composting applied to contaminated...

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.


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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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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.



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.


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.

31

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

33

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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