Hazardous and Toxic Waste Treatment of Soils & Sludges
John Poullain, P.E.
Course Outline
This three-hour
online course provides general guidelines for the treatment of hazardous and
toxic waste (HTW) at uncontrolled hazardous waste sites. The guidelines are
intended for the selection of remedial actions and treatment of hazardous waste
contaminants by various biological, chemical, physical or thermal methods or
combinations of them. Treatment of contaminated soils and sludges by biological
treatment, thermal desorption, solidification/stabilization, incineration and
evaporation methods are discussed in this course. Treatment methods for liquid
wastes are not discussed here. Several methods such as, biological and stabilization/solidification
however are applicable for treating contaminated liquid wastes. Remedial actions
performed at a contaminated site must comply with federal and state regulations.
This course includes a multiple-choice quiz at the end, which is designed to
enhance the understanding of the course materials.
Learning Objective
At
the conclusion of this three-hour course, the student will:
Intended Audience
This course is intended for civil engineers and planners.
Benefit to Attendees
The student will
become familiar with several methods used for treating contaminated soils at
hazardous and toxic waste sites. The basic guidelines for O&M of a treatment
method, their advantages and disadvantages and guidance in the selection of
the most appropriate method for treatment are discussed. Potential environmental
risks caused by treatment, measures for minimizing risks and beneficial uses
for a treatments' final products are also discussed.
The methods and basics of incineration and thermal desorption methods for disposing
of contaminated material in waste landfills are also discussed.
Course
Introduction
This course provides general technical guidelines and elements for methods of treatment at uncontrolled hazardous and toxic waste disposal sites. Remedial action at an uncontrolled hazardous waste site consists of on site control, on site treatment, on site storage or off site disposal or combinations of these. On site and off site landfill disposal is a viable option when the volume of HTW material is within the feasible or economic limits of available technology. Disposal methods for radioactive waste are not discussed here since satisfactory disposal requires special landfills that are regulated by the Nuclear Regulatory Commission (NRC).
Biological Treatment
Methods (In Situ) Biological methods are relatively slow compared to other
treatment processes. However many in situ applications provide adequate remediation
to permit on site use of the treated soils instead of expensive offsite disposal
as hazardous waste. Oily sludge has been treated with biodegradation but chlorinated
solvents such as perchloroethylene (PCE) and trichoroethylene (TCE) present
problems for dechlorination of residual contaminant.
An anaerobic process being field-tested called anaerobic reductive dechlorination
(ARD) speeds the in situ bioremediation of PCE and TCE by injections of electron
carbon sources into the subsurface. Sites being treated by air sparge/soil vapor
extraction (AS/SVE) methods showed diminishing returns from the site treatments
with about a 85 - 90% reduction of VOCs in the groundwater. Some were converted
over to anaerobic systems such as ARD, which continued additional reductions
in the chlorinated solvent levels after AS/SVE treatments had plateaued.
Also being studied is injection of soluble and insoluble substrates. Solubles
such as methanol or sodium lactate penetrate further into the subsurface to
enable the anaerobic environment for ARD to be established. Insolubles such
as vegetable oil emulsion are a slow-release electron donor and serve to maintain
the anaerobic condition.
It was concluded the total time for remediation of soils and sludge containing
PCE and TCE were reduced with ARD anaerobic treatment and took less time than
if only one method had been applied to the sites. Contaminated sites in New
Jersey for instance had promising VOC reductions to closure levels of safety
with the anaerobic method, which served as a polishing step for the remediation.
Field data in 2003-2004 for sites in New Jersey did indicate after two years
perimeters and down gradient areas required additional injection points for
completion. Overall success for ARD was on a site by site basis and is being
further evaluated.
Biological Treatment
Methods Ex situ biological treatment methods include Bioslurry Reactors
(BSR), composing, biopiles and landfarming. BSRs have advantages over other
ex situ methods in mixing techniques, which provides more certainty in the uniformity
of treatment. Since BSRs operate in a controlled environment they can better
homogenize, screen and continuously mix the contaminated material. The treatment
time is shorter because the oxygen transfer and microbe populations are improved.
Oxygen transfer is especially easier to maintain than in situ methods.
BSRs can operate in both aerobic and anaerobic modes. In the aerobic mode it
is continuously supplied with oxygen which is being depleted by the treatment
process. Degradation of contaminants is possible in the anaerobic mode by using
an alternative electron acceptor or oxidizer such as nitrate, sulfate or carbon
dioxide.
Permeable Treatment Bed Method This treatment method uses a shallow aquifer
to remediate contaminants. It's basically an underground reactor made of materials
like limestone, activated carbon or green sand. The reactor may lose capacity
rapidly depending on the amount of contaminants carried by groundwater and the
amount of reactor material used by becoming plugged. The treatment bed is therefore
no longer permeable and will allow groundwater to diver the reactor or to channel
through the bed.
Stabilization/ Solidification Treatment Methods Sorbents like fly ash,
kiln dust or pumice chemically react with water in contaminated material to
form a cementious matrix for safer and improved handling of the material. Sorbents
function by raising the pH, which helps to precipitate and immobilize some metal
contaminants to their least mobile form. Metals that are toxic to microorganisms
are immobilized at higher pH. Elevating the pH can protect the microorganism
from toxic poisoning and thus maintain their decontamination. However the solidified
material may be porous at that stage and must be sealed or placed in an approved
landfill to total immobilize the contaminants. The solidified and concentrated
contaminants can be leached out by groundwater and contaminate the groundwater
and aquifers at the site.
Remedial actions must comply with the regulatory guidelines of the Department
of Defense Environmental Restoration Program (DERP), the Formerly Used Defense
Sites (FUDS) Program, Resources Conservation and Recovery Act (RCRA), the US
Environmental Protection Agency (EPA) and the Comprehensive Environmental Response,
Compensation and Liability Act (CERCLA or commonly called "superfund").
Waste sites must be investigated for a wide range of conditions, including ground
water levels, surface drainage and subsurface ground conditions.
The advantages and disadvantages of various hazardous waste treatment methods
are compared. The treatment methods present certain environmental risks and
other concerns for consideration. Considerations for a treatment method include
energy use and O&M costs, experience of personnel, requirements for soil
dewatering and excavation, odors and adequate treatment performance. Environmental
risks include mismanagement of condensation drainage, inadequate treatment levels
and air pollution control. Leachate, migration of contaminants, runoff and wind
erosion can contaminate the subsoil, groundwater and nearby surface water.
If treatment of HTW materials is required before disposal, incineration or thermal
desorption and other methods discussed here are employed for decontamination.
These systems also serve to reduce the land required for disposal. Incineration
and thermal desorption methods are similar but differ primarily in their operating
temperatures. Thermal desorption has high enough heat that vaporizes or turns
the contaminant into gas (max. temperature about 1000° F) but does not combust
the contaminated material. This method is effective for low boiling contaminants
and uses less energy. Thermal desorption alone does not destroy organics. Incineration
is a combustion process that oxidizes the contaminants by thermal destruction
at temperatures ranging from about 1300° F to 3000° F.
Course Content
This course is based primarily on Chapter 4, sections II and III of the US Army Corps of Engineers Manual, "Technical Guidelines for Hazardous and Toxic Waste Treatment and Cleanup Activities", EM 1110-1- 502 (1994 Edition, 43 pages), PDF file. The course is also based on pages 2-15 to 3-2 of the US EPA document “Engineered Approaches to In Situ Bioremediation of Chlorinated Solvents”, EPA 542-R-00-008 (2000 Edition, 6 pages), PDF file.
“Engineered Approaches to In Situ Bioremediation of Chlorinated Solvents”
You need to open or download above documents to study this course.
Course Summary
State and federal
regulations have to be complied with at hazardous and toxic waste sites in order
to remove any threat to human health, welfare or to the environment. Hazardous
and toxic waste includes materials defined as hazardous waste, hazardous substance
and pollutants. Among HTW substances are heavy metals, including lead, cadmium
and mercury and PCBs, dioxins, chlorine, sulfur, potassium and explosives. Bioslurry
reactors, solidification/stabilization, evaporation, incineration and other
methods discussed can be used to remediate contaminated soils and sludges prior
to final disposal and to reduce the land needed for disposal.
References
For additional technical information related to this subject, please refer to:
http://www.epa.gov/epaoswer/osw/hazwaste.htm
US EPA comprehensive information about hazardous waste, landfills, definitions
and RCRA requirements.
http://www.epa.gov/garbage/landfill/sw_combst.htm
US EPA information on combustion and pollution control, energy production from
waste incineration.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
