H HAZARDOUS WASTE MANAGEMENT HISTORICAL OVERVIEW The development of the Resource Conservation and Recovery Act of 1976 dates to the passage of the Solid Waste Disposal Act of 1965, w
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HAZARDOUS WASTE MANAGEMENT
HISTORICAL OVERVIEW
The development of the Resource Conservation and Recovery
Act of 1976 dates to the passage of the Solid Waste Disposal
Act of 1965, which first addressed the issues of waste
dis-posal on a nationwide basis Prior to the 1960s land disdis-posal
practices frequently included open burning of wastes to
reduce volume, and were controlled only by the general need
to avoid creating a public health impact and nuisance, such
as a bad smell or visual blight—problems that one could see,
smell, taste or touch At that time, what few landfill
con-trols existed were generally focused only on the basics of
sanitation, such as rodent control, and the prevention of fires
The early concept of the “sanitary” landfill was to cover the
waste with soil to reduce pests and vermin, create separate
chambers of earth to reduce the spread of fire, and control
odor and unsightly appearance—the key environmental
con-cerns of the time
Throughout the ’60s and into the ’70s, the use of
indus-trial pits, ponds or lagoons on the land were viewed as
legit-imate treatment systems intended to separate solids from
liquids and to dissipate much of the liquids They were not
only intended to store waste, but also to treat it That is,
solids would sink when settling occurred and the liquid
could be drained, evaporated, or allowed to percolate into
the ground The accumulated solids ultimately would be
landfilled
Similarly for protection of receiving waters,
pollu-tion control laws prior to the mid-1960s were generally
concerned with water-borne diseases and nuisances The
concept of water pollution was far more closely linked to
the bacterial transmission of disease and physical
obstruc-tion or offense than it was to the impact of trace levels of
chemicals Waterways were viewed as natural systems that
could handle waste if properly diluted and if the
concentra-tions were within the assimilative capacity of the rivers and
streams The environmental concerns were primarily odor,
appearance, oxygen content, and bacterial levels Individual
chemical constituents and compounds, at this time, were not
typically regulated in a waterway
The science of testing for and measuring individual con-taminants was unrefined and typically not chemical specific until the 1970s Water and wastewater analyses were gen-erally limited to indicator parameters, such as Biochemical Oxygen Demand, turbidity, suspended solids, coliform bac-teria, dissolved oxygen, nutrients, color, odor and specific heavy metals Trace levels of individual chemical com-pounds and hazardous substances as we know them today were not among the parameters regularly analyzed
“Hazardous waste” became a household word in the late 1970s with the publicity surrounding the Love Canal inci-dent How much waste has been disposed of is still ques-tionable Unfortunately, significant amounts were “thrown away” over the past decades and have endured in the envi-ronment in drum disposal sites such as “The Valley of the Drums” and in land disposal facilities where they have not degraded
Throughout the ’70s and ’80s significant changes were made in the laws governing environmental protection New laws adopted in the ’70s include the Clean Air Act, the Federal Water Pollution Control Act, Safe Drinking Water Act, Resource Conservation and Recovery Act (RCRA), Toxic Substance Control Act, Marine Protection Research and Sanctuaries Act, and in 1980 the “Superfund” (CERCLA) statute Of all the laws passed in the ’70s, RCRA has had the greatest impact on the definition of wastes and the manner
in which these wastes were to be managed, treated and handled RCRA 1 required the US Environmental Protection Agency to establish management procedures for the proper disposal of hazardous wastes These procedures are part of the Code of Federal Regulations dealing with environmental protection They cover a “cradle-to-grave” procedure which regulates generators, transporters, storers and disposers of hazardous materials Regulations for generators and trans-porters of hazardous wastes may also be found in the Code
of Federal Regulations. 2,3
Subsequent revisions to RCRA in 1984 included the pro-visions dealing with underground tanks, the restriction of land disposal of a variety of wastes, corrective action require-ments for all releases, and the inclusion of a requirement of
Trang 2the EPA to inspect government and privately owned facilities
which handle hazardous waste
Today the law is again being considered for revision, and
among the issues that are always under discussion include
“how clean is clean” when remediating industrial and landfill
sites The cleanup standards are not consistent among state and
federal programs, frequently causing significant discussion
among responsible parties and regulators At this time, risk
assessments are used more often in an effort to design remedial
programs that are appropriate for the media, and the resources
being protected A risk assessment might provide, for example,
the necessary information to set differing groundwater cleanup
goals in a sole source aquifer, than in an industrialized area
sit-uated above a brackish water-bearing zone where the
ground-water will not again be used for potable purposes
With the preceding paragraphs as general background,
the brief discussion which follows on hazardous wastes
emphasizes some of the technologies that have been
suc-cessfully used for the treatment and disposal of hazardous
wastes, and remediation of contaminated properties
HAZARDOUS WASTE DEFINED
Hazardous wastes encompass a wide variety of materials In
1987, the US EPA estimated that approximately 238 million
tons could be classified as hazardous This number is probably
generous but suffice it to say that a great deal of material of a
hazardous and dangerous nature is generated and disposed of
every year
The Resource Conservation and Recovery Act defines a
hazardous waste as a solid waste that may cause or
signifi-cantly contribute to serious health or death, or that poses a
substantial threat to human health or the environment when
improperly managed Solid waste, under the present
guide-lines, includes sludges, liquids, and gases in bottles that are
disposed of on the land
From this working definition, a number of wastes have
been defined as hazardous These include materials that are
ignitable, corrosive, reactive or explosive or toxic These
char-acteristic identifiers are further delineated in the regulations. 4
In addition, using these general characteristics and specific
tests, the US Environmental Protection Agency has listed
materials from processes, such as electroplating, or specific
classes of materials, such as chlorinated solvents, or
speci-fic materials, such as lead acetate, or classes of compound, such
as selenium and its compounds, which must be managed as
“hazardous wastes” when they are disposed This list changes
periodically In many cases disposers have treated materials
not on the list as hazardous if they believe them to be so
Some general classes of materials such as sewage,
mining and processing of ore wastes are excluded by law at
the present time
Managing Wastes
Advancements in science and technology have given us
opportunities to address environmental contamination issues
in ways that are technologically more advanced, and more cost and time efficient than ever before Technologies that were unknown, unproven and unacceptable to regulatory agencies just a few years ago, now exist and are being imple-mented at full scale Regulations have changed, as have gov-ernment policies governing cleanup and enforcement
On a technical level, many ideas for hazardous waste treatment and remediation were rejected a few years ago
by the engineering, business and regulatory community as being unproven or unreliable Entrepreneurial scientists and engineers have adapted their knowledge of manufacturing process chemistry and engineering to the sciences of geol-ogy and hydrogeolgeol-ogy and have refined the necessary equip-ment and techniques for waste treatequip-ment and remediation Technologies have been tested at bench and pilot scale, and many have proven effective on a large scale Pressure by the industrial community for engineers and regulators to reach a common ground has driven the process
Contaminated soil and groundwater remedial techniques have tended toward the “active” end of the spectrum, with the installation of pumps, wells and above ground treatment systems of the capital and labor intensive variety Progress has been made at the opposite end of the spectrum, rang-ing from intrinsic bioremediation, which involves no active treatment, to incremental levels of treatment that are far less
costly than ex-situ pump and treat methods
Programs like the EPA SITE (Superfund Innovative Technology Evaluation) Program and other Federal test and evaluation facilities, University research organizations and privately sponsored technology incubator and test evaluation facilities have been very successful in testing and establishing new hazardous waste treatment and disposal technologies Currently, there are several dozen organizations nationally that specifically focus on the development of emerging haz-ardous waste treatment technologies The results have been very positive, and many of today’s front-edge technologies are the offspring of programs such as these
On a regulatory/compliance level, the extensive time frame for receipt of approvals led many companies down the path of the traditional treatment and disposal methods, since they were “proven,” as well as being approvable by the regulatory agencies Environmental agencies have become more sophisticated, and cleanup levels are more often based
on risk rather than standards set at an earlier data in tech-nical and regulatory development More than ever, agency personnel are now trained as specialists in the various seg-ments of the environmental industry, including risk assess-ment, hydrogeology, remediation engineering and personal protection As a result, the agencies are often more willing
to engage in discussions regarding site specific conditions and remedial goals Further, modifications to state permit-ting programs have allowed variations on typical operapermit-ting permits for new and emerging technologies that appear to have promise
An analysis of Superfund remediation activities indi-cates that significant progress has been made in the use of innovative technologies for site remediation The predomi-nant new technologies used at Superfund sites include soil
Trang 3vapor extraction (SVE) and thermal desorption It is
impor-tant to note that there are many derivative technologies that
will now stand a greater chance of receiving government and
industry support as a result
Remediation technologies that are derived from soil
vapor extraction include dual phase extraction and sparing
The two phases are typically a) removal of free product or
contaminated groundwater and b) vapor The in-situ addition
of certain compounds by sparging into the soil and
ground-water has made bioremediation attractive The addition of
the additional components to an earlier technology that was
moderately successful has made the modified treatment train
much more effective The new treatment train is therefore
more approvable
On a financial level, methods have been developed for
the evaluation of large projects to provide a greater degree
of financial assurance The concept of the “unknown” cost
of remediation due to the inability of scientists to accurately
see and measure subsurface contamination is diminishing
Probabilistic cost analyses are frequently completed on
assignments so that final remediation costs can be predicted
within a much narrower range
Management practices have changed dramatically over
the past 20 years at most industries They have been driven
by the improvements in technologies, as well as the laws and
regulations The real estate boom of the 1980s also impacted
operating practices, as many properties were bought and sold
during this time The desire of buyers to be assured that they
were purchasing “clean” properties, as well as some state
environmental property transfer requirements, was the
gen-esis of facility environmental audits as we now know them
For purposes of discussion, hazardous wastes fall
primar-ily into two categories, organic and inorganic Some
manage-ment technologies will apply to both, but in general organic
material can be destroyed to relatively innocuous end
prod-ucts while inorganic material can only be immobilized The
key technologies for hazardous waste management include:
• Pollution Prevention
• Recycling and Reuse
• Waste Minimization
• Chemical Treatment and Detoxification
• Destruction
• Stabilization
• Land disposal
Of these, land disposal is the least attractive alternative from
the standpoint of long-term liability exposure and
environ-mental impact
Waste Concentration—A Key Where a waste must be
ulti-mately disposed of, concentration or volume reduction is
beneficial The simplest approach to this is to separate wastes
at the source; that is, at the place of origin This will increase
handling costs and effort, but will more than pay dividends in
minimizing analytical and disposal costs First, it will mean
that analysis must be done less frequently Second, waste can
be disposed of at the lowest degree of care consistent with the
most hazardous contaminant, thus minimizing the volume of waste that must get a greater degree of care because of slight cross-contamination by a more toxic material This is true whether the material is in the liquid or solid state
Another method of reducing volume is concentration For liquids, this generally means distillation or evapora-tion Evaporation to date has been acceptable, however, with increased emphasis on the presence of volatile hazardous materials in the atmosphere, evaporation ponds, will, in all probability, no longer meet the necessary standards for waste control and management In addition, ponds must be per-mitted under RCRA, which imposes additional financial and operating requirements on the waste concentrator Double and triple effect evaporators and distillation units will be acceptable but are very energy-expensive Innovative tech-niques will be required because of the high energy of the traditional liquid separation systems
Where a material is dissolved in water or an organic sol-vent, precipitation may be advisable The solid can then be separated out from the majority of the liquid by filtration
or other liquid/solid separation technology Typical of this would be the precipitation of lead by the use of a sulfide salt, resulting in lead sulfide which has extremely low solubility The solid may be suitable for reclamation at present or be stored in a secure landfill in a “non- or less-hazardous form” for eventual reuse
Pollution Prevention The passage of Pollution Prevention
Laws has driven many industries toward better utilization of their resources Many companies now actively participate
in the preparation and update of a pollution prevention pro-gram, designed to guide personnel toward goals established
to improve waste generation and disposal practices
Traditional environmental quality and pollution control programs typically focus on an end-of-pipe approach The pollution prevention plan approach typically begins earlier
in the “equation” by reviewing an operation and making modifications that will positively impact a facility Some examples include reducing harmful chemical purchases, increasing operation efficiencies, and ultimately generating
a smaller quantity of waste
The pollution plan approach will include involvement
by a wider range of facility personnel than the traditional environmental management approach Purchasing, account-ing, production and engineering all participate Proponents suggest that a program is easy to implement, although corpo-rate personnel involved in the effort know that it is an effort which requires broad-based management support, is time consuming, and not necessarily inexpensive to implement The benefits are potentially significant, as reduced emissions make it easier to comply with discharge standards, and will reduce long-term liabilities
Recycling and Reuse In many cases, in addition to
eco-nomically attractive alternatives, a very attractive alternative will be recycling or reuse of hazardous wastes The eco-nomic realities of the regulations, where disposal of a barrel
of waste can demand a 5–$10 per gallon, and up to $1,200 per
Trang 4ton or greater fee, may make processing for recycling and/or
reuse the best practice In the present context, we are defining
recycling as internal to the plant, and reuse as external to the
plant This is not a legal definition which defines recycling as
essentially both internal and external, but it is helpful in this
discussion
Internal recycling will require, in general, high efficiency
separation and potential additional processing Thus, if a
sol-vent is being recycled, impurities such as water, by-products,
and other contaminants must be removed Depending on the
volumes involved, this may be done internally to the process
or externally on a batch basis
Reuse involves “selling” the waste to a recycle and
reclaimer The reclaimer then treats the waste streams and
recovers value from them The cleaned-up streams are then
his products for sale
From a regulatory, liability perspective, there are
advan-tages to reuse as the liability for the waste ends when it is
successfully delivered to the reclaimer Because he
pro-cesses the material, he then assumes responsibility for the
products and wastes that are generated If the material is
internally recycled, then the recycler, that is the plant,
main-tains responsibility for any wastes that are generated as a
result of the recycling operation
In some cases, it may be desirable to dispose of wastes
directly to the user This is particularly true when there are
large quantities involved and a beneficial arrangement can be
worked out directly Waste exchanges have been organized
to promote this type of industrial activity Detailed
discus-sions of their mode of operation can be obtained directly
from the exchanges
Waste Minimization The alternative scenario
develop-ment will be not only site, but substance specific Two basic
approaches to hazardous waste management are:
1) In-process modifications
2) End-of-pipe modifications
Each will have advantages and disadvantages that are
pro-cesses, substance, and site specific
In-process alternatives include changing process
con-ditions, changing feedstocks, modifying the process form
in some cases, or if necessary eliminating that process and
product line
In-process modification is generally expensive and must
be considered on a case-by-case basis There are some
poten-tial process modifications that should be considered to
mini-mize the production of toxic materials as by-products These
include minimization of recycling so side-reaction products
do not build up and become significant contributors to the
pollution load of a bleed stream For example, waste must
be purged regularly in the chlorination of phenols to avoid
the build-up of dioxin It may also be desirable to optimize
the pressure of by-products For example, phenol is produced
and found in condensate water when steam-cracking naphtha
to produce ethylene unless pressures and temperatures are
kept relatively low
It may be desirable to change feedstocks in order to elim-inate the production of hazardous by-products For example, cracking ethane instead of naphtha will yield a relatively pure product stream
Hydrazine, a high energy fuel, was originally produced
in a process where dimethylnitrosamine was an intermediate
A very small portion of that nitrosamine ended up in a waste stream from an aqueous/hydrocarbon separation This waste stream proved to be difficult, if not impossible, to dispose of
A new direct process not involving the intermediate has been substituted with the results that there are no noxious wastes
or by-products
In the ultimate situation, production of a product may
be abandoned because either the product or a resulting by-product poses an economic hazard which the corpo-ration is not willing to underwrite These include cases where extensive testing to meet TSCA (Toxic Substances Control Act) was required They include the withdrawal of pre-manufacturing notice applications for some phthalate ester processes However, production of certain herbicides and pesticides was discontinued because a by-product or contaminant was dioxin
Treatment/Destruction Technology
Chemical Treatment/Detoxification Where hazardous mate-rials can be detoxified by chemical reaction, there the mol-ecule will be altered from one that is hazardous to one or more that are non-hazardous, or at least significantly less hazardous For example, chlorinated hydrocarbons can be hydro-dechlorinated The resulting products are either HCl
or chlorine gas and nonchlorinated hydrocarbons A number
of these processes are being developed for the detoxification
of PCB (polychlorinated biphenols) and are being demon-strated as low concentrations of PCB’s in mineral oil The end products, if concentrated enough, can be useful as feed-stocks or the hydrocarbons may be used as fuel
Cyanide can be detoxified using any number of chemi-cal reactions These include a reaction with chlorine gas to produce carbonate and chlorine salt Cyanide can also be converted to cyanate using chlorine gas In addition, ozone can be utilized to break up the carbon-nitrogen bond and produce CO 2 and nitrogen
Hexavalent chromium is a toxic material It can be reduced to trivalent chromium which is considerably less hazardous and can be precipitated in a stable form for reuse
or disposal as a non-hazardous material Chromium reduc-tion can be carried out in the presence of sulfur dioxide to produce chromium sulfate and water Similar chemistry is utilized to remove mercury from caustic chlorine electroly-sis cell effluent, utilizing sodium borohydride
Lead, in its soluble form, is also a particularly difficult material Lead can be stabilized to a high insoluble form using sulfur compounds or sulfate compounds, thus remov-ing the hazardous material from the waste stream
Acids and bases can most readily be converted to non-hazardous materials by neutralizing them with appropriate
Trang 5base or acid This is probably the simplest chemical
treat-ment of those discussed and is widely applicable; care must
be taken, however, to insure that no hazardous precipitates or
dissolved solids forms
Incineration Incineration has been practiced on solid
waste for many years It has not, however, been as widely
accepted in the United States as in Europe where
incin-eration with heat recovery has been practiced for at least
three decades Incineration of industrial materials has been
practiced only to a limited extent; first, because it was more
expensive than land disposal, and second, because of a lack
of regulatory guidelines This has changed because
land-fills are not acceptable or available, costs for landfilling are
becoming extremely high, and regulatory guidance is
avail-able Equipment for incineration of industrial products has
been, and is available, however, it must be properly designed
and applied
Incineration is the oxidation of molecules at high
tem-peratures in the presence of oxygen (usually in the form
of air) to form carbon dioxide and water, as well as other
oxygenated products In addition, products such as
hydro-gen chloride are formed during the oxidation process The
oxidation, or breakdown, takes place in the gaseous state,
thus requiring vaporization of the material prior to any
reac-tion The molecules then breakdown into simpler molecules,
with the least stable bonds breaking first This occurs at
rela-tively lower temperatures and shorter times It is followed by
the breakdown of the more stable, and then the most stable
bonds to form simple molecules of carbon dioxide, water,
hydrogen chloride, nitrogen oxides, and sulfur oxides, as
may be appropriate
Thus, the primary considerations for successful
oxi-dation or destruction are adequate time and temperature
Good air/waste contact is also important Regulatory
guide-lines require a destruction and removal efficiency (DRE)
of 99.99% thus, time and temperature become all the more
important For the most refractory compounds, such as
PCB’s, residence times in excess of three seconds and
tem-peratures in excess of 1000°C are required These
tempera-tures may be reduced in light of special patented processes
utilizing oxidation promoters and/or catalysts As a result of
the high required DRE, a test burn is required to demonstrate
adequate design
In addition to time and temperature considerations,
there are other important factors which must be
consid-ered when designing or choosing equipment to incinerate
industrial waste Most important is adequate emission gas
controls Where materials which contain metals, chlorides,
or sulfides are to be incinerated, special provisions must be
made to minimize emission of HCl, SO 2 , and metal oxides
Usually a scrubber is required, followed by a system to
clean up the scrubber-purge water This system includes
neutralization and precipitation of the sulfur and metal
oxides In addition, where high temperature incineration
is practiced, control of nitrogen oxides to meet air quality
emissions standards must be considered These substances
do not present insurmountable technological challenges, as
they have been handled satisfactorily in coal-fired power plant installations, but they do present added economic and operating challenges
Several types of incineration facilities should be con-sidered Unfortunately, the standard commercial incinera-tor utilized or municipal waste will generally not prove adequate for handling industrial waste loads because the temperatures and residence times are inadequate Municipal incinerators are designed to handle wastes with an energy content below 8000 Btu/pound, while industrial wastes can have heating values as high as 24000 Btu/pound Municipal incinerators are generally not designed to accept industrial wastes
A number of incinerator facilities have been built for industrial wastes Small, compact units, utilizing a single chamber with after-burner, or two-stage, multi-chamber combustion are available In general, a single-state unit will not suffice unless adequate residence time can be assured Rotary kiln incinerators are of particular interest for the disposal of industrial materials Generally, they are only applicable for large-scale operations, and can handle
a large variety of feedstocks, including drums, solids and liquids Rotary cement kilns have been permitted to accept certain types of organic hazardous materials as a fuel supplement
Of increasing interest for industrial incineration is the fluid bed incinerator This has the additional advantage of being able to handle inorganic residues, such as sodium sulfate and sodium chloride These units provide the addi-tional advantage of long residence time, which may be desir-able when the waste is complex (e.g., plastics) or has large organic molecules On the other hand, gas residence times are short, and an after-burner or off-gas incinerator is often required in order to achieve the necessary DRE
Incineration has been used successfully for the disposal
of heptachlor, DDT, and almost all other commercial chlori-nated pesticides Organo-phosphorous insecticides have also been destroyed, but require a scrubbing system, followed by
a mist eliminator, to recover the phosphorous pentoxide that
is generated
Some special incineration applications have been imple-mented These include:
• An ammonia plant effluent containing organics and steam is oxidized over a catalyst to form CO 2 , water and nitrogen;
• Hydrazine is destroyed in mobile US Air Force trailers which can handle 6 gpm of 100% hydra-zine to 100% water solutions, and maintain an emission has which contains less than 0.03 pound/
minute of NO x ;
• Chlorate-phosphorous mixtures from fireworks ammunition are destroyed in a special incinerator which has post-combustion scrubbing to collect
NO x , P 4 O 10 , HCl, SO 2 and metal oxides;
• Fluid bed incinerators which handle up to 316 tons per day of refinery sludge and 56 tons of caustic are being utilized
Trang 6Wet Air Oxidation Although not strictly incineration, wet
air oxidation is a related oxidation process Usually air, and
sometimes oxygen, is introduced into a reactor where
haz-ardous material, or industrial waste, is slurried in water at
250° to 750°F
Operating pressures are as high as 300 psig Plants have
been built to treat wastes from the manufacture of polysulfite
rubber and other potentially hazardous materials Emissions
are similar to those obtained in incineration, with the
excep-tion that there is liquid and gaseous separaexcep-tion Careful
eval-uation of operating conditions and materials of destruction
are required
Pyrolysis Pyrolysis transforms hazardous organic
materi-als by thermal degradation or cracking, in the absence of an
oxidant, into gaseous components, liquid, and a solid
resi-due It typically occurs under pressure and a temperature
above 800°F
To date, the process has found limited commercial
applica-tion but continues to be one that will eventually be economically
attractive, the prime reason being the potential for recovery of
valuable starting materials A great deal of experimentation has
been carried out both on municipal and industrial wastes For
example, polyvinyl chloride can be thermally degraded to
pro-duce HCl and a variety of hydrocarbon monomers, including
ethylene, butylene, and propylene This is a two-stage
degrada-tion process with the HCl coming off at relatively low
tempera-tures (400°C) and the hydrocarbon polymer chain breakdown
can be obtained with Polystyrene, with styrene as the main
product, and most other polymers Experimental work carried
out in the early 1970s by the US Bureau of Mines, indicates
that steel-belted radial tires can be pyrolyzed to reclaim the
monomers, as well as gas and fuel oil
Other target contaminant groups include SVOCs and
pesticides The process is applicable for the treatment of
refinery, coal tar, and wood treating wastes and some soils
containing hydrocarbons
Disposal Technology
Land Storage and Disposal Disposal of hazardous
mate-rials to the land remains the most common practice It
is highly regulated and a practice which has been limited
because of public pressure and federal rules which require
the demonstration of alternate means of disposal The design
of secure landfills for the acceptance of hazardous materials
must be such that ground waters, as well as local populations
are protected The US Environmental Protection Agency has
implemented strict landfills In practice all landfills
accept-ing hazardous wastes must insure that the wastes stored in
close proximity are compatible so that no violent reactions
occur should one or more waste leak
Federal and State regulations prohibit the disposal of
liquids in landfills Of equal importance to the disposal of
hazardous wastes, whether solid or semi-solid, is the
assur-ance that material will not leach away from the landfill or
impoundment This assurance is provided by the use of
“double-liners” with a leak detection system between the liners, a leachate collection system for each cell, and a leach-ate treatment system designed and operleach-ated for the facility
In dilute form liquid wastes can be “landfarmed” where microbial action will decompose the compounds over time This methodology has been utilized over many years for hydrocarbons and has worked well For highly toxic com-pounds, such as chlorinated organics, it is less attractive even though decomposition does occur Land treatment of PCB contaminated soils has been tested with some success
Stabilization The stabilization of hazardous materials prior
to land disposal is frequently practiced Generally, the stabi-lization is in the form of fixing the hazardous material with
a pozzolanic material, such as fly ash and lime, to produce a solid, non-leachable product which is then placed in land dis-posal facilities Typically, this methodology is applicable to inorganic materials Most of the commercial processes claim that they can handle materials with some organic matter Polymer and micro-encapsulation has also been uti-lized but to a significantly lesser extent than the commer-cially available process which utilize pozzolanic reactions Polymers which have been utilized include polyethylene, polyvinylchloride and polyesters
Grube 9 describes a study of effectiveness of a waste solidification/stabilization process used in a field-scale demonstration which includes collecting samples of treated waste materials and performing laboratory tests Data from all extraction and leaching tests showed negligible release
of contaminants Physical stability of the solidified material was excellent
Remediation Technologies
Natural Attenuation and Bioaugmentation The concept of
natural attenuation, or intrinsic bioremediation, has gained
a greater acceptance by the regulatory community as data presented by the scientific community have demonstrated the results of natural attenuation, and the costs and time frames associated with traditional remedial methods. 1 This approach is most appropriate for the dissolved phase ground-water contamination plume It is still necessary to remove or remediate the source zone of an affected aquifer, after which natural attenuation may be a reasonable approach to the dis-solved phases
Natural attenuation should not be considered “No Action.” It requires a solid understanding of the contami-nant, geologic and aquifer characteristics, and a defined plan
of action The action involves demonstrating that the con-taminants will breakdown, will not migrate beyond a speci-fied perimeter, and will not impact potential receptors It may involve the stimulation of microorganisms with nutrients
or other chemicals that will enable or enhance their ability to
and groundwater, such as soil excavation/disposal, groundwater and-treat using air stripping and granulated carbon polishing
Trang 7degrade contaminants Some limitations may include
inappro-priate site hydrogeologic characteristics (including the inability
of the geostrata to transport adapted microorganisms) and
con-taminant toxicity Monitoring and reporting is required, and a
health-based risk assessment may be required by regulators
Natural attenuation is frequently enhanced by several
components, such as the creation of a barrier or the addition
of a chemical or biologic additive to assist in the degradation
of contaminants
The overall economics of this approach can be
sig-nificantly more favorable than the typical pump-and-treat
approach One must be careful to consider, however, that the
costs of assessment will equal or exceed that necessary for
other methods, and the costs associated with sentinel
moni-toring will be borne for a longer period of time
Barriers This has been used in instances where the
over-all costs of the remedial action is very high, and the
geo-logic features are favorable It involves the installation of
a physical cut-off wall below grade to divert groundwater
The barriers can be placed either upgradient of the plume
to limit the movement of clean groundwater through the
contaminated media, or downgradient of the plume with
openings or “gates” to channel the contaminated
groundwa-ter toward a remedial system This technology has proven
to be more efficient and less costly than traditional pump
and treat methods, but also requires favorable hydrogeologic
conditions It allows for the return of treated groundwater to
the upgradient end of the plume with a continuous
“circu-lar” flushing of the soil, rather than allowing the dilution by
groundwater moving from the upgradient end of the plume
The result is greater efficiency, and a shorter treatment time
period While the cost of the cutoff wall is significant, it is
important to conduct a proper analysis of long-term
pump-and-treat costs, including the operation and maintenance of
a system that would otherwise be designed to accept a much
larger quantity of groundwater
The creation of a hydraulic barrier to divert upgradient
groundwater from entering the contaminant plume allows
the pumping of groundwater directly from the affected area
and often allows the reinjection of the treated water back
into the soils immediately upgradient of the plume This
allows for the efficient treatment of the impacted area,
with-out unnecessary dilution of the contaminated groundwater
plume It does, however, require an accurate assessment of
the groundwater regime during the assessment stage This
promising concept is not radical, but its use in connection
with natural remediation is growing rapidly
Passive Treatment Walls Passive treatment walls can be
constructed across the flow path of a contaminant plume to
allow the groundwater to move through a placed media, such
as limestone, iron filings, hydrogen peroxide or microbes
The limestone acts to increase the pH, which can
immobi-lize dissolved metals in the saturated zone Iron filings can
dechlorinate chlorinated compounds The contaminants will
be either degraded or retained in concentrated form by the
barrier material
Physical Chemical Soil Washing Soil is composed of a
multitude of substances, with a large variance in size These substances range from the very fine silts and clays, to the larger sand, gravel and rocks Contaminants tend to adsorb onto the smallest soil particles, as a result of the larger sur-face per unit of volume Although these smaller particles may represent a small portion of the soil volume, they may contain as much as 90% of the contamination
Soil washing involves the physical separation, or clas-sification, of the soil in order to reduce the volume requiring treatment or off-side disposal It is based on the particle size separation technology used in the mining industry for many decades The steps vary, but typically begin with crushing and screening It is a water-based process, which involves the scrubbing of soil in order to cause it to break up into the smallest particles, and its subsequent screening into various piles The fraction of the soil with the highest concentra-tion of contaminaconcentra-tion can be treated using technologies fre-quently used by industry The goal is to reduce the quantity
of material that must be disposed The clean soil fractions can often be returned to the site for use as fill material where appropriate
The use of soil washing technology has some limitations, including a high initial cost for pilot testing and equipment setup It will be most useful on large projects (requiring reme-diation of greater than 10,000 cubic yards of soil) Sites with
a high degree of soil variability, and a significant percentage
of larger particles will show the greatest economic benefit
Soil Vapor Extraction Soil Vapor Extraction (SVE) is an
effective method for the in-situ remediation of soils
contain-ing volatile compounds Under the appropriate conditions volatile organic compounds will change from the liquid phase to the vapor phase, and can be drawn from the subsur-face using a vacuum pump There are several factors neces-sary for the successful use of this technology, including 1) the appropriate properties of the chemicals of concern (they must be adequately volatile to move into a vapor phase), and 2) an appropriate vapor flow rate must be established through the soils
Air is drawn into the soils via perimeter wells, and through the soils to the vapor extraction well It is drawn to the surface by a vacuum pump and subsequently through a series of manifolds to a treatment system such as activated carbon or catalytic oxidation
A concentration gradient is formed, whereby in an effort
to reach equilibrium, the liquid phase volatile contaminants change into the vapor phase and are subsequently transported through the soils to the treatment system
This technology is particularly effective for defined spill areas, with acceptable soils It is most effective in remediating the soils in the vadose zone, the area that is in contact with the fluctuating groundwater table Groundwater contaminated with these compounds and similar soil conditions can be reme-diated using air sparging, a variation of soil vapor extraction
A variation of this technology is thermal enhanced SVE, using steam/hot air injection or radio frequency heating to increase the mobility of certain compounds
Trang 8Air Sparging Air sparging is the further development of
soil vapor extraction, wherein that process is extended so that
soils and groundwater in the capillary fringe can be
effec-tively treated Air sparging involves injecting air or oxygen
into the aquifer to strip or flush volatile contaminants from
the groundwater and saturated soils As the air channels up
through the groundwater, it is captured through separate vapor
extraction wells and a vapor extraction system The entire
system essentially acts as an in-situ air stripper Stripped,
volatile contaminants usually will be extracted through soil
vapor extraction wells and usually require further treatment,
such as vapor phase activated carbon or a catalytic
oxida-tion treatment unit This technology is effective when large
quantities of groundwater must be treated, and can provide
an efficient and cost-effective means of saturated zone soil
and groundwater remediation
The biological degradation of organic contamination
in groundwater and soil is frequently limited by a lack of
oxygen The speed at which these contaminants are degraded
can be increased significantly by the addition of oxygen in
either solid or liquid form Air sparging is often combined
with in-situ groundwater bioremediation, in which nutrients
or an oxygen source (such as air or peroxide) are pumped
into the aquifer through wells to enhance biodegradation of
contaminants in the groundwater
Oxygen Enhancement/Oxidation In this in-situ process,
hydrogen peroxide is used as a way of adding oxygen to
low or anoxic groundwater, or other oxidative chemicals are
added as an oxidant to react with organic material present,
yielding primarily carbon dioxide and water The application
of this technology is typically through the subsurface
injec-tion of a peroxide compound It has been injected as a liquid,
above the plume, and allowed to migrate downward through
the contaminated plume Alternately, it has been placed as a
solid in wells located at the downgradient edge of the plume;
in this fashion it can act as a contamination “barrier,” limiting
the potential for contaminated groundwater to move offsite
As the organic contaminated groundwater moves through the
high oxygen zone, the contaminant bonds are either broken,
or the increased oxygen aid in the natural biodegradation of
the compounds
The process is exothermic, causing a temperature
increase in the soils during the process This acts to increase
the vapor pressure of the volatile organic compounds in the
soil, and subsequently increases volatilization of the
con-taminants This process can be utilized in connection with
a soil vapor extraction and/or sparging system to improve
remediation time frames
It does not act, however, on the soil groundwater vadose
zone This may not be a critical flaw, however, since the
strate-gic placement of the wells may positively impact the
contami-nant concentrations adequately to meet cleanup standards
Dual Phase Extraction Dual phase extraction is an
effec-tive method of remediating both soils and groundwater in
the vadose and saturated zones where groundwater and
soil are both contaminated with volatile or nonvolatile
compounds It is frequently used for contaminant plumes with free floating product, combined with known contami-nation of the vadose zone This technique allows for the extraction of contaminants simultaneously from both the
saturated and unsaturated soils in-situ While there are
several variations of this technique, simply put, a vacuum
is applied to the well, soil vapor is extracted and ground-water is entrained by the extracted vapors The extracted vapors are subsequently treated using conventional treat-ment methods while the vapor stream is typically treated using activated carbon or a catalytic oxidizer
The process is frequently combined with other technolo-gies, such as air sparging or groundwater pump-and-treat to minimize treatment time and maximize recovery rate
Chemical Oxidation and Reduction Reduction/oxidation
reactions chemically convert hazardous contaminants to nonhazardous or less toxic compounds that are more stable, less mobile and/or inert The oxidizing agents typically used for treatment of hazardous contaminants are ozone, hydrogen peroxide, hypochlorites, chlorine and chlorine dioxide These reactions have been used for the disinfec-tion of water, and are being used more frequently for the treatment of contaminated soils
The target contaminant group for chemical reduction/oxi-dation reactions is typically inorganics, however hydrogen
peroxide has been used successfully in the in-situ treatment
of groundwater contaminated with light hydrocarbons
Other Technologies Many other technologies are being applied with increasing frequency The following is only a very brief description of several that have promise
• Surfactant enhanced recovery Surfactant flushing
of non-aqueous phase liquids (NAPL) increases the solubility and mobility of the contaminants in water, so that the NAPL can be biodegraded more easily in the aquifer or recovered for treatment aboveground via pump-and-treat methods
• Solvent extraction Solvent extraction has been successfully used as a means of separating haz-ardous contaminants from soils, sludges and sediments, and therefore reducing the volume
of hazardous materials that must be treated An organic chemical is typically used as a solvent, and can be combined with other technologies, such as soil washing, which is frequently used
to separate, or classify, various soil particles into size categories The treatment of the concentrated waste fraction is then treated according to its spe-cific characteristics Frequently, the larger volume
of treated material can be returned to the site
• Bioremediation using methane injection The method
earlier described for the injection of hydrogen per-oxide into wells has also been successfully utilized using methane It is claimed that this bioremedia-tion process uses microbes which co-metabolize methane with TCE and other chlorinated solvents,
Trang 9potentially cutting treatment costs and time frames
by 30 to 50%
• Thermal technologies The EPA has conducted
tests of thermally-based technologies in an
evalu-ation of methods to treat organic contaminants
in soil and groundwater Low temperature
ther-mal desorption is a physical separation process
designed to volatilize water and organic
contami-nants Typical desorption designs are the rotary
dryer and the thermal screw In each case,
mate-rial is transported through the heated chamber via
either conveyors or augers The volatilized
com-pounds, and gas entrained particulates are
subse-quently transported to another treatment system
for removal or destruction
Mobile incineration processes have been developed
for use at remedial sites While permitting is frequently a
problem, the economics of transporting large quantities of
soil can drive this alternative One method is a circulating
fluidized bed, which uses high-velocity air to circulate and
suspend the waste particles in a combustion loop Another
unit uses electrical resistance heating elements or
indirect-fired radiant U-tubes to heat the material passing through
the chamber Each requires subsequent treatment of the off
gases Also certain wastes will result in the formation of a
bottom ash, requiring treatment and disposal
In summary, the current business and regulatory climate
is positive for the consideration of alternate treatment
tech-nologies The re-evaluation of ongoing projects in light of
regulatory and policy changes, as well as new technological
developments may allow cost and time savings The
arse-nal of techniques and technologies has developed
substan-tially over the years, as has our knowledge of the physical
and chemical processes associated with the management of
wastes Effluents and contaminated media are now easier to
target with more efficient and cost-effective methods
BIBLIOGRAPHY
1 Pojasek, R.B (ed.), Toxic and Hazardous Waste Disposal, 1, Processes
for Stabilization and Solidification, Ann Arbor Science, Ann Arbor,
Michigan, 1979
2 Merry, A.A (ed.), The Handbook of Hazardous Waste Management,
Technomic, Westport, Connecticut, 1980
3 Overcash, M.R., Decomposition of Toxic and Nontoxic Organic
Com-pounds in Soils, Ann Arbor Science, Ann Arbor, Michigan, 1981
4 Toxic and Hazardous Industrial Chemicals Safety Manual The
Inter-national Technical Information Institute, Tokyo, 1981
5 Bertherick, L., Handbook of Reactive Chemical Hazards, Butterworths,
London, 1979
6 Hatayma, H.K., et al., A Method of Determining Hazardous Waste
Compatibility, USEPA, Cincinnati, 1981
7 Kaing, Y and Metry, A.A., Hazardous Waste Processing Technology,
Ann Arbor Science, Ann Arbor, Michigan, 1982
EPA/430/9–80/004, USEPA, Washington, 1980
Con-ference Proceedings, USEPA, 1980
10 Stoddard, S.K., et al , Alternatives to the Land Disposal of Hazardous
Wastes — An Assessment for California, Office of Appropriate Technol-ogy, State of California, 1981
11 Grube, W.E., Jr., “Evaluation of Waste Stabilized by the Solid Tech Site
Technology,” J Air Waste Manag Assoc (1990)
12 Evanoff, S.P., Hazardous Waste Reduction in the Aerospace Industry,
Chem Eng Prog , 86, 4, 51 (1990)
13 Jackson, D.R., Evaluation of Solidified Residue from Municipal Solid
Waste Combustor, EPA Repot 600/52–89/018 Feb 1990
14 Innovative Hazardous Waste Treatment Technologies: A Developers
Guide to Support Services, Third Edition, EPA Report
EPA/542-B-94–012, September 1994
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17 Remediation Case Studies: Soil Vapor Extraction, USEPA Report
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Profiles Seventh Edition, USEPA Report, EPA/540/R-94/526,
Novem-ber 1994
19 Superfund XV Abstract Book, Hazardous Materials Control Resources
Institute, November 1994
USEPA Report, EPA 542-B-93–005, July 1993
21 Remediation Case Studies: Thermal Desorption, Soil Washing, and In
Situ Vitrification, USEPA Report, EPA-542-R-95–005, March 1995
22 Proceedings, Fifth Forum on Innovative Hazardous Waste Treatment
Technologies: Domestic and International, USEPA Report, EPA/540/
R-94/503, May 1994
23 LaGreca, M.D., Buckingham, P.L., Evans, J.C., Hazardous Waste
Man-agement, McGraw-Hill, Inc., 1994
24 Freeman, H.M (ed.), Standard Handbook of Hazardous Waste
Treat-ment and Disposal, McGraw-Hill, Inc., 1989
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Edition, Van Nostrand Reinhold, 1992
26 Corbitt, R.A (ed.), Standard Handbook of Environmental Engineering,
McGraw-Hill, Inc., 1990
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Effective Policies & Practices, McGraw-Hill, Inc., 1994
REFERENCES
1 PL 95-580, Resource Conservation and Recovery Act of 1976, 42 USC
6901, 1976
2 40 CFR 262
3 40 CFR 263
4 40 CFR 261
5 40 264, 265
6 SW-968, Permit Applicants’ Guidance Manual for the General Facility Standards of 40 CFR 264, Oct 1983
7 Lindgren, G.D., “Managing Industrial Hazardous Waste: A Practical Handbook,” 350 pp., 1989, Lewis Publ., Boca Raton, FL
8 Industrial Pollution Prevention Planning, Meeting Requirements Under the New Jersey Pollution Prevention Act, New Jersey Department of Environmental protection, Office of Pollution Prevention, September
1985, Second Edition
9 Grube, W.E., Jr., “Evaluation of Waste Stabilized by the Solid Tech Site
Technology,” J Air Waste Manag Assoc , 40 310 (1990)
RICHARD T DEWLING GREGORY A PIKUL
Dewling Associates, Inc