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