on In-Situ
Chemical Oxidation for Site Remediation, (Oct. 1997).
Kline, Steven, "Enhanced Soil Mixing with Hydrogen Peroxide and Potassium Permanganate",
presented at WEFTEC Workshop on In-Situ Chemical Oxidation for Site Remediation, (Oct.
1997).
6
Pignatello, J.J. and Katharina Baehr, "Ferric Complexes as Catalysts for "Fenton" Degradation
of 2,4-D and Metolachlor in Soil", presented at the Conference on Chemical Oxidation:
Technology for the 1990's, Vanderbilt Univ. (Feb. 1994).
Gates, D.D. et.al., "Laboratory Evaluation of the In-Situ Chemical Oxidation of Volatile and
Semi-Volatile Organic Compounds Using Hydrogen Peroxide and Potassium Permanganate,"
Oak Ridge National Laboratory (1994).
Watts, Richard J. et.al. "On Site Treatment of Contaminated Soils Using Hydrogen Peroxide",
Project Report T9234-06, Washington State Transportation Center, Washington State Univ.
(1994).
Kelley, R.L. et.al., "An Integrated Chemical and Biological Treatment (CBT) System for Site
Remediation", presented at 19th Annual RREL Hazardous Waste Research Symposium, New
Orleans (Oct. 1993).
Gates, D.D. et.al., "Laboratory Evaluation of Chemical Oxidation Using Hydrogen Peroxide,"
ORNL/TM-12259, Report from The X-231B Project for In-Situ Treatment of Physicochemical
Processes Coupled with Soil Mixing, Oak Ridge National Laboratory (1993).
Ravikumar, J.X. and M.D. Gurol, "Fenton's Reagent as a Chemical Oxidant for Soil
Contaminants", presented at the Conference on Chemical Oxidation: Technology for the 1990's,
Vanderbilt Univ. (Feb. 1992).
Baehr, Katharina and Joseph Pignatello, "Use of Ferric Chelates for Fenton (Fe/H2O2)
Treatment of Pesticide Contaminated water and Soil at Neutral pH", in Proc. Int. Conf. Haz.
Waste Mgmt. , Atlantic City, NJ (1992).
Sun, Yunfu and Joseph J. Pignatello, "Chemical Treatment of Pesticide Wastes. Evaluation of
Fe(III) Chelates for Catalytic Hydrogen Peroxide Oxidation of 2,4-D at Circumneutral pH", in J.
Agric. Food Chem., vol. 40, pp 322-327 (1992).
Watts, Richard J. "Hydrogen Peroxide for Physicochemically Degrading PetroleumContaminated Soils", Remediation, 2:413 (1992).
Gurol, Mirat D. et.al. "Chemical Oxidation of Hazardous Compounds in Soil", National R&D Conf.
On the Control of Haz. Mat., Anaheim, CA (Feb. 1991)
Watts, Richard J., "Treatment of Contaminated Soils Using Catalyzed Hydrogen Peroxide",
presented at Conference on Chemical Oxidation: Technology for the 1990's, Vanderbilt Univ.
(Feb. 1991).
Pignatello, J.J., "Mineralization of Chlorophenoxy Herbicides using Iron - Hydrogen Peroxide
Reagents", presented at the I&EC Symposium, Amer. Chem. Soc., Atlanta (Oct. 1-3, 1991).
Sato, C., et.al. "Decomposition of PCB's and PCE with Fenton's Reagent", presented at the
I&EC Symposium, Amer. Chem. Soc., Atlanta (Oct. 1-3, 1991).
Sato, C. et.al. "Decomposition of PCB's in Soils Using Hydrogen Peroxide and Fe(II) Solutions",
presented at 64th Annual WPCF Conference, Toronto (Oct. 1991).
Dasappa, S.M. and R.C. Loehr, "Toxicity Reduction in Contaminated Soils Bioremediation
Processes". Water Research, vol. 9, pp. 1121-1130 (1991).
7
Kelley, R.L. et.al. "Application of Fenton 뭩 Reagent as a Pretreatment Step in Biological
Degradation of Polyaromatic Hydrocarbons", 57IIA8, v.3 (1991).
Kelley, R.L. et.al. "Application of Fenton's Reagent as a Pretreatment Step in Biological
Degradation of Polyaromatic Hydrocarbons", in Gas, Oil, Coal, and Environmental
Biotechnology III, eds: Cavit Akin and Jared Smith, pp. 105-120 (1991).
Watts, Richard J. et.al., "Treatment of Octachlororbidenzo-p-dioxin (OCDD) in Surface Soils
Using Catalyzed Hydrogen Peroxide", in Chemosphere, vol. 39, pp. 949-956 (1991).
Gurol, Mirat D. et.al "Enhancement of Biodegradation of Pentachlorophenol by Chemical
Oxidation", Proc. Water Env. Fed. Conf., Washington D.C. (Oct. 1990).
Miller, Christopher M. et.al. "Chemical Oxidation and Toxicity Reduction of PesticideContaminated Soils"
Watts, Richard J., "Treatment of Pentachlorophenol-Contaminated Soils Using Fenton's
Reagent", in Hazardous Waste and Hazardous Materials, vol. 7, pp. 335-345 (1990).
Piotrowski, Michael R. and J.Robert Doyle, "In-Situ Biogeochemical Reduction of Hydrocarbon
Contamination of Groundwater: A Superfund Case Study", presented at 62nd Annual WPCF
Conference (Oct., 1989).
Miller, Christopher M. et.al. "Chemical Oxidation and Toxicity Reduction of PesticideContaminated Soils", in Bioremediation of Recalcitrant Organics, pp. 175-181.
Shea, Patrick J., and S.D. Comfort, "Remediating Munitions Contaminated Soils."
Watts, Richard J., "Hazardous Waste - Source, Pathways, and Treatment". John Wiley, Chapter
5 (in press).
Other References (Investigators/Contractors)
BioSystems Technology, Inc., (800) 866-7645.
CleanOX Environmental Services, Inc., 17 Watchung Ave., Chatham, NJ 07928, (201) 7011288.
Dianne Gates, Martin Marietta Energy Systems, P.O. Box 2008, Oak Ridge, TN 37831, (615)
576-0427.
Geo-Cleanse International, Inc., 4 Mark Road, Suite C, Kenilworth, NJ 07033, (908) 686-5959.
In-Situ Oxidation Technologies, Inc. 51A Everett Dr., Lawrenceville, NJ 08648.
Oak Ridge National Laboratory, Oak Ridge, TN.
Relevant Patents
U.S. Patent 5,520,483 (May 28, 1996), "Method and system for remediation of groundwater
contamination", Ronald Vigneri inventor, CleanOX Environmental Services, Inc. assignee.
U.S. Patent 5,525,008 (Jun. 11, 1996), "Remediation Apparatus and Method for Organic
Contamination in Soil and Groundwater", James T. Wilson inventor, Geo-Cleanse International,
Inc. assignee.
8
U.S. Patent 5,286,141 (Feb. 15, 1994), "Method and system for remediation of groundwater
contamination", Ronald Vigneri inventor, CleanOX Environmental Services, Inc. assignee.
U.S. Patent 5,376,182 (Dec. 27, 1994), "Surfactant soil remediation" Lorne G. Everett et.al.
inventors, Remsol Corporation (Santa Barbara, CA) assignee.
9