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land remediation
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LAND REMEDIATION By Ms Nor Haniza Mustafar Kamar Lecturer, PUO, Malaysia
cn301.blogspot.com
LAND REMEDIATION TECHNOLOGY
Pollutants enter the environment directly as a result of
accidents, spills during transportation, leakage from waste
disposal or storage sites, or from industrial facilities
Problems associated with the cleanup of petroleum-
contaminated sites have demonstrated that there is a need
to develop remediation technologies that are feasible,
quick, and deployable in a wide range of physical setting.
In situ methods Ex situ methods
In-situ Treatment
Solidification/ Stabilization
Chemical Oxidation
Soil Flushing Electrokinetic
Separation
Soil Vapor Extraction
(SVE)
In-situ Treatment
Soil Vapor Extraction (SVE)
SVE is a physical treatment process for in
situ remediation of volatile contaminants in
vadose zone (unsaturated) soils
SVE is based on mass transfer of
contaminant from the solid (sorbed)
and liquid (aqueous or non-aqueous)
phases into the gas phase, with
subsequent collection of the gas
phase contamination at extraction
wells.
The effectiveness of SVE, that is, the
rate and degree of mass removal,
depends on a number of factors that
influence the transfer of contaminant
mass into the gas phase. The effectiveness of SVE is a function of the contaminant
properties (e.g., Henrys Law constant, vapor pressure, boiling point, adsorption coefficient), temperature in the
subsurface, vadose zone soil properties (e.g., soil grain size,
soil moisture content, permeability, carbon content),
subsurface heterogeneity, and the air flow driving force
(applied pressure gradient)
In-situ Treatment
Solidification/ Stabilization
Remediation of contaminated sites with cement,
also called solidification/stabilization with cement
(S/S with cement) is a common method for the safe
environmental remediation of contaminated land with
cement. SOLIDIFICATION refers to processes that encapsulate a waste to form a solid material
and to restrict contaminant migration by
decreasing the surface area exposed to
leaching and/or by coating the waste with low-
permeability materials. Solidification can be
accomplished by a chemical reaction between a
waste and binding (solidifying) reagents or by
mechanical processes. Solidification of fine
waste particles
is referred to as microencapsulation, while
solidification of a large block or container of
waste is referred to as macro-encapsulation
STABILIZATION refers to processes that involve chemical reactions that reduce the
leachability of a waste. Stabilization
chemically immobilizes hazardous
materials or reduces their solubility through
a chemical reaction. The physical nature of
the waste may or may not be changed by
this process.
In-situ Treatment
Chemical Oxidation
In situ chemical oxidation (ISCO), a form of
advanced oxidation processes and advanced oxidation
technology, is an environmental remediation technique
used for soil and/or groundwater remediation to reduce
the concentrations of targeted environmental
contaminants to acceptable levels.
ISCO is accomplished by injecting or
otherwise introducing strong chemical
oxidizers directly into the contaminated
medium (soil or groundwater) to
destroy chemical contaminants in
place. It can be used to remediate a
variety of organic compounds,
including some that are resistant to
natural degradation.
In-situ Treatment
Soil Flushing
Soil flushing is a technology used for extracting
contaminants from the soil. It works by applying water
to the soil. The water has an additive that enhances
contaminant solubility.
Contaminants that are dissolved in the
flushing solution are leached into the
groundwater, which is then extracted and
treated. In some cases, the flushing
solution is injected directly into the
groundwater. This raises the water table
into the capillary fringe just above the
surface of the water table, where high
concentrations of contaminants are
typically found. In many instances,
surfactants (i.e., detergent-like substances)
or solvents are used as the additive. The
effectiveness of this process is dependent
on hydro-geologic variables (e.g., type of
soil, soil moisture) and the type of
contaminant.
In-situ Treatment
Electrokinetic Separation
Electrokinetics remediation, also termed electrokinetics, is
a technique of using direct electrical current to remove
organic, inorganic and heavy metal particles from the soil by
electric potential. The use of this technique provides an
approach with minimum disturbance to the surface while
treating subsurface contaminants.
Electrokinetic remediation is applied to many
contaminants that can be dissolved within
groundwater. Heavy metals are one of the main
contaminants that are removed by the electrokinetics
process
Biology Treatment
Bio-venting
Phytoremediation
Aerobic venting
Anaerobic venting
Cometabolic venting
Phytoextraction
Rhizodegradation
Phytodegradation
Phytostabilization
Phytovolatilazation
Biology Treatment
Bio-venting
Aerobic venting
- Aerobic bioventing has a robust track record in treating
aerobically degradable contaminants (such as fuel)
- Bioventing involves supply oxygen to contaminated
unsaturated soils with low oxygen concentrations to
facilitate aerobic microbial degradation.
- Using the supplied oxygen, the microbes oxidize the
contaminants to gain energy and carbon for growth.
- Oxygen is typically introduced by air injection wells that
push air into the subsurface.
Biology Treatment
Bio-venting
Anaerobic venting
- Some chlorinated compounds are not effectively treated aerobically. Microbes
may degrade these contaminants directly via anaerobic reductive
dechlorination or through anaerobic cometabolic pathways.
- Anaerobic reductive chlorination is a biological mechanism, typically marked
by sequential removal of chlorine ions from a molecule.
- Microbes possessing this pathway gain energy from this process.
- In some situations, microorganisms fortuitously degrade contaminants, while
gaining energy and carbon from other compounds (cometabolites).
- These organisms usually do not obtain any benefit from contaminant
degradation, and the removal process is called cometabolism.
- Anaerobic bioventing may involve both anaerobic reductive dechlorination
and anaerobic cometabolism to destroy the contaminants of concern.
Biology Treatment
Bio-venting
Cometabolic venting
- Cometabolic bioventing involves injecting air into the subsurface along with a
suitable gaseous substrate to promote cometabolic reactions with the target
compound.
- The organisms usually do not obtain any benefit from contaminant degradation.
- A suitable substrate should be determined in the lab but may include methane,
ethane, propane, butane and pentane.
- The delivery system is similar to other bioventing technologies.
- This method is applicable to contaminants that resist aerobic degradation. (e.g.
TCE, ethylene dibromide and dichloroethane).
Phytoremediation describes the treatment of environmental problems through the
use of plants that mitigate the environmental problem without the need to excavate
the contaminant material and dispose of it elsewhere.
Biology Treatment
Phytoremediation
Phytoremediation
RHIZODEGRADATION
Thermal Treatment
Electrical Resistance
Heating
Conductive Heating
Steam Injection &
Extraction
Radio Frequency
Heating
In-situ Vitrification
Thermal Treatment Electrical Resistance
Heating
Electrical Resistance Heating (ERH) is an intensive in situ environmental
remediation method that uses the flow of alternating current electricity to heat soil
and groundwater and evaporate contaminants
Electric current is passed through a targeted soil volume between subsurface
electrode elements.
The resistance to electrical flow that exists in the soil causes the formation of
heat; resulting in an increase in temperature until the boiling point of water at
depth is reached.
After reaching this temperature, further energy input causes a phase change,
forming steam and removing volatile contaminants. ERH is typically more cost
effective when used for treating contaminant source areas.
Thermal Treatment Electrical Resistance
Heating
Thermal Treatment Steam Injection &
Extraction
Steam injection was first developed by the petroleum industry for the enhanced recovery of oils from reservoirs.
In petroleum industry applications, steam is injected to lower the viscosity of heavy oils and to increase the volatility of light oils.
As much as 50 percent of the original oil in place may remain in the reservoir when the process becomes uneconomical and is discontinued.
In the past several years, steam injection has been adapted for the recovery of organic contaminants from the subsurface, and extensive laboratory and field
research has been done.
When steam injection is used for subsurface remediation, the objective is to remove as much of the contamination as possible, thus reducing the residual to very low
levels.
The subsurface conditions dealt with by the petroleum industry versus remediation purposes are generally very different - the petroleum industry dealing with deep,
confined reservoirs and the remediation industry with the shallow, generally
unconfined subsurface.
Thus, the petroleum industry technique and the technique for remediation purposes differ in significant ways
Thermal Treatment Steam Injection & Extraction
Thermal Treatment Conductive Heating
The energy that is injected into the
subsurface mobilizes volatile and semi-
volatile organic contaminants so that they
are easy to remove. Then contaminants,
groundwater, and vapors are pumped out
and treated or sent off site for disposal.
Thermal Conduction Heating (TCH), also known
as In-Situ Thermal Desorption (ISTD)
ISTD is the simultaneous application of heat, by
TCH, and vacuum to the subsurface to remove
organic chemicals.
Heat is applied by installing electrically powered
heaters at regular intervals throughout the zone to
be treated. The heat moves out into the inter-well
regions primarily by thermal conduction.
Thermal conduction heating of fractured bedrock sites is capable of:
i. achieving thorough heating of the bedrock (matrix and fractures),
ii. preventing unwanted condensation of steam and CVOC vapors, and
iii. capture and removal of the CVOC mass liberated from the bedrock and
unconsolidated deposits.
Thermal Treatment Radio Frequency
Heating
Radio wave = type of electromagnetic radiation RFH is generated by propagation of radio waves at 30-300MHz RFH is heat generated at a molecular level due to a rubbing effect similar to a microwave oven, but at lower frequency.
RF energy propagates through all media (solid, liquid and gas) over a volume =
heats evenly and quickly over relatively large volume
The distribution of RF energy is not limited by structural features, permeability
or heterogeneity of the host (overburden or bedrock)
RF energy preferentially heats the target = polar molecules such as water,
oil, contaminants over the host (OB and rock)
Thermal Treatment
In-situ Vitrification
In situ vitrification uses electrical power to heat and melt soil,
sludge, mine tailings, buried
wastes and sediments
contaminated with organic,
inorganic and metal-bearing
hazardous wastes.
The molten material cools to form a hard, monolithic, chemically
inert, stable glass and crystalline
product that incorporates and
immobilizes the thermally stable
inorganic compounds and heavy
metals in the hazardous waste.
The slag product material is glass like with very low leaching
characteristics.
In-situ Barriers
Slurry Walls
Drainage
trenches & wells
In-situ Barriers
Slurry
Walls
The slurry wall is in place to limit the spread of
contaminated ground water off the site. It is made
of a two-foot wide trench cut into the ground then
back-filled with a clay and water mix.
In addition to the slurry wall, the sheet pile wall blocks the spread of
contaminants off the site. The sheet wall is made of interlocking steel
sheets and is located on the east side of the site.
Slurry walls are used to contain or divert
contaminated groundwater from drinking
water intake, divert uncontaminated
groundwater flow from contaminated sites,
and/or provide a barrier for the ground water
treatment system.
Drainage
trenches &
wells
In-situ Barriers
One of the most significant disadvantages
of slurry trench construction is the
extensive field setup required. The major
construction process involved in the
installation of a slurry trench include
preconstruction planning and mobilization, preparation of the site, slurry mixing and
hydration, excavation of soil, backfill
preparation, placement of backfill, cleanup
of the site and demobilization (USEPA, 1995). In order to accomplish all of this, a
large site is typically required to
accommodate the various mixing areas,
storage of soils excavated, heavy
machinery, etc.
Trenches are often used in cases that the waste mass of the
contaminant is too large for treatment or where soluble and
mobile constituents pose an imminent threat to a source of
drinking water (Van Deuren et al., 2002).
RISK ASSESSMENT he risk assessment process consists of four major steps. These steps are data
collection and evaluation, exposure assessment, toxicity assessment, and
risk characterization.
data collection and evaluation
exposure assessment
toxicity assessment
risk characterization
Sampling Methodology
Biota
Quality Assurance/Quality Control
Screening for Chemicals of Potential Concern
Chemical-Specific Issues
Selection of Exposure Pathways
Determining Exposure Point Concentrations
Determining Chemical Intakes and Exposure
Concentrations
Carcinogens
Non-Carcinogens
RISK ASSESSMENT
Carcinogenic
Risks
Non-Carcinogenic
Risks
Chemical contamination is a worldwide problem and represents a significant
threat to the environment, to the functioning of ecosystems, and to human
health
RA by risks type
RISK ASSESSMENT Example Modules:
Data Analysis and Interpretation Data Analysis and Programming Skills Data Assimilation and Integration Disaster Management Environmental Applications of Isotope Geochemistry Environmental Radioactivity Environmental Sampling and Analysis for Trace Organics Environmental Toxicology Geoinformatics Geological Hazards Numerical Skills Safety and Environmental Impact Assessment: An Industrial
Perspective
Behaviour of Pollutants in the Environment Chemical Risk Assessment Contaminated Land and Remediation Dissertation Project Pollution Microbiology
Other modules include:
If the risk assessment indicates that there are unacceptable risks, the participant
should propose remediation levels to lower the risk to acceptable levels. If a
participant wishes to deviate from the risk goal when setting remediation levels for
a site, a detailed rationale should be provided for VDEQ review and approval.
For non-carcinogens, an unacceptable risk is defined as a hazard index greater
than one for contaminants affecting the same target organ. For an individual
contaminant a hazard quotient exceeding one indicates that adverse effects cannot
be ruled out.
However, even if individual contaminants result in a hazard quotient less than one,
contaminants that affect the same target organ are assumed to have additive
toxicity.
Remediation levels for non-carcinogens should therefore be concentrations that,
when added together, would not result in a hazard index greater than one.
RISK ASSESSMENT
By Ms Nor Haniza Mustafar Kamar Lecturer, PUO, Malaysia
cn301.blogspot.com