Composting Applied To Contaminated Sites
Presented To: Dr. Michael Broaders
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The Project Is Submitted In Part Fulfillment Of The BSc.(Year 4) In
Environmental Science & Technology Requirement For Waste
Management
"Composting Applied To Contaminated Soil"
Was Undertaken By:
Nevin Traynor,
Martina Mulligan,
And
Oliver Fitzsimmons
Table Of Contents:
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Section Contents 1.0 Introduction 2.0 Main Types Of Composting
2.1 Landfarming 2.2 Biopiles 2.3 Windrow 2.4 Bioventing 3.0 Type Of Co-Composting
3.1 Slurry-phase Bioremediation
4.0 Addational Methods Of Composting
4.1 Injection Of Hydrogen Peroxide 4.2 PX-700 4.3 Bioslurping 4.4 Hydronamic In-situ Treatment (injection tm)
5.0 Conclusion 6.0 References 1.0 Introduction
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A problem that many landowners are faced with in today's environmentally conscious
society is the cleanup of contaminated soils. Often, with contaminated soil, petroleum
based products are the type of contaminant which is found. There are a number of
process designs used in composting.
Composting is defined as a controlled biological process by which organic
contaminants (e.g., PAHs) are converted by microorganisms (under aerobic and
anaerobic conditions) to innocuous, stabilised byproducts. Typically, thermophilic
conditions of 54 to 65 °C must be maintained to properly compost soil contaminated
with hazardous organic contaminants. The increased temperatures result from heat
produced by microorganisms during the degradation of the organic material in the
waste. In most cases, this is achieved by the use of indigenous microorganisms.
Maximum degradation efficiency is achieved through maintaining oxygenation (e.g.,
daily windrow turning), irrigation as necessary, and closely monitoring moisture
content, and temperature. These hydrocarbon contaminated soils may be cleaned in
several ways. If Volatile Organic Compounds (VOC) or Semi Volatile Organic
Compounds (SVOC) contaminants are present in soils, off-gas control may be
required.
Bioremediation, the process of using living organisms (usually bacteria, fungi,
actinomycetes, cyanobacteria and to a lesser extent, plants) to reduce or eliminate
toxic pollutants. These organisms may be naturally occurring or laboratory cultivated.
Certain microorganisms can digest organic substances such as fuels or solvents that
are hazardous to humans. The microorganisms break down the organic contaminants
into harmless products, mainly carbon dioxide and water.
Once the contaminants are degraded, the microorganism population is reduced
because they have used their entire food source. Dead microorganisms or small
populations in the absence of food pose no contamination risk.
Bioremediation harnesses this natural process by promoting the growth and/or rapid
multiplication of these organisms that can effectively degrade specific contaminants
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and convert them to non-toxic by-products. Importantly, bioremediation can also be
used in conjunction with a wide range of traditional physical and chemical
technologies to enhance their efficiency.
Bioremediation results vary depending on the level, type and age of contaminants
involved as well as the site conditions, such as temperature, weather, and soil or water
chemistry. Total Petroleum Hydrocarbon reduction requires a period of between 90
and 150 days, but it could take up to 18 months.
There are two methods of bioremediation: Augmented and Non-augmented.
Augmented bioremediation involves adding microbes that break down contaminants
to the soil. Non-augmented bioremediation uses chemicals to activate the local
microbes already present in the soil to breakdown the unwanted elements.
Before implementing any bioremediation scheme, you would need to conduct an
environmental audit of the site to determine the type of contaminant and whether
biotechnology would offer a suitable cure. At the moment, treatable contaminants
include: grease, hydraulic and lubricating fluids, petrol, antifreeze, brake fluids, oil,
diesel and paint thinner. The scale and levels of contamination are critical to a site
evaluation, as is the soil condition and the target standard. Also, this audit would
establish whether the soil needed to be removed, to be treated, or whether everything
could be sorted out on site.
The microbes' necessary must be dispersed throughout the soil. These microbes have
to be activated before being applied; usually by being mixed with water. This
solution is then added to the soil by a variety of techniques. Methods range from
simply spraying it on the surface of the contaminated area to dispersing it by
perforated plastic tubes sunk in the ground.
In order to sustain efficient rates of hydrocarbon degradation, the biopile environment
must provide certain essential elements to promote bacterial population growth.
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The most efficient form of hydrocarbon degradation is accomplished by aerobic
bacteria. To survive, aerobic bacteria need oxygen, moisture and nutrients.
Bioremediation is estimated to cost 30-50% less than conventional cleanup
techniques, such as landfill or incineration. Environmentally, bioremediation offers a
better solution as the contaminants are broken down completely rather than simply
transported to another site or released into the atmosphere.
There is a number of steps in preparing a sound design for bio-treatment of
contaminated soil, these include:
Site characterisation.
• Soil sampling and characterisation.
• Contaminant characterisation.
• Laboratory and/or field treatability studies.
• Pilot testing and/or field demonstrations.
Site, soil, and contaminant characterisations will be used to:
• Identify and quantify contaminants.
• Determine requirements for organic and inorganic amendments.
• Identify potential safety issues.
• Determine requirements for excavation, staging, and movement of contaminated soil.
• Determine availability and location of utilities (electricity and water).
Laboratory or field treatability studies are needed to identify:
• Amendment mixtures that best promote microbial activity.
• Potential toxic degradation byproducts.
• Percent reduction and lower concentration limit of contaminant achievable.
• The potential degradation rate.
Bioremediation applications fall into two broad categories: In-situ and Ex-situ.
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In-situ techniques does not require excavation of the contaminated soils so it may be
less expensive, create less dust, and cause less release of contaminants than ex-situ
techniques. Also, it is possible to treat a large volume of soil at once. However In-
situ techniques, may be slower than ex situ techniques, it may be difficult to manage,
and are most effective at sites with permeable (sandy or uncompacted) soil.
In most cases, indigenous bacteria present in petroleum contaminated soil break down
petroleum hydrocarbons, which are a source of energy for the bacteria.
The advantage of treating petroleum contaminated soils using ex-situ techniques is the
ability to amend the contaminated soil with nutrients, bacteria and bulking agents.
By amending the contaminated soil, it is possible to construct a biopile with a more
conducive environment for bacterial growth, thus accelerating the breakdown of
petroleum compounds in the soil as compared to natural attenuation in-situ.
Petroleum compounds alone do not supply all the nutrients required by soil bacteria.
Nutrients already present in the soil vary from one soil type to another.
A common ratio to determine appropriate nutrient requirements is 100 parts total
carbon to 10 parts nitrogen to 1 part phosphorus.
Bacterial degradation occurs through a range of moisture field capacities of
approximately 20 to 80 percent. The optimum moisture field capacity for biopiles is
approximately 40 percent. This concentration represents a balance between having an
adequate supply of water in the soil matrix pore spaces without preventing effective
diffusion of oxygen.
2.0 Main Composting Methods Used In Bioremediation
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2.1 Landfarming
Landfarming, also known as land treatment or land application, is an aboveground
remediation technology for soils that reduces concentrations of petroleum constituents
through biodegradation. This technology usually involves spreading excavated
contaminated soils in a thin layer on the ground surface and stimulating aerobic
microbial activity within the soils through aeration and/or the addition of minerals,
nutrients, and moisture. The enhanced microbial activity results in degradation of
adsorbed petroleum product constituents through microbial respiration. If
contaminated soils are shallow (i.e., less than 3 feet below ground surface), it may be
possible to effectively stimulate microbial activity without excavating the soils. If
petroleum-contaminated soil is deeper than 5 feet, the soils should be excavated and
reapplied on the ground surface
Application
Landfarming has been proven effective in reducing concentrations of nearly all the
constituents of petroleum products typically found at underground storage tank (UST)
sites. Petroleum products generally encountered at Underground Storage Tank sites
range from those with a significant volatile fraction, such as gasoline, to those that are
primarily nonvolatile, such as heating and lubricating oils.
Petroleum products generally contain more than one hundred different constituents
that possess a wide range of volatility. In general, gasoline, kerosene, and diesel fuels
contain constituents with sufficient volatility to evaporate from a landfarm. Lighter
(more volatile) petroleum products (e.g., gasoline) tend to be removed by evaporation
during landfarm aeration processes (i.e., tilling or plowing) and, to a lesser extent,
degraded by microbial respiration.
The mid-range hydrocarbon products (e.g., diesel fuel, kerosene) contain lower
percentages of lighter (more volatile) constituents than does gasoline. Biodegradation
of these petroleum products is more significant than evaporation. Heavier (non-
volatile) petroleum products (e.g., heating oil, lubricating oils) do not evaporate
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during landfarm aeration; the dominant mechanism that breaks down these petroleum
products is biodegradation. However, higher molecular weight petroleum constituents
such as those found in heating and lubricating oils, and, to a lesser extent, in diesel
fuel and kerosene, require a longer period of time to degrade than do the constituents
in gasoline.
Operation Principles
Soil normally contains large numbers of diverse microorganisms including bacteria,
algae, fungi, protozoa, and actinomycetes. In well-drained soils, which are most
appropriate for landfarming, these organisms are generally aerobic. Of these
organisms, bacteria are the most numerous and biochemically active group,
particularly at low oxygen levels. Bacteria require a carbon source for cell growth and
an energy source to sustain metabolic functions required for growth. Bacteria also
require nitrogen and phosphorus for cell growth. Although sufficient types and
quantities of microorganisms are usually present in the soil, recent applications of ex-
situ soil treatment include blending the soil with cultured microorganisms or animal
manure (typically from chickens or cows). Incorporating manure serves to both
augment the microbial population and provide additional nutrients.
The metabolic process used by bacteria to produce energy requires a terminal electron
acceptor (TEA) to ensymatically oxidize the carbon source to carbon dioxide.
Microbes are classified by the carbon and TEA sources they use to carry out
metabolic processes. Bacteria that use organic compounds (e.g., petroleum
constituents and other naturally occurring organic) as their source of carbon are
heterotrophic; those that use inorganic carbon compounds (e.g., carbon dioxide) are
autotrophic. Bacteria that use oxygen as their TEA are aerobic; those that use a
compound other than oxygen, (e.g., nitrate, sulfate), are anaerobic; and those that can
utilise both oxygen and other compounds as TEAs are facultative. For landfarming
applications directed at petroleum products, only bacteria that are both aerobic (or
facultative) and heterotrophic are important in the degradation process.
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The effectiveness of landfarming depends on parameters that may be grouped
into three categories:
1. Soil characteristics
2. Constituent characteristics
3. Climatic conditions.
1.Soil Characteristics:
Soil texture affects the permeability, moisture content, and bulk density of the soil. To
ensure that oxygen addition (by tilling or ploughing), nutrient distribution, and
moisture content of the soils can be maintained within effective ranges, you must
consider the texture of the soils. For example, soils that tend to clump together (such
as clays) are difficult to aerate and result in low oxygen concentrations. It is also
difficult to uniformly distribute nutrients throughout these soils. They also retain
water for extended periods following a precipitation event.
2.Constituent Characteristics:
The volatility of contaminants proposed for treatment by landfarming is important
because volatile constituents tend to evaporate from the landfarm, particularly during
tilling or ploughing operations, rather than being biodegraded by bacteria.
Controlling of volatile organic compounds (VOCs) before they are emitted to the
atmosphere maybe required by passing them through an appropriate treatment process
before being vented to the atmosphere. Control devices range from erected structures
such as a greenhouse or plastic tunnel to a simple cover such as a plastic sheet.
Although nearly all constituents in petroleum products typically found at UST sites
are biodegradable, the more complex the molecular structure of the constituent, the
more difficult and less rapid, is biological treatment. Most low molecular weight
(nine carbon atoms or less) aliphatic and monoaromatic constituents are more easily
biodegraded than higher molecular weight aliphatic or polyaromatic organic
constituents.
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3.Climatic Factors:
Typical landfarms are uncovered and, therefore, exposed to climatic factors including
precipitation and wind, as well as ambient temperatures. Rainwater that falls directly
onto, or runs onto, the landfarm area will increase the moisture content of the soil and
cause erosion. During and following a significant precipitation event, the moisture
content of the soils may be temporarily in excess of that required for effective
bacterial activity. On the other hand, during periods of drought, moisture content may
be below the effective range and additional moisture may need to be added. Erosion
of landfarm soils can occur during windy periods and particularly during tilling or
ploughing operations. Wind erosion can be limited by ploughing soils into windrows
and applying moisture periodically. In very cold climates, special precautions can be
taken, including enclosing the landfarm within a greenhouse-type structure or
introducing special bacteria (psychrophiles), which are capable of activity at lower
temperatures. In warm regions, the landfarming season can last all year.
System Design
Landfarm Construction Includes: site preparation (grubbing, clearing and grading);
ditches; liners (if necessary); leachate collection and treatment systems; soil pre-
treatment methods (e.g., shredding, blending and amendments for fluffing, pH
control); and enclosures and appropriate vapour treatment facilities (where needed).
This technology involves the construction of an engineered treatment cell. This cell
consists of a synthetic liner (only required if leachate has the potential to cause
groundwater contamination) covered by a layer of sand. Plastic drain tiles are placed
in the cell within the sand layer. The sand layer provides a drainage system for
liquids by gravity flow to a collection area. Collected liquids are pumped to an
aboveground holding tank for application to the treatment cell as a supplementary
moisture source or for discharge to a public owned treatment works. A ditch like
structure cell called a "Berm" is constructed around the cell parameters to:
(a) contain run-off within the cell,
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(b) divert it so it does not contact the contaminated soil
To support bacterial growth, the soil pH should be within the 6 to 8 range, with a
value of about 7 (neutral) being optimal. Soils with pH values outside this range prior
to landfarming will require pH adjustment prior to and during landfarming operations.
Soil pH within the landfarm can be raised through the addition of lime and lowered by
adding elemental sulfur.
Soil microorganisms require moisture for proper growth. Excessive soil moisture,
however, restricts the movement of air through the subsurface thereby reducing the
availability of oxygen that is also necessary for aerobic bacterial metabolic processes.
In general, the soil should be moist but not wet or dripping wet. The ideal range for
soil moisture is between 40 and 85 percent of the water-holding capacity (field
capacity) of the soil or about 12 percent to 30 percent by weight. Periodically,
moisture must be added in landfarming operations because soils become dry as a
result of evaporation, which is increased during aeration operations (i.e., tilling and/or
ploughing). Excessive accumulation of moisture can occur at landfarms in areas with
high precipitation or poor drainage. These conditions should be considered in the
landfarm design. For example, an impervious cover can mitigate excessive
infiltration and potential erosion of the landfarm.
Water management systems for control of run-on and runoff are necessary to avoid
saturation of the treatment area or washout of the soils in the landfarm. Run-on is
usually controlled by ditches that intercept and divert the flow of storm-water.
A leachate collection system at the bottom of the landfarm and a leachate treatment
system may also be necessary to prevent groundwater contamination from the
landfarm.
Soil Erosion Control from wind or water generally includes terracing the soils into
windrows, constructing water management systems, and spraying to minimize dust.
Microorganisms require inorganic nutrients such as nitrogen and phosphorus to
support cell growth and sustain biodegradation processes. Nutrients may be available
in sufficient quantities in the site soils but, more frequently, nutrients need to be added
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to landfarm soils to maintain bacterial populations. However, excessive amounts of
certain nutrients (i.e., phosphate and sulphate) can repress microbial metabolism.
If the site is located in an area subject to annual rainfall of greater than 30 inches
during the landfarming season, a rain shield (such as a tarp, plastic tunnel, or
greenhouse structure) should be considered in the design of the landfarm.
pH adjustment and nutrient supply methods usually include periodic application of
solid fertilizers, lime and/or sulfur while disking to blend soils with the solid
amendments, or applying liquid nutrients using a sprayer. The composition of
nutrients and acid or alkaline solutions/solids for pH control is developed in
biotreatability studies and the frequency of their application is modified during
landfarm operation as needed.
Air Emission Controls (e.g., covers or structural enclosures) may be required if
volatile constituents are present in the landfarm soils. For compliance with air quality
regulations, the volatile organic emissions should be estimated based on initial
concentrations of the petroleum constituents present. Vapours above the landfarm
should be monitored during the initial phases of landfarm operation for compliance
with appropriate permits or regulatory limits on atmospheric discharges. If required,
appropriate vapour treatment technology should be specified, including operation and
monitoring parameters.
It is important to make sure that system operation and monitoring plans have been
developed for the landfarming operation. Regular monitoring is necessary to ensure
optimisation of biodegradation rates, to track constituent concentration reductions,
and to monitor vapour emissions, migration of constituents into soils beneath the
landfarm (if unlined), and groundwater quality.
Advantages and Disadvantages
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Advantages
Disadvantages
Relatively simple to design and implement.
Concentration reductions greater than 95%
and constituent concentrations less than 0.1
ppm are very difficult to achieve.
Short treatment times (usually six months to
two years under optimal conditions).
May not be effective for high constituent
concentrations (greater than 50,000 ppm total
petroleum hydrocarbons).
Cost competitive: $30-60/ton of
contaminated soil.
Presence of significant heavy metal
concentrations (greater than 2,500 ppm) may
inhibit microbial growth.
Effective on organic constituents with slow
biodegradation rates
Volatile constituents tend to evaporate rather
than biodegrade during treatment.
Requires a large land area for treatment.
Dust and vapor generation during landfarm
aeration may pose air quality concerns.
May require bottom liner if leaching from the
landfarm is a concern.
2.2 Biopiles
A Biopile is defined as an aerated static pile composting process in which compost is
formed into piles and aerated with blowers or vacuum pumps.
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Biopiles, are also known as biocells, bioheaps, biomounds, and compost piles.
Excavated soils are mixed with soil amendments and placed in above ground
enclosures. The "heap" method or "compost pile" method of bioremediation involves
the placement of the soils into a pile over a prepared bed of aeration piping on a
plastic liner.
Biopiles are similar to landfarms in that they are both above-ground, engineered
systems that use oxygen, generally from air, to stimulate the growth and reproduction
of aerobic bacteria which, in turn, degrade the petroleum constituents adsorbed to soil.
While landfarms are aerated by tilling or ploughing, biopiles are aerated most often by
forcing air to move by injection or extraction through slotted or perforated piping
placed throughout the pile.
Application:
Are used to reduce concentrations of petroleum constituents in excavated soils through
the use of biodegradation. Biopile treatment has been applied to treatment of Non
Halogenated Volatile Organic Compounds and fuel hydrocarbons. Halogenated
Volatile Organic Compounds, Semi Volatile Organic Compounds, and Pesticides also
can be treated, but the process effectiveness will vary and may be applicable only to
some compounds within these contaminant groups.
Technology Description :
This technology involves heaping contaminated soils into piles and stimulating
aerobic microbial activity within the soils through the aeration and/or addition of
minerals, nutrients, and moisture. Contaminated soil is piled in heaps several meters
high over an air distribution system.
Aeration is provided by pulling air through the heap with a vacuum pump.
Moisture and nutrient levels are maintained at levels that maximise bioremediation.
The soil heaps can be placed in enclosures. Volatile contaminants are easily
controlled since they are usually part of the air stream being pulled through the pile.
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The enhanced microbial activity results in degradation of adsorbed petroleum-product
constituents through microbial respiration.
The plastic liner bed or cell for heap method bioremediation is prepared in the same
manner as the landfarming cell, but the overall amount of space required for the heap
method cell is considerably less.
For example, the 300 cubic yard pile of the "typical" contaminated soil would be
placed into a pile as follows :
300 cubic yards shaped into a pile with a cross section of a 40 foot width piled 5 feet
high with a 45 degree slope on the sides has a volume of 162.5 cubic feet per linear
foot. Therefore, each linear foot has a capacity of 162.5 cubic feet divided by 27
cubic feet per cubic yard = 6.0 cubic yards per linear foot, and the site would require :
300 cubic yards / 6.0 yards per linear foot cross section = 50 linear feet
Overall, the heap method site would require an area of approximately 40' X 50' or
2000 square feet, which is approximately 1/4 of the area required for the landfarming
method.
Once the area required for the treatment cell has been defined, the layout of the piping
network and the quantity of piping required can be calculated.
The use of standard 4" PVC Sewer is recommended and drain tile for the aeration
piling. The Piping network is constructed with the pipes laid out on 5 foot centers
with a header pipe at either or both ends of the pile, depending upon the overall pile
length.
In the event that a smaller area is all that is available, the piles can be constructed to
be higher with steeper sides, but this will require that an additional set of aeration
pipes be installed.
Testing of the soil pile should follow those guidelines for a landfarming style project
with monthly sampling events for analytical and biological parameters.
Effectiveness Of Treatment
The degradation of hydrocarbons by introducing air are subject to the "law of
asymptotes." This means that the rate of degradation falls on a half-life curve
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(logarithmic decay), such that it becomes incrementally more difficult to degrade
contaminants over time. Under these conditions, it will take as long to go from
600 ppm to 300 ppm, in a latter phase of clean-up, as it does to go from 10,000 ppm
to 5,000 ppm in an initial
The mid-range hydrocarbon products (e.g., diesel fuel, kerosene) contain lower
percentages of lighter (more volatile) constituents than does gasoline. Biodegradation
of these petroleum products is more significant than evaporation. Heavier (non-
volatile) petroleum products (e.g., heating oil, lubricating oils) do not evaporate
during biopile aeration; the dominant mechanism that breaks down these petroleum
products is biodegradation. However, higher molecular weight petroleum constituents
such as those found in heating and lubricating oils, and to a lesser extent, in diesel fuel
and kerosene, require a longer period of time to degrade than do the constituents in
gasoline. Biopile treatment has been demonstrated for fuel-contaminated sites.
Where Has It Been Used
The Minnesota Department of Transportation in the United States Of America has
developed a low technology composting treatment alternative. They have been
recycling petroleum contaminated soil, animal manure and low grade wood chips in
an environmentally sound process since 1991.
Minnesota Department Of Transportation has successfully treated several thousand
cubic meters of excavated petroleum contaminated soils by using the biopile treatment
technique. The process has not only been effective but also has the advantage of
being generally accepted by local bodies of government and the public with little
opposition. Because the process is low maintenance, the biopile technique has shown
substantial cost savings over alternative treatments.
Minnesota Department of Transportation has removed hundreds of fuel underground
storage tanks from their various maintenance facilities, and during highway
construction projects since 1988. The majority of these tank removals have
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encountered petroleum contaminated soil as a result of leaking tank systems or spills
experienced during product delivery.
The Minnesota Pollution Control Agency (MPCA) requires treatment of excavated
petroleum contaminated soil to a current cleanup threshold for soils treated by
landspreading or biopile technology of 10 ppm as total petroleum hydrocarbons.
During the late 1980s, Minnesota Department of Transportation primarily treated the
contaminated soil by land application. Minnesota regulations generally allow only a
single application of petroleum contaminated soils at an approved landspread location.
In 1993 the EPA expressed interest in Minnesota Department of Transport successes
with passive aeration biopiles. A grant from the EPA, aided the Minnesota
Department of Transport constructed biopiles for the bioremediation of various soils
with various soil amendments.
Economic analysis
Costs are dependent on the contaminant, procedure to be used, n
post-treatment, and need for air emission control equipment. Bi
and require few personnel for operation and maintenance. Typ
bed and liner are $130 to $260 per cubic meter ($100 to $200 pe
Advantages And Disadvantages
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Advantages Disadvantages
Relatively simple to design and
implement.
Concentration reductions 95% and
constituent concentrations 0.1 ppm are
very difficult to achieve.
Short treatment times: usually 6 months
to 2 years under optimal conditions.
May not be effective for high constituent
concentrations ( 50,000 ppm total
petroleum hydrocarbons).
Cost competitive: $30-90/ton of
contaminated soil.
Presence of significant heavy metal
concentrations ( 2,500 ppm) may inhibit
microbial growth.
Effective on organic constituents with
slow biodegradation rates.
Volatile constituents tend to evaporate
rather than biodegrade during treatment.
Requires less land area than landfarms. Requires a large land area for treatment,
although less than landfarming.
Can be designed to be a closed system;
vapor emissions can be controlled.
Vapor generation during aeration may
require treatment prior to discharge.
Can be engineered to be potentially
effective for any combination of site
conditions and petroleum products.
May require bottom liner if leaching
from the biopile is a concern.
.
2.3 Windrow Composting
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Windrow composting is usually considered to be the most cost-effective composting
alternative. Meanwhile, it may also have the highest fugitive emissions. If VOC or
SVOC contaminants are present in soils, off-gas control may be required. Windrow
composting is a process that biodegrades aerobically organic material and with the
production of heat, destroys pathogens, producing a stabilized compost product for
use as mulch, soil conditioner, and topsoil additive.
System Design
After contaminated soil is excavated, large rocks and debris are removed.
Amendments such as straw, alfalfa, manure and agricultural wastes are then added.
The organic material is left to decompose outdoors, aided only by watering and
mechanical turning for aeration. This method is simple, non-intensive, has a very low
capital cost. It is the slowest large scale method used to produce compost.
Oxygen and temperature are key environmental parameters that must be maintained
within a specific range to provide optimum conditions for the microorganisms. The
temperature must be high enough to kill pathogens and weed seeds but not kill the
microorganisms as well. The process of decomposition produces heat, and the
organic material itself provides insulation. Oxygen is required for aerobic
decomposition. A well aerated and properly mixed compost pile should not produce
unpleasant odours.
Compost is formed into long piles called windrows that are typically 1.5 to 3.0 meters
high, three to six meters wide, and up to 100 meters or more in length. Windrows can
be placed directly on the soil or paved area. The land requirement for a windrow
composting facility is dependent on the volume of material processed. Generally, all
of the materials handling and pile building can be accomplished with a front-end
loader. The windrows can be aerated mechanically by turning with a front end loader
for smaller operations or using a windrow turner.
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Moisture, pH, temperature, and contaminant concentrations are monitored. At the
completion of the composting period the windrows are disassembled and the compost
is taken to the final disposal area.
Economic Analysis:
The cost of constructing and operating a windrow composting facility will vary from
one location to another. The operating costs are dependent on the volume of material
processed, the soil fraction in the compost, availability of amendments, the type of
contaminant, and the type of process design employed. The use of additional feed
materials, such as paper and mixed municipal solid waste, will require additional
capital investment and materials processing labor. The capital costs include compost
pads, grinder, compost mixer, trommel screen, front end loader, windrow turner, and
offices. Estimated costs for full-scale windrow composting of explosives-
contaminated soils are approximately $190 per cubic yard for soil volumes of
approximately 20,000 yd3. Estimated costs for static pile composting and
mechanically agitated in vessel composting are $236 and $290, respectively.
Composting may be an economic alternative to thermal treatment, however, when
cleanup criteria and regulatory requirements are suitable.
Application
Windrow composting has been demonstrated as an effective technology for treatment
of explosives-contaminated soil. During a field demonstration conducted by USAEC
and the Umatilla Depot Activity (UMDA), TNT reductions were as high as 99.7% in
40 days of operation, with the majority of removal occurring in the first 20 days of
operation. Maximum removal efficiencies for RDX and HMX were 99.8% and
96.8%, respectively. The relatively simple equipment requirements combined with
these performance results make windrow composting economically and technically
attractive.
Advantages And Disadvantages
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Advantages Disadvantages
Rapid drying of wet material during
turning It is not space efficient.
Drier compost resulting in easier
separation of bulking agent (if any)
during screening
Equipment maintenance costs may be
considerable
Capacity to handle high volumes of
material
Requires careful monitoring to assure aeration and temperature rise are adequate to assure odor control
and pathogen destruction.
Good product stabilization Odor release when piles are turned may
become public relations problem
Relatively low capital investment
Composting process may be adversely affected or delayed by
rain. Enclosure of the system increases capital costs.
Requires larger volume of bulking agent
than in-vessel systems.
2.4 Bioventing
Bioventing is a process that makes use of bioremediation and soil vapor extraction.
Airflows are sustained at a level that maintains oxygen in the subsurface soil.
Microorganisms in the soil can then biodegrade volatile as well as nonvolatile
contaminants under the proper environmental conditions.
Volatile emissions to the atmosphere are reduced as substantial quantities of volatile
compounds are biodegraded in the soil rather than stripped to the surface. Costs for
activated carbon trapping of the volatiles, typically a substantial cost in operations
such as these, are thus reduced.
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Effectiveness Of Treatment
Bioventing is considered optimal in cases where the contaminant is of marginal
volatility or highly miscible but is aerobically biodegradable. In this process, oxygen,
generally the parameter that most limits the biodegradation process, is delivered to the
source area to enhance biological activity. Bioventing can provide the simplest and
least expensive means of oxygen delivery by circulating the oxygen available in the
atmosphere. Additional nutrients, generally, nitrogen and phosphorous, can be
supplied to the contaminated soil zone if also required.
Application
Bioventing systems deliver air from the atmosphere into the soil above the water table
through injection wells placed in the ground where the contamination exists. The
number, location, and depth of the wells depend on many geological factors and
engineering considerations.
Bioventing has the capability of addressing semivolatiles: nutrients (usually nitrogen
and phosphorous), in conjunction with the enhanced oxygen environment.
Bioventing therefore addresses more difficult semivolatiles, and with bioventing,
biodegradation is enhanced by the air movement and concentrations in the resulting
off-gas can often be reduced with the appropriate design.
Bioventing has proven to be an efficient and economical technology for remediating
soils contaminated with petroleum hydrocarbons. It is among the most effective
methods of supplying indigenous microorganisms with enough oxygen to support
degradation of hydrocarbon contaminants. An air blower may be used to push or pull
air into the soil through the injection wells. Air flows through the soil and the
oxygen in it is used by the microorganisms. Nutrients may be pumped into the soil
through the injection wells. Nitrogen and phosphorous may be added to increase the
growth rate of the microorganisms.
Site Evaluation
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There is a four-step site evaluation protocol to determine the suitability of a site for
remediation by bioventing. These steps are conducted sequentially for rapid
screening of sites:
(i) Soil-Gas Survey:
A soil-gas survey is conducted at a candidate site to determine whether the subsurface
is oxygen limited. Soil gas is withdrawn from the ground and analyzed for oxygen
and carbon dioxide content to determine the site's amenability to bioventing.
(ii) Soil Permeability Testing:
A soil-gas permeability test is conducted to determine whether air can be injected at
rates sufficient to aerate the soil. The test involves injection/withdrawal of air and
measuring the changes in subsurface pressures at discrete distances from the point of
injection. The resulting data are fed into a computer program that calculates the soil
gas permeability. Soils that demonstrate sufficient permeability are prime candidates
for bioventing.
(iii) In Situ Respirometry:
Once the soils have been determined to be oxygen limited and sufficiently permeable,
an in situ respiration test to determine biological degradation rates in the contaminated
soils and compare them to background respiration rates in an uncontaminated area.
Typically, the tests involve aerating the soils for a 24-hour period followed by
monitoring the oxygen and carbon dioxide levels in the soil gas after terminating the
air injection. The oxygen utilization rate is then translated into hydrocarbon
degradation rates, which can be used to calculate an estimate of the amount of time
that will be required to remediate the site.
(iv) Pilot-And Full-Scale Remediation Projects:
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The need for pilot testing prior to full-scale remediation is determined by evaluating
the contamination and site characteristics. Pilot-scale demonstrations can be
conducted and designed for full-scale remediation projects or provide full-scale
remediation services leading up to and including site closure.
Bioventing Feasibility Studies
Petroleum hydrocarbons are aerobically biodegradable. However, natural
biodegradation of contaminants quickly becomes oxygen-limited because
hydrocarbon-degrading bacteria use oxygen more rapidly than it diffuses into the
soil from the atmosphere. Bioventing enhances natural biodegradation by
supplying indigenous hydrocarbon-degrading bacteria with oxygen.
Where Has It Been Used :
ABB ENVIRONMENTAL SERVICES implemented a bioventing system at a vehicle
maintenance facility in Southern California. Diesel fuel and gasoline contamination
were present to a depth of 60 feet in sandy soil and groundwater is approximately 110
feet below surface. Total Petroleum Hydrocarbons levels varied, but were as high as
1,000 mg/kg.
Bioventing in site soil reduced VOC's to below a 0.5 ppm and identifiable SVOC's by
98 percent. Biodegradation was responsible for 80 to 95 percent of VOC reduction.
The capital and one year operating costs are expected to be $275,000.
Terra Vac, a U.S based environmental bioremediation company, have successfully
applied BIOVAC (R) technology to many sites in the United States. Terra Vac
successfully remediated sites having extremely tight soils by utilizing pneumatic
fracturing in conjunction with vapor extraction. For sites which have groundwater
containing volatile or semivolatile contaminants, Terra Vac's Dual Extraction (TM) or
entrainment extraction process can be used in conjunction with vapor extraction to
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successfully remediate the soil and groundwater simultaneously. For groundwater
containing high levels of volatile or semivolatile contaminants, Terra Vac's Sparge
Vac (TM) system can remediate the groundwater in situ with substantial cost savings
over the traditional pump and treat technology if site conditions are suitable.
Economic analysis
The cost of a bioventing approach varies greatly with the site conditions and
remediation strategy selection. As a baseline comparison, a 2,000 square foot areas
contaminated at the depth from 2' to 10' below ground surface in permeable soils with
average diesel levels of 2,000 mg/kg, may requre a total project funding of $40,000 to
$60,000 to obtain site design information, design and construction of the treatment
system, and operation and monitoring of the treatment system for a two year treatment
period. Economy of scale is realised on bioventing projects due to the relatively fixed
cost of the blower system and monitoring.
Advantages And Disadvantages
Advantages Disadvantages
The system provides low cost, in situ
passive remediation of a variety of
compounds.
The system is not appropriate for metals
and other compounds that are not
biodegradable or volatile.
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Bioventing increases the volatilization
of volatile organic compounds (VOC)
into the vapor phase while optimal
conditions are increased for the
biodegradation of the remaining
semivolatile compounds.
Complex soils may limit the performance
of the system. Indigenous microorganisms
capable of synthesizing site contaminants
may be limited depending on subsurface
conditions
The system requires relatively low
maintenance and operational costs. It
also provides treatment on site and in
situ, thereby reducing long-term
liability associated with off-site options
Bioventing is not cost-effective for
treating soil contaminated with chlorinated
solvent or pesticides in the absence of
significant amounts of degradable organic
compounds such as petroleum wastes.
In situ treatment also allows for
minimal disturbance of a site while
treatment is occurring.
Bioventing, similiar to air sparging, may
require expensive air controls.
Bioventing provides treatment of a
broad spectrum of contaminants.
Bioventing is dependent upon the rate at
which the biological degradation will take
place, and may require extensive treatment
time-frames.
The site must be capable of supporting
drilling operations in the locations where
the vapor extraction wells are desired.
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3.0 Type Of Co-Composting
3.1 Slurry-phase bioremediation.
In Slurry-phase bioremediation contaminated soil are combined with water and other
additives in a large tank called a "bioreactor" and mixed to keep the microorganisms -
- which are already present in the soil -- in contact with the contaminants in the soil.
Nutrients and oxygen are added, and conditions in the bioreactor are controlled to
create the optimum environment for the microorganisms to degrade the contaminants.
Upon completion of the treatment, the water is removed from the solids, which are
disposed of or treated further if they still contain pollutants.
Effectiveness Of Treatment
Slurry-phase biological treatment can be a relatively rapid process compared to other
biological treatment processes, particularly for contaminated clays.
The success of the process is highly dependent on the specific soil and chemical
properties of the contaminated material. This technology is particularly useful where
rapid remediation is a high priority.
Where Has It Been Used
At the French Ltd. Superfund site in Texas, slurry-phase bioremediation was used to
treat 300,000 tonnes of lagoon sediment and tar-like sludge contaminated with
volatile organic compounds, semi-volatile organic compounds, metals, and
pentachlorophenol, over a period of 11 months. The treatment system was able to
meet the cleanup goals set by Environmental Protection Agency in The United States
Of America.
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4.0 Additional Methods Of Composting
4.1 Injetion of Hydrogen Peroxide.
This process delivers oxygen to stimulate the activity of naturally occurring
microorganisms by circulating hydrogen peroxide through contaminated soils to speed
the bioremediation of organic contaminants. Since it involves putting a chemical
(hydrogen peroxide) into the ground (which may eventually seep into the
groundwater), this process is used only at sites where the groundwater is already
contaminated. A system of pipes or a sprinkler system is typically used to deliver
hydrogen peroxide to shallow contaminated soils. Injection wells are used for deeper
contaminated soils.
4.2 PX-700
PX-700 is a natural plant extract from kelp meal and aloe. Two terms used to define
PX-700 would be bioenhancer or bacterial nutrient. PX-700 stimulates the
microorganisms already present in the environment. As a result of this stimulation,
the microorganisms become increasingly active and will feed on the food supply
provided by organic mater or hydrocarbons. As long as you provide the
microorganisms with a food supply and the nutrient PX-700 they will maintain a high
level of activity.
Application:
Two important considerations when dealing with bioremediation and the use of PX-
700 are the pH of the contaminated soil and the use of harsh chemicals such as
pesticides. The pH of the soil must be in a range that microorganisms will not be able
to thrive. Harsh chemicals present in you soil will also restrict the activity of any
microorganisms. The important thing to remember is that the microorganisms are
living creatures and need to be treated as such.
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Benefits Of Using PX-700:
The benefits of using PX-700 for soil bioremediation are numerous. One is to speed
up the time needed to clean up the site. By activating the microorganisms with PX-
700 and putting them to work for you, the clean-up may be accomplished two or three
times faster than without PX-700. After treatment with PX-700 the microorganisms
are more resilient to changes in their environment. The method of application is very
easy and special handling or precautions need be taken by employees. The
remediation may be done on-site, thereby avoiding the high costs of transporting the
soil to a treatment plant and then having the soil returned.
Quantity of PX-700 Required:
Each individual site needs to be evaluated separately to adequately address the issue
of quantity of PX-700 needed to clean-up the contaminated soil. Information such as
quantity and type of contaminants, local weather conditions, pH of the soil, and
presence of harsh chemicals are important.
4.3 Bioslurping
Bioslurping is a dynamic new technology that combines vacuum-assisted free-product
recovery with bioventing to simultaneously recover free product and remediate the
vadose zone. The bioslurper system withdraws groundwater, free-product, and soil
gas in the same process stream. Groundwater is separated from the free product,
treated (when required), and discharged. Recovered free product can be recycled.
Soil-gas vapor is treated (when required) and discharged. Bioslurper systems are
designed to minimize discharges of groundwater and soil gas to the environment.
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4.4 Hydronamic in situ treatment (Injescol tm)
Description of the technology
The Injecsol technology is an accelerated in situ treatment for contaminated soils and
groundwater. It uses a set of multifunctional injection/extraction points allowing total
hydraulic control and uniform distribution of the treating solutions. Hydrodynamic,
physical, chemical and biological principles are used to leach out the contaminants;
the wash-water is then treated in a mobile physical-chemical unit. The procedure
allows for effective, uniform treatment of a wide variety of contaminants under
varying geological conditions. It is particularly suited to treating soil and
groundwater under buildings or other structures. The restoration work does not
interrupt activities under way in the affected area.
The technology runs under continuous computer control and in most cases a job can
be completed in a few weeks. The decontaminated soil is left on site after
treatment, thereby eliminating a major expense item-transportation.
Performance
The technology requires no excavation before treatment. Special reagents are injected
directly into the soil through a set of injection/extraction points. It is thus possible to
treat areas which are normally difficult to reach (under a building for example).
Treatable contaminants are petroleum products, dangerous chemicals and inorganic
contaminants. Oil extraction can be as much as 1.5 kg/m3/day, and liquid solutions
can be extracted at up to 400 L/min.
The process can achieve a 98% reduction in the monocyclic aromatic hydrocarbons
(benzene, toluene, ethylbenzene, xylene) in the soil or water. Oils and greases can be
reduced to as little as 1000 ppm in soil and 1 mg/L in the liquid effluent.
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Installation and Operation
Installation of the equipment takes about two weeks. The technology can be adapted
to all environments, and the injection points are selected on the basis of site
characteristics (slope, vegetation, infrastructures etc).
The work is done by a team of specialised technicians supervised by an engineer. The
workers comply with construction site safety standards, especially when handling
chemicals.
The equipment runs day and night, consuming about 150 kW of power from a
generator or the regular power supply. To optimise the treatment, biodegradable, non-
toxic surfactants as well as nutrients (nitrogen, phosphorus) are added to the
circulating liquid.
Limitations
The best performance is achieved when:
• the hydraulic conductivity of the soil is greater than 10-6 cm/s;
• the contaminant concentration does not exceed 20%;
• the thickness of the contaminated soil layer is less than 10 m.
Work can be done during the winter if the site is sheltered (a building or a temporary
structure).
Economic Analysis
The cost, between $100 and $250/m3, includes:
• feasibility study (determination of contamination type and laboratory testing);
• installation of the equipment;
• in situ decontamination work;
• effectiveness check;
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5.0 Conclusion
Enormous quantities of organic and inorganic compounds are released into the
environment each year as the result of human activities. In some cases, these releases are
deliberate and well regulated (e.g., industrial emissions) while in other cases they are
accidental and largely unavoidable (e.g., chemical spills). Many of these compounds are
both toxic and persistent in terrestrial and aquatic environments. Soil contamination is the
result of the accumulation of these toxic compounds in excess of permissible levels.
The cost of restoring the burgeoning global inventory of contaminated ecosystems is
virtually incalculable. As a result, government, industry and the public have recognised
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the need for more cost effective alternatives to traditional physical and chemical methods
of contaminant remediation. Bioremediation, the degradation or stabilisation of
contaminants by microorganisms (e.g., bacteria, fungi, actinomycetes, and cyanobacteria)
is a safe, effective, and economic alternative to traditional methods of remediation.
Bioremediation can also be used in conjunction with a wide range of physical and
chemical technologies. Bioremediation alternatives are currently being researched using
a combination of physical, microbiological, chemical and molecular based methods.
.
6.0 References
1.Alexander, M. 1994. Biodegradation and Bioremediation. San Diego, CA: Academic
Press.
2.Flathman, P.E. and D.E. Jerger. 1993. Bioremediation Field Experience. Boca Raton,
FL: CRC Press.
3.Freeman, H.M. 1989. Standard Handbook of Hazardous Waste Treatment and Disposal.
New York, NY: McGraw-Hill Book Company.
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4.Grasso, D. 1993. Hazardous Waste Site Remediation, Source Control. Boca Raton, FL:
CRC Press.
5.Norris, R.D., Hinchee, R.E., Brown, R.A., McCarty, P.L., Semprini, L., Wilson, J.T.,
Kampbell, D.H., Reinhard, M., Bower, E.J., Borden, R.C., Vogel, T.M., Thomas, J.M.,
and C.H. Ward. 1994. Handbook of Bioremediation. Boca Raton, FL:CRC Press.
6.Norris, R.D., Hinchee, R.E., Brown, R.A., McCarty, P.L., Semprini, L., Wilson, J.T.,
Kampbell, D.H., Reinhard, M., Bower, E.J., Borden, R.C., Vogel, T.M., Thomas, J.M.,
and C.H. Ward. 1993. In-Situ Bioremediation of Ground Water and Geological Material:
A Review of Technologies. Ada, OK: U.S. Environmental Protection Agency, Office of
Research and Development. EPA/5R-93/124.
7.Pope, Daniel F., and J.E. Matthews. 1993. Environmental Regulations and Technology:
Bioremediation Using the Land Treatment Concept. Ada, OK: U.S. Environmental
Protection Agency, Environmental Research Laboratory. EPA/600/R-93/164.
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