Table Of ContentN P
ATURAL ROCESSES
S
AND YSTEMS FOR
H W
AZARDOUS ASTE
T
REATMENT
SPONSORED BY
Natural Processes and Systems for Hazardous Waste Treatment Task
Committee of the Environmental Council
Environmental and Water Resources Institute (EWRI)
of the American Society of Civil Engineers
EDITED BY
Say Kee Ong
Rao Y. Surampalli
Alok Bhandari
Pascale Champagne
R. D. Tyagi
Irene Lo
Published by the American Society of Civil Engineers
Library of Congress Cataloging-in-Publication Data
Natural processes and systems for hazardous waste treatment / sponsored by Natural
Processes and Systems for Hazardous Waste Treatment Task Committee of the
Environmental Council [and] Environmental and Water Resources Institute (EWRI) of the
American Society of Civil Engineers ; edited by Say Kee Ong … [et al.].
p.cm.
Includes bibliographical references and index.
ISBN-13: 978-0-7844-0939-8
ISBN-10: 0-7844-0939-0
1. Hazardous wastes--Natural attenuation. 2. Hazardous wastes--Biodegradation. 3.
Hazardous wastes--Environmental aspects. I. Ong, Say Kee. II. Environmental and Water
Resources Institute (U.S.). Natural Processes and Systems for Hazardous Waste Treatment
Task Committee.
TD1060.N386 2008
628.4'2--dc22 2007041025
American Society of Civil Engineers
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Copyright © 2008 by the American Society of Civil Engineers. All Rights Reserved.
ISBN 13: 978-0-7844-0939-8 ISBN 10: 0-7844-0939-0
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Preface
Man is constantly creating new chemical compounds to meet specific
industrial applications and for human uses. Release of these compounds into the
environment is inevitable resulting in contamination of natural resources, including
soils and groundwater. The fate of these compounds and their impact on human
health and the environment will remain an important global ecological concern. There
is a need to understand whether these compounds will persist in the environment or
will eventually break down to innocuous compounds. Many compounds degrade in
the presence of various natural processes.
The ASCE’s Technical Committee on Hazardous, Toxic and Radioactive
Waste identified natural processes as an important area that will be of interest to
practicing professionals and the book will serve as a reference and as a text for
undergraduate or graduate courses. This book presents a discussion of the various
natural processes for the attenuation and degradation of hazardous compounds and its
application in inexpensive natural systems.
The organization of this book is based on the types of natural processes with
C hapter 1 introducing the topic. Chapter 2 presents a brief discussion on sorption,
sequestration and binding of organic compounds to soils and sediments. Chapter 3
explores oxidation-reduction reactions and precipitation while Chapter 4 discusses
biodegradation and bioassimilation of hazardous compounds. Chapter 5 discusses
photolysis and photocatalytic processes. Phyto-process and phyto-assimilation are
discussed in Chapter 6. An extension of phyto-processes is the application of
wetlands for the treatment of wastewater and contaminated groundwater. This is
discussed in Chapter 7. The final chapter discusses the various physical processes
such as diffusion and dispersion and the application of natural attenuation.
The editors acknowledge the hard work and patience of the all authors who
have contributed to this book.
- SKO, RS, AB, PC, RDT and IL
iii
Contents
Chapter 1 Introduction 1
1.1 Background 1
1.2 Natural Processes 1
Chapter 2 Sorption, Sequestration and Binding of 4
Contaminants to Soils
2.1 Introduction 4
2.2 Organic Contaminants 5
2.3 Desorption 17
2.4 Inorganic Contaminants 22
2.5 Implications for Site Remediation 32
Chapter 3 Couples of Precipitation-Dissolution and 41
Reduction-Oxidation Reactions
3.1 Introduction 41
3.2 Precipitation and Dissolution 42
3.3 Reduction and Oxidation 46
3.4 Removal of Contaminants by Reduction and Precipitation 55
Processes
3.5 Natural Occurring of Reduction and Precipitation Processes 73
3.6 Engineering Application 76
3.7 Summary 83
Chapter 4 Biological Assimilation and Degradation 94
4.1 Introduction 94
4.2 Definitions 96
4.3 Common Degradation Pathways and Mechanisms 97
4.4 Rates of Transformation and Half-Lives 107
4.5 Pollutants and Persistency/Bioavailability 108
4.6 Factors Affecting Degradation 108
4.7 Case Studies 109
4.8 Conclusion 114
Chapter 5 Photolysis and Photocatalytic Degradation 120
5.1 Introduction 120
5.2 Basic Principles of Photochemistry 120
5.3 Light Absorption in Natural Water Bodies 124
5.4 Photochemical Reaction in Natural Water Bodies 126
5.5 Photoreactions of Organic Compounds 131
v
5.6 Factors Influencing Photolysis 144
5.7 Case Studies 148
5.8 Conclusion and Implications 152
Chapter 6 Phytoprocesses 161
6.1 Introduction 161
6.2 Definitions 161
6.3 Influence of Environmental Factors Affecting Phytoprocesses 168
6.4 Processes Responsible for Contaminant Removal/Detoxification 170
6.5 Mechanisms Responsible for Phytoprocesses 171
6.6 Common Compounds Remediated by Phytoprocesses 173
6.7 Case Studies 179
6.8 Field Applications of Phytoprocesses 181
Chapter 7 Wetlands 189
7.1 Introduction 189
7.2 Wetland System Definitions 189
7.3 Wetland Structure and Function 197
7.4 Constituent Cycling and Removal in Wetlands 208
7.5 Case Studies 240
7.6 Conclusion 247
Chapter 8 Physical Processes and Natural Attenuation 257
8.1 Introduction 257
8.2 Diffusion 257
8.3 Advection 259
8.4 Hydrodynamic Dispersion 260
8.5 Volatilization 264
8.6 Advection-Dispersion-Reaction Equation 266
8.7 Application of Attenuation Processes 267
8.8 Case Study: Natural Attenuation of a Coal-Tar-Contaminated
Site 270
8.9 Summary 274
Index 277
vi
CHAPTER 1
Introduction
SAY KEE ONG
1.1 Background
There are about 87,000 chemicals listed in the inventory of the Toxic
Substances Control Act and about 10% or about 8,300 of the listed chemicals are
currently being manufactured and sold in significant amounts (Hogue, 2007). The
acute and long term effects of some of these chemicals are not known although the
physical-chemical and biological properties of these chemicals may provide clues as to
their persistency and impact on humans and the environment. Of interest is the fate
and transport of these chemicals when they are dispersed in the environment.
Chemical are released into the environment through many routes: during the
manufacture and processing of the chemicals, industrial use of these chemicals,
atmospheric discharge from industrial facilities, wastewater discharges, disposal of
products containing these chemicals, and use of products containing these chemicals.
In the environment, there are many natural processes that can attenuate these
chemicals. Some chemicals are completely attenuated while some chemicals are
sufficiently persistent and do not degrade in the environment. Some chemicals are
partially attenuated. The attenuated compound or daughter compounds may undergo
further attenuation or become more susceptible to attenuation and degradation by
processes that are unable to degrade the parent compound. In some cases, these
daughter products formed may be more toxic than the parent chemicals.
1.2 Natural Processes
Figure 1 provides a general illustration of the different natural processes in the
environment that may attenuate organic and inorganic chemicals. Chemicals dispersed
into the media (air and water) are diluted through mixing which reduces the
concentration of the chemicals in the environment but the chemicals are not destroyed
in the process. Dispersion plays an important role in distributing the chemicals in air
and water. Lowering the chemical concentration reduces their impact on the
environment and humans and reduces acute toxicity situations. However, the total
mass of the chemical in the environment remains the same unless it is degraded.
Chemicals that are persistent may move up the food chain, eventually manifesting in
1
2 NATURAL PROCESSES AND SYSTEMS FOR HAZARDOUS WASTE TREATMENT
humans and resulting in chronic toxicity. Photolysis and photocatalysis are important
attenuation pathways in the environment for the degradation of organic chemicals.
Chemicals dispersed in lakes and sediments are subjected to oxidation or reduction
environments which may impact the chemical. Organic chemicals that are highly
oxidized are more likely to degrade in a reductive environment while organic
chemicals that are neutral or reduced are more likely to be oxidized in an oxidizing
environment. Inorganic chemicals which are toxic in one form may be made less toxic
or more toxic under different oxidizing/reducing conditions. In addition, under
different redox environment and in the presence of other chemicals, inorganic
chemicals may precipitate and be removed from one medium into another, making
them less available. Other than precipitation, many chemicals are sorbed by the
various solid media such as soils and sediments. These chemicals may be strongly
sorbed to soils or sediment making them unavailable and therefore their impacts are
diminished.
Figure 1.1 Various Natural Attenuation Processes
Degradation by various organisms is an important natural process for the
attenuation of organic chemicals. Microorganisms in the environment can acclimatize
to these organic chemicals by using them as carbon and energy sources. In some cases,
these organic compounds may be degraded fortuitously through cometabolism. Higher
forms of lives such as plants can be used to attenuate both inorganic and organic
NATURAL PROCESSES AND SYSTEMS FOR HAZARDOUS WASTE TREATMENT 3
chemicals through accumulate of the chemicals in plant tissues or degraded at the
roots of the plants or within the plant. One common system that has been used for the
attenuation of waste is using wetlands plants.
This book describes the various natural processes providing information on the
basic principles of each processes and examples of chemicals that are attenuated by
these processes. In some chapters, these processes are elaborated further by illustrating
the use of these processes in an engineered system. There is much to be learned from
nature. We still do not sufficiently understand some of these processes or have harness
their potential. We also have not fully identified or characterized the various
microorganisms in the environment that can assimilate and degrade these
anthropogenic chemicals. Learning from the natural processes of the environment and
applying them will provide a more sustainable approach in dealing with the problem
of hazardous compounds in the environment.
References
Hogue, C., (2007) The future of US chemical regulation, C&EN, 85(2):34-38
CHAPTER 2
Sorption, Sequestration and Binding of Contaminants
to Soils
ALOK BHANDARI AND KANG XIA
2.1 Introduction
Sorption is a mass-transfer process resulting from the migration of solute
molecules from a fluid phase to an adjacent solid surface or a second fluid phase
accompanied by a reduction in the solute’s localized entropy (Adamson, 1990).
During sorption, a relatively minor component of one fluid is transferred to a second
fluid phase or a solid surface without significant changes in thermodynamic properties
of either phase (Weber, 2001). In dilute solutions, such as those associated with trace
environmental pollutants, it is assumed that no net heat flow occurs during the
establishment of sorption equilibrium between the fluid and solid phases. The
chemical potential of the solute remains unchanged in each phase and the solute is
assumed to obey Henry’s Law.
The term “sorption” is often used to describe processes that may include
absorption, adsorption, or a combination of the two. Absorption describes the inter-
phase dissolution resulting from the complete mixing of solute molecules throughout
the sorbent phase. Such dissolution or “partitioning” of a solute can occur between
gas-gas, gas-liquid, liquid-liquid, gas-solid or liquid-solid phases. Adsorption, on the
other hand, is a surface phenomenon and refers to mass-transfer of a solute from a
fluid to the surface of a solid or its accumulation at the interface between two phases.
Adsorption processes are further described as physisorption if the solute-sorbent
interactions are primarily through weak van der Waal’s forces, or chemisorption if
stronger chemical bond formation occurs between the solute and sorbent surfaces.
Sorption processes occurring in natural systems may include complex combinations of
absorption, physisorption and chemisorption, and can exert significant control on the
environmental fate of the pollutants by altering their mobility and biodegradability.
The objective of this chapter is to provide the reader with a basic understanding of the
sorption-desorption dynamics and equilibria of organic contaminants and heavy metals
in the context of natural treatment processes for hazardous waste remediation.
4
NATURAL PROCESSES AND SYSTEMS FOR HAZARDOUS WASTE TREATMENT 5
2.2 Organic Contaminants
Organic contaminants at hazardous waste sites may include petroleum
hydrocarbons, polynuclear aromatic hydrocarbons (PAHs), chlorinated solvents and
persistent organic contaminants including polychlorinated biphenyls (PCBs),
halogenated pesticides, and dioxins. These solutes can participate in a variety of
physical and chemical interactions with soil and sediment components. Some of these
interactions are illustrated in Figure 2.1 and include (i) surface adsorption, electrostatic
interactions, hydrogen bonding, or ion-exchange of the solute with mineral surfaces,
(ii) precipitation, crystallization or nonaqueous liquid formation on soil or sediment
surfaces, (iii) hydrophobic interactions, sequestration, ion-exchange, proton-transfer,
coordination reactions or covalent bond formation with soil or sediment organic
matter, and (iv) diffusion into mineral or organic matter micropores. This section will
focus on the impact of sorption, sequestration and humification processes on the fate
and transport of organic solutes as related to natural processes and systems for
hazardous waste treatment.
2.2.1 Sorption
Soils, sediments, aquifer material, and plant-derived detritus constitute the
principal sorption domains in natural systems by providing large surface areas and
secondary phases for the mass transfer of hydrophobic organic solutes from aqueous
media. At the particle-scale, sorption of organic contaminants is affected by their
interactions with mineral surfaces, soil organic matter, and microporosity or
crystallinity associated with these domains (Figure 2.2). Various modes of interaction
between organic solutes and soil components, and the impact of sorption rates and
equilibria on such interactions are described in this section.
2.2.1.1 Sorption Mechanisms
In natural environments dominated by minerals with low organic contents, such as
aquifer systems, the sorption of organic solutes is affected by the presence of polar
hydroxyl- and oxy- groups on the surfaces. These surface moieties readily bind water
molecules via hydrogen-bonding forming a clathrate structure that extends several
molecule layers into the bulk aqueous medium. Sorption of organic solutes to such
mineral surfaces requires the displacement of the tightly-bound water molecules.
Hydrophobic organic contaminants exist in thermodynamically unfavorable
surroundings in aqueous solutions and are attracted toward soil mineral surfaces by
van der Waals forces. The energy released during sorption of the organic solute to the
mineral surface is compensated by the energy required to displace the vicinal water
molecules, and the overall sorption process is often thermodynamically neutral or even
slightly endothermic. The vicinal water layer often plays an important role in the
sorption of hydrophobic organic compounds on mineral surfaces by providing a
“partitioning” domain for solute accumulation prior to adsorption to surface sites.
