CONTAMINATED SOIL TREATMENT:

Abstract: Over the past twenty years, a number of ideas have been put forward, some developing into legitimate technologies, designed to clean up the contamination left behind in our soil from industry, wars and other polluting sources. The contaminates can range from
mild pesticides and hydrocarbons to heavy metals and very toxic substances, all of which can
wreak havoc if left untreated for periods of time, especially with the underground water
supply.

The most common contaminates are in the hydrocarbon family: organic compounds in
concentrations of less than 60,000 mg/kg or parts/million, left over from oil spills, gas
stations, storage tank farms, agriculture and industrial applications. These hydrocarbons range from gasoline, BTEX and solvents up to compounds on the higher hydrocarbon chain such as lubrication oils, PAH and Bunker C.

This Presentation will explore some of the technologies that have been and are being used for Contaminated Soil Treatment: their strengths and weaknesses. We will then give a brief
history of one of the most recognized methods of treatment, Thermal Desorption. The
evolution of this technology and the reasons improvements were needed, culminating with the latest innovations in Thermal Treatment will be presented. This industry has come a long way over the past twenty years and is now poised to become the “method of choice” for
Contaminated Soil Treatment.

Keywords: Contaminated soil, remediation, hydrocarbons, Thermal Desorption, air
emissions, THERMOCLEAN, Klean Machine

Introduction:
Soil contamination has been recognized by the United Nations as a major problem throughout the world. Developing countries wanting to tap into World Bank funding must first demonstrate a desire to improve their environmental record, and this often involves cleaning up their contaminated soil sites and improving their drinking water sources in conjunction with or prior to receiving World Bank funding.

Much of the soil pollution in the world has been caused by hydrocarbons or oil-related
substances, called Volatile Organic Compounds or VOCs. An organic compound is
considered volatile if it produces a vapor or gas at room temperature and normal
atmospheric pressure. Some of these fumes are dangerous to humans when inhaled in great quantities or over a long period of time, and are also form harmful ozone.

 Contaminants in the soil can adversely affect the water table and pollute the drinking water so necessary for life.

The Source of Soil Contaminants:
The oil drilling industry and the associated industrial applications such as storage tanks,
service stations and spills have been major contributors to soil contamination. Airport,
railways, seaports and other industrial operations have contributed to the inventory of
contaminated sites. Insurgence, wars and military operations have also caused many countries to suffer from damage to the environment and contamination of soil and water supplies.

Remedial Methods and Technologies:
Many jurisdictions in both developed and undeveloped countries continue to ignore the
problem of contaminated soil. Others consider moving the pollutants to landfills as a viable
solution. Both these options tend to just store the problems for future generations to deal with. A number of technologies have emerged over the past twenty years, most originating in North America or Europe, to try and find an effective and viable way to treat contaminated soil. From each technology mentioned there are spin off remedial processes also.

Some methods include:

a. Landfarming: A process where contaminated soil is spread out over a large area, usually
on top of a liner material, and tilled like farm soil. This tilling action allows the sun and
rain to evaporate and wash the contaminants from the soil. Runoff water must be
captured and treated in some cases. The advantages of this treatment method are its
relative low cost and simplicity, whereas the disadvantages are the need for large soil bed
areas and the atmosphere gets the contaminates in the form of vapour, thus adding to the
global warming and acid rain problems in many instances.

b. Bioventing: Organisms already living in the soil are used to degrade contaminants. Breakdown is enhanced by injecting air and sometimes nutrients into the soil above the
water table. Vapours may need to be captured. This is a long-term remediation system
and has had limited success. Capturing of the vapours is a challenge.

c. Vapour Extraction: Soil Vapour Extraction (SVE) is an in situ (in the soil) remediation
process that removes the VOC contaminants from the ground. The contaminants are
pulled out of the soil with a vacuum pump, removing the need to excavate and haul the
soil from the site to a landfill or other treatment site. A network of wells are dug or
drilled into the substrate and perforated pipes inserted into soil to allow the vapours to be
drawn into the pipes by a powerful vacuum. When the contaminants are pulled from the
ground, they often carry moisture that is present in the soil or the water table. A knockout
pot separates the water from the air and the water must be treated separately. This system
can also be used with Air Sparging – forcing air into the ground to speed and help
extraction of vapours.

The vapours pulled from the soil are just as harmful to the air as they are to the water
table, so they cannot be pumped into the atmosphere, but first must be treated. This is
generally done by oxidising them. Add the right amount of heat and oxygen and oxidation
occurs. The process is: CnH(2m)+(n + ml2) 02 => n C02 + rnH.20 + Heat (where m=n+ 1). This process breaks the harmful compounds into their basic components and
energy, then combines them into safe compounds such as water vapour and carbon
dioxide naturally. Once this process has occurred, the air can be discharged into the
atmosphere and the liquids treated separately.

Vapour Extraction is in wide use for soil remediation and works quite well on smaller
sites. Its main drawback is the tremendous amount of time it takes to extract all the VOC
from the area. This can be measured in years rather than cubic meters per hour. Costs are
lower than other systems but only marginally.

d. Soil Washing: This method uses water to flush out contaminants from soils. The process
works by either dissolving or suspending contaminants in the wash solution and is often
used in conjunction with other physical separation technologies. This method does not
destroy or immobilise the contaminants, hence the concentrated soil must be disposed of
carefully. Wash water requires treatment and air emissions can be a problem. This
technology is fairly widespread in Europe but not so in North America. It appears to work
for removing semi-volatile organic compounds (SVOC), fuels and some heavy metals,
plus selected VOCs and pesticides. The drawbacks are the length of time, cost and air
emission problems.

e. Bioremediation: This system has been the buzz word of the 1990s. It may be performed
in situ or by building a biopile. Microbes or minute bugs (bacteria) are injected into the
soil or biopile, (sometimes along with nutrients to speed up the process), and they go to
work to eat the hydrocarbon contaminants. As the microbes die off, this adds to the
organics of the soil. In some cases the soil may have sufficient bacteria of its own to
perform this task, however the system generally takes considerable time, so microbes are
added to enhance the process. Costs for this system can be comparable with other
systems and it is the closest system to emulating natural biodegradation. The major
drawbacks to this technology are the temperature constraints: the technology only works
when the ambient temperature is kept between 68 – lOO°F or 20 – 37°C. Once the
temperature drops below this threshold, the microbes become dormant and often die off,
necessitating a reintroduction of microbes when the weather improves. Some attempts
have been made to cover and heat the biopiles, but this increases the costs significantly.
The other drawback is the length of time it requires to complete this process.

f. Thermal Desorption: This system uses heat to separate (desorb as opposed to absorb)
the contaminants from the soil. Early attempts at this technology were in the form of
adapting crop dryers and later asphalt plants to perform this separation process. As the
need to remediate contaminated sites increased in the 1980s and up to 1996, several
companies began manufacturing equipment specific to desorbing hydrocarbon
contaminates from the soil. These systems are based on theRotary Kiln design where soil
is conveyed into a cylindrical drum and heat applied either directly or indirectly to the
drum as it is rotated. By thus heating the soil, contaminants are vaporised and driven or
sucked off where they can be destroyed in an afterburner or purged through a filtration
system. Nicknamed “dirt-burners”, approximately 144 of these systems were built during
the late 1980s and early 1990s and a number are still in operation world wide. The
throughput capacity and speed of remediation made rotary kiln thermal desorbers a very
attractive option to low temperature treatment methods. As air emission regulations
became more restrictive, many of these systems could no longer meet permitting requirements and had to cease operation. Attempts to control spurious air emissions
associated with a rotating drum have been largely ineffective, and throughput capacities
have often been sacrificed to prevent exceeding the air emission standards. The other
major drawback to rotary kiln systems is their size: often requiring 4 to 7 trailers to carry
the equipment components, thus making mobilisation and demobilisation cumbersome
and the area required (footprint) to operate within fairly large.

Improvements in Thermal Desorption Technology:

With the various drawbacks to all the existing technologies for soil remediation, and
the problems encountered by manufacturers of Thermal equipment, a gentleman from North Bend, WA, USA, by the name of John D. Anderson, began to explore alternative methods of performing this needed task of soil treatment. Anderson raised two patents in the early 1990s for a new technology in Thermal Desorption he termed a “cascading soil system”. In this system, called the “Klean Machine®”, soil is transported to the top of the machine by conveyor and dropped into a feed hopper. The soil is then picked up by an auger and moved horizontally to another chamber where it cascades downward like a curtain or waterfall by means of a patented spill-trough design into another auger. This action is repeated several times until the soil is deposited into a discharge auger at the bottom of the processor. Simultaneously, heat by means of a propane (or natural gas) burner is inserted into the processor just above the discharge auger. The heat moves upward, being drawn by a powerful induction fan and passes through the various chambers and through the soil curtains, vaporising the VOCs in the soil as it passes upward. The temperature varies from chamber to chamber, thus covering the full scope of boiling points associated with the carbon chain from solvents to Bunker C. Vapours are then pulled through a baghouse or Filtration System to remove any dust particles that may be present in the vapour stream. The gases continue on into a secondary heat chamber, the Thermal Oxidiser, where this secondary heat source is used to destroy the contaminants, discharging clean air into the atmosphere that meets or exceeds air emission standards. The soil, meanwhile, now devoid of contaminants, continues to exit from the discharge auger onto a discharge conveyor to be used as clean backfill onsite or other general soil uses. This system does not destroy the organics in the soil, but simply separates the contaminants from the soil and destroys them in the Thermal Oxidiser.

Mr. Anderson’s first prototype, the Klean Machine® 1 (KM-l), was built in 1991 and
is still operating in eastern Washington State. The second system,KM-2 was built in 1994
and the capacity was increased considerably. Special care was taken to affect a soil seal at
both the feed hopper and discharge auger to assure the system operates under a negative
pressure, thus assuring that no spurious air emissions occur and that excess air is not
introduced into the system to compromise the heating process. TheKM-2 unit operated successfully from its manufacturing until 1996 when it was sold to an Alaskan company.
Modifications were made to the unit from time to time to improve its operation.

In 1999, the KM-2 unit was purchased by Enviro-Klean Technologies Inc. (EKTI) of
British Columbia, Canada, and moved to Langley, Be. Here it was opened up and thoroughly
examined for wear internally and for areas and ways that it could be improved upon. Very
little physical wear was found within the KM-2, and repairs were made as needed.
Modifications were made to the feed system, fines recovery system and discharge soil seal, then extensive testing performed to verify the improved operation of the machine. The KM-2
was then returned to service and began operating in British Columbia and Alberta, Canada.

EKTI technology reverted to Jentek Environmental Industries Inc in 2005 and the equipment was redesigned and renamed as the ThermoClean series of mobile Thermal Desorption, TC-2000, TC-3000, TC3000HT. This company adopted a mandate to begin marketing the THERMOCLEAN® technology to the world market. By incorporating the various changes developed from the inspection and testing of earlier produced equipment, new designs and improvements were developed. A full-scale model of the TC-3000 processor was built and fully tested to assure an even and consistent airflow through the machine. Since 2005, Jentek has refurbished older machines and designed new machines for Europe and North America.

The mobility of the THERMOCLEAN® technology has a wide appeal within the industry.
Rather than 4 to 7 trailers, these systems are all contained aboard one trailer, with the
feed/discharge systems contained on a separate trailer. They have a very small footprint
compared to all other methods: a 15 m2 (50 ft by 40 ft) area is all that is needed. They can be
moved by conventional highway trucks to a job site, set up in less than two hours, and begin
processing soil. Each system carries an onboard electrical generator for remote power, all
controls are solid state electronic controls and motors are controlled with variable frequency-drives (VFD’s) from the main panel. The systems can be operated with one operator and a helper, plus a front end loader and operator to feed soil into the machine and possibly remove cleaned soil if required. All burners operate on propane or natural gas, both available fuels in most jurisdictions. Other fuels could be used if neither of these is available, provided the burners are adjusted to operate on the selected fuel.

TC-3000 Flow Diagram

TC-3000 HT

Summation:  

All methods of treating contaminated soil mentioned within this report have their
various strengths and weaknesses. Certain application may be better adapted to one method over another, depending on the circumstances, so persons wishing to select the best method for their particular project should study all aspects of the technologies and the project before determining the most suitable method of remediation.

The trend today appears to be moving towards the improved Thermal systems as a
general fix-all for the hydrocarbon contamination problem in soil. Some of the factors that
have determined this are:  

1. The mobility and ease of movement of this equipment from one site to another and the
   small footprint they require. 
2. The ease and speed of setting up the equipment and being able to operate it at remote
   sites because of its onboard electrical supply system. 
3. The speed that the remediation process can achieve compared to other methods. These
   systems are measured in tons or cubic meters per hour rather than in months or years.
   New systems being designed are expected to achieve throughputs of over 40 tons/hour on
   a single trailer by twinning the Processors. A Euro Model is being developed with a lower
   throughput, but designed to travel on the narrow roads and under the low overpasses as
   found in Europe and other parts of the world.
4. The cost per ton or cubic meter of soil is comparable and often less than other methods,
   making these systems very viable and attractive to the industry.
5. Low Capital costs make entry into the remediation business viable to even small
   companies.
6. The removal of as many moving parts as possible has now made these systems very
   reliable and not prone to high maintenance costs.

The disadvantages include:

1. The reliance on a fuel source for the heat such as propane or natural gas.
2. The inability to operate well when moisture levels in the soil are very high.
3. The systems also require personnel to operate them on a continuous basis as opposed to
   just leaving the system running and letting time do the work.

Again, the customer must choose what they want: speed and efficiency of remediation, or
potential lower cost and much longer timeframes to achieve the cleanup. What requirements the site is scheduled for and the urgency of the remediation will determine what method is most suited to a particular project. Maybe a combination of technologies would work best in some cases. Ignoring the problem is gaining less tolerance in the eyes of the public daily.

REFERENCES:

National Center for Environmental Research, Office of Research & Development
United States Environmental Protection Agency (EPA)

Underground Storage Tank Bureau,

United States Environmental protection Agency

Interstate Technology & Regulatory Co-operation (ITRC),
Western Governors Association report, May 29, 1996

United States Department of the Navy, Environmental Sector (NFESC)

First Annual Conference on Hydrocarbon Contaminated Soils

Enviro-Klean Technologies Inc., Klean Machine® technology

Research Papers: Regional citizens Advisory Council (RCAC), Alaska

Global Technologies Handbook

Other references obtained from internet sources