CE 510Hazardous Waste EngineeringDepartment 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

Second Priority: LNAPL

Second Priority: DNAPL

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 regiongroundwater flow

treatmenthttp://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

eCC

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

kCC

o 11

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

eCC

Textbook Problem 12.18A 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 exampleIf (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.