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Ch. 15 Hazardous Waste - title

Chapter 15 Hazardous

Waste

Environmental engineers design systems to manage hazardous

waste properly and consider the impacts

of designs on the end-of-life management.

15.1 DEFINING HAZARDOUS WASTE

15-1

A hazardous substance is defined in the United States by the USEPA as any

substance that because of its quantity, concentration, or physical, chemical, or

infectious characteristics may cause, or significantly contribute to, an increase in

mortality; or cause an increase in serious irreversible or incapacitating reversible

illness; or pose a substantial present or potential hazard to human health and the

environment when improperly treated, stored, transported, or disposed of, or

otherwise managed.

Table 15.1 pg 519

15-2

Hazardous waste is a name given to material that, when intended for disposal,

meets one of two criteria (Table 15.1).

Global System to Classify and Label Chemicals

15-3

The Globally Harmonized System (GHS) of

Classification and Labeling of Chemicals is a

worldwide initiative to promote standard criteria for

classifying chemicals according to their health,

physical, and environmental hazards.

It uses pictograms, hazard statements, and signal

words such as “Danger” and “Warning” to

communicate hazard information on product labels

and material safety data sheets (MSDSs).

The GHS system defines how to classify hazards

based on scientific information and standardized

tests.

Table 15.2 pg 520

Hazardous Waste

15-5

It contains one or more of the criteria pollutants or

those chemicals that have been explicitly identified

(listed) as hazardous. Over 50,000 chemicals are

thus identified.

The waste can be defined (by laboratory tests) to

have at least one of the following characteristics:

• flammability

• reactivity

• corrosivity

• toxicity.

Hazardous Waste

15-6

Flammable materials are defined as those liquids

with flash points below 60◦C or those materials that

are “easily ignited and burn vigorously and

persistently.”

Corrosive materials are those which, in an

aqueous solution, have pH values outside the range

2.0 to 12.5 or any liquid that exhibits corrosivity to

steel at a rate greater than 6.35 mm per year.

Reactive wastes are classified as unstable and

either can form toxic fumes or can explode.

Hazardous Waste

15-7

The greatest difficulty in defining hazardous waste

comes from establishing what is and what is

not toxic.

Toxicity is almost impossible to measure. Toxic to

which animals (or plants?), at what concentrations,

over what time periods?

The USEPA defines toxicity in terms of four

criteria:

• bioconcentration

• LD50 • LC50 • phytotoxicity.

Hazardous Waste

15-8

Bioconcentration is the ability of a material to be

retained in animal tissue to the extent that

organisms higher up the trophic level will have

increasingly higher concentrations of this chemical.

Many pesticides, for example, will reside in the

fatty tissues of animals and will not break down very

quickly.

As the smaller creatures are eaten by the larger

ones, the concentration in the fatty tissues of the

larger organisms can reach toxic levels for them.

The trophic level of an organism is the position it

occupies in a food chain (Chapter 8: page 217)

Hazardous Waste

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LD50 is a measure of the amount of a chemical

that is needed to kill half of a group of test

specimens, such as mice.

The animals in a toxicity study are fed

progressively higher doses of the chemical until half

of them die, and this dose is then known as the

median lethal dose (50%), or LD50.

The lower the amount of the toxin used to kill 50%

of the specimens, the higher the toxic value of the

chemical.

Some chemicals, such as dioxin and PCBs

(Polychlorinated Biphenyls),show incredibly low

LD50s, suggesting that these chemicals are

extremely dangerous to small animals and other

test species.

Example 15.1

Example 15.1 problem contd…

Hazardous Waste

15-12

LC50 is the concentration at which some chemical

is toxic, and this is used where the amount ingested

cannot be measured, such as in the aquatic

environment or in evaluating the quality of air.

As a rough guideline, a waste is considered toxic

if it is found to have a LD50 of less than 50 mg/kg

body weight or if the LC50 is less than 2 mg/kg.

Finally, a chemical is considered toxic if it exhibits

phytotoxicity, or toxicity to plants.

Thus, all herbicides are, by this definition, toxic

materials, and when they must be disposed

of, they must be treated as hazardous wastes.

Hazardous Waste

15-13

A final criterion for being hazardous is if the

material is radioactive.

Radioactive wastes are, however, handled

separately and are governed by separate rules and

regulations.

One concern in hazardous waste disposal is the

speed with which the chemical can be set free to

produce toxic effects in plants or animals.

For example, one oft-used method of hazardous

waste disposal is to mix the waste with a slurry

consisting of cement, lime, and other materials (a

process known as stabilization/solidification).

Hazardous Waste

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When the mixture is allowed to harden, the toxic

material is safely buried inside the block of

concrete, from which it cannot escape and cause

trouble.

As a crude approximation of such potential

leaching, the EPA uses an extraction procedure,

where the solidified waste is crushed, mixed with

weak acetic acid, and shaken for a number of

hours.

This process is known as the Toxicity

Characteristic Leaching Procedure (TCLP).

Table 15.3 pg 524

15.2 Hazardous Waste Management

Toxic Substances Control Act (TSCA) Preventing the creation of materials that

may eventually prove damaging or difficult

to dispose of safely

Resource Conversation and

Recovery ACT (RCRA)

Addresses the disposal of hazardous

wastes by establishing standards for

secure landfills and treatment processes

Comprehensive Environmental

Response, Compensation and

Liability ACT (CERCLA)

Directed at correcting the mistakes of the

past by cleaning up old hazardous waste

sites and is usually referred to as

superfunds

Hazardous and Solid Waste Amendments (HSWA)

Superfund Amendments and Reauthorization ACT (SARA)

Hazardous Waste Management

15-17

Several remedial action options are available:

Natural attenuation: Chemical will eventually

metabolize into harmless end products.

Containment: is used where there is no need to remove

the offending material and/or if the cost of removal is

prohibitive. Containment is usually the installation of slurry

walls, which are deep trenches filled with bentonite clay or

some other highly non-permeable material, and continuous

monitoring for leakage out of the containment.

Extraction and treatment: is the pumping of

contaminated groundwater to the surface for either

disposal or treatment or the excavation of contaminated

soil for disposal or treatment. Sometimes air is blown into

the ground and the contaminated air is collected.

Figure 15.3 pg 531

Hazardous Waste Management

15-19

Aquiclude: An impermeable body of rock or

stratum of sediment that acts as a barrier to the flow

of groundwater.

Once the contaminated water is extracted, it must

be treated

The choice of treatment depends on the nature of

the problem

If the contamination is from hydrocarbons, such as

trichloroethylene, it is possible to remove this with

AC.

Some type of biological treatment system or

distillation process may also be used

If the contamination is from metals, then a

precipitation or redox process may be used

Hazardous Waste Management

15-20

Some soils may be so badly contaminated that

the only option is to excavate the site and treat the

soil ex-situ

In case of PCB (polychlorinated biphenyl)

contamination, the soil is dug out and usually

incinerated to remove the PCBs, and then returned

to the site or landfilled

Biodegradation in reactors may be used

In situ treatment of the contaminated soil involves

the injection of either bacteria or chemicals that will

destroy the offending material

If heavy metals are of concern, these can be tied

up chemically to reduce leaching into the GW

Treatment of Hazardous Waste

15-21

Chemical treatment is commonly used, especially

for inorganic wastes.

In some cases a simple neutralization of the

hazardous material will render the chemical

harmless.

In other cases oxidation is used, such as for the

destruction of cyanide.

Ozone is often used as the oxidizing agent.

In a case wherein heavy metals must be removed,

precipitation is the method of choice.

Treatment of Hazardous Waste

15-22

Most metals become extremely insoluble at high

pH ranges, so the treatment consists of the addition

of a base, such as lime [CaO, Ca(OH)2] or caustic

[a property of various corrosive properties; Exmp.

NaOH] and the settling of the precipitate (similar to

the lime-soda softening process).

Other physical–chemical methods employed in

industry include reverse osmosis, electrodialysis,

solvent extraction, and ion exchange.

If the hazardous material is organic and is readily

biodegradable, most often the least expensive and

most dependable treatment is biological.

Treatment of Hazardous Waste

15-23

One of the most widely used treatment techniques

for organic wastes, however, is incineration.

Ideally, hazardous waste incinerators produce

carbon dioxide, water vapor, and an inert ash.

In actuality, no incinerator will achieve complete

combustion of the organics.

It will discharge some chemicals in the emissions,

concentrate others in the bottom ash, and produce

various compounds called products of incomplete

combustion (PIC).

Treatment of Hazardous Waste

15-24

For example, polychlorinated biphenyls (PCBs)

are thought to decompose within the incinerator

to highly toxic chlorinated dibenzo furans (CDBF),

which, although organic, do not oxidize at normal

incinerator temperatures.

Despite these problems, hazardous waste

incinerators must achieve high levels of removal

efficiencies, often 99.99% or higher, which is

commonly referred to as “four nines.”

In some cases removal efficiencies require five or

even six nines.

Example 15.2

publicly accessible website, in whole or in part.

Example 15.2

Disposal of Hazardous Waste

15-27

Read pages from 533-534

Radioactive Waste Management

15-28

A special type of hazardous material emits

ionizing radiation, and in high doses this radiation

can be highly detrimental to human health.

Radiation is a form of energy due to the decay of

isotopes.

An isotope of an element has the same atomic

number (number of protons) but a different mass

number (number of neutrons and protons) than the

standard element.

Remember that the atomic number defines an

element

For example, the atomic number of uranium is 92.

Uranium 235 (U-235), therefore, is an isotope of

uranium (U-238).

Radioactive Waste Management

15-29

To regain equilibrium, the isotopes decay by

emitting protons, neutrons, or electromagnetic

radiation to carry off energy.

This natural spontaneous process is radioactivity.

The isotopes that decay in this manner are called

radioisotopes.

The energy emitted by this decay that is strong

enough to strip electrons and sever chemical bonds

is called ionizing radiation.

There are four kinds of ionizing radiation: alpha

particles, beta particles, gamma (or photon) rays,

and X-rays.

Radioactive Waste Management

15-30

All radioactive isotopes decay and will eventually

reach stable energy levels.

The decay of radioactive material is first order, in

that the change in the activity during the decay

process is directly proportional to the original activity

present, or

dA/dt = -kA

Where, A = activity

t = time

k = radioactive decay constant

A = A0e (-kt)

where, A0 = activity at time zero

Radioactive Waste Management

15-31

Of particular interest is the half-life of the

isotope, meaning that half of the nuclei

have decayed in this time.

Inserting A = A0/2 into the preceding

equation and solving, the half-life is

calculated as:

t1/2 = ln 2/k = 0.693/k

The half-life is characteristic of an

isotope.

Therefore, if you know the isotope, you

know the half-life and vice versa

Example 15.3

Table 15.4 pg 536

Risk Associated with Ionizing Radiation

15-34

The exposure of human tissue to ionizing radiation

is complicated by the fact that different tissues

absorb radiation differently.

Different types of radioactivity can create different

effects

Not all tissue react the same way to radiation

The rem, or roentgen equivalent man was

invented

The rem takes into account the biological effect of

absorbed nuclear radiation. So, it measure the

extent of biological injury

The rem is a biological dose

Risk Associated with Ionizing Radiation

15-35

When different sources of radiation are compared

for possible damage to human health, rems are

used as the units of measurement.

Modern radiological hygiene has replaced the

roentgen with a new unit, the gray(Gy)

Gy is defined as the quantity of ionizing radiation

that results in absorption of one joule of energy per

kg of absorbing material

But the same problem exists, in that the

absorption may be the same, but the damage might

be different

Hence, the sievert (Sv) was invented

Risk Associated with Ionizing Radiation

15-36

A Sv is an absorbed radiation dose that

does the same amount of biological damage

to tissue as one Gy of gamma radiation or X-

ray

One Sv is numerically equal to 100 rem

The damage from radiation is chronic as

well as acute

Over time, lower levels of radiation

exposure can lead to cancer and mutagenic

effects

Risk Associated with Ionizing Radiation

15-37

The sources of exposure of humans to

radioactivity can be classified as:

- Involuntary background radiation

- voluntary radiation

- Involuntary incidental radiation

- Involuntary radiation exposure due to

accidents

Risk Associated with Ionizing Radiation

15-38

Background radiation: It is due mostly to cosmic

radiation from space, the natural decay of

radioactive materials in rocks (terrestrial), and

radiation from living inside buildings (internal)

A very special kind of background radiation is

Radon

Radon 222 is a natural isotope with a half-life of

about 3.8 days

It is the product of uranium decay in earth’s

surface

Radon is a gas and because uranium is so

ubiquitous in soil and rock, there is a lot radon

present

Risk Associated with Ionizing Radiation

15-39

For it’s long half-life, it stays around long

enough to build up high concentrations in

buildings

Its decay products are known to be dangerous

isotopes that can produce cancer

The best technique for reducing the risk from

radon is to first monitor to see if a problem exists

and if, necessary, ventilate the radon to the

outside

Risk Associated with Ionizing Radiation

15-40

Voluntary radiation: It can occur from such

sources as diagnostic X-rays

One dental X-ray can produce hundreds of

times the background radiation, and these should

be avoided unless critically necessary

Another source of voluntary exposure is from

high-altitude flights in commercial airlines

Earth’s atmosphere is a good filter for cosmic

radiation, but there is little filtering at high

altitudes

Risk Associated with Ionizing Radiation

15-41

Involuntary Incidental radiation: It would be

from such sources as nuclear power plants,

weapons facilities, and industrial sources

Involuntary radiation from accidents: It is from

accidents, and this is a different matter

The most publicized accidental exposure to

radiation has been from accidents or near-

accidents at nuclear plant plants

Radiation poisoning in Goiania, Brazil: Read

page 539

Table 15.5 pg 540

Treatment and Disposal of Radioactive Waste

15-43

The most important distinction to be made in

radioactive waste disposal is the level of

radioactivity emitted.

While there appears to be an increasingly complex

system of characterization for radioactive wastes,

the broad classification is as high-level, intermediate

level, and low-level waste.

High-level wastes occur mostly from the

production of electric power, and these are identified

by activities in the range of curies per liter.

Treatment and Disposal of Radioactive Waste

15-44

Intermediate level wastes are produced by

weapons manufacture and although their activities

are in the range of millicuries, the particular isotopes

are long-lived, so these wastes require long-term

storage

Low-level wastes, characterized as those with

activities in the range of microcuries per liter, are

produced in hospitals and research laboratories.

The long-term storage of high-level radioactive

waste has been debated for decades.

Over protests, a site in Nevada at Yucca Flats has

been selected and is being prepared.

Treatment and Disposal of Radioactive Waste

15-45

Low-level radioactive waste should not

represent a disposal problem.

Because the activity levels of these wastes are

so low that they can be handled by direct contact

It would seem that, with judicious volume

reduction such as incineration, any secure landfill

would be adequate.

Sustainable Materials Management

15-46

 Two strategies to support sustainable materials

management:

- Dematerialization

- Detoxification

Dematerialization means reducing the amount of

material in a product without decreasing the quality of the

service it provides.

It reduces the flow of virgin materials into and through

the industrial/economic system.

Strategies for dematerialization include reducing the

weight or thickness of packaging materials promoting

recycling and secondary materials industries to keep

materials cycling in industrial loops rather than relying on

virgin resources.

Sustainable Materials Management

15-47

 The strategy of detoxification includes:

• substituting benign alternatives for problematic

chemicals (e.g., substituting rapidly biodegradable

surfactants for surfactants that degrade into toxic

byproducts)

• generating toxics on demand or just-in-time to

avoid the need for storage and transportation

• designing new chemicals and materials that are

benign with respect to human health and the

environment

Sustainable Materials Management

15-48

 The design of such chemicals is the domain of the

growing field of green chemistry.

Green chemistry has emerged as an effective

strategy for detoxification and as a means to design

chemical products and processes to create

sustainable materials and products.

Green chemistry is the design of chemical products

and processes that reduce or eliminate the use and

generation of hazardous substances

The focus of green chemistry is on design because

decisions are made at the level of design that impact

the performance, toxicity, and fate of chemicals

Sustainable Materials Management

15-49

 Green chemistry is a tool for chemists,

chemical engineers, and others who design

chemicals and materials to help move society

toward the goal of sustainability

It is defined by a set of 12 principles

articulated by Anastas and Warner in 1998.

Atom Economy

15-51

 “The key lies in the concept of atom economy:

“synthetic methods should be designed to maximize

the incorporation of all materials used in the process

into the final product”.

For example, the reduction of a ketone to the

corresponding secondary alcohol using sodium

borohydride or molecular hydrogen as the reductant.

Reduction with the former has an atom economy of

81% while reduction with the latter are 100% atom

economic, that is everything ends up in the product

and, in principle, there is no waste.”

https://www.acs.org/content/acs/en/greenchemistry/what-is-green-

chemistry/principles/green-chemistry-principle--9.html

Atom Economy

15-52

https://www.acs.org/content/acs/en/greenchemistry/what-is-green-

chemistry/principles/green-chemistry-principle--9.html

Atom Economy

15-53

 “Unfortunately, hydrogen does not react with

ketones to any extent under normal conditions.

For this we need a catalyst such as palladium-on-

charcoal.

A catalyst is defined as “a substance that changes

the velocity of a reaction without itself being changed

in the process”.

It lowers the activation energy of the reaction but in

so doing it is not consumed.

 This means that it can be used in small amounts

and be recycled indefinitely, that is it doesn’t generate

any waste

https://www.acs.org/content/acs/en/greenchemistry/what-is-green-

chemistry/principles/green-chemistry-principle--9.html

Catalysis

15-54

 Catalytic reagents are better than stoichiometric

reagents “because the catalytic reagents have

higher activiation energy than stoichiometric

reagent

A catalyst speeds up a reaction and is in no way

affected during a reaction

A stoichiometric reaction is used up during the

reaction

https://www.acs.org/content/acs/en/greenchemistry/what-is-green-

chemistry/principles/green-chemistry-principle--9.html

Sustainable Materials Management

15-55

 Please Read pages 542 -548

Pollution Prevention

15-56

 More widely practiced aspect of sustainable

materials management is pollution prevention.

The EPA defines pollution prevention as the

following:

“The use of materials, processes, or practices

that reduce or eliminate the creation of

pollutants or wastes at the source. It includes

practices that reduce the use of hazardous

materials, energy, water or other resources

and practices that protect natural resources

through conservation or more efficient use.”

Pollution Prevention

15-57

 Originally, pollution prevention was applied to

industrial operations with the idea of either reducing

the amount of the wastes being produced or

changing their characteristics to make them more

readily disposable.

Many industries changed to water-soluble paints,

for example, thereby eliminating organic solvents,

cleanup time, etc., and often ended up saving

considerable money.

Pollution Prevention

15-58

 With the passage of the Pollution Prevention Act

of 1990, the EPA was directed to encourage

pollution prevention by setting appropriate standards

for pollution prevention activities, assist federal

agencies in reducing wastes generated, work with

industry to promote the elimination of wastes by

creating waste exchanges and other programs

In general, the procedure for the implementation of

pollution prevention activities is to

• recognize a need

• assess the problem

• evaluate the alternatives

• implement the solutions.

Example 15.5

Example 15.5 problem contd…

Example 15.5

Example 15.5 solution contd…

publicly accessible website, in whole or in part.

Hazardous Waste Management and

Future Generation

15-64

Please read pages 552-555