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Remediation Treatment Technologies:
Reference Guide for Developing Countries Facing
Persistent Organic Pollutants
by
Loretta Li, Ph.D., P.Eng.
Associate Professor
Department of Civil Engineering
The University of British Columbia
6250 Applied Science Lane
Vancouver, B.C. V6T 1Z4
to
Dr. Mohamed EISA, Chief of POPs Unit
UNITED NATIONS INDUSTRIAL DEVELOPMENT ORGANIZATION
(UNIDO)
Vienna International Centre
P.O. Box 300, A-14000 Vienna
Austria
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i
Table of Contents
PageList of Tables ..................................................................................................................... iii
List of Figures .................................................................................................................... iv
Acknowledgements..............................................................................................................v
Disclaimer.......................................................................................................................... vi
1. Introduction.................................................................................................................1
2. Methodology...............................................................................................................2
3. Full Scale Technology Profiles...................................................................................2
4. Development of a Screening Matrix...........................................................................3
4.1. Logistics..........................................................................................................4
4.2. Grading System for the Developed Screening Matrix....................................8
5. The Potential for Improvement of Existing Remediation Techniques .......................9
6. Address the Potential Improvement of Incinerator.....................................................9
6.1. Methodology.................................................................................................10
6.2. Incineration of Hazardous Waste Materials/POPs........................................10
6.3. Conclusion ....................................................................................................15
7. Address the Potential Improvement of Landfilling for POPs...................................15
7.1. Methodology.................................................................................................16
7.2. Landfilling: Engineered Landfill for Hazardous Waste Materials/POPs .....16
7.3. Conclusion ....................................................................................................19
Appendix A Overviews of established, demonstrated and emerging technologies........21
A-1 Incineration ...................................................................................................22
A-2 Bioremediation (DARAMEND
& XenoremTM) ........................................29
A-3 Solvent Extraction.........................................................................................41
A-4 Vitrification (PACT, PLASCONTM& GeoMeltTM) .....................................45
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A-5 Solidification/Stabilization ...........................................................................50
A-6 Gas Phase Chemical Reduction ....................................................................56
A-7 Alkali Metal Reduction (Sodium Reduction) ...............................................61
A-8 Pyrolysis and Gasification ............................................................................64
A-9 Ball Milling/ Mechano-Chemical Dehalogenation (MCDTM) ......................70
A-10 Thermal Desorption ......................................................................................74
A-11 Supercritical Extraction (SCE) .....................................................................83
A-12 Soil Washing.................................................................................................92
A-13 Chemical Dehalogenation...........................................................................100
A-14 Phytoremediation ........................................................................................105
Appendix B Soil Effect on Cost of Technology ...........................................................111
Appendix C Treatment Technology Combinations......................................................117
Appendix D Chemical abbreviations, synonyms and trade names of 12 POPs
identified by UNIDO in the Stockholm Convection................................119
Bibliography ..................................................................................................................122
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List of Tables
Page
Table 1 The list of reviewed technologies ......................................................................3Table 2 Proposed screening matrix system choosing an appropriate technology
for a specific site in each developing country....................................................6
Table 3 Grading System for screening matrix ................................................................8
Table B1 Soil Characteristics Affecting Cost of Remedial Technology ((USEPA
1989; Evans 1990; USEPA 1991a; USEPA 1992b; USEPA 1994b;
USEPA 1995b; USEPA 1997; USEPA 2004a; USEPA 2005) .....................113
Table B2 Critical Characteristics Affecting Cost Ranges for Technology
Alternatives for Remediating POP- Contaminated Soil and Sediment
(Dvila et al., 1993) .......................................................................................114
Table B3 Cost Summary of Each Technology and the Estimated Cost in 2007
U.S. Dollars using Construction Cost Index..................................................115
Table B4 Annual Construction Cost Index....................................................................116
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List of Figures
Page
Figure C1 Common combinations of treatment technologies applied in remedialactions (USEPA 2004b).................................................................................118
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ACKNOWLEDGEMENTS
Special acknowledgment is given to Dr. John R. Grace of the Department of Chemical
and Biological Engineering at The University of British Columbia for his contributions to
the section on combustion technology; Tamer Gorgy, my Ph.D. student, who performed a
literature search and prepared a compilation of existing technologies; Dr. Raymond Li of
CH2MHILL for his cooperation and thoughtful suggestions during the preparation of this
report.
I also express my special thanks to the United Nation Industrial Development
Organization (UNIDO) for its financial support for this project.
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DISCLAIMER
This report compiles information on a wide range of technologies for remediation of
POPs in soil and stockpiles based on available published and unpublished information
available to the author. In preparing this review, technical literature and reports from
various organizations have been surveyed. Note that the evaluation is based on existing
available information, some of which may not be complete or fully accurate.
This report is provided as a reference guide, but it is not intended to provide guidance
regarding selection of a specific technology or vendor. It also should not be construed in
any manner as constituting endorsement, recommendation or discouragement for the useof any trade name or commercial product.
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1. Introduction
Persistent organic pollutants (POPs), originating from a variety of human
activities (agricultural and industrial), are toxic chemical compounds that resist chemical
and biological breakdown in the environment. POPs can be conveyed for thousands of
miles through air or water currents, and may be found in remote ecosystems far from
their source, even in locations where POPs have never been used (EUROPA 2007).
Through bioaccumulation, animals, like humans, higher in the food chain, are more likely
to have higher concentrations of these pollutants, often to the degree that the substances
may cause cancer, as well as neurological and immune system disorders (USEPA 2007,
OMoE 2005).
The United Nations Environment Programme (UNEP) Stockholm Convention on
Persistent organic Pollutants is a global agreement intended to protect human health and
the environment from POPs. It was signed on May 23 2001 and entered into force on
May 17 2004. Parties to the Stockholm Convention agree to the management and control
of POPs (UNEP 2003). Because of their adverse health effects and associated
environmental hazards, remediation of POPs in stockpiles and soils has been underway in
many developed countries. Unfortunately, industrialization of many developing
countries has resulted in extensive use of these chemicals, causing serious environmental
pollution and resulting in serious negative social impacts.
Many advanced soil remediation techniques have been commercialized and
adopted in industrialized and developed countries. These include Gas Phase Chemical
Reduction (GPCR), Mechanochemical dehalogentation (MCD),and Thermal Desorption.
Some promising techniques such as Base Catalyzed Decomposition (BCD) and Sonic
technology are still either at the laboratory stage or at the pilot study. However, due to
the financial constraints, many advanced technologies are unlikely to be adopted by the
developing countries. The success of finding suitable and affordable technologies is
critical in solving problems in the developing countries.
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The objective of this report is to review existing commercially available and
sustainable techniques of remediating POPs and to explore the potential for adopting or
improving existing remediation techniques for use in developing countries.
Existing technologies are first summarized. A set of criteria is then provided as
an aid to developing countries in identifying which technology is most suitable in each
case based on country specific factors and site-specific conditions.
2. Methodology
Both well developed and commercialized combustion and non-combustion
technologies for remediation of POPs in soil and stockpiles are summarized here, basedon available information. In preparing this review, technical literature and reports from
various organizations have been surveyed. Sources which are especially useful are:
USEPA Reference Guide to Non-Combustion Technologies for Remediation of
Persistent Organic Pollutions in Stockpiles and Soil (2005)
UNEP, Science and Technology Advisory Panel (STAP) of the Global
Environmental facilities (GEF) Review of Emerging, Innovative
Technologies for the Destruction and Decontamination of POPs and the
Identification of Promising Technologies for Use in Developing
Countries (2004)
IHPA and North Atlantic Treaty Organization (NATO) Committee on the
Challenges of Modern Society (CCMS) Pilot Study Fellowship Report
Evaluation of Demonstrated and Emerging Remedial Action
Technologies for the Treatment of Contaminated Land and Groundwater
(Phase III) (2002)
3. Full Scale Technology Profiles
As listed in Table 1, Appendices 1 to 14 of this report provide overviews of
established, demonstrated and emerging technologies for remediation of POPs-
contaminated soils and sediments. The information there includes process descriptions,
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site requirements, estimated costs, by-products, and performance (covering where
possible laboratory-, bench, pilot- and full-scale test results). The advantages and
limitations of the various technology options, as well as their applicability in developing
countries are also considered briefly.
Table 1. The list of reviewed technologies
Technology Appendix
Incineration 1
Bioremediation (DARAMEND& XenoremTM) 2
Solvent Extraction 3
Vitrification (PACT, PLASCONTM& GeoMeltTM) 4
Solidification/Stabilization 5
Gas Phase Chemical Reduction 6
Alkali Metal Reduction (Sodium Reduction) 7
Pyrolysis (STARTECH) 8
Established
Ball Milling/ Mechano-Chemical Dehalogentaiotn
(MCDTM)
9
Thermal Desorption 10
Super Critical Extraction (SCE) 11
Soil Washing 12
Demonstrated
Chemical Dehalogenation 13
Emerging Phytoremediation 14
4. Development of a Screening Matrix
Screening Matrices are common tools for screening potentially applicable
commercialized technologies for POPs remediation projects. A matrix allows the user to
screen in-situ (with a few exceptions) technologies to treat POPs for countries at various
stages of development. The US Federal Remediation Technologies Roundtable (FRTR
2007) has developed a similar screening matrix for remediation technologies.
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In this report, three sets of criteria have been developed to form the screening
matrix. The matrix provides a foundation for decision-making and for choosing an
appropriate technology for a specific site in each developing country. The matrix can be
readily expanded as more commercial technologies become available.
4.1. Logistics
The criteria for comparison are based on on-site technology (in-situ/ex-situ)
except for landfilling and incineration. All the criteria are grouped under three major
headings: (a) technical considerations, (b) health and environmental considerations, and
(c) economic considerations. These three subtitles are intended to encourage a wide-
ranging evaluation of the technologies, not only including financial factors, but also
taking into consideration technical and environmental criteria. Equal weight is applied
here to each criterion, but weighting factors can be established to reflect the differing
relative importance of different criteria in each jurisdiction. However each factor should
at least be considered in all cases. Note that the evaluation is based on existing available
information, some of which may not be complete or fully accurate.
(a) Technical considerations
Site Specific Requirements:
Soil Temperature Dependence
Soil Moisture Dependence
Particle Size Distribution of Soil
Permeability/Clay Content
Organic matter (insufficient data and information to be included in the
matrix)
Space available
Proximity of population or sensitive sites
Resource/Technical Requirements:
Pretreatment
Power/energy/fuel
Water quantity, quality and seasonal variations
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Chemicals
Equipment
Monitoring
Skilled labour
Transportation: roads, rail, canals, etc.
Off-gas treatment
Post-treatment
Excavation
(b) Health and Environmental Considerations
Impact on the local, regional and global environment in all aspects, i.e. air,
water, soil and sediments
Hazardous by-product(s)
Worker health and safety
Odours, aesthetic factors
(c) Economic considerations
Pretreatment cost
Labour cost
Monitoring cost
Power/fuel cost
Equipment cost
Installation/decommissioning cost
Operating and maintenance cost
Disposal cost
Transportation cost
Water cost
Intellectual property cost
Post treatment cost
Influence on regional economy
Table 2 displays the proposed matrix system for considering these various factors.
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Table 2. Proposed screening matrix system choosing an appropriate technology for a specific site in each developing country
Combustion Non Combustion
IncinerationThermal
DesorptionSuper Critical
Extraction Phytoremediation Bioremediation GPCRSolvent
Extraction
In/Ex situ Ex Ex Ex/In Ex In In/Ex Ex Ex
On Site/Off site On site Off site On Site On Site On Site On Site On Site On site
Efficient 99.99% 99.99% 93-99.8% 99.99% 60-80% 99.99% 95-99%
Estimate cost ($/m3) * 140-360 350-450/350-700 122-154* partial cost 147-626 55-360 500-630 125-400
Technical Consideration
Site Specific Requirement
Soil Temperature Dependence 1 1 2 2 2 3 3 1
Soil Moisture Dependence 3 3 3 3 3 3 3 3
Particle Size 2 2 3 3 2 3 2 2
Permeability/clay content 1 1 1 1 1 3 1 3
Space Requirement 2 1 2 2 1 3 2 3
Resource Requirement
Pretreatment 2 2 2 3 1 1 3 2
Power 3 1 3 1 1 1 3 3
Water 1 1 1 3 2 3 1 2
Chemical/enemzy 1 1 1 3 1 3 3 3
Monitoring 3 1 3 3 1 1 3 3
Skill Labour 3 1 3 3 1 2 3 3
Transportation 1 3 1 1 1 1 1 1
Off Gas Treatment 2 1 3 3 1 1 3 1
Post Treatment 1 1 1 3 1 1 1 3
Excavation 3 3 3 3 1 1 3 3
Sub total 29 23 32 37 20 30 35 36
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Table 2 (continued)
Combustion Non Combustion
IncinerationThermal
DesorptionSuper Critical
Extraction Phytoremediation Bioremediation GPCRSolvent
Extraction Health & Environm ental
ConsiderationImpact to Environment 2 2 1 1 1 1 1 1
Bi-products
Hazardous 3 3 1 1 1 1 3 1
Sub total 5 5 2 2 2 2 4 2
Financial Consideration
Pretreatment Cost 1 1 3 3 1 1 3 2
Labour cost 2 2 2 3 3 2 2 3
Monitoring Cost 3 1 3 3 2 2 3 3
Power/fuel Cost 3 1 3 2 1 1 3 1 Equipment Cost 3 2 3 3 1 1 3 2 Installation/DecommissioningCost 2 1 3 3 1 1 3 2
Operational & Maintenance Cost 2 1 3 3 2 2 3 2
Chemical (or equivalent) Cost 1 1 1 3 1 2 3 3
Disposal Cost 1 3 1 1 1 1 1 1
Transportation Cost 1 3 1 1 1 1 1 1
Water Cost 1 1 1 3 2 3 1 1
Patent Cost 1 1 3 3 1 1 3 1
Post Treatment Cost 1 1 1 3 1 1 3 3
Sub total21 18 25 31 17 18 29 23
Rating Code : 1 - No/Low
2 - Average
3 - Yes/high
* See Appendix A for detail information on cost
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4.2. Grading System for the Developed Screening Matrix
The symbols used in the treatment technologies screening matrix are simple.
Table 3 provides an explanation of this grading system.
Table 3. Grading System for screening matrix
Rating Code Explanation
1 - No/Low Low degree of intensity or not required - in cost, negative impact or
skilled labour
2 - Average Average degree of intensity - in cost, negative impact or skilled labour
3 - Yes/high High degree of intensity or requirement - in cost, negative impact or
skilled labour
In this matrix evaluation, the lower the score, the better the technology for a
specific site. Completing the matrix is a valuable tool for the site owner, as well as for
government agents who are responsible to determine which available technology is most
suitable for managing POPs. Each criterion can be weighted by multiplication by
weighting factors, accounting for the varying importance of different attributes. The
sum of all scores, multiplied by the corresponding weighting factors results in a total
qualification grade for comparing alternatives and selecting the best technology for the
specific site subject to its own local and specific conditions. The weighting factor for
each item can be adjusted upward or downward as circumstances change, depending on
local factors. Note that there is no a priori methodology to assign the right weighting
factors for the criteria in Table 2. It is up to site owners to assign the appropriate
weighting factor for each criterion based on local priorities and regulatory requirements.
For example, the cost of water and energy can vary radically between difference
communities, so that their weighting factors are likely to differ. Also, the regulatory
requirements for developing countries can differ greatly from those of developed
countries. Therefore, again the corresponding weighting factors with respect to
environmental impacts are likely to differ in such cases.
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5. The Potential for Improvement of Existing Remediation Techniques
Many of the remediation technologies described in the previous sections are
proprietary and protected by patents. Know-how needed to exploit existing technologies
can also be proprietary to design firms or other private interests. Because of the
competition between technologies for the existing market and differences in local
conditions, there may well be potential for improvement of proprietary techniques, or for
adaptations that would make them more suitable to local situations in developing
countries.
Incineration and landfilling are the two most common technologies which are
unlikely to require consideration of patents. Although they have been in practice in manycountries for many year, they are still have potential for improvement, e.g. those based on
the directorate of the Stockholm Convention. The facilities must exist for safe and
appropriate reuse and/or reformulation; they must present no additional unacceptable
hazards, and they must benefit both people and the environment.
6. Address the Potential Improvement of Incinerator
Incineration is a combustion technology which if not designed or operating
optimally, can create products of incomplete combustion such as polychlorinated
dibenxo-p-dioxins (dioxins) and polychlorinated dibenzo-p-furans (furans). Note that
dioxins and furans are often synthesized de novo, i.e. formed downstream, at an
intermediate temperature range e.g. ~400C. According to Carroll (2003) the key to
reduction of generation and emissions of dioxins and furans (PCDD/Fs) is proper design
and operation of the combustor. The uniformity of conditions is significant because
problems often occur when part of the stream by-passes the hot zone. Attention alsoneeds to be paid to free radical reactions which can result in the synthesis of a wide
variety of compounds, some of which are harmful. Specification and operation of
pollution control equipment requires utilization of good combustion practices, often
expressed as the "Three T's": Time in the combustion zone, Temperature of combustion
and combustion gases, and strong Turbulence to ensure good mixing and favourable
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contacting with oxygen. Successful governmental policy reflects these requirements as a
condition for operation of incinerators, especially those burning toxic and other special
wastes. With more research on combustion and careful attention to detail, incineration is
one of the best and most economic technologies for POPs.
6.1. Methodology
In preparing this section, I have relied on:
Review of a number of recently published papers and unpublished material relating to
incineration of POPs, PCBs and emissions of dioxins/furans.
Input from a world-recognized process engineer and research scientist, with
experience related to combustion of a wide range of materials, reactors, high-
temperature processes, and air pollution control, including special waste incineration.
Some available material with respect to the Canadian experiences at the Swan Hills,
Alberta facility and the Sydney Tar Ponds, Nova Scotia facility are used for
illustration purposes.
6.2. Incineration of Hazardous Waste Materials/POPs
Incineration of waste materials is commonly employed as a method for converting
waste carbonaceous materials into relatively harmless substances, mostly carbon dioxide,water and ash. The flue gas also includes oxides of nitrogen (NOx) and sulphur (mostly
SO2), as for combustion of fossil fuels; when the combustible material contains chlorine,
hydrogen chloride (HCl) is also a product. Control of these three gases is standard,
practiced routinely, e.g. in furnaces, boilers and power generation. Inevitably small
amounts of other undesirable products like carbon monoxide (CO) will also be present in
the flue gas. Traces of highly undesirable products of combustion, in particular products
of incomplete combustion, such as chlorinated dioxins and furans, also occur in
combustion processes. The major objective in incineration is to keep the concentrations
of these substances to extremely low and tolerable levels, while effectively destroying the
waste materials fed to the incinerator.
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The main challenges facing the designers and operators of an incinerator for
destroying POPs are:
Effective destruction and removal efficient (DRE) for the waste material;
Minimization of the production and emission of noxious pollutants, like
dioxins and furans, which can be formed in incineration systems.
Effective control of the emissions of heavy metals.
Controlling the emissions of standard combustion pollutants like NOx, SO2,
CO and particulates.
These will be considered in turn, followed by some general observations.
(a) Destruction of POPs (e.g. PCBs) and Other Fed Waste Materials
A rotary kiln is the most common type of hazardous waste incinerator. This type
of high-temperature reactor is also often employed in cement-making, limestone
calcination and pulp and paper operations. Waste liquid and/or solids are fed into one
end of a slightly-inclined rotating cylinder which has been heated (by auxiliary fuel such
as oil) to approximately 1200C or more. The temperature is maintained at that level by
the calorific value of the waste stream, supplemented if needed by fossil fuel such as oil
or natural gas. The wastes are lifted and dropped repeatedly by the revolving furnace,
leading to effective contact with combustion air. Excess air is employed (i.e. more than
required for stoichiometric combustion) in order to promote complete burning of the
wastes. Typically 30 - 50% excess air is recommended. The standards required for the
incinerator need to be fixed, but previous experience (Grace 2007) with rotary kiln
furnaces has shown that they are capable of meeting usual incinerator standards of six
nines (99.9999%) destruction of PCBs, and four nines (99.99%) destruction of
polyaromatic hydrocarbons like naphthalene and anthracene. Well-designed and properly
operating commercial incinerators exceed these values, frequently by a factor of 10 to
100. Operating conditions which are most important to achieve high DREs are the mean
temperature level, temperature uniformity, sufficient excess oxygen concentration (e.g.
>4% oxygen by volume in the flue gas), uniform feeding, and turbulence or other
effective contacting mechanisms in the furnace. To further improve the combustion
efficiency, the off-gases are fed to a secondary combustion chamber (often called an
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afterburner), to assist in oxidizing any unburnt gases. In addition, downstream pollution
control devices, such as scrubbers, filters and/or electrostatic precipitators, are added to
capture fine particulates (fly ash) and gaseous component which would otherwise escape.
A revolving fluidized bed incinerator has demonstrated destruction with at least
six nines efficiency for coke wastes (tar containing a number of potentially harmful
constituents, in particular polycyclic aromatic hydrocarbons (PAHs), PCBs, and heavy
metals, as well as small amounts of volatile organic compounds). Tests by Jia et al.
(2005) of Natural Resources Canada have also indicated that tar sludge can be efficiently
destroyed in circulating fluidized bed combustors. These combustors operate at
significantly lower mean temperatures (typically 850 - 900C, though with greater
temperature uniformity than rotary kilns.) PCB wastes, with much higher concentrations
than those of the tar sludge, are also routinely incinerated in the rotary kiln incinerators at
Swan Hills in Alberta, Canada, with DREs well in excess of six nines. Rotary kiln
incinerators in other countries have had similar success. When problems are
encountered, these can often be related to materials handling in delivering the wastes to
the incinerator, not to the incinerator itself. For example, with Sydney tar ponds wastes in
Nova Scotia, Canada, incineration failed in tests carried out two decades ago due to
problems in pumping the sludge material up hill to the level of the incinerator (Campbell
2002).
(b) Minimization of Dioxins, Furans and Other Products of Incomplete Combustion
Considerable work has been completed in a number of countries on the
mechanisms by which it is possible to form and emit noxious substances, in particular
poly-chlorinated dioxins and furans, in combustion facilities. Some of the key factors
needed to minimize their generation are the same as those cited above with respect to
achieving high destruction and removal efficiencies, i.e. high and uniform temperatures,
uniform feeding, sufficient excess oxygen, effective gas/waste contacting through
turbulence, and proper downstream separation devices. In addition, it is very important
that the cooling of the flue gases through the temperature interval from ~ 400 to 300C be
as quick as possible to prevent de novosynthesis of dioxins and furans downstream of the
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incineration chambers. These stipulations are generally well-known to operators of
incinerators. If an experienced vendor is chosen, with a well designed and effectively
operated and maintained incinerator, it should be possible to operate within normal
hazardous waste limits.
(c) Emissions of Heavy Metals
Some wastes and by-products contain small amounts of heavy metals, which are
present in the material fed to the incinerator. For instance, in coke tar, the metals of
concern are likely to be arsenic, beryllium, cadmium, chromium, copper, lead, mercury,
nickel, selenium, silver, vanadium and zinc. It is important to minimize emissions of
these metals. Mercury is the most volatile of these metals, and its control depends on
effective capture of fly ash entrained by the flue gases, i.e. on efficient gas-solid
separation in the off-gases. Standard separation techniques like scrubbers, bag filters and
electrostatic filters are available to control such emissions. The less-volatile metals are
likely to end up predominantly in the bottom ash. Careful controls can ensure that the
heavy metals emissions satisfy the applicable codes, both in terms of emissions and levels
at point of impingement. Residual (fly and bottom ashes) from the incinerator could be an
issue and must be disposed of and handled properly.
(d) Emissions of Standard Combustion Pollutants
Incinerators must also meet standard emission limits for pollutants (e.g. acid gases
like SO2 and NOx, as well as CO) commonly controlled in stationary combustion. There
is a need to keep the oxygen concentration in the flue gas higher than about 4% to
achieve uniform combustion with good burnout. If this is done, emissions of CO and
unburnt hydrocarbons should be low. The need to control mercury and other heavy
metals also requires effective capture of particulates, so that particulate emissions should
be well controlled by filters, scrubber or precipitator. If opacity is controlled, this should
also be readily achievable given the other controls. Given the oxidizing conditions, gases
like hydrogen sulphide and ammonia will not be problematic.
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(e) Materials Handling Issues
An incinerator is only as good as its auxiliaries, with continuous and uniform
feeding being of the utmost importance. This can sometimes be overlooked. Special
attention to handling and feeding of the waste is needed. As noted above, an attempt to
utilize incineration for Sydney Tar Ponds sludge failed because of materials handling
issues. An accident at the Swan Hills facility in the 1990s was also attributed to materials
handing problems.
(f) Continuous Operation
It is preferable for incinerators to maintain operation night-and-day once
incineration has been started up and to have scheduled shutdowns only in frequently, e.g.
once per year, since steady state continuous operation facilitates trouble-free operation.
(g) Pilot-Scale Testing
Pilot scale testing of POPs burning may be required to prove the successfulness of
the design combustion conditions and operation for a given waste material. Some
companies and government laboratories have pilot scale facilities that can be used for this
purpose. Normally, the test results should be conservative in that a full-scale incinerator
will have greater residence times than those in a pilot unit, and therefore if the pilot unit
meets the requirements, the full-scale should also do so.
(h) Operation and Maintenance
The safety of any technology can be compromised by improper operation or
failure to provide proper maintenance. It is not only vital that proper equipment be
chosen, designed, fabricated, installed and commissioned, but that the operations and
maintenance be at the top level for the full period of operation. The role of government
in assuring quality and continuity of operation is vital to the safety of incinerator
facilities.
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(i) Monitoring and Emissions Testing
Standard substances like oxygen, NOx, SO2, CO, unburnt hydrocarbons and HCl
should be monitored continuously. Their levels can provide a good overall indication
that the incinerator is working properly, and upsets can be detected, e.g. through a sudden
drop in oxygen level and increase in off-gas CO concentration. Testing for complex
organics like dioxins/furans, PAHs and PCBs requires specialized stack testing. While
this would normally be done annually, it is appropriate to conduct additional tests in the
first year in addition to the initial testing required for acceptance of an incinerator.
6.3. Conclusion
Incineration is a widely-practised technique for destroying wastes, including those
containing POPs. Well designed, well constructed and well maintained incinerators with
appropriate monitoring, downstream air pollution control and stack, can often be an
appropriate technique for destruction of hazardous organic substances.
7. Address the Potential Improvement of Landfilling for POPs
Landfilling is a technique which can contain the migration of POPs. Since
landfilling does not normally destroy POPs, every effort has to be used to prevent the
migration. Proper lining and monitoring are required to ensure that there is no leakage
from the landfill containment system. The engineer/control landfill can be considered as
a temporary measured until the destructive technologies for POPs become available for
developing countries, which provide environmental sustainability and fall within
economical affordability.
Developing countries should follow the most up-to-date requirements and
technologies to build landfills which are suitable to handle the disposal of POPs. Two
types of liners can be used: flexible membrane and clay liners. Measurement of the liner
compatibility is critical to success. Flexible membranes deteriorate over time, particular
when they are chemically incompatible with the leachate. Flexible membranes contain
pinholes and therefore cannot be made leak-free. Organic chemical solutions affect the
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hydraulic conductivity of clay liners. Therefore, it is suggested that a flexible membrane,
compatible with POPs, underlain by a clay liner, is the minimum requirement of a landfill
for disposal of POPs. Although there is no universal method to test the compatibility,
two test methods have been promoted (EPA 1992c). They are NSF (National Sanitation
Foundation) Standard No. 54 and EPA Test Method 9090.
Local soil materials or waste materials with high adsorptivity and low hydraulic
conductivity could be explored for possible use as containment barrier materials. If
appropriate for adoption, these materials can benefit the local economy and may possibly
gain a global market for such a material for containment purpose.
7.1. Methodology
In preparing this section, I have relied on the following:
Review of a number of recently published papers and some unpublished
material relating to landfill, clay liner, properties of POPs and soil minerals.
Personal experience with landfill liners, waste containment systems, soil-
contaminant interactions, mobility/immobility of contaminants, and
remediation of contaminated sites, including those involving organic
contaminants. Some available material with respect to experiences in different research and
consulting projects related to remediation of contaminants in soils and landfill
liner studies.
7.2. Landfilling: Engineered Landfill for Hazardous Waste Materials/POPs
Landfilling is generally regarded as the most economical and practical method for
disposal of large volumes of municipal and industrial solid wastes. Land disposal has
been in practice throughout human history. Traditionally waste was dumped in
depressions (e.g. holes left after quarries and gravel were mined) or in open spaces
without any lining system. This led to air, soil and water pollutions, and also to landfill
fires. In developing countries where there is a lack of environmental awareness,
economical means and technological infrastructure to use other treatment options, waste
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will continue to be discarded onto land, whether or not it is regarded as an option for
POPs. Many POPs are still being stored or disposed onto land, regardless of the
development level of the country.
Many environmental problems from landfill sites arise due to lack of
understanding of science, including geology, hydrogeology, soil conditions, properties of
contaminants and the resulting leachate. The legitimate environmental concern with
respect to landfilling is whether pollutants contained in, or generated from, the wastes can
be safely contained in landfills. Flexible membrane liner or clay liners (waste
containment barriers) are frequently installed at waste disposal sites as a means of
preventing pollutant migration and minimizing or eliminating the potential for
groundwater contamination. In this section, I focus on the improvement of clay liners
because many countries have access to clay minerals which may be suitable barrier
materials. These include smectite/bentonite, vermiculate and illite. In using clays as a
liner material in landfill construction, one relies on the effectiveness of the clay barrier to
impede transport of contaminants due to the low permeability of the barrier. In addition,
the ability of the clay barrier to adsorb (accumulate) contaminants (Li and Li 2001) can
make a very useful contribution to the attenuating capability of the clay liner.
Waste containment barriers are in the form of landfill liners and covers, lagoon
liners, and slurry walls. However, the use of cay barriers below waste disposal sites to
protect underlying groundwater resources has become a contentious issue following
experimental and field evidence of failure due to clay-leachate incompatibility and other
factors such as the mineralogical and physical properties (e.g. wetting/drying of clays that
may cause cracking of the liner. Siting and construction of a landfill can be as important
as selection and design of the liner system.
(a) Landfill SitingAttention must be paid to the local geological and hydro-geological situation in
selecting a landfill site. Avoid:
Flood-hazard areas and wetlands
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Areas subject to heavy rainfall
Highly permeable soil (i.e. silt, sand, gravel)
Public water supply watersheds
Groundwater aquifers, recharge areas, areas with high water tables
Limestone bedrock
Designated parks, forests, historic areas, and wildlife refuges
Seismic-risk zones
Environmental impacts must be assessed for environmental impacts (i.e. air
pollution, noise, water pollution, soil contamination and ecological risks); consider
economic impacts also; then plan for preventive and mitigation measures.
(b) Liner materialsLocal clay minerals (montmorillolite, vermiculite, illite and kaolinite) and soil
minerals (zeolite) should be explored as possible liner barrier materials for their
adsorptivity, compatibility and hydraulic conductivity for POPs. The methodology and
approach have been outlined by Li and Li 2001, Li and Denham 2000 and others
(http://www.civil.ubc.ca/people/faculty/lli/li_personalpage.html). Clay is an inexpensive
material, widely used as a barrier in containment systems because of its low hydraulic
conductivity (k) and high adsorptivity. However, the surface of clay is hydrophilic
because of the strongly hydrated metal ions (principally Na+ and Ca2+) occupying the
cation exchange sites (Li and Denham 2000). Hydrophobic organic contaminants (HOCs)
such as POPs are repelled by this environment and are therefore not adsorbed well by
natural clay. Thus, HOCs in landfill leachate may pass through clay barriers and into
ground or surface waters. It is possible to make clays more adsorptive to HOCs by using
cationic surfactants (Li and Denham 2000). These surfactants consist of a cationic,
hydrophilic moiety and a non-ionic, hydrophobic moiety. The cationic ends of the
surfactant molecules using simple ion exchange reactions replace the native inorganic
cations on the clay surface. The modified clay is called organoclay. Large portions of the
organoclay surface are rendered hydrophobic due to the hydrophobic moieties of the
surfactant molecules. Thus, organoclay adsorbs many HOCs very well. Clay/soil
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minerals such as zeolite and bentonite can be modified and adsorb HOC. The inclusion of
organoclay in a clay barrier can effectively immobilize hydrophobic organic chemicals.
Organic matter is an important constituent of soils with very high cation exchange
capacity and very high specific surface areas. It partitions organic contaminants onto its
surface. Admixing organic matter into soil liners may increase the retention ability of
contaminants because many surface functional groups are available on soil organics for
forming complexes (Sparks 1995). There is a lack of studies addressing alternative
materials or reuse waste materials that would improve POPs compatibility.
(c) Construction and Design
A landfill site needs to have a sound design with daily cover, and a leachate
collection and removal system. The construction must ensure a safe and secure landfill.
Proper training of skilled workers is also needed.
(d) No co-disposal of municipal or other wastesMost POPs are hydrophobic or have low solubility. However, in landfill situation
when these are interactions with other organic solvents or humic substance, POPs have
been detected in landfill leachates.
(e) Composite Landfill LinersDepending on the locally available material, landfill liners can be composite liners
or admixed with different materials which achieve the high retention capacity and low
hydraulic conductivity with POPs. Detailed tests of materials need to be conducted before
implementation to ensure that the environment is protected.
7.3. Conclusion
Lined/engineered landfill could be an option to temporary store POPs for
developing country. Hazardous waste landfill design criteria have been set by many
developed countries such as Canada, Australia, USEPA, and EU, and can be adopted.
Local natural materials should be explored for use as landfill liners. Understanding of the
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Appendix A Overviews of Established,
Demonstrated and Emerging Technologies
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A-1 Incineration
Overview
Incineration treats POPs in solids and liquids by subjecting them to temperatures
typically greater than 500oC in the presence of oxygen. These conditions cause
volatilization, combustion, and destruction of the organic compounds. The technology
can be scaled-down, with trailer-mounted versions of conventional rotary kiln and
fluidized bed incinerators in existence. At large sites where the cleanup will require
several years, it may be feasible to construct an incinerator onsite. Economic reasons are
often the key factor in determining whether mobile, transportable, fixed, or off-site
commercial incineration will be provided at a given site. In addition to the furnace,
incinerator systems also include subsystems for waste preparation and feeding,
combustion of feed, air pollution control (APC), and residue/ash handling (Oppelt 1987).
The three major wastestreams generated by incineration are solids from the incinerator
and the associated APC system, water from the APC system, and gaseous emissions from
the incinerator (Freeman and Harris 1995).
The applicability of incineration to the remediation of POP- contaminated soil or
sediment may be limited by the types and concentrations of metals present in the waste to
be treated. When soil or sediment containing metals is incinerated, some metals
vaporize, reacting to form other metal species, while less volatile metals remain with the
soil residuals. Metals in ash, scrubber sludge, or stack emissions, if improperly managed,
can result in potential exposures and adverse health effects (USEPA 1992a). For
example, lead, a metal commonly found associated with polychlorinated biphenyl (PCB)-
contamination, volatilizes at most incinerator operating temperatures and must be
captured before process off-gases are released into the atmosphere (USEPA 1992a). It is
therefore essential to adequately characterize the metal content of the soil or sediment
when considering incineration systems for treatment of PCB and other POPs.
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Weber (2007) describes three mechanisms that affect the emissions of
polychlorinated dibenzo-para-dioxins (PCDDs) and polychlorinated dibenzofurans
(PCDFs) for high-temperature incinerators:
(a) Formation of PCDDs/PCDFs within the high-temperature zone due to free radical
reactions.
(b) Emission of PCDD/PCDF precursors from high temperature processes and
formation of PCDDs/PCDFs in the cooling zone.
(c) Formation of PCDDs/PCDFs via degradation of products of incomplete thermal
destruction (soot, polyaromatic hydrocarbons (PAHs), etc.) in the cooling zone.
If POPs waste and its associated thermal decomposition products are exposed to
elevated temperatures for sufficient residence times, the POP components can be virtually
completely destroyed. For combustion, the times required for destruction are typically
only milli-seconds for gaseous compounds in the active flame zones. On the other hand,
combustion times of the order of seconds may be required for complete destruction of
small solid particles. A combustion temperature of 850oC and residence time of 2s,
respectively, are generally believed sufficient to destroy all chlorinated organic molecules
including PCBs and PCDDs/PCDFs (Weber 2007). However, this relies on all waste
elements travelling through the hot zones something that is difficult to achieve.
For sufficient safety margins state-of-the-art hazardous waste incinerators are
required to operate at temperatures above 1100oC and with a residence time in excess of
2s (Weber 2007). Conditions in cement kilns are even more severe (temperature
>1400oC and several second residence time). Therefore for such facilities, bypassing
around the hot zone has the greatest potential impact on total PCDD/PCDF formation (ifstable operation is maintained) (Weber 2007). This is probably similar for other high
temperature technologies, which can operate steadily at appropriate high temperatures
and sufficient residence time. In addition, all high temperature technologies will face the
challenges of PCDD/PCDF formation during cooling (so-called de novo synthesis),
posing the additional challenge of investigating, minimizing and documenting these
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formations, while also ensuring that off-gas streams cool rapidly through the temperature
range of ~250 - 500C (Weber 2007).
Treatment Process
The primary stages in the incineration process are waste preparation, waste feed,
combustion, and off-gas treatment. Waste preparation includes excavation and/or
transporting the waste to the incinerator. Depending on the requirements of the
incinerator, various equipment is used to remove oversized particles and obtain the
necessary feed size for soil and sediments (USEPA 1997). Blending of the soil or
sediment and size reduction are sometimes required to achieve uniformity of feed size,moisture content, temperature, and contaminant concentrations (USEPA 1989).
The waste feed mechanism, which varies with the type of incinerator, must introduce the
waste smoothly and continuously into the combustion system. The feed mechanism sets
the requirements for waste preparation. Bulk solids are usually shredded; contaminated
media are usually ram or gravity fed (USEPA 1992a). The combustion reactor usually
consists of one of three major systems: rotary kiln, infrared furnace, or circulating
fluidized bed. The primary factors affecting the design and performance of the system arethe uniformity of feeding, the temperature at which the furnace is operated, the time
during which the combustible material is subjected to the high temperature (residence
time and time distribution), and the turbulence required to control (APC) equipment to
remove particulates and capture and neutralize acid gases. APC equipment includes
cyclones, venturi scrubbers, wet electrostatic precipitators, bag-houses, and packed
scrubbers. Rotary kilns and infrared processing systems may require both external
particulate control and acid gas scrubbing systems. Circulating fluidized beds do not
require scrubbing systems because limestone can be added directly into the combustor
loop; however, they are likely to require a downstream system to remove particulates
such as cyclones, bag filters or electrostatic precipitators (USEPA 1992a; USEPA 1997).
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Site Requirements
The site should be accessible by truck or rail, and a graded or gravel area is
required for setup of onsite mobile systems (USEPA 1997). Concrete pads are required
for some equipment (e.g., rotary kiln). For a typical commercial-scale unit, 2 to 5 acres
are required for the overall system site including ancillary support. A stack of height
exceeding that of local buildings and trees should be available or provided as part of the
project. Standard high-voltage, three-phase electrical service is generally needed. A
continuous water supply must be available at the site. Various ancillary equipment may
also be required, such as liquid or sludge transfer and feed pumps, ash collection and
solids handling equipment, personnel and maintenance facilities, and process-generated
waste treatment equipment. In addition, a feed-materials staging area, decontamination
trailer, ash handling area, water treatment facilities, and a parking area may be required
(USEPA 1992a). Special handling measures should be provided to hold any process
residual streams until they have been tested to determine their acceptability for disposal
or release. Depending on the site and the nature of the waste, a method to store waste that
has been prepared for treatment may also be necessary. Storage capacity depends on
waste volume and equipment feed rates (USEPA 1992a).
Cost
The cost of incineration includes the relatively fixed costs of site preparation,
permitting, and mobilization/demobilization; and variable operational costs, such as
labour, utilities, and auxiliary fuel. Average costs of the treatment system were said to
range from $140- $360/m3 (1989 dollars) (USEPA 1997).
By-products
Three major waste streams generated by incineration are solid ash from the incinerator
and any solids captured by the APC system, water from the APC system, and gaseous
emissions from the incinerator.
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Ash is commonly either air-cooled or quenched with water after discharge from
the combustion chamber. Dewatering or solidification/stabilization of the ash may also
have to be applied since the ash could contain leachable metals at concentrations above
regulatory limits. The alkalinity of the matrix may influence the leachability of the ash
(USEPA 1989).
The flue gases from the incinerator should treated by an APC system such as an
electrostatic precipitator, scrubber or filter before discharge through a stack. A high- or
low-pH liquid waste may be generated by the APC system, specifically by a scrubber or
wet precipitator. This liquid waste may contain high concentrations of chlorides, volatile
metals, trace organics, metal particulates, and other inorganic particulates. Wastewater
requiring treatment may be subjected to neutralization, chemical precipitation, reverse
osmosis, settling, evaporation, filtration, or carbon adsorption before discharge (USEPA
1997).
Performance
Incineration technologies were selected as the remedial action at 65 U.S.Superfund sites with VOC and SVOC- contaminated soil or sediment (USEPA 1991a;
USEPA 1993). Incinerator performance is most often measured by comparing initial PCB
concentrations in feed materials with both final concentrations in the ash and
concentrations present in off-gas emissions. In all the reported pilot and field scale
studies, removal efficiencies exceeded 99.99% (USEPA 1997).
Advantages and Limitations
A well designed incinerator will have the following advantages:
Capability of the highest overall degree of destruction and control for the broadest
range of hazardous waste streams. The technology has effectively treated soils,
sludges, sediments, and liquids containing all organic contaminants found at wood
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preserving sites, such as PCDDs/PCDFs, PCP, PAHs, and other halogenated and
nonhalogenated VOCs and SVOCs (Oppelt 1987; USEPA 1997).
Treatment can achieve stringent cleanup levels.
Broad application capability, for example with respect to different POP-contaminated
soils.
The limitations of this treatment technology are:
The inorganic components of hazardous wastes are not destroyed by the process,
mostly reporting to the bottom ash, and thus requiring either further treatment or
disposal under stringent regulatory procedures.
Continuous perfectly stable operation of a man-made facility operated by humans
with heterogeneous or variable feed streams is unattainable. Technical defects, fatigue
of construction materials and sensors, mistakes of operators, problems in power
supply etc. sometimes lead to unstable operation. This may lead to some
PCDD/PCDF/POPs emission (Weber 2007).
Performance can be limited by the physical properties and chemical content of the
waste stream, if not accounted for in the system design. Oversized particles (e.g.,
stones, debris) can hinder processing and can cause high particle loading from fines
carried through the process. Feeds with high moisture content increase feed handlingand energy requirements.
Applicability to Developing Countries
Incineration is a viable treatment method since many countries possess the
infrastructure of incineration systems for municipal solid waste disposal and cement
kilns. These facilities can use the contaminated soil as part of the fuel source, if the
system is upgraded to include APC systems, and maintain proper ash treatment or
disposal methods.
Where there are high precipitation rates or where contaminated site is in a flood
hazard plain, there may be problems with incineration, since the soil has to be predried to
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provide the desired outcome, with minimal dioxin/furan emissions. Also high moisture
content soils require more energy needs to achieve dryness.
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A-2 Bioremediation (DARAMEND & XenoremTM)
Overview
Bioremediation usually refers to the use of microorganisms to break down
complex organic contaminants into simpler compounds. The technology usually involves
enhancing natural biodegradation processes by adding nutrients, oxygen (if the process is
aerobic), and in some cases, microorganisms to stimulate the biodegradation of
contaminants. Anaerobic processes utilize microorganisms that are capable of degrading
contaminants in the absence of oxygen. Bioremediation is typically performed by adding
essential nutrients, adjusting moisture levels, and controlling the concentration of oxygen
in the treatment area or vessel. Microorganisms already present in the soil may be
biodegraders, or additional strains may be introduced.
Solid-phase bioremediation uses conventional soil management practices, such as
tilling, fertilizing, and irrigating, to accelerate microbial degradation of contaminants in
above-ground treatment systems. If necessary, highly contaminated soils can be diluted
with clean soils in order to reduce the contaminants to levels conducive to
biodegradation.
Composting uses bulking agents, such as straw or wood chips, to increase the
porosity of contaminated soils or sediments. Additional components may be added to
increase nutrients and readily available degradable organic matter. These additives
include manure, yard wastes, and food-processing wastes. The resulting mixture often
favours the growth of thermophilic microorganisms which are capable of degrading theorganic contaminants of concern (USEPA 1997).
In-situ bioremediation is accomplished by providing electron acceptors (e.g.,
oxygen and nitrate), nutrients, moisture, or other amendments to soils or sediments,
without disturbing or displacing the contaminated media. In-situ bioremediation is often
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used in conjunction with traditional pump-and-treat and soil flushing groundwater
systems, in which the treated water is amended, as required, to stimulate microbial
activity. It is then re-injected into the zone of contamination. An example of that is
bioventing, where vacuum extraction wells, air injection wells, or both are installed and
operated at relatively low flow rates, providing increased oxygen to the microorganisms
in the soil (NRC 1993).
There are several commercialized bioremediation bio-amendment substances that
are in use. These include: using blood meal, DARAMENDand XenoremTM.
Treatment Processes
Bioremediation can occur under anaerobic or aerobic conditions. These will be
presented separately in the following paragraphs.
Anaerobic Bioremediation
In anaerobic bioremediation, bacteria replace chlorine substituents with electron-
donating hydrogen (from H2) on the organic molecule. Under anaerobic conditions, PCB,
PCDD and PCDF reduction is known to occur as a co-metabolic process, where thesecompounds are transformed during the metabolism of another compound. However,
PCDDs and PCDF have shown resistance to breakdown. There are 2 known
dechlorinating organisms for PCBs, o-17 and DF-1 which depend on 2,3,5,6
tetrachlorobiphenyl (tetraCB) for growth and require acetate to survive (Cutter et al.,
2001).
Anaerobic bioremediation can involve two major remedial actions: bio-
stimulation and bio-augmentation. Bio-stimulation involves addition of a primer to
galvanize a targeted dechlorinating population. Primers include FeSO4, which provides
free sulfate, consumed by sulfate reducers. The bioenergetics favour sulfate reducers
over methanogens. This process is favourable for in-situ applications because it is cheap
and environmentally benign (Bedard et al., 1996). In addition, the procedure can
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introduce halogenated organics to prime processes which are recalcitrant to degradation
(Abraham et al., 2002). Bio-augmentation, involves enriching a contaminated site with
organisms capable of degrading the targeted compound.
Anaerobic degradation of POPs is generally faster than aerobic degradation.
Anaerobic degradation usually involves dechlorination, which has little effect on the total
mass of the target contaminant, but can reduce toxicity by targeting highly chlorinated
congeners (Mondello 2002). Hence dechlorination is sometimes used prior to aerobic
remediation to decrease the reluctance of contaminants to undergo biodegradation.
Usually a sequential of anaerobic and aerobic processes yields better overall degradation
results.
No practical and effective universal systems for bioremediation of PCBs, Dioxins
and furans in soil have been developed for several reasons. PCBs, PCDD/Fs are mixtures
of congeners having different physical and chemical properties. Microorganisms cannot
use PCBs, PCDD/Fs as source of carbon and energy growth. Thus they have no selective
advantage by which they expend energy to perform these reactions (Wiegel and Wu
2000; Smidt and de Vos 2004). It is also difficult to promote successful cometabolic bio-
transformation. The available data are limited, and major differences between lab-scale
and site conditions often exist (Zhang and Bennett 2005). Contaminants can be more bio-
available in the laboratory than on site. In addition, discrepancies are also common in
reported results due to volatilization, redistribution of congeners, and partitioning to
equipment in lab studies (Mondello 2002; Wu et al., 2002; Zhang and Bennett 2005). In
laboratory-scale studies, bacteria are commonly made more competitive or conditions are
adjusted to their favour (Mondello 2002; Wu et al., 2002; Zhang and Bennett 2005).
Aerobic Bioremediation
Aerobic degradation of POPs can be carried out by a variety of aerobes acting
synergistically. The degradation usually attacks lightly-chlorinated congeners (e.g. in
PCBs 5 or fewer) (Bedard et al., 1996; Abraham et al., 2002).
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Studies have shown that a broad range of gram-negative and gram-positive
bacteria can breakdown PCBs. The range is narrower for PCDD/Fs. Extensive research
found strains of PCB-degrading-bacteria, especially in contaminated soils: Enterobacter
sp. SA-2, Ralstonia sp. SA-4, and Pseudomonas sp. SA-6. e.g., Achromobacter sp.,
Alcaligenes, sp., Acinetobacter sp., Corynebacterium sp., Rhodococcus sp., Burkholderia
sp. and Pseudomonas sp. that can metabolize PCBs or, in the case of congeners
containing one or two chlorines, use them as a sole source of carbon and energy
(Adebusoye et al., 2007). Burkholderia xenovorans LB400 and Rhodococcus sp. strain
RHA1 are two of the more promising strains for application in the aerobic stage of a PCB
biotreatment process because of their abilities to degrade a wide range of PCB congeners
(Rodrigues et al., 2006). However, like other PCB-degrading microorganisms, they have
only limited ability to grow on PCBs, so repeated addition (bio-augmentation) would be
required for bio-treatment (Rodrigues et al., 2006).
In-situ bioremediation takes place in the vadose zone of soils and in the top few
millimetres of sediments, ensuring aerobic conditions. This often leads to the production
of chlorobenzoic acid (CBA) due to enzymatic degradation of the ring resulting in fewer
attached chlorine atoms, with release of the second ring as CBA. If accumulated, CBA
itself can be toxic (Abraham et al., 2002). Rodrigues et al (2006) reported that PCB
degraders cannot catalyze degradation CBA, with the consequence being a buildup of the
metabolite.
Performance
Aerobic Studies
Bench, Laboratory and Pilot Scale Studies
Laboratory scale studies commonly experience greater effectiveness than field
treatment because they are conducted under more controlled, uniform and favourable
conditions than in the field (NRC 1993). Laboratory studies can provide upper limit
results, but caution must be exercised when forecasting results expected in full scale and
field bioremediation. Most reported studies have been done on PCB bioremediation in
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particular on Aroclor, including 1221,1242 and 1254 incubated in aerated sludge reactors.
The mono- and dichlorinated PCBs rapidly degraded and the rate decreased as percent
chlorine of Aroclors increased (Mondello 2002). Studies on high-density PCB-degrading
bacteria suspended in buffer solution with a PCB mixture revealed that degradation
occurred, except to Aroclor 1254 (Furukawa et al., 1983).
In bioreactor studies, PCB reduction was up to 80% in bench scale systems
(Mondello 2002). Degradation of Aroclor 1248, 1254 and 1260 has been studied in 8
different types of agricultural and forest soils (Mondello 2002). Results showed
degradation rates up to 80%. The least degraded mixtures were those containing highly-
chlorinated congeners like 1254 and 1260.
Field Studies
Field studies results show less degradation than in laboratory investigations. The
following provides some examples of recorded field studies:
(a)Glenn Falls, NY (Mondello, 2002)
The site consisted mainly of sandy soil contaminated with Aroclor 1242, at levels
of 50-500 mg/kg. Many di- and trichlorobiphenyls were degraded.
The study attempted to stimulate the process by adding Pseudomonas strain
LB400 (which is known to degrade a wide variety of PCBs). Laboratory scale
test, showed 85% degradation.
In the field study the strain was repeatedly dosed over a designated area for a
period of 4 months.
Only 20% of the PCBs degraded.
In an adjacent plot, which was repeatedly dosed with nutrient solution and no
bacteria introduction relying only on native microorganisms, there were negligible
degradation.
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After 373 days, hexa- to nona-CBs decreased from 68% to 26%. However, TriCB
increased. Overall there was no net reduction in total PCB concentration.
(b)Anaerobic Bioremediation of Toxaphene using Blood Meal (USEPA 2005)
This method uses blood meal as a nutrient to the native anaerobic bacteria. The
contaminated soil was treated for toxaphene by bio-stimulation. The soil was
mixed with blood meal and saturated with water (0.3 m above the soil).
In ex-situ systems, the soil was placed on lined cells, covered and incubated for
several months.
The by-products from this process were lower chlorinated chlorobenzenes,
chloride ions and cell mass, in addition to H2S and methane.
An attempt to treat chlorobenzenes by blood meal under aerobic conditions
achieved 90% dechlorination.
Anaerobic-Aerobic Remediation
Aerobic bacteria do not degrade highly chlorinated compounds such as PCBs.
Coupled systems of anaerobic and aerobic phases may be implemented, where highly
chlorinated compounds are dechlorinated, to enhance aerobic degradation.
DARAMEND
and XenoremTM
are commercialized technologies utilized in this
coupled system.
DARAMEND
(USEPA 2005)
The process includes addition of DARAMEND (which contains nutrients and zero-
valent iron) with water to produce an anoxic phase causing bio-stimulation.
Periodic tilling of the soil is performed to promote oxic conditions. Watering and
tilling are performed several times to achieve effective treatment. The technology can be implemented using land-farming techniques for ex-situ or in-
situ conditions:
o Ex-situ requires excavated soil to be placed on lined cells after removal of
debris.
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o In-situ is only applicable for surface soil or soil within reach of tilling
equipment. The soil must be screened to remove large debris.
By-products of concern are the leachate produced, if cells are not covered on top to
prevent exposure to rainfall.
This technology is generally not feasible for highly contaminated soils.
XenoremTM
This is a patented technology developed by Stauffer Management Company, a
subsidiary of AstraZeneca Group PLC of Mississauga, Ontario, Canada. Recently,
this technology was sold to the University of Delaware (USEPA 2005). It is an ex-
situ bioremediation technology utilizing aerobic and anaerobic cycles with enhanced
composting (USEPA 2005). The anaerobic conditions promote dechlorination of
organochlorine compounds. The duration of the anaerobic phase is determined by
bench-scale studies. At the end of the anaerobic phase, the amended soil is mixed
again creating aerobic conditions (USEPA 2005; Rubin and Burhan 2006).
XenoremTM treats low-strength wastes containing chlordane,
dichlorodiphenyltrichloroethane (DDT), dieldrin and toxaphene.
Organic amendments such as manure and wood chips are added to the contaminated
soil. This can increase the final amended soil volume by as much as 40% (Rubin andBurhan 2006).
The metabolic activity is increased due to the presence of high levels of nutrients
from the amendment, depleting the oxygen content and creating anaerobic conditions
(USEPA 2005; Rubin and Burhan 2006).
The anaerobic and aerobic cycles are repeated until the desired contaminant
reductions are achieved (USEPA 2005; Rubin and Burhan 2006).
The organic amendments are reportedly spent after 14 weeks (USEPA 2005; Rubin
and Burhan 2006).
This technology was applied in a full-scale cleanup at the Stauffer Management
Company Superfund site in Tampa, Florida (Jackson and Gray 2001).
o The site is the location of a pesticide manufacturing and distribution facility
that operated from 1951 to 1986 (Jackson and Gray 2001).
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o Soil was contaminated with chlordane, dichlorodiphenyldichloroethane
(DDD), dichlorodiphenyldichloroethylene (DDE), DDT, dieldrin, molinate,
and toxaphene.
o The technology was applied to two batches of soil.
o DDD, DDE, DDT and toxaphene were reduced by 65%, 68 %, 88 %, and 94
%, respectively; however, neither batch achieved the site cleanup goals for
DDT and toxaphene (USEPA 2005; Rubin and Burhan 2006).
Site Requirements
Space requirements depend on the specific technology employed. In general, in-
situ applications do not require large areas. Installation of infiltration galleries and wells
to circulate amendment-laden water, however, requires from several hundred to several
thousand square meters of clear surface area (Mondello 2002; USEPA 2004b; USEPA
2005). During ex situ applications, more open space is typically required to accommodate
equipment.
Cost
Cost varies from $55 to $360/m3(2005 dollars) (USEPA 2005) .
Costs at the higher end mainly apply to ex-situ, and mechanical bioremediation.
technologies.
Vendor-related technologies, such as DARAMEND and XeonremTM
, incur high
costs if exported.
By-products
Offensive odours from anaerobic degradation.
More soluble chlorinated compounds, needing further treatment.
Chloride ions.
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Leachates generated from uncovered systems.
Biomass from microorganisms.
Minerals and salts from completely degraded compounds.
Advantages and Limitations
Advantages of bioremediation are:
Both in-situ and ex-situ bioremediation technologies have been shown to be
successful in treating both water-soluble and relatively insoluble compounds. Organic
compounds that are highly soluble in water may biodegrade rapidly, particularly in
slurry-phase systems. In general, the rate of biodegradation of a given compound is
proportional to the solubility of that compound in water.
Slurry-phase bioremediation also has the advantage of allowing more precise control
of operating conditions (e.g., temperature, mixing regimes) than solid-phase or in situ
applications. Slurry-phase systems utilizing tanks can be operated under anaerobic or
aerobic conditions, either sequentially in the same tanks, or in series with multiple
vessels. Slurry-phase bio-remediation allows improved contaminant monitoring due
to increased homogeneity of the contaminated media.
Solid-phase bioremediation and composting offer several advantages common to
slurry-phase operations and other ex-situ treatment technologies: better process
control, increased homogeneity, and improved contaminant monitoring. In addition,
treatment units can be built to accommodate large quantities of media.
Composting also enriches the treated soil, providing nutrients for revegetation
(Petkewich 2001). In situ bioremediation minimizes the need for excavation and
transport of contaminated soils, sediments, or sludges.
Energy costs required for bioremediation treatment are typically less than for
alterative remedial approaches.
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Limitations include:
Many factors affect the success of bioremediation. The physical form, amount,
location, and distribution of contaminants have major impacts on the degree to which
contaminants are degraded (Downwy et al., 2004).
Biodegradable contaminants may undergo mineralization (complete degradation to
inorganic constituents); however, incomplete degradation (ending with the formation
of organic intermediates) is also possible.
Soil characteristics, including particle size distribution, moisture content, and
permeability, also affect the success of bioremediation.
Soil and contaminant characteristics affect bioavailability (the extent to which
contaminants can be degraded by microorganisms).
The contaminated soil must not exceed 10 % by volume of the treated soil (Bedard et
al. 1996).
Bioavailability of contaminants in soil can decrease with time, as the contaminants
age and become more strongly sorbed to soil particles.
Bioremediation is slower than many other technologies and may require frequent
monitoring during startup. Monitoring and sampling will also be necessary to
determine when prescribed cleanup levels have been achieved.
Temperature, moisture content and pH values below or above the optimal range for
the microorganisms retard or halt bioremediation. In some cases, excessive biomass
growth may impede further remediation.
Bioremediation has not proven to be effective on PCDDs/PCDFs.
Breakdown of contaminants may generate more toxic by-products or contaminants
which are mobile.
Chlorinated compounds used as bioaugmentation, may cause increased contamination
by chlorinated compounds at the site. Ex-situ remediation practices require large surface areas to treat large quantities of
contaminated soil. This is a disadvantage for heavily populated countries where land
is very expensive.
Aerobic remediation is not applicable to sites prone to flooding, because water
logging leads to anaerobic conditions.
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In addition to these general limitations, in situ and, to a lesser extent, solid-phase
bioremediation present potential difficulties in determining the performance of the
treatment. Contaminant spatial heterogeneity, fate and transport, and sorption
dynamics all lead to variability in results across the site and over time. Sorption
dynamics are particularly important for composting, since contaminants may bind
strongly to the added organic matter, reducing bioavailability. Degradation rates,
therefore, may be limited by desorption kinetics rather than microbial activity.
Especially when recalcitrant contaminants such as PCBs are present. PCBs are often
tightly bound to soil particles, resisting enzymes of dechlorination and making it
difficult to establish and stimulate PCB organisms in remediation sites (Abraham et
al., 2002).
Applicability to Developing Countries
Many bioremediation options are affordable.
If contaminated land is expensive, then time-consuming technologies are likely to be
infeasible.
Countries with extreme weather conditions require more controlled treatment
environments since bioremediation technologies are sensitive to moisture content and
temperature.
Many developing countries are subject to high precipitation and to flooding
conditions. In this case, aerobic remediation is only feasible if conducted in protected
sites or ex-situ locations.
Ex-situ bioremediation involving soil spreading requires large surface areas,
especially when large quantities of soil are contaminated. For highly populated
countries suffering from lack of free land, ex-situ remediation tends to be veryexpensive.
In-situ bioremediation technology can be promising for areas with relatively moderate
climates. Technologies involving farming equipment are feasible, since such
equipment is often already present in such areas.
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A-3 Solvent Extraction
Overview
Solvent extraction is an ex-situ process in which contaminants are separated from
soils, sludges, and sediments, thereby reducing the volume of waste that must be treated.
In the process, the contaminated soil or waste material is brought into contact with a fluid
that selectively dissolves the contaminants.
Treatment Process
The primary stages of the solvent extraction technology are media preparation,
contaminant extraction, solvent/media separation, contaminant collection, and solvent
recycling. Waste preparation includes excavation or moving the waste material to the
process where it is normally screened to remove debris and large objects. Depending
upon the process vendor and whether the process is semi-batch or continuous, the waste
may need to be made mobile (pumpable) by the addition of a solvent or water.
In the extractor, the soil or sediment and solvent are contacted with each other,
and the organic contaminant dissolves into the solvent. The extraction behaviour
exhibited by this technology is usually similar to other mass-transfer-controlled
processes, like liquid-liquid extraction, although equilibrium considerations often become
limiting factors when the time of contacting is long. It is important to conduct a
laboratory-scale
treatability test to determine whether mass transfer or equilibrium is likely to be the
controlling factor, since the controlling factor is critical to the design of the unit and to
the determination of whether solvent extraction technology is appropriate for treatment of
the particular waste.
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After a predetermined extraction time, the solid and the fluid are separated, and
the target contaminants are concentrated in the extraction fluid. The number and length
of the extraction stages are selected based on the remediation criteria, i.e. to achieve the
required degree of extraction. The extracted organics are removed from the extractor
with the solvent and go to a separator, where the pressure and/or temperature is changed,
causing the organic contaminants to separate from the solvent by forming different
phases (Rowe 1987). The solvent is then recycled to the extractor, and the concentrated
contaminants are removed from the separator (Rowe 1987).
Soil properties affect the efficiency of the treatment method. Optimal soil
conditions for treatment include less than 15% clay in the soil and less than 20% moisture
in the soil (USEPA 1995b). Higher moisture contents require drying of the soil and /or
solvent distillation to reduce accumulation of water in the solvent.
Soils containing more than 20% moisture must be dried prior to treatment.
Excess water dilutes the solvent, reducing contaminant solubilization and transport
efficiency (USEPA 1995b). Water buildup in the stock solvent requires the addition of a
distillation step to maintain solvent integrity. Excessive clay concentrations require
additional wash cycles and physical handling to reduce clay aggregate size (USEPA
1995b).
Site Requirements
Typical commercial-scale units (50 to 70 tons per day) may require a total
treatment area of 930 m2 and a power supply (USEPA 1995b). Water must also be
available at the site (USEPA 1995b).
Cost
One time start-up (including capital) cost is estimated at $175,000 for a commercial
unit.
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Average treatment cost range between $125-$400/m3 (in 1995 dollars) (USEPA
1995b)
By-products
There are three main by-product streams generated by this technology:
The extract containing concentrated contaminants, after the organic contaminants
being separated from the solvent, which requires further treatment.
The treated soil or sludge may need to be dewatered before being returned to the site.
Water involved in the process. The volume of the water depends on the inherent
dewatering capability of the liquid-solid separation process, the specific water
requirement for feed slurrying, and the initial water content of the soil or sediment
(USEPA 1997).
Performance
Solvent extraction technologies have been selected as the remedial action at
several U.S. Superfund sites. This section briefly summarizes pilot and full-scale studies.
Laboratory, Bench and Pilot Scale Studies
Treatability pilot studies on different PCB contaminated soils of different soil
properties have been conducted, with varying number of wash cycles. The process
resulted in a removal efficiency of 95-99%, with better removal as the number of wash
cycles increased (USEPA 1995b).
Full Scale Studies Removal efficiency at 4 U.S. Superfund sites contaminated with PCBs was 99%
(USEPA 1997).
A full scale study of solvent extraction on DDT-contaminated soil resulted in a 98.8%
contaminant reduction (USEPA 1995b).
Recommended