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CE 510Hazardous Waste Engineering
Department of Civil EngineeringSouthern Illinois University Carbondale
Instructor: Jemil YesufDr. L.R. Chevalier
Lecture Series 11:Overview of Hazardous Waste Remediation, Treatment and Disposal
Course Goals Review the history and impact of environmental laws
in the United States Understand the terminology, nomenclature, and
significance of properties of hazardous wastes and hazardous materials
Develop strategies to find information of nomenclature, transport and behavior, and toxicity for hazardous compounds
Elucidate procedures for describing, assessing, and sampling hazardous wastes at industrial facilities and contaminated sites
Predict the behavior of hazardous chemicals in surface impoundments, soils, groundwater and treatment systems
Assess the toxicity and risk associated with exposure to hazardous chemicals
Apply scientific principles and process designs of hazardous wastes management, remediation and treatment
Major Concepts
Top priority is waste minimization and pollution prevention Reduction Recycling
Second tier of waste management is treatment Emphasis on the destruction of the
hazardous chemicals Selection of treatment processes based on
Properties of chemical(s) Concentrations Complexity of the matrix
Major Concepts Final option is long-term containment
with no treatment Landfill disposal However, landfill disposal represents a long-
term threat of potential environmental releases
Hence low priority as a management alternative
Priorities in hazardous waste management, minimization and prevention
Waste Generation
Source and Volume Reductions• Materials substitution• Segregation• Reuse• Process modification
Recycling• Solvents• Process water• Acids
Treatment• pH neutralization• Metals removal• Organic removal• Thermal treatment
Disposal• Landfills
Hierarchy of Source Removal and Remediation Methods
First Priority Drums Tanks Sludges Other containers of source materials (e.g. bags, bins,
etc.) Second Priority
Contaminated surface soils Contaminated subsurface solids LNAPL DNAPL
Third Priority Contaminated groundwater Contaminated surface waters
Hazardous Waste Treatment
Ex-situ processes - Removal Removal – treatment - disposal
Groundwater Vadose zone subsurface soil Surface soil
More expensive than in-situ Easier to control than in-situ
contaminated region
groundwater flow
treatment
http://www.frtr.gov/matrix2/section1/list-of-fig.html#2
Injection wellRecovery well
Pump-and-treat
Hazardous Waste Treatment
In-situ “in place” No excavation Groundwater is not pumped out and
treated Less labor intensive (cost savings) Minimal site disturbance
Hazardous Waste Treatment: Effects of Sorption
CCkdtdC
s
Contaminant Saturation conc.
Contaminant conc. In aqueous phase
Coefficient for contaminant desorption
Hazardous Waste Treatment: Effects of Sorption
Effects of sorption on groundwater remediation through 1) asymptotic approach to reaching clean-up levels and 2) the release of contaminants to the aqueous phase after the pump-and-treat process has stopped
Because of the dependence of pump-and-treat groundwater remediation on sorption/desorption, its use has been in decline.
Most designs and analyses of engineering processes are based on mass balance and reactor analysis
Three models Batch Reactors CFSTRs Plug- flow reactors
Hazardous Waste Treatment: Reactor Analysis
Batch Reactors No influent or effluent Wastes treated by
adding reagents First order reaction is
expressed as
Hazardous Waste Treatment: Reactor Analysis
kt
o
eC
C
Continuous flow stirred tank reactors (CFSTR) Effluent concentration is the same as
the concentration in the reactor First order reaction is expressed as
Hazardous Waste Treatment: Reactor Analysis
kC
C
o 1
1
Plug-flow reactors (PFR) Characterized by no mixing or
dispersion Water moves in a “plug” through the
reactor First order reaction is expressed as
Hazardous Waste Treatment: Reactor Analysis
k
o
eC
C
Textbook Problem 12.18
A groundwater containing 560 µg/L of tolune is to be treated to 5 µg/L in a plug-flow UV/H2O2 reactor. If the steady-state hydroxyl radical concentration is 2x10-10 M, determine the required detention time in the reactor. kOH- for tolune is 4x109.
Hazardous Waste Treatment: Reactor AnalysisAlmost all hazardous waste
treatment systems are designed using reactor fundamentals
See figures 12.9 through 12.11
Classification of Remediation and treatment Processes Environmental engineering treatment
systems classification: Physiochemical Biological
Hazardous waste treatment systems are complex due to: Thousands of contaminants Widely varying concentration and
characteristics Treatment required for different media
Classification of Remediation and treatment Processes Classification of remedial and treatment
technologies based on pathways and function
http://www.frtr.gov/matrix2/section1/list-of-fig.html#2
- Sorption- Volatilization- Abiotic- Biotic- Neutralizatio
n- Stabilization- Thermal
processes
Sorption Processes
GAC, Ion Exchange , Stabilization (a.k.a. Solidification or fixation), soil washing and thermal desorption
GAC High surface area: 1000-1400 m2/g Hydrophobic surface characteristics
GAC made from many sources: Wood Bituminous coal materials Coconut shells and Nutshells Lignite
GAC Treatment Dynamics of gravity flow GAC treatment
Exhausted carbon
Adsorption zone (MTZ)
Unused carbon
Influent
Effluent
Stabilization Stabilization: Addition of stabilizing material to
hazardous waste so as to alter the chemistry of the waste and render it less toxic, less mobile and less soluble
Solidification: the modification of a liquid or slurry waste to a solid material by adding solids or other reagents
Wastes treated by stabilization Liquid and slurry organic and inorganic
hazardous wastes generated under RCRA Hazardous wastes at contaminated sites Residuals from other treatment processes
Stabilization Agents Organic agents:
Organically modified lime Organic polymers (polyethylene) Bitumen Asphalt
Inorganic agents: Cement, Lime
Volatilization Processes Air stripping, Soil Vapor Extraction (SVE) Air stripping has been used for decades for the
removal of ammonia, sulfur dioxide, and hydrogen sulfide from water
When hazardous waste is stripped from aqueous phase into gaseous phase, contaminants may become hazardous air pollutants
Hence, GAC scrubbers and other secondary process modifications are implemented to lower concentration below regulation levels
SVE SVE is a cleanup technology commonly used to
remove VOCs and semi-VOCs from the vadose zone or from piles of excavated soils
Most important variables for SVE process selection include Porosity, and Contaminant volatility
SVE is one of the most accepted remediation technology since 1970s
SVE has been used in 25% of the 170 superfund sites
Physical components of SVE include: A vapor extraction well, a vacuum blower, air water separator, and vapor treatment system (GAC or biofilters)
Abiotic Transformation processes Chemical oxidation/reduction: converts HWs to
non-hazardous or less toxic compounds that more stable, less mobile, and/or inert states.
Involves the transfer of electrons from one compound to another, i.e., one reactant is oxidized (loses electrons) and one is reduced (gains electrons)
Most common design application is the Advanced oxidation processes (AOPs) with oxidizing agents such as:
Ozone, UV/ozone, H2O2/ozone, UV/H2O2 Fentons’s Reagent (H2O2/catalysts)
Class example
If (a) O3 is present at 10-5 mM or (b) OH· at 10-5 mM, what is the time required to oxidize 10 mg/L TCE to 1 µg/L TCE? The rate constant for the reaction of ozone with TCE is 17 M-
1sec-1. Assume oxidant concentrations are constant.
Biotic Transformation processes Application of biological processes Bioremediation techniques are destruction
techniques directed toward stimulating microorganisms to grow and use the contaminants as a food and energy source
The main process variables in the design and operation of bioremediation include:
Oxygen supply pH Bioavailability Nutrients Toxicity Temperature
Biotic Transformation processes
Plume of sorbed contaminants
Electron donor source
Recovery wellInjection well
An in situ groundwater bioremediation system
GW flow
Terminal electron acceptor
Nutrients
Other Treatment processes Bioventing Landfarming Thermal processes-Incineration Air sparging Phytoremediation Biopiles Composting Slurry phase biological treatment More reference on remediation technologies can
be accessed at http://www.frtr.gov/matrix2/top_page.html
Ultimate Disposal- HW Landfills Primary goals of HW management are:
Minimization and pollution prevention Treatment (emphasis on destruction)
Some HWs cannot be minimized or treated E.g. some PCBs and metal bearing soils,
residues from other treatment processes Hence, need for Landfill disposals Landfills are designed to contain waste,
while minimizing releases to environment See figs. 12.22 and 12.23
Summary of Important Points and Concepts The priorities of managing HWs, in
decreasing order of importance, are minimization/prevention, treatment/remediation, and disposal.
HW minimization efforts hold the potential of decreasing the mass, volume and toxicity of wastes at the source
HW remediation and treatment processes may be considered applications of hazardous waste pathways. Therefore, treatment processes may be grouped into sorption, volatilization, abiotic transformation, and biotic transformation processes. Another class-Thermal processes
Summary of Important Points and Concepts HW remediation and treatment processes
may also be classified by schemes such as in situ and ex situ processes OR as RCRA wastes or CERCLA-type HW sites.
Treatment process selection and design requires consideration of the contaminant characteristics and the matrix of the waste (i.e., liquid, soil, sludge, etc.)
Almost every HW management system may be conceptualized as a reactor as a basis for analysis and design.