Environmental Electrochemistry. Fundamentals and Applications in Pollution Abatement

769 Pages·1997·11.71 MB·English

by  Krishnan Rajeshwar and Jorge G. Ibanez (Auth.)

ECAFERP
The field of environmental science and technology has made enormous
strides in recent years. This rapid growth has been stimulated both by the
concerted efforts of scientists and engineers trained in traditional environ-
mental disciplines, as well as by the diffusion of ideas from other (non-envi-
ronmental) fields. This book is about the positive role that electrochemical
science and engineering can play in the detection, quantification, and treat-
ment of environmental pollutants. It is targeted both at an environmental
specialist audience and at the practicing electrochemist. In so designing the
theme, compromise necessarily had to be made between depth, breadth of
coverage, and the size of the book; it is our hope that an appropriate balance
has been achieved.
The book is divided into eight chapters. The first two are introductory
chapters. Those well versed in environmental problems will find httle that is
new in Chapter .1 Similarly, practicing electrochemists can safely skip Chap-
ter .2 Chapter 3 provides a survey of the electrochemical data base on com-
mon types of environmental pollutants. Chapters 4 through 7 attempt to
delve into the details of environmental electrochemical analyses (Chapter 4),
electrochemical methods for pollution abatement (Chapter 5), photo-assisted
XV
xvi Preface
methods for pollution control (Chapter 6), and water/air disinfection ap-
proaches (Chapter .)7 The reference list is extensive in each case, and ought to
facilitate easy entry into the specialized literature. Illustrations are liberally
employed to illustrate a particular principle or approach.
We realize that this book describes an evolving discipline, and undoubtedly
there are many shortcomings. We hope to hear from readers about the flaws - in
detail, logic, or in other respects - that have escaped our notice. The purist may
also find some of our discussion approaches to be rather unconventional. For
example, the classification of environmental pollutants into neat little "boxes"
(see Table 1.3) is completely arbitrary, and has been done only to facilitate a con-
cise review. Similarly, many environmentalists may be taken aback by the vir-
tual lack of material related to nuclear waste treatment. Unfortunately, neither
of us are knowledgeable enough about this topic to write about it.
Many people made meaningful contributions to the preparation of this
book. Gloria Madden managed to transcribe (with her usual efficiency) un-
readable drafts into the final manuscript version, improving the organization
along the way. Ivonne Konik, Flor Gomez Esparza and Yolanda Alegre also
helped in the preparation of the manuscript. Sanjay Basak, AnnaLou Busboom
and her staff at the Media Center, University of Texas at Arlington, and Alberto
Sosa and Marco Antonio Villasefior at the Universidad Iberoamericana, suc-
ceeded in translating primitive drawings into (hopefully more presentable) il-
lustrations. Hannah Frieser and her staff, at the Office of University Publica-
tions, University of Texas at Arlington, spent countless hours preparing the
text and illustrations for camera-ready production. The University of Texas at
Arlington and the Universidad Iberoamericana both contributed time and re-
sources toward the completion of this book. We gratefully acknowledge the
many authors (too numerous to list!) who made preprints/reprints available
to us, as well as companies that provided brochures and information on their
products and services (Chapter .)8 Last but not least, we thank David Packer
and Jackie Garrett at Academic Press for their patience and encouragement.
Finally, we offer simple thanks to our wives Rohini and Luz Teresa, and
our daughters Reena, Rebecca, Georgina and Lucia, for their encouragement,
patience, and understanding during the writing of this book.
Krishnan Rajeshwar
Jorge G. Ibanez
RETPAHC
ENO
1.1. INTRODUCTION
Spectacular advances in technology and improvements in the quality of
everyday life, especially in the industrialized parts of the world, unfortunately
have come at the expense of ravages to our resource base and the environment.
Several human-made chemical disasters in recent history (Table 1.1) tell only
part of the environmental story. Every day our atmosphere, water resources
and soil are being contaminated with human-made pollutants at levels that
are unnoticed, and thus far more environmentally potent in a cumulative
sense. We understand fairly well the health hazards associated with the acute
overdose of many chemicals, but the same cannot be said about the long-term
consequences of chronic exposure to them.
Fortunately, however, environmental awareness also has grown dramatically,
especially in the past few years. Several nations around the world are taking the
lead in the implementation of new laws that regulate, and in many cases
even ban, the use and disposal of hazardous chemicals. Figure 1.1 provides
a perspective of how these legislative mandates have grown in an exponential
manner in the United States. 1 Concomitantly, people and institutions are
becoming increasingly aware that their actions can have not only local but
also global environmental consequences; this bodes well for the future.
2 Chapter I
Table 1.1. Examples of Documented Instances of Environmental Disasters
Attributable to Hazardous Chemical Exposure
Comments Incident(s) Period
Lead poisoning and the 1845 Members of this ill-fated expedition from England
Franklin Expedition to discover the Northwest Passage through the
Canadian Arctic are suspected to have died from
lead poisoning from the lead solder which was used
for the crew's provision storage.
Mercury poisoning in 1953-1960 About 200 people died from mercury poisoned fish
Minamata in this Japanese fishing village off Minamata Bay.
Love Canal pollution 1942-1953 Approximately 23,000 tons of chemical wastes
were dumped in this canal in Niagara Falls, New
York. A health emergency was declared by the
State in 1978, and cleanup efforts began.
The Reed Paper controversy 1962-1970 About 10 tons of mercury were lost from the
chlor-alkali plant into the Wabigoon-English
River system. This plant supplied the chemicals
needed to bleach the pulp at the pulp mill in
Dryden, Ontario.
The vinyl chloride episode 1971-1974 Exposure to this chemical--an integral
component of the plastics (PVC) industry--is
now regulated following studies of cause-and-effect
relationship between vinyl chloride and human
angiosarcoma of the liven
PCB poisoning in Yusho 1968, 1978 Contamination of rice oil with PCB occurred in
and Yu-Cheng Japan and Taiwan in which thousands of people
were afflicted with skin problems.
TCDD pollution in 1976 Although no human deaths were attributed to
Seveso and Times Beach, these incidents, entire neighborhoods were
Missouri evacuated in these communities in Italy and in the
United States.
Lekkerkerk 1986 The Rhine River drains a vast basin in four
countries (Switzerland, Germany, France and the
Netherlands) as it runs from the Alps to the
North Sea. The basin is heavily industrialized
and the river accumulates and transports to the
Netherlands a heavy load of pollutants.
Bhopal explosion 1984 A chemical plant explosion in India released
methyl isocyanate causing more than 3,000
deaths and blindness and other permanent
injuries to thousands in the adjacent village
community.
Castleford explosion 1992 An explosion in a distillation vessel associated
with a mononitrotoluene plant killed five people
and injured many others in this incident in the
United Kingdom.
1.1. Introduction 3
(cid:12)9 SARA
(cid:12)9 MWPA
20-- (cid:12)9 RCRA
(cid:12)9 CERCLA
(cid:12)9 RCRA
(cid:12)9 FWPCA
(cid:12)9 SDWA
15-- (cid:12)9 CAA
(cid:12)9 TSCA
(cid:12)9 RCRA
0
(cid:12)9 FIFRA
6 (cid:12)9 HMTA
z
10-- (cid:12)9 SDWA
(cid:12)9 FEPCA
(cid:12)9 FIFRA
(cid:12)9
(cid:12)9 CAA
5-- (cid:12)9 OSHA
(cid:12)9 NEPA
(cid:12)9 FHSA
(cid:12)9 FHSA
(cid:12)9 FIFRA
I I I I
0
1945 1955 1965 1975 1985 1995
Year
ERUGIF 1.1. Growth fo evitalsigel mandates rof latnemnorivne quality lortnoc ni eht detinU
.setatS decudorpeR( with noissimrep morf .illessarG )1
This chapter begins with a bird's-eye view of pollutants in the environment.
A survey of existing technologies for pollutant sensing and treatment is given
next. While there can possibly be no argument about the importance of
developing new assay techniques, pollution control itself and an extensive
discussion of this topic may be considered retrograde. In other words, is it not
true that efforts to discover new approaches for controlling pollution is an
admission that pollution is a necessary evil of growth? Indeed, it has been
stated that the time has come to move away from "end-of-the-pipe" thinking
toward pollution reduction (or even prevention) at the source. 3,2 While this is
indeed a laudable approach, it is unlikely that we can dispense with the
"command-and-control" strategy altogether, especially giventhe cumulative
result of the widespread use of harmful chemicals over the past decades and the
growing recognition that pollution is not a local but a global problem. Advocates
of the new (pollution prevention) strategy also associate the command-and-control
approach with the problem of moving pollution from air to land to water and
back. This is undoubtedly true with many of the current pollution control
strategies, as we shall see shortly. However, there are many important exceptions
to this trend.
4 Chapter I
The strategy of treating potential pollutants at the discharge end of the
pipe also is not incompatible with the concept of chemical recycling. Indeed,
the argument could be made that a parallel strategy to the reduction (or abolition)
of the use of h ~ chemicals (and a search for potentially more costly alternative
synthetic routes) could involve efficient recycling of chemicals back into the
process. This latter approach is likely to be more universally applicable
and, equally important, more economically viable in many cases. Many
electrochemical approaches to pollution control are amenable to incorporation
of chemical recycling, and this is well exemplified by the Cr(III) ~ Cr(VI)
conversion system discussed later in this book.
In summation of this discussion, all three approaches to environmental
remediationmnamely, pollution prevention, pollution control, and chemical
recyclingmare likely to continue to play important roles in the foreseeable
future. An increased level of understanding nature's capacity to repair itself
from environmental damage is equally important but beyond the scope of
this book.
1.2. SOME DEFINITIONS AND CLASSIFICATION OF POLLUTANTS
Environmental science and technology cuts across many disciplines. Thus,
the definition of the underlying terminology and the "trade jargon" is a necessary
prelude to undertaking an overview of the field.
We begin with the term pollutant. A reasonable definition of a pollutant is
a substance present in greater than natural concentration as a result of human
activity and that has a net detrimental effect upon its environment or upon
something of value in that environment. Interestingly enough, time and place
determine what may be called a pollutant. Thus, the phosphate that has to be
removed from wastewater in a sewage treatment plant is chemically indistin-
guishable from the commodity that anearby farmer buys at high prices as fertil-
izer! A contaminant causes a deviation from the normal composition of an
environment. Contaminants are not normally classified as pollutants unless they
have a deleterious effect on the environment. Every pollutant has a source from
which it originates. This source can be either natural or anthropogenic (i.e.,
human-made).
The definition of waste has been problematical. 3 Waste has been defined
by the U.S. EPA as any material emanating from a process that is not directly
used in another process. Under this definition, many chemical products (even
benign ones) could reasonably be considered as wastes and thus subjected to
1.2. Some Definitions and Classification of Pollutants 5
regulatory restrictions. A further conceptual roadblock to this definition is that
it does not make sense to expect an output from a chemical process to be
reduced or eliminated, but rather is to be increased in the interest of enhanced
industrial productivity! An alternative and perhaps more reasonable definition
would be to classify waste as something released into the environment. Hazardous
wastes have been classified according to their source or their characteristics. 4
Thus, in the first category, the U.S. EPA has compiled a list of industrial sources
that generate hazardous substances (mostly chemicals). As many as 13 lists of
chemicals are similarly available in a computerized database, s The second
category comprises waste materials not listed but that exhibit one or more of
five hazardous characteristics: ignitability, toxicity, corrosivity, reactivity, or
biological activity.
This brings us to another controversial issue; the definition of toxicity. The
standard method for measuring the toxicity of a chemical is to perform bioassays
on genetically sensitive animals. Unfortunately, these laboratory tests require
relatively high chemical dosagemmuch higher than levels typical of the en-
vironment-to generate adverse effects in the test animals. Predictive models
are then used to extrapolate to the lower doses to which people are usually
exposed. However, whether it is even meaningful to extrapolate data from test
animals to humans is far from settled, as are conclusions drawn from epide-
miological studies.
Given all these, it is perhaps not surprising that there is disagreement
between scientific experts and public opinion on the seriousness of risks from
hazardous waste, relative to other environmental problems. Table 1.2 illus-
trates this priority gap in the United States. 7,6 Indeed, the controversial
Superfund legislation in the United States quietly passed legislation for clean-
ing up abandoned hazardous waste sites in spite of concerns expressed about
the economic viability of (and even the need for) such remedial action. 8
In Table 1.3 we have attempted a classification of pollutants commonly
found in air, water, soil, and biota. We shall discuss them in more detail in a
subsequent section of this chapter. It must be noted that the examples listed in
Table 1.3 are by no means comprehensive. The four types of environmental
media provide the path that the pollutants take from the source to the sink,
where they remain for a long time, though not necessarily indefinitely.
We review next the major transport pathways for the pollutants in
environmental media, and then discuss the individual categories of the
pollutants listed in Table 1.3 later in this chapter. Finally, examples of specific
pollutants are provided, along with identification of their sources and their
toxic effects.
6 Chapter I
Table 1.2. A Comparison of the U.S. Public Environmental Concerns and the
Priorities of the U.S. Environmental Protection Agency
The Public's Concerns a EPA's 12 Highest Concerns
(ranked) (not ranked)
.1 Active hazardous waste sites (67%) Ecological risks
2. Abandoned hazardous waste sites (65%) Global climate change
.3 Water pollution from industrial wastes Stratospheric ozone depletion
(63%) Habitat alteration
4. Occupational exposure to toxic Species extinction and biodiversity
chemicals (63%) b loss
5. Oil spills (60%) Health risks
.6 Destruction of the ozone layer (60%) b Criteria air pollutants (e.g., smog)
.7 Nuclear power plant accidents (60%) Toxic air pollutants (e.g., benzene)
.8 Industrial accidents releasing pollutants Radon
(58%) Indoor air pollution
9. Radiation from radioactive wastes Drinking water contamination
)%85( Occupational exposure to chemicals
.01 Air pollution from factories (56%) 8 Application of pesticides
.11 Leaking underground storage tanks (55%) Stratospheric ozone depletion
.21 Coastal water contamination (54%)
.31 Solid waste and litter (53%)
.41 Pesticides risks to farm workers (52%) b
.51 Water pollution from agricultural
run-off (51%)
.61 Water pollution from sewage plants
(50%)
.71 Air pollution from vehicles (50%) b
.81 Pesticide residues in foods (49%)
.91 Greenhouse effect (48%) b
20. Drinking water contamination (46%) b
21. Destruction of wetlands (42%)
22. Acid rain (40%)
23. Water pollution from city runoff (35%)
24. Non-hazardous waste sites (31%)
25. Biotechnology (30%)
26. Indoor air pollution (22%)
27. Radiation from X-rays (21%)
28. Radon in homes (17%) b
29. Radiation from microwave ovens (13%)
a Figures in parentheses represent the percentages of those surveyed who rated the problem
as "very serious."
b Also appears on EPA's list of highest concerns.
Source: Kunreuther and Patrick 6 and Roberts. 7
1.2. Some Definitions and Classification of Pollutants 7
Table 1.3. Classification of Pollutants in the Environment and Some Examples
Organics Inorganics Microorganisms
Herbicides Metals Bacteria
Alachlor Lead Escherchia coli
Butachlor Cadmium Salmonella typhi
Atrazine Mercury Pseudomonas aeruginosa
Cyanazine Copper Salmonella enteritis
Dioxin Chromium Shigella dysenteriae
Shi gella paradysenteriae
Insecticides Metalloids Shigella flexneri
Chlordane Arsenic ShigeIla sonnei
Dieldrin Selenium Staphylococcus aureus
Heptachlor Legionella pneumophilia
Vibrio cholerae
Solvents Anions Viruses
Acetone Chloride Poliovirus 1
Benzene Cyanide Coliphage
Toluene Bromide Hepatitis A virus
Ethylbenzene Nitrate Rotavirus AS 11
Xylene Fluoride
Trichloroethylene Phosphate
Chloroform
Polycyclic Aromatic Gases Protozoan cysts
Hydrocarbons (PAHs) SO ,x NO Giardia muris
Benzo(a)pyrene Ozone Acanthamoeba castellanii
Cyclopenta(cd)pyrene Carbon dioxide Cryptosporidium
Carbon monoxide
Ammonia
Dyes and Surfactants Algae
Other Industrial Organics
Phenols
Formaldehyde
Polychlorinated biphenyls
)sBCP(
Chlorofluorocarbons
)sCFC(
8 Chapter I
1.3. ENVIRONMENTAL MEDIA AND POLLUTANT TRANSPORT
Traditional control of environmental pollution has focused primarily on
the immediate vicinity of the pollution source. For example, tall stacks were
once hailed as the panacea to local sulfate emissions from coal-fired power
plants. However, acid rain is now recognized as a global environmental problem.
Similarl)~ CO 2 emissions are leading to global climate w~g~ and chlorofluorocarbon
(CFC) releases are resulting in the depletion of the earth's protective ozone layer. 9
Other dramatic examples for the global transport of pollutants include the finding
of high lead levels in Greenland snow, and the detection of polychlorinated biphenyls
(PCBs) and pesticides in the Arctic. ~1 It is clear that multimedia environmental
transport models u are needed to account for global distribution of pollutants.
Concomitantly, pollutant regulation has gradually shifted from local governments
to national level and even to an international scale. A recent example of the latter
is the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. This
unprecedented international regulatory action requires the signatory nations
to severely curtail the production and use of five CFCs. This accord sets two
important precedents. It recognizes the atmosphere as a limited, shared
resource, and it curtails the right of individual countries to release wastes to
the atmosphere. Regulation of other regional and global pollutants such as
CO ,2 NO ,x and SO x on an international level, however, appears to be much
more difficult.
We shall now discuss each environmental medium in turn.
1.3.1. Air
The atmosphere's composition has changed at a significantly faster pace
in the past two centuries than it has at any time in human history. Yet the
,2N(
concentrations of the major constituent gases 02, and the inert gases) have
remained nearly constant over a timespan much longer than human life on this
planet. On the other hand, trace level constituents such as methane, CO, SO ,x
and NO/and pollutants such as the CFCs have largely undergone increases in
their concentrations with rather disastrous environmental consequences in-
cluding acid rain, photochemical smog, and climatic changes.
A good rule of thumb for understanding pollutant transport is the
partitioning rule; that is, chemicals, once they are released into the
environment, seek out the environmental medium in which they are
most soluble. For example, volatile organics (see Table 1.3) such as benzene
and trichloroethylene (TCE) are most soluble in air. Hence, they tend to partition
into the vapor phase and inhalation is the principal means of human exposure.