Eckenfelder, w. wesley hansard, william ney understanding water quality management - technology and applications-de-stech publications (2004)

Understanding
Water Quality Management
TECHNOLOGY AND APPLICATIONS
William Ney Hansard
W. Wesley Eckenfelder
Brown & Caldwell, Inc.
EMSI Solutions, Inc.

Understanding Water Quality Management
DEStech Publications, Inc.
1148 Elizabeth Avenue #2
Lancaster, Pennsylvania 17601 U.S.A.
Copyright © 2004 by DEStech Publications, Inc.
All Rights Reserved
Chapter photographs from USEPA National Water
Quality Inventory reports 1992–2000.
No part of this publication may be reproduced, stored in a
retrieval system, or transmitted, in any form or by any means,
electronic, mechanical, photocopying, recording, or otherwise,
without the prior written permission of the publisher.
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Entry under main title:
Understanding Water Quality Management: Technology and Applications
A DEStech Publications book
Bibliography: p. 175
Includes index p. 177
ISBN: 1-932078-21-5

LAWYERS who practice in the environmental field face a double challenge.
Not only are the laws and rules mind-boggling in their complexity, but the
underlying subject matter is dominated by concepts from biology, chemistry,
statistics and engineering. While the environment is a very emotional and even
moral issue for most of us, to be effective in the area, as one practitioner put it,
you need a good engineer, not a poet.
And yet many lawyers, and others, who work on environmental issues spent
more time in college studying poetry than science. To help bridge this gap, I
developed and now edit the Environmental Science Deskbook, published by
Thomson West. This book takes the basic scientific and technical concepts that
are most pervasive in environmental law and regulation and explains them in
plain English. (See www.westgroup.com).
When I was looking for prospective authors to write sections on surface
water quality and wastewater treatment, my first call went to my friend and
colleague Bill Hansard. Not only did I know and respect his work, I also knew
he could lead me to the acknowledged father of industrial wastewater
treatment, Wes Eckenfelder.
This book is an expanded version of those sections. In addition to providing a
clear and comprehensive overview of water quality issues and the various
mechanisms for wastewater treatment, the book contains entirely new sections
on land treatment and waste minimization—the ultimate solution to wastewater
problems. It strikes a rare balance in being accessible to the non-technical
reader and informative to technical audiences.
I highly recommend this book.
JAMES W. CONRAD, JR.
Counsel
American Chemistry Council
xi
Foreword

Preface
OVER the past decade there has been increased awareness of the importance
of water quality. Many municipalities and industrial facilities have
upgraded or installed new technologies to meet the demand for clean water.
Advances in water quality science show that further improvements are needed
to ensure a plentiful water supply and to protect the natural environment.
Water quality management is a complex field that requires participation by
many diverse disciplines. People from all walks of life, including government
workers, attorneys, engineers, scientists, business managers, educators,
economists, politicians, environmental advocates and the general public need
to know more about water quality management.
This volume has been prepared to provide an understanding of the basic
concepts and principles of managing surface water and industrial wastewater
quality.
Many universities currently offer introductory courses in environmental
management, primarily for environmental professionals. This book represents
a primary text for courses in water pollution.
It is our hope that this volume will provide a greater understanding of the
challenges facing, and the solutions to, effective water pollution control.
xiii

Table of Contents
xi
Preface xiii
Acknowledgements xv
CHAPTER 1: SURFACE WATER QUALITY AND
AQUATIC ECOSYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Progress in Water Quality 1
1.2 Leading Sources of Water Quality Impairment 2
1.3 Pollutant Loadings to Receiving Streams:
Total Maximum Daily Load (TMDL) Program 3
1.4 General Characteristics of Aquatic Ecosystems 5
CHAPTER 2: POLLUTANT CATEGORIES AND EFFECTS
ON SURFACE WATERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 Leading Causes of Water Quality Impairment 15
2.2 Pollution of Surface Waters 15
CHAPTER 3: CLASSIFICATION AND MEASUREMENT
OF POLLUTANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.1 Conventional Pollutants 31
3.2 Other Pollutants 33
CHAPTER 4: WASTEWATER PRE-TREATMENT
TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1 Wastewater Treatment Unit Operations 41
4.2 Screening and Grit Removal 43
4.3 Equalization 44
vii
Foreword

4.4 Primary Clarification 47
4.5 Neutralization 48
4.6 Oil Removal 49
4.7 Flotation 54
CHAPTER 5: BIOLOGICAL TREATMENT
TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.1 Activated Sludge Treatment 60
5.2 Other Suspended Growth Biological
Treatment Systems 70
5.3 Attached Growth Systems 75
5.4 Anaerobic Biological Treatment Systems 76
CHAPTER 6: PHYSICAL/CHEMICAL TREATMENT
TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.1 Activated Carbon Adsorption 87
6.2 Ion Exchange Systems 92
6.3 Stripping 95
6.4 Coagulation and Flocculation 99
6.5 Heavy Metals Removal 104
6.6 Chemical Oxidation and Reduction 106
6.7 Hydrothermal Oxidation 108
CHAPTER 7: PHYSICAL SEPARATION
TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
7.1 Filtration 111
7.2 Membrane Technologies 113
CHAPTER 8: DISINFECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
CHAPTER 9: NUTRIENT REMOVAL. . . . . . . . . . . . . . . . . . . . . . . . 125
9.1 Phosphorus Removal 125
9.2 Nitrogen Removal 128
CHAPTER 10: SLUDGE HANDLING AND DISPOSAL . . . . . . . . . 133
10.1 Types of Sludges 135
10.2 Sludge Thickening 135
10.3 Sludge Dewatering 137
10.4 Sludge Disposal 141
Table of Contents
viii

CHAPTER 11: LAND TREATMENT. . . . . . . . . . . . . . . . . . . . . . . . . 147
11.1 Spray Irrigation and Overland Flow Systems 147
11.2 Wastewater Characteristics and Design Considerations 149
CHAPTER 12: WASTE MINIMIZATION AND
WATER REUSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
12.1 Waste Minimization Techniques 153
12.2 Waste Minimization Assessment 154
12.3 Pollution Reduction Methods 154
12.4 Case Histories and Examples 157
12.5 Recycle/Reuse and Treatment Cost Considerations 161
CHAPTER 13: ECONOMICS OF WASTEWATER
TREATMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
13.1 Capital Cost Estimates 165
13.2 Operation and Maintenance Cost Estimates 168
13.3 Present Value Cost Analysis 168
References 173
Bibliography 175
Index 177
About the Authors
Table of Contents ix
192

CHAPTER 1
Surface Water Quality and
Aquatic Ecosystems
1.1 PROGRESS IN WATER QUALITY
IN the 1970s, much of Lake Erie was little more than a eutrophied cesspool.
Agricultural runoff and organic and nutrient loadings from untreated or
partially treated sewage and industrial waste caused dissolved oxygen levels in
the lake to drop, introduced toxic effects, and stimulated an explosion in algal
growth, leading to eutrophication and strangulation of the lake’s aquatic
ecosystems. In the early 1970s, anglers could only catch “trash” fish such as
carp and eel in many sections of the lake, and much of the lake was posted
against swimming due to the presence of pathogens and toxic chemicals.
Around the same time, the Cuyahoga River in Ohio caught fire due to
pollution from chemical plants and refineries. The Kanawha River at
Charleston, West Virginia was essentially an open chemical sewer in the early
1970s. Severely mutated fish and other aquatic organisms were frequently
found. Polychlorinated biphenyls (PCBs) were found in polar bear flesh in the
Arctic Circle and in mothers’ milk in the United States. The pesticide DDT
weakened eggshells in the brown pelican, bald eagle, and other birds feeding at
the top of their food chain, and threatened them with extinction.
Loss of habitat and the effects of pollution have significantly endangered
America’s aquatic wildlife. In the Illinois River, for example, approximately 66
percent of the indigenous fish species have vanished because of water
pollution. In Muscle Shoals, Alabama, 30 of 63 mussel species disappeared
after the construction of a major dam. In the Chesapeake Bay, fish and shellfish
harvests have been off dramatically since the 1960s—a 96 percent decline for
hickory shad catches alone.
As governmental regulation has clamped down on point sources of water
pollution, significant progress towards recovery has been made. Yet, much
remains to be done.
Every two years, EPA submits its National Water Quality Inventory report to
1

Congress. This report summarizes water quality data collected by all 50 states,
Interstate Water Commissions, American Indian Tribes, and the District of
Columbia. By 2000, government agencies had surveyed approximately
700,000 miles of rivers and streams (approximately 19 percent of the nation’s
total); 17,339,080 acres of lakes (43% of the total); and 31,072 square miles of
estuaries (36% of the total).
Table 1.1 summarizes some of the results of EPA’s 2000 National Water
Quality Inventory [1], and indicates whether the surface waters surveyed
support their intended uses. As can be seen from this table, only 53 percent of
the nation’s rivers and streams, 47 percent of lakes, and only 45 percent of
estuaries surveyed are considered to be of good quality, supporting most or all
of the water quality needs and objectives.
1.2 LEADING SOURCES OF WATER QUALITY IMPAIRMENT
Table 1.2, reproduced from the 2000 National Water Quality Inventory,
summarizes the leading causes and sources of water quality impairment in the
United States today.
The public has the general impression that industrial plants are the major
cause of water pollution. Thus, many people are surprised to find that the
current leading causes of surface water pollution are from agriculture,
municipal wastewater point sources, hydrologic modification (channelization,
flow regulation and dredging), and urban runoff/storm sewers. This is because
industrial wastewater point sources of pollution are now treated prior to
discharge, due primarily to enforcement of the Clean Water Act. Prior to that
act, this was not the case.
Later chapters of this book describe the various technologies that have been
driven by the Clean Water Act’s massive regulatory regime for point sources.
This regime will continue to impose more stringent limits as the technology
SURFACE WATER QUALITY AND AQUATIC ECOSYSTEMS
2
TABLE 1.1. Summary of Quality of Assessed Rivers,
Lakes and Estuaries [1].
Total Size
Amount
Assessed
(% of Total)
Good
(% of
Assessed)
Good but
Threatened
(% of
Assessed)
Polluted
(% of
Assessed)
Rivers and
Streams (miles)
3,692,830 699,946
(19%)
367,129
(53%)
59.504
(8%)
269,258
(39%)
Lakes, Ponds and
Reservoirs (acres)
40,603,893 17,339,080
(43%)
8,026,988
(47%)
1,348,903
(8%)
7,702,370
(45%)
Estuaries (square
miles)
87,369 31,072
(36%)
13,850
(45%)
1,023
(<4%)
15,676
(51%)

continues to advance. But the results will yield declining returns, particularly
compared to the significant problems currently caused by agricultural and
urban non-point source runoff. Many of the techniques that will be required to
remedy these challenging problems are much simpler, technically speaking, but
far more challenging politically to impose. Nonetheless, this difficult work
must be continued to bring all of the nations’ waterways to the desired level of
quality.
1.3 POLLUTANT LOADINGS TO RECEIVING STREAMS:
TOTAL MAXIMUM DAILY LOAD (TMDL) PROGRAM
Section 303(d) of the Clean Water Act (CWA) requires each state to identify
the sections of lakes, rivers and streams that are impaired; i.e., they do not meet
at least one water quality standard established for them. (It does not necessarily
mean that the pollution is so bad that it represents a threat to human health or a
serious threat to the environment.) The states are then required to establish a
total maximum daily load (TMDL) for each pollutant affecting each impaired
aquatic ecosystem.
A TMDL is the amount of a pollutant that a water body can receive in a day
and still meet water quality standards. The TMDL has been termed a “pollution
budget.” The TMDL is a calculated amount that must account for seasonal
variability in water quality, and include a margin of safety to ensure that the
water body can meet the water quality standards the state has designated. By
establishing TMDLs, it is believed, states and communities can identify the
causes and sources of the specific pollutants impairing each water system, and
develop plans to stop the pollution.
Pollutant Loadings to Receiving Streams 3
TABLE 1.2. Leading Causes and Sources* of Impairment in Assessed
Rivers, Lakes and Estuaries [1].
Rivers and Streams
Lakes, Ponds, and
Reservoirs Estuaries
Causes Pathogens (Bacteria)
Siltation
(Sedimentation)
Habitat Alterations
Nutrients
Metals (Primarily mercury)
Siltation (Sedimentation)
Metals (Primarily
mercury)
Pesticides
Oxygen-Depleting
Substances
Sources Agriculture
Hydrologic Modification
Habitat Modification
Agriculture
Hydrologic Modification
Urban Runoff/Storm
Sewers
Municipal Point
Sources
Urban Runoff/Storm
Sewers
Industrial Discharges
*Excluding unknown, natural, and “other” sources.

The EPA is then charged with approving or disapproving State submissions.
If the EPA is not satisfied with the state’s submissions, § 303(d) of the Act
authorizes the agency to develop a priority list for the state and make its own
TMDL determinations.
Currently, the EPA estimates that about 21,000 polluted river segments,
lakes and estuaries—comprising over 300,000 river and shore miles and five
million lake acres—are impaired. Excess nutrients, sediments and harmful
microorganisms are the leading reasons for impairment. The 1998 303(d) list
reports that 43% of the impairment is caused by non-point source pollution,
10% is caused by point sources, and that 47% of the impaired waters are
impacted due to a combination of non-point and point sources of pollution.
TMDLs have been approved by the EPA for the following pollutants and
parameters, among others:
∑ Sediments
∑ Pathogens
∑ Nutrients
∑ Metals
∑ Dissolved Oxygen
∑ Temperature
∑ pH
∑ Pesticides
∑ Mercury
∑ Organics (measured as oxygen-demanding substances or as the actual
organic compounds)
When TMDLs are established, wastewater treatment plants for communities
and industry may need new technologies to meet more stringent discharge
standards. States and EPA enforce the TMDLs through NPDES and Industrial
User permits.
The CWA does not regulate non-point source runoff, and there are no other
Federal regulatory programs specifically designed to control these sources of
pollution. The primary implementation measures for non-point pollutants are
expected to be state-run non-point source management programs, coupled with
state, local, and federal land management and agricultural programs and
authorities.
Implementation of the TMDL program could cause major changes in
traditional methods of agriculture, construction, recreation, urban
development, and many other areas of human endeavor. Farmers and ranchers
may be asked to use alternative methods in their operations to prevent fertilizers
and pesticides from reaching rivers. Golf courses may be required to reevaluate
their intensive fertilization and pesticide/herbicide programs. Cities may be
required to control and treat storm water runoff from their communities and
streets.
4

As of this writing, the TMDL program has not been approved and may be
withdrawn or substantially modified. In any case, it is likely that some form of
TMDL scheme will eventually be implemented to minimize impairment of
surface water quality.
1.4 GENERAL CHARACTERISTICS OF
AQUATIC ECOSYSTEMS
The simplest aquatic ecosystem involves enormous complexity in its
interactions of chemistry and life. In order to comprehend the dynamic
imperatives of an aquatic ecosystem, one needs to understand three
fundamental biological concepts: food webs, energy and material transfer, and
population dynamics. These three concepts are inextricably interrelated. An
effect upon one usually causes significant changes in the others.
1.4.1 Food Webs
Most people are familiar with the term food chain. It is useful for portraying,
in a very gross fashion, the concept of trophic, or nutritional, relationships. The
term food chain demonstrates the concept that higher organisms are dependent
on lower organisms for nutrition and survival. A common food chain describes
humans as being at the top, as carnivores or omnivores, who feed on herbivores,
which in turn feed upon plants, which derive their nutrition directly from the
sun and the earth. This very simple food chain is representative of only a few
organisms, as most rely upon multiple sources of nutrition. Trophic
relationships between two separate organisms, for example, might be separated
by hundreds of other species or other energy inputs into the system.
The term food web is used to describe these more complex relationships.
Food Web: A simplified food web for the herring Clupea harengus is
presented in Figure 1.1. Even this simplified food web represents an extremely
complex trophic system. At the bottom of the food web are diatoms, flagellates,
and other phytoplankton. These are fed upon by zooplankton represented in
large part in this food web by copepods. Proceeding up the food web, the
organisms are progressively more complex.
In examining the food web, one can observe that the herring’s diet changes as
it grows. As it grows, it feeds on a larger variety of organisms. This food web
stops with the adult herring. It could be extended to show the myriad trophic
relationships among organisms that depend principally or in part on the herring
for nutrition, including humans.
Most trophic relationships between organisms in aquatic ecosystems are
extremely complex and sensitive to outside interruption. Pollution can affect
the food web in several ways. One of the most common effects can be
General Characteristics of Aquatic Ecosystems 5

illustrated in the following scenario, using the herring food web as an example.
A toxic pollutant (vinyl chloride, for example) is discharged in the effluent of a
plastic pipe manufacturing company into a river. The pollutant enters an
aquatic ecosystem and exerts mutagenic (i.e., DNA-damaging) effects on
developing copepod larvae resulting in a brood reduction of 50 percent. This
will correspond later to an approximate total reduction of available zooplankton
biomass of about 80 percent.
The effects on the food web community would be catastrophic. The herring
fry would have very little to eat (since most of the copepods are no longer
present) and would become weakened and subject to disease and increased
predation. The larger herring can shift their eating habits to include other
organisms, thereby placing additional strain on these populations. Eventually,
the adult herring populations would be affected, perhaps significantly. The
effects of pollution are most seriously felt by organisms during their critical life
stage (usually early in the organism’s life cycle; e.g., egg, embryo, larval, sac
fry, etc.).
There are literally thousands of instances where fish harvests at numerous
locations have declined significantly or have been eliminated altogether
because of pollutant impacts in the food web. A seemingly minor amount of
pollutant could cause the elimination of a single species or entire classes of
organisms, resulting in serious impacts on community organisms that depend
upon them for nutrition.
In the past, environmental engineers and scientists were concerned about
removing gross contamination, in the belief that the assimilative capacities (the
6
Figure 1.1. Partial Herring Food Web (After Hardy, 1959) [2].

ability of aquatic systems to rejuvenate themselves by dilution, degradation,
and biological uptake of pollutants) would be sufficient to restore the systems
to near pristine conditions.
Much more needs to be done to improve the quality of wastewater discharges
if the objective is to restore our rivers, lakes, oceans, and streams to their natural
condition. One of the primary challenges is to halt or minimize disruptions to
the food web so that the natural system dynamic can be allowed to express
itself.
The first step in this process is to understand the trophic state of a particular
water body. Conventionally, there are five such states:
Trophic States of Surface Waters
Oligotrophic Clear waters with little organic matter or sediment and
minimum biological activity.
Mesotrophic Waters with more nutrients and, therefore, more biological
productivity.
Eutrophic Waters extremely rich in nutrients, with high biological
productivity. Some species may be choked out.
Hypereutrophic Murky, highly productive waters, closest to the wetlands
status. Many clearwater species cannot survive.
Dystrophic Low in nutrients, highly colored with dissolved humic
organic matter. (Not necessarily a part of the natural trophic
progression.)
The next step in improving one’s understanding of water quality and effects
of pollution is to address the interplay between trophic states and the balance
and transfer of mass and energy in a water body.
1.4.2 Energy and Material Transfer
It is useful to view a receiving stream, lake, ocean, or any aquatic
environment as a dynamic system, much as the human body is a dynamic
system. The human body receives nutrition, is exposed to sunlight, exerts
energy, respires, produces heat and biomass, excretes wastes, and eventually
dies and decomposes. An aquatic ecosystem expresses this same dynamism for
millions of living organisms. Some of this activity is represented by the trophic
relationships of the food web. The food web expresses only a portion of the
biochemical, chemical, and physical activity occurring in an aquatic
ecosystem, however.
Figure 1.2 represents energy and material transfers in riffle communities of
the Berry Creek Experimental Stream under studies conducted by Warren, et
al., in the mid-1960s [3]. These energy and mass balance diagrams illustrate
the dynamic interdependence of organisms in an aquatic ecosystem. In the

Figure 1.2. Differences in Biomass and in Energy and Material Transfer in Riffle Communities of
Berry Creek Experimental Stream, Oregon, Occasioned by Continuous Enrichment with Sucrose
[3].
8

experiment, light energy and leaf fall (the principal sources of input energy and
chemicals) are maintained at fairly even levels for both Riffles A and B. This is
to establish that the primary external energy inputs to the two systems are the
same. Other researchers have shown that doubling light energy levels results in
an approximate doubling of plant biomass production and a corresponding
doubling in insect and fish biomass [4]. Obviously it is important to control
these critical input values so that the experimental effect can be observed
without interference from control inputs.
The experimental effect was the introduction of low concentrations of a
simple organic compound, sucrose (a sugar). Riffle A is the control unit and
Riffle B is the experimental unit in which sucrose was continuously introduced
at a concentration of about 4 mg/l. This low concentration could not exert
oxygen depletion of any significance in this system, nor have any other
significant impacts on water quality. Yet researchers were surprised at the
results of the experiment. Over the period of a year the seemingly low, 4 mg/l,
concentration of sucrose added up to an energy input into the Riffle B system of
130,000 kcal/m2.
Refer to the bottom left portion of the Riffle B diagram. The introduction of
sucrose stimulated a rapid growth of bacteria, primarily Sphaerotilus, a
bacterium familiar to wastewater scientists and engineers. The Sphaerotilus
became a major source of previously unavailable nutrition for protozoa,
copepods, insects, snails, and other organisms. Herbivorous insect biomass
increased by 250 percent, carnivorous insects by 400 percent, and snail biomass
by nearly 650 percent over the control Riffle A. The new food source
reverberated throughout the food web, resulting in significantly increased
production of biomass for vertebrates and other complex organisms, as well as
for lower organisms.
Increases are also to be expected in community respiration, waste
production, heat output, decompositional biomass, and export of materials. In
other ecosystems, this overabundance of input energy could exceed the
assimilative capacity of the system and possibly result in anaerobic (without
oxygen), eutrophic, or other undesirable conditions that could cause massive
fish kills, declining populations of desirable organisms, and increasing
populations of undesirable organisms.
Pollution can cause many detrimental effects on the energy and material
ecosystem balances. Even trace concentrations of pollutants can have
cumulative effects that can negatively impact ecosystem stability.
1.4.3 Population Dynamics
As the foregoing shows, the principal consequence of changes in trophic
state and in energy/material balance is change in populations of living
creatures. The two principal constituents of population dynamics are species

diversity and population density. Healthy ecosystems generally have a high
species diversity of organisms, reflecting the diversity of the trophic levels in
the ecosystem. Healthy systems with numerous trophic levels are expected to
have good species diversity. Unhealthy systems with fewer trophic levels
generally do not. Population density refers to the number of organisms per unit
of living space.
Bacteria and more complex microbes such as protozoans (rotifers,
vorticella, amoeba, ciliates, etc.) occupy the bottom of the food web, feeding on
dissolved chemical constituents in the water and on solid/semi-solid matter
such as fish slime, detritus, decomposing organisms, benthic (bottom) material,
and other sources of nutrition.
Algae populations directly reflect the chemistry of the water in which they
live. Too much nitrogen and phosphorus can lead to excessive algal growth,
resulting in algae-choked streams, massive fish kills, and eutrophied lakes. To
be in equilibrium in a natural system, the growth of algae must be the same as
the loss by death, over the period of the growing season. Also, a system with
good diversity will exhibit representatives from more than one of the algae
groups (red, green, and blue-green).
The plankton (free-floating organisms) exist at the next level of the web, with
the phytoplankton (plants) deriving their principal source of nutrition through
photosynthesis, and the zooplankton (animals) feeding on living and
decomposing plant and animal material.
Further up the food web are the macro-organisms, those organisms that can
be readily seen without the benefit of a microscope. These are represented by
crustacea, insects, oligiochetes (worms), fish, and other higher organisms.
A healthy system exhibits good species diversity and population density as
determined by the trophic and environmental dynamics of the system.
Unhealthy aquatic ecosystems generally exhibit low species diversity and
relatively high populations of organisms resistant to pollution.
Figure 1.3 illustrates the effects of pollution on macro-organism diversity
and populations caused by wastewater discharge into a clean stream. Referring
to Figure 1.3, at miles 24 to 0 upstream, the water column and benthic dwelling
organisms are represented by excellent diversity in species. At mile 0, the point
of wastewater discharge, water quality is rapidly degraded, resulting in a
correspondingly sharp decrease in species diversity but an increase in
populations of pollution-resistant organisms, notably sludge worms and other
benthic creatures.
As one would expect, waste discharges also affect the populations and
diversity of microorganisms, as illustrated in Figure 1.4. This figure illustrates
the enormous population shifts at the point of waste discharge (river mile 0),
where a sudden increase in pathogens and sewage bacteria is seen. The sewage
bacteria degrade the sewage and decline in numbers as their food source
disappears. They, in turn, are fed upon by the ciliates, which are themselves
10

11
Figure 1.4. Effects of Waste Discharge on Population Distribution of Microorganisms [5].
Figure 1.3. Changes in Population of Macro-Organisms Caused by Waste Discharge into a Clean
Stream [5].

Figure 1.5. Present State and Desired Future State of the Lower Green Bay Ecosystem [6].
12

prey for the rotifers and crustaceans, and so on up and through the food web.
Waste discharges can exert profound effects on the food web and population
dynamics by seriously altering the trophic opportunities and relations in the
aquatic ecosystem.
Water pollution can affect species diversity and population densities of
aquatic organisms in a very significant fashion.
Figure 1.5 illustrates the difference in species diversities and population
densities of a polluted and a healthy aquatic ecosystem. Note the significantly
increased species diversity in the “Future State” illustration, and the
significantly lower species diversity in the “Present State” illustration.

CHAPTER 2
Pollutant Categories and Effects
on Surface Waters
2.1 LEADING CAUSES OF WATER QUALITY IMPAIRMENT
WATER pollution is a general term used to describe the degradation of water
quality resulting from the loss of the productive or aesthetic uses of the
receiving stream. Water pollution causes water quality impairment. However,
there are several broad categories of pollution, arising from a number of
chemicals, combinations of chemicals, or other polluting factors. Some
chemicals can cause or contribute to more than one type of pollution.
Ammonia, for example, can contribute to oxygen depletion and eutrophication.
At elevated concentrations, and in certain water quality situations, ammonia
can also exert acute toxic effects on aquatic organisms.
The 1996 National Water Quality Inventory [7] ranked the five leading
causes of water quality impairment (Table 2.1) for surface waters.
Figure 2.1 illustrates the effects of certain pollutant categories (nutrients,
sediments, and toxicants) on the aquatic flora and fauna of Chesapeake Bay.
Note the ecological differences between the healthy and the polluted systems
and the effects of the different pollutant categories on stream health.
2.2 POLLUTION OF SURFACE WATERS
This section provides a description and some examples of each of the
principal adverse effects caused by the following types of pollution:
∑ Oxygen Depletion
∑ Eutrophication
∑ Temperature Effects
∑ Toxicity and Radiological Effects
∑ Pathogens
∑ Siltation/Turbidity
∑ Salinity
15

2.2.1 Oxygen Depletion
Oxygen depletion is brought about by the introduction of oxygen-demanding
wastewaters into aquatic ecosystems. This results in lowered dissolved oxygen
concentrations, and in extreme cases, anaerobic (without oxygen) conditions
that completely alter ecosystem chemistry, food webs, population dynamics,
and energy and materials transfer, making conditions uninhabitable for many
organisms. Most fish require a minimum of 2.0 mg/l dissolved oxygen for
TABLE 2.1. Five Leading Causes of Water Quality Impairment [7].
Rank Rivers Lakes Estuaries
1 Siltation Nutrients Nutrients
2 Nutrients Metals Bacteria
3 Bacteria Siltation Priority Toxic Organic Chemicals
4 Oxygen-Depleting
Substances
Oxygen-Depleting
Substances
Oxygen-Depleting Substances
5 Pesticides Noxious Aquatic Plants Oil and Grease
Figure 2.1. Effects of Pollutants in the Chesapeake Bay [6]. Source: Redrawn from Alice J.
Lipson. In: Maryland Tributary Strategies—Restoring the Chesapeake. Overview. Maryland
Department of the Environment, Baltimore, MD.
POLLUTANT CATEGORIES AND EFFECTS ON SURFACE WATERS
16

survival, and some (trout for example) cannot survive without much higher
oxygen concentrations.
Fish existing in large zones of oxygen-depleted water will suffocate if
they cannot swim out of those zones. Most fish kills are caused by oxygen
depletion.
Dissolved oxygen (D.O.) is molecular oxygen (O2) dissolved in water. The
solubility of D.O. depends on atmospheric pressure, temperature, and stream
salinity. At 15∞C and 1 atm pressure the solubility limit of oxygen, i.e., when it
is at saturation, is only about 10 mg/l or 0.001 percent—very little, when one
considers that ambient air contains approximately 21 percent O2.
In a receiving stream, oxygen is replenished via atmospheric reaeration
(incorporation of air into water by splashing, etc.), dynamic equilibrium (direct
dissolution of oxygen from air into water due to atmospheric pressure), and
photosynthesis. The rate of reaeration is generally just enough to sustain D.O.
concentrations at near saturation levels on the surface of the water column, and
at progressively lower levels down to the bottom (or benthic) level. The
introduction of millions of gallons per day (MGD) of oxygen-demanding
wastewater is sufficient to cause oxygen depletion or suppression in many large
receiving streams.
Wastewaters that cause oxygen depletion are said to exert an oxygen demand
on the receiving stream. There are two main ways of describing oxygen demand
in receiving streams: biochemical oxygen demand (BOD) and chemical oxygen
demand (COD). BOD is expressed as mg/l of oxygen consumed in a bioassay
test procedure, whereas COD is a measurement of the amount of oxygen
consumed in a wet chemistry laboratory procedure. Most wastestreams exhibit
both types of oxygen demand.
2.2.1.1 Biochemical Oxygen Demand (BOD)
Most oxygen demanding wastes contain biodegradable compounds. These
wastewaters contain organic and inorganic constituents that act as a food or
energy source to microorganisms in the receiving stream. The wastewater
constituent chemicals dissolve in the stream and come into contact with
microbes, which absorb them or attack them biochemically to break complex
molecules down into simpler molecules that can be metabolized by the
microbes. Oxygen is used in this metabolic process, known as biochemical
oxidation, and is thus extracted from the river or stream.
Organic carbon compounds are the most important category of these
constituents, and organic enrichment is a term used to describe this type of
pollution. BOD exerted by such compounds is referred to as carbonaceous
oxygen demand. Compounds built around elements other than carbon can also
feed microorganisms and thus give rise to BOD. For example, nitrogen
compounds can yield significant amounts of nitrogenous oxygen demand as
Pollution of Surface Waters 17

organisms degrade them in a process called nitrification (see discussion on
“Nitrogen Removal”).
The degree of degradation and associated oxygen consumption can be
extensive enough to cause oxygen depletion in the stream. It can take from 1 to
1.5 lbs of oxygen to completely degrade 1 lb of BOD, or about 600 gallons of
wastewater containing 200 mg/l BOD. A spill of only 100 lbs of BOD can
deplete the oxygen in about 3 to 12 million gallons of water. The low solubility
of oxygen in water (averaging about 6 to 10 mg/l for most surface streams)
contributes to its ready depletion. The oxygen balance in aquatic ecosystems is
one of the more sensitive limiting factors in maintaining system health and
viability.
2.2.1.2 Chemical Oxygen Demand (COD)
Some waste streams contain inorganic chemicals that consume oxygen
directly without the involvement of living organisms. These substances engage
in oxidizing reactions in water. A simple example is iron which, when in
contact with water, will consume oxygen while oxidizing into iron oxide or
rust. Waste streams containing such substances are said to exert a chemical
oxygen demand. The COD test procedure measures wastewater chemical
oxygen demand and, for most but not all wastewaters, includes biochemical
oxygen demand.
Figures 1.3 and 1.4, shown earlier, represent the effects of oxygen depletion
on aquatic organisms in a flowing stream (these figures are representative of
any flowing stream, rivers, creeks, etc.).
Figure 2.2 shows a classic depiction of oxygen depletion, or D.O. sag
(pronounced “doe sag”). Upstream of the Town and Sewage Plant (river miles
-25 to -10), stream D.O. is near saturation at 8.0 mg/l. Storm water runoff from
the Town (river mile -15) causes a slight increase in stream BOD, but exerts no
discernible effect on river D.O. The stream is able to assimilate this relatively
light pollutant loading.
At river mile -10, effluent from the Sewage Plant enters the stream and has
an immediate effect. The sewage exerts a strong oxygen demand, as stream
BOD increases from about 5 mg/l to 25 mg/l, and stream D.O. drops from 8
mg/l to zero mg/l, all in less than 5 stream miles. Most fish cannot tolerate D.O.
concentrations of much less than 2.0 mg/l. If they are able, they will leave the
area and seek D.O. in order to respire properly. If they are unable to escape the
D.O. sag, they will perish.
The stream begins a slight recovery, reducing BOD somewhat, between river
miles -5 and zero, but this improvement is largely overcome by pollutant
loadings from the Industrial Plant at river mile five. BOD in the Industrial Plant
discharge introduces a BOD spike and the BOD loadings continue to suppress
18

dissolved oxygen until gradual recovery is evidenced between river miles 10 to
25.
Some streams have sufficient assimilative capacity to absorb
oxygen-depleting wastewaters. That is, these streams possess sufficient flow
rate to dilute and distribute the wastewater, and sufficient reaeration
(oxygenation) capacity, bacteria, and other environmental factors, to allow the
degradation of the wastes without significant impacts to the aquatic
ecosystem.
2.2.2 Eutrophication
Eutrophication encompasses a number of processes that lead to the decline in
productivity of desirable species and aesthetic value of an aquatic system.
These processes include an accumulation of organic matter and nutrients
(especially nitrogen and phosphorus), an increase in total biomass production
(especially algae and microorganisms) and respiration, and a decrease in depth
of the system (due to buildup of sediments).
Increased nutrient loadings generate increases in both plant and animal
Figure 2.2. Typical Dissolved Oxygen Sag.

biomass. Animal biomass exerts BOD, as just explained. Plants, on the other
hand, consume CO2 and expel O2, the reverse of animals. At first glance,
therefore, the increasing plant growth in eutrophied water bodies (mostly algae)
would seem to satisfy the BOD caused by increasing animal biomass. However,
such plant growth is often runaway, the most notable example being algae
blooms, as illustrated in Figure 2.3. The decomposition of such large quantities
of dead plant matter can exert massive BOD, causing dramatic D.O. sag and
catastrophic animal die-offs.
Eutrophication is a natural process for lakes and streams, although the
completion of a natural eutrophication cycle can take hundreds to thousands of
years. However, the introduction of concentrated industrial wastewaters and
sewage effluents to surface waters has accelerated this process a thousand-fold
in some systems.
Figure 2.4 illustrates the gradual effects of natural stream aging compared to
the accelerating effects of pollution on the process.
Eutrophication leads to a reduction in species diversity and, generally, an
increase in population densities of a relatively few species. One of the most
widely investigated instances of eutrophication has been that of the Great Lakes
beginning in the 1950s. During the post-war industrialization and population
explosion in this region, significant increases of untreated or partially treated
industrial wastes and sewage were introduced into the Great Lakes, most
notably Lake Erie. Oxygen-demanding and nutrient-rich wastewaters
accelerated the eutrophication process to the extent that it became necessary to
introduce regulations forbidding the untreated discharge of wastes into the
lakes. Figure 2.5, Commercial Production of Selected Fish in Lake Erie,
Figure 2.3. Lake Impairments Caused by Excessive Nutrient Loadings [7].
20

Figure 2.4. The Progression of Eutrophication [8]. (left column) The progression of natural lake
aging or eutrophication through nutrient-poor (oligotrophy) to nutrient-rich (eutrophy) sites.
Hypereutrophy represents extreme productivity characterized by algal blooms or dense
macrophyte populations (or both) plus a high level of sedimentation. The diagram depicts the
natural process of gradual nutrient enrichment and basin filling over a long period of time (e.g.,
thousands of years). (right column) Cultural eutrophication in which lake aging is greatly
accelerated (e.g., tens of years) by increased inputs of nutrients and sediments into a lake, as a result
of watershed disturbance by humans. Source: NC Lake Assessment Report. NCDEHNR, DEM.
Report No. 92-02. June 1992.
21

Figure 2.5. Commercial Production of Selected Fish in Lake Erie [9].
22

illustrates the decline of commercial fish stocks in Lake Erie from the turn of
the century to the mid-1960s, due principally to the effects of eutrophication.
As can be seen in Figure 2.5, the commercial stocks of some species were
wiped out altogether. Carp, eel, and other undesirable fish populations
increased dramatically. The eutrophied lake evidenced classical symptoms of
eutrophic pollution: high production of undesirable biomass (algae, sludge
worms, trash fish, and bacteria), low species diversity, and a decline in
population of desirable species.
Since the advent of modern wastewater treatment facilities and discharge
restrictions, the Great Lakes have recovered considerably, but have far to go to
reach the aquatic quality of the early 20th century. Notably, many of the
pollution problems still afflicting the Great Lakes can be traced to air
deposition of metals and other bioaccumulative compounds, rather than to
wastewater discharges.
2.2.3 Temperature Effects
Thermal pollution is associated with large industrial facilities that use great
quantities of water for cooling purposes. These include fossil and nuclear
power plants, and pulp and paper mills. Discharge of this water adds heat to
receiving streams.
Parker and Krenkel [10] summarized the effects of thermal pollution on
aquatic organisms in their report entitled Thermal Pollution: Status of the Art.
Research by Laws [11] in his book Aquatic Pollution also contributes
significantly to the understanding of thermal pollution. Both sources were used
to develop the following summary of the effects of thermal pollution. Thermal
pollution has been found to result in:
∑ A shift in population structure of the ecosystem. Reduced diversity and
shifts in the predominant species have been observed.
∑ Death beyond certain temperatures. Many organisms throughout the
food web are intolerant of elevated temperatures and die upon exposure.
∑ Sublethal functional response. “Extreme temperature is a killer, of
course; but within the zone of tolerance, temperature is a catalyst, a
depressant, an activator, a restrictor, a stimulator, a controller.
Temperature is one of the most important and influential water quality
characteristics to life in water (Federal Water Pollution Control
Administration, 1967).”
∑ Decreased resistance to toxic substances. Toxicity usually increases with
increased temperature, and specimens subjected to toxic materials are
less tolerant of temperature extremes.
∑ Increased respiratory demand of aquatic organisms.
∑ Reduced solubility of oxygen in water.

∑ Stratification or further stratification of the water column so that
reoxygenation of subsurface water is inhibited. As any scuba diver will
attest, water often forms thermoclines, stratified layers of warmer water
underlain by layers of colder water. These thermoclines inhibit
movement of water in the vertical direction, to the detriment of
inhabitants of the lower layers.
∑ Attracting fish to thermal plumes and then trapping and killing them in
water intake systems.
2.2.4 Toxicity And Radiological Effects
The effects of exposure of aquatic organisms to toxic chemicals and radiation
are similar and include acute (short-term) and chronic (long-term) effects. The
effects of exposure to toxic chemicals and radionuclides include death,
increased susceptibility to disease, development of cancers and lesions, and
behavioral changes. Both exposure to toxic chemicals and radiation have been
observed to result in genetic damage and higher incidence of teratogenic
effects (non-genetic damage to embryos) in fish and other aquatic organisms.
Acute toxicity often results in the death of aquatic organisms. For example, in
soft water, lead is lethal to fathead minnows at a concentration of 5 to 7 mg/l.
Other acute effects include paralysis, muscle spasms, and unconsciousness.
Acute toxicity can be defined in terms of the Lethal Concentration50 (LC50), or
Median Tolerance Limit (TLm) bioassay test. The LC50 is the concentration at
which 50 percent of test organisms die within a specified period of time, usually
96 hours or less. In addition to assessing the acute toxicity of a particular
pollutant such as lead, this test can also be used to assess the toxicity of an
effluent stream generally; the test organisms are introduced into effluent of
some specified dilution, and their survival over time is measured. This process,
called the whole effluent toxicity or WET test, is increasingly specified as an
independent permit limitation that a waste stream must meet before discharge.
Table 2.2 presents 96-hr LC50 data for fathead minnows, daphnia (waterfleas),
and rainbow trout exposed to a number of the priority pollutant organic
compounds, metals, and ammonia.
Concentrations of pollutants that have no observable acute effects on test
species may nonetheless exert chronic, or sublethal, effects on them. Chronic
effects can include growth or behavioral effects, mutation, reduced or impaired
reproduction, disease, and eventual death. While the effects of chronic toxicity
can be subtle and highly variable, chronic stresses can eventually be just as
destructive to aquatic communities as acute effects.
Bioaccumulation is a chronic effect experienced by aquatic organisms
exposed to certain chemicals. Heavy metals, pesticides, herbicides, PCBs, and
radioactive materials are all categories of substances known to
bioaccumulate—the body does not metabolize or excrete them. Instead, the
24

TABLE 2.2. Acute Toxicity of Selected Compounds (96-hr LC50)a
[12].
Units
Fathead
Minnow Daphnia
Rainbow
Trout
Organicsb
Benzene mg/l 42.70 35.20 38.70
Carbon tetrachloride mg/l 17.30 15.20 14.50
Chlorobenzene mg/l 13.20 11.60 11.10
1,1-Dichloroethane mg/l 120.00 96.40 113.00
1,1,2-Trichloroethane mg/l 88.70 72.60 81.10
2-Chlorophenol mg/l 21.60 18.60 18.40
1,4-Dichlorobenzene mg/l 3.72 3.46 2.89
1,2-Dichlorobenzene mg/l 87.40 71.10 80.50
2,4-Dinitrophenol mg/l 5.81 5.35 4.56
4,6-Dinitro-o-cresol mg/l 2.79 2.65 2.10
Pentachlorophenol mg/l 170.00 – –
Ethylbenzene mg/l 11.00 9.97 9.47
Methylene chloride mg/l 325.00 249.00 325.00
Toluene mg/l 31.00 26.00 27.40
Trichloroethylene mg/l 55.40 46.20 49.50
Phenol mg/l 39.60 33.00 35.40
1,4-Dinitrobenzene mg/l 1.68 1.61 1.24
2,4,6-Trichlorophenol mg/l 5.91 5.45 4.62
2,4-Dichlorophenol mg/l 9.27 8.35 7.49
Naphthalene mg/l 5.57 5.07 4.44
Nitrobenzene mg/l 118.00 95.40 110.00
1,1,2,2-Tetrachloroethane mg/l 31.10 26.70 26.70
Metalsb
Arsenic 15,600 5,278 13,340
Chromium, hexavalent 43,600 6.400 69,000
Cadmium 38.2 0.29 0.04
Copper 3.29 0.43 1.02
Lead 158.00 4.02 158.00
Mercury – 5.00 249.00
Nickel 440.00 54.00 –
Selenium 1,460.00 710.00 10,200
Silver 0.012 0.00192 0.023
Zinc 169.00 8.89 26.20
Inorganics
Unionized ammonia (Total
Ammonia)c
PH 7.0 mg/l 0.093 (23) 0.093 (23)
PH 8.5 mg/l 0.260 (6.8) 0.260 (6.8)
aEstimation of 96 hour LC50 in mg/l for common aquatic test organisms based on the primary mode of action
and structure-activity relationship.
bFrom: EPA/Montana State QSAR (Quantitative Structure Activity Relationship) system.
cHighly variable depending on pH and Temperature (Federal Volume Register 50, No. 185, Monday, July 29,
1985, pp. 10786). Data represent criteria to protect aquatic life at pH 7.0 and 20∞C and pH 8.5 at 20∞C, one
hour average, mg/l.
25

substances continue to accumulate in the tissues and/or bones of receptor
organisms. When these organisms are, in turn, consumed by other organisms,
these substances bioaccumulate still further, contributing to enhanced or
amplified bioaccumulation up through the food web.
Fish that have accumulated mercury or pesticides, for example, do not
ordinarily acquire the chemicals through direct ingestion or exposure, but
rather consume them in their daily diet of a variety of organisms which have
themselves acquired the toxins through the consumption of plants and prey
animals exposed to the toxicants. These chemicals travel up and through the
food web (enhanced bioaccumulation) through consumption by predator
species, including humans. A well-known example of enhanced
bioaccumulation is the bald eagle’s brush with extinction due to DDT that had
concentrated up the food web dominated by the eagle.
Toxic chemicals can bioaccumulate in organisms until a threshold
concentration is reached that can exert acute or chronic effects. Certain toxins
accumulated in tissue or fat can be released into the vascular system during
periods of stress, thereby causing acute or chronic effects.
2.2.5 Pathogens
Infectious organisms enter surface water supplies by the discharge of
untreated wastewater, diluted sewage bypassed into receiving streams from
overflowing sanitary sewers or overloaded treatment plants, from wildlife, and
from animal feedlot runoff. For the most part these organisms die soon after
exposure to surface water because they are enteric organisms; i.e., organisms
that live inside the intestines (or bodies) of warm-blooded host organisms.
Four classes of pathogens are of most concern: bacterial pathogens, viral
pathogens, protozoan pathogens, and parasitic worms. Some of these
pathogens affect aquatic organisms as well as humans, and some, such as the
hepatitis virus, can infect shellfish, which are later consumed by humans who
may then contract hepatitis. The principal pathogens found in surface waters
are summarized in Table 2.3.
The primary route of exposure to pathogens for humans is by the ingestion of
contaminated water or shellfish. Infection by some of these organisms may
result in acute effects, even fatality. Cholera, tuberculosis, and polio are the
three most dangerous common waterborne pathogens and have been
responsible for the deaths of millions of people in numerous epidemics around
the world.
Ingestion is not the only route of exposure for some pathogens. Leptospira
enters the blood stream through skin abrasions or mucus membranes. This
bacteria can cause acute infections in the kidney, liver, and central nervous
system. Humans are most often exposed when swimming in waters in which
26

infected warm-blooded animals have urinated. Exposure to leptospira often has
severe and sometimes fatal effects.
Another deadly organism is the Naegleria gurberi amoeba. This odious
organism enters the body through the nasal membranes and migrates to the
brain, spinal fluid, and blood stream, causing the fatal disease amoebic
meningocephalitis. Swimming in polluted waters is the most common form of
exposure. Figure 2.5 depicts some of the causes and effects of pathogen
pollution.
Of potential concern to the environmental scientist is the release into nature
of genetically engineered microorganisms (GEMs) from agricultural, industrial
and domestic wastewater treatment operations. No ill effects have yet been
noted, but the potential for very serious environmental effects, and impacts on
humans, does exist. In addition to scientifically modified organisms, mutated
bacteria and higher organisms have been observed in nature whose genetic
alterations have been attributed to residual hormones, antibiotics, pesticides
and other xenobiotic (man-made) compounds present in aquatic ecosystems. In
addition to natural pathogens, the possibility exists for the formation and
introduction of mutated destructive organisms that could potentially exert
pathogenic effects on an unknown scale. It is likely that, in the future, more
attention will be placed on the release of bioactive xenobiotic compounds and
genetically altered organisms.
2.2.6 Siltation/Turbidity
Siltation generally refers to the loading of suspended, but generally
TABLE 2.3. Pathogens in Surface Water [13].
Bacteria Viruses Protozoans Parasitic Worms
Salmonella Poliovirus Entamoeba histolytica Beef tapeworm
Shigella Echovirus Giardia lamblia
G. instestinalis
Ascaris
lumbricoides
(round worm)
Enteropathogenic
E. coli
Vibrio cholera
Coxsackievirus A
Coxsackievirus B
Naegleria gruberi Schistosoma
Leptospira Enteroviruses Trypanosoma
the Tularemia
pathogen
Hepatitis type A
Tuberculosis
bacteria
Gastroenteritis type A
Rotavirus
Reovirus
Adenovirus
Parvovirus

settleable, particulates to a receiving stream. The leading cause of siltation is
soil erosion caused by agricultural practices, although land development is also
an increasingly important source. Siltation disrupts benthic activity at the
bottom of receiving streams by covering habitat and creating a layer of
sediment over the original benthic system. It can interfere with the feeding
activities of animals that feed by filtration, affect the vision of other organisms,
and may be abrasive to sensitive structures like the gills of fish. Siltation has
been known to cause fish kills and to destroy fish spawning beds.
Turbidity generally refers to the loading of colloidal/suspended solids to a
receiving stream. Turbidity can also indicate the density of algae in a water
body. Solids that produce turbidity have a specific gravity close to that of water,
such that the particles remain in suspension in the water column and do not
readily settle. Turbidity can impact photosynthesis in algae and aquatic plants
by shading sunlight. Figure 2.7 depicts some of the causes and effects of
siltation/turbidity.
2.2.7 Salinity
Salinity is a measurement of the amount of dissolved inorganic salts in
solution. Industrial wastes high in salinity, such as effluent from pulp and paper
mills, petroleum refining, and coke and chemical plants can exert a deleterious
effect on the receiving stream by altering stream salinity or total dissolved
solids. Salinity is also a problem in estuaries, where salinity incursions from
ocean tidal currents occurs, or generally, wherever dams, irrigation diversion,
and other man-made changes in natural river courses and drainage patterns
have reduced or increased natural salinity levels.
28
Figure 2.6. Pathogen Indicators [9]. Some bacteria, such as fecal coliforms, provide evidence that
an estuary is contaminated with fecal material that may contain pathogenic bacteria and viruses
harmful to people. Often, the pathogenic viruses and bacteria do not adversely impact aquatic life
such as fish and shellfish. However, shellfish may accumulate bacteria and viruses that cause
human diseases when ingested. Therefore, officials restrict shellfish harvesting in contaminated
waters to protect public health. Bacteria also impair swimming uses because come pathogenic
bacteria and viruses can be transmitted by contact with contaminated water.

The natural salinity of a receiving stream is a critical factor in the support of
aquatic life. Altering the natural salinity content, by either increasing or
decreasing it, can have extremely deleterious effects on water quality. For
example, an industrial discharge that increases receiving stream salinity
increases the concentration of sodium, sulfate, calcium, chloride, or potassium
ions.
Both fresh and salt water fish are constantly challenged to regulate the
amount of water and salts in their bodies. They accomplish these tasks by
osmoregulation, ionic regulation, and excretion, primarily through the gills and
kidneys. Many fish can only accomplish these balances in water and salt
content within narrow ranges of salinity and cannot adapt to sudden
fluctuations in stream salinity. Organisms other than fish are also affected by
salinity. Decreases in coastal estuary or bay salinities have been known to
cause severe coral kills and to decrease the reproduction and growth of oyster
larvae.
Figure 2.7. The Effects of Siltation in Rivers and Streams [14]. Salination is one of the leading
pollution problems in the nation's rivers and streams. Over the long term, unchecked siltation can
alter habitat with profound adverse effects on aquatic life. In the short term, silt can kill fish directly,
destroy spawning beds, and increase water turbidity resulting in depressed photosynthetic rates.

CHAPTER 3
Classification and Measurement
of Pollutants
WASTEWATER pollutants are generally classified under the Clean Water
Act as conventional, non-conventional, and toxic or priority pollutants.
Each of these three categories is discussed below. In most cases, the “pollutant”
being regulated corresponds to one of the pollutant categories discussed above.
For example, ammonia, nitrogen, temperature, and turbidity are specific
conventional pollutants. In other cases, however, the regulated “pollutant” is a
parameter that can be correlated with the actual pollutant. For example, siltation
potential is measured by total suspended solids or turbidity while salinity is
measured by total dissolved solids.
The measurement of pollutant concentrations, or the concentrations of
specific chemical species, is performed by the conduct of test procedures that
are meticulously described in Standard Methods for the Examination of Water
and Wastewater; SW-846 Test Methods for Evaluating Solid Waste,
Physical/Chemical Methods; test methods specified in the Code of Federal
Regulations and in other standardized publications.
3.1 CONVENTIONAL POLLUTANTS
Defined by 40 CFR § 401.16, conventional pollutants are defined as:
∑ Biochemical oxygen demand
∑ Fecal coliform
∑ Total suspended solids
∑ Oil & grease, and
∑ pH
3.1.1 Biochemical Oxygen Demand
The Biochemical Oxygen Demand (BOD) test is a bioassay procedure
31

measuring the oxygen requirements of microbes in an enclosed BOD test bottle
as they assimilate and oxidize the organic and inorganic pollutants in the test
bottle. Seed organisms, nutrients, wastewater or surface water, and a quantity of
dilution water are placed in the BOD test bottle and incubated at 20∞C for five
days (BOD5). The initial and final dissolved oxygen (D.O.) concentrations are
measured and the BOD is calculated as the difference between them. For
example, if the original D.O. was 9 mg/l and the concluding value was 2 mg/l,
the BOD of the wastewater would be approximately 7 mg/l.
BOD can be caused by a number of compounds, primarily carbon and
nitrogen-based compounds. The BOD test can be conducted in a way that
inhibits nitrification, in order to determine how much oxygen demand is
attributable to nitrogenous oxygen demand and how much to carbonaceous
demand. This can be important in the design of wastewater treatment systems.
Ammonia-nitrogen, for example, requires about 4.33 lbs of oxygen to oxidize
one lb of ammonia-nitrogen. This can be a significant consideration in the
specification and sizing of aeration systems.
Most carbonaceous BOD is exerted in the test bottle in five days.
Nitrogenous oxygen demand and refractory BOD (i.e., BOD that is resistant to
degradation) may continue beyond that for many days. Convention has
established the concept of ultimate BOD, equivalent to the 20-day BOD
bioassay (BOD20).
3.1.2 Fecal Coliform
Coliform bacteria live in the intestinal tract of people and many other
animals. Some coliform bacteria live in soils (woodland coliforms) and, while
they do not represent enteric bacteria, they do produce positive test results when
present. Fecal coliforms are a subset of the Total Coliform Group and are
incubated at 45.5∞C, human body temperature. Fecal coliforms are those found
to be present in fecal matter and are an indicator that harmful pathogens may be
present in a sample.
3.1.3 Total Suspended Solids
Total Suspended Solids (TSS) is a measurement of the filterable residue of a
water sample. A sample is filtered through a glass fiber filter with a 0.45 micron
porosity, contained in a porcelain crucible, and then dried at 105∞C. TSS is
expressed in mg/l as the difference between the dry weight of the filter and
crucible before use, and the weight of the filter, crucible and dried residue
afterwards.
CLASSIFICATION AND MEASUREMENT OF POLLUTANTS
32

3.1.4 Oil And Grease
O & G is a measurement of the fats, oils, greases, and other freon extractable
organic chemicals in a water sample. A sample is prepared (the method of
preparation depends on the analytical method) and extracted with CFC 113 or
n-hexane. The extractant is then filtered and the solvent driven away by heat.
The residue on the filter media represents freon extractable materials and is
weighed. The results are expressed as mg/l O & G.
3.1.5 pH
The pH of a solution is a measurement of its hydrogen ion (H+)
concentration. In simple terms, it is a measurement of the degree of acidity or
alkalinity of a solution and is easily measured using a pH meter. A solution’s
pH is expressed in standard units (SU), on a scale from 0 to 14.
Any solution with a pH below 7.0 is acid and any with a pH above 7.0 is
basic. A solution with a pH of 7.0 is neutral, having equal concentrations of
hydrogen (H+) and hydroxyl (OH-) ions. The pH scale is logarithmic. A change
in one whole unit represents a tenfold increase or decrease in hydroxyl or
hydronium ion concentration.
3.2 OTHER POLLUTANTS
3.2.1 Nitrogen
Many tests exist to measure for the presence of nitrogen compounds, which,
as noted earlier, are powerful and frequently problematic nutrients. Total
Kjeldahl Nitrogen (TKN-N) refers to a test method that measures nitrogen
compounds of biological origin, some nitrogen compounds found in industrial
waste, and ammonia. The test will not detect certain amines, nitro compounds,
hydrazines, and a number of other nitrogen-bearing compounds found in
industrial wastes.
Ammonia nitrogen (NH3-N) is a measurement of the ammonia-nitrogen in
solution. Ammonia is a primary nutrient for aquatic ecosystems and a primary
cause of eutrophication. Ammonia is also toxic to fish at relatively low
concentrations.
Organic nitrogen (ORG-N) is generally taken to be the difference between
TKN and NH3-N.
Nitrate-nitrogen (NO3-N) is a measurement of the concentration of
nitrate-nitrogen in solution. Nitrate is a critical nutrient and an indicator of
nitrification (or ammonia oxidation). Nitrate is also a groundwater contaminant
Other Pollutants 33

principally known for causing methemoglobinemia (blue baby syndrome) in
infants.
Nitrite-nitrogen (NO2-N) is toxic to aquatic microorganisms and is used as a
preservative in many foods to prevent spoilage by bacterial decomposition.
Nitrite is an intermediate metabolite in the denitrification of nitrate to nitrogen
gas.
3.2.2 Phosphorus
Phosphorus in the form of phosphate is found in most agricultural fertilizers
and is a primary nutrient for aquatic ecosystems, and a causative factor for
eutrophication. Not surprisingly, agricultural runoff is an important source of
this pollutant. Other sources include household detergents, sewage effluent,
and industrial discharges, especially metal finishing phosphate rinses.
Phosphates are usually present in aquatic ecosystems as orthophosphate,
polyphosphate, and organic phosphate. Most of the forms of orthophosphate
(PO4, HPO4, H2PO4, and H3PO4, for example) are available for use in microbial
metabolic activities without further breakdown. The polyphosphates will
hydrolyze to orthophosphate in aqueous solution, albeit very slowly. Organic
phosphates are bound to organic matter and must be decomposed to free the
phosphate for metabolism, and in this respect they are of lesser concern as
aquatic pollutants. Organic phosphates will, however, eventually solubilize and
release phosphorus.
Phosphorus is analyzed as total phosphorus and as Orthophosphate and the
results expressed as Tot-P and Ortho-P in mg/l.
3.2.3 Cyanide
Cyanide is found in the wastewaters of coke and chemical plants, oil
refineries, blast furnaces, plating shops, specialty chemical manufacturing
plants, and other sources. Most forms of cyanide are biodegradable but some
are not (notably cyanuric acid). Cyanide can form complexes with certain
metals, making its removal more difficult. However, several effective
treatment technologies exist, and cyanide is no longer considered to be a
significant contaminant in most watersheds.
3.2.4 Surfactants
Surfactants (short for “surface active agents”) cause foaming in wastewater
treatment plants and in receiving streams. Before 1965, synthetic detergents
contained alkyl-benzenesulfonate (ABS), which was extremely resistant to
biodegradation and caused a considerable degree of concern. ABS was
replaced with linear-alkyl-sulfonate (LAS), which is biodegradable and
34

considerably reduced the foaming problem. The concentration of surfactants is
determined by reacting a sample with a standard solution of methylene blue dye
and measuring the change in color of the reacted sample. Another name for
surfactants is Methylene Blue Active Substances (MBAS).
3.2.5 Chemical Oxygen Demand
The Chemical Oxygen Demand (COD) test is a wet chemical method used to
determine the amount of oxygen demanding substances in a test sample. The
COD test is performed by combining a sample of wastewater with a strongly
acidic dichromate solution and other chemicals and heating. The dichromate
oxygen is consumed by oxygen-demanding chemicals in the wastewater, and
that difference which remains corresponds to the chemical oxygen demand of
the sample. Two COD test methods are in use: macro COD by reflux digestion
and titration, and micro COD by sealed digestion and spectrometry.
3.2.6 Total Organic Carbon
Total Organic Carbon (TOC) is a measurement of organic carbon (as
opposed to inorganic carbon), and is another means of estimating the organic
strength of a test water sample. A sample is injected into an instrument that
heats it and combusts its organic constituents to CO2. The sample is then
measured for CO2 and the results calculated as mg/l TOC.
3.2.7 Volatile Suspended Solids
Volatile Suspended Solids (VSS) measures the volatile fraction of TSS and is
often used as a measurement of biomass in surface waters and wastewater
treatment facilities. The dried crucible from the TSS test is placed in a muffle
furnace and burned at 550∞C. This high temperature carbonizes the residue,
driving off as CO2 and other vapor products the portion of the residue that is
volatile at that temperature (which is usually most of it). The difference
between the TSS and ash residue is calculated as mg/l VSS.
3.2.8 Total Dissolved Solids
Total Dissolved Solids (TDS) is a measurement of the soluble solids in a
solution; that is, ions or molecules (both inorganic and organic) with a diameter
of 10-3 microns or less. TDS is measured by filtering a sample through a glass
fiber filter to remove TSS and evaporating the filtrate in an evaporating dish. As
the water in the dish evaporates, the dissolved solids are deposited onto the
dish. This residue is then weighed and calculated as mg/l TDS. TDS consists
primarily of salts and salt products such as sulfate, chloride, sodium, carbonate,
Other Pollutants 35

and potassium compounds. TDS serves as a useful surrogate or proxy for
salinity. Salinity can also be measured directly by a specific conductance meter
and expressed as ∝mhos/cc.
3.2.9 Total Solids
Total solids is a measurement of both the non-filterable (TSS) and filterable
(TDS) residue in water. The test is conducted the same way as the TDS test,
except that the sample is not filtered. The test involves evaporating a whole
water sample and weighing the residue. The results are expressed as mg/l Total
Solids.
3.2.10 Settleable Solids
Settleable solids, an index of siltation potential, is a volumetric measurement
of solid material that will settle to the bottom of a one liter, graduated
volumetric cone in a 2-hour period. The results are expressed as ml/l.
3.2.11 Pathogens
Pathogens are disease-causing microorganisms. Table 2.3, Pathogens in
Surface Water, lists the disease organisms of most concern. Specialized tests
are needed to detect the presence and numbers of most of the pathogens listed in
Table 2.3. Three coliform bacteria tests are routinely employed to measure
pathogens associated with sanitary discharges and water quality.
Total Coliforms represents a measurement of the number of coliform colony
forming units in water. Coliform or Total Coliform Group bacteria include
aerobic and facultative anaerobic gram negative bacteria that ferment lactose at
35∞C, in 24 to 48 hours. Most coliform bacteria are harmless to people, but the
Total Coliform test does serve as a useful indicator of the presence of this group
of enteric (occurring in the gastrointestinal tract) bacteria. Coliform units are
expressed as colony-forming units per 100 ml (CFU/100 ml).
Fecal Coliforms are a group of bacteria that primarily live in the lower
intestines of warm-blooded animals, including humans. Many types of fecal
coliforms are harmless to humans, but some strains cause serious water-borne
diseases, like dysentery and cholera.
Fecal Streptococci are predominately found to result from human feces in
surface waters, although many other warm-blooded animals excrete these
organisms as well. The ratio of fecal coliforms to fecal streptococci (FC/FS) has
been used to trace the source of sanitary discharges to receiving streams.
3.2.12 Turbidity
Turbidity as a pollutant denotes loadings of suspended or colloidal solids that
36

tend not to settle. As an effluent limitation, turbidity is a measurement of the
light penetration or opacity of a sample of water caused by such solids. A
Nephelometer is used to compare the intensity of light scattering within a water
sample with a reference sample. The units are expressed as nephelometric
turbidity units (NTU).
3.2.13 Odor
Odor in wastewater can be an extremely vexing problem, not just for
treatment facilities in the vicinity of residential neighborhoods. Odors from
some manufacturing process such as pulp and paper and specialty chemicals
can travel for many miles from the source. Most odors are caused by the
decomposition of organic matter. Odors from offal processing or sewage
treatment plants are frequently caused by decomposing organic solids. Odor is
not as much of a problem as it has been in the past, mainly due to pressure from
the public upon industries and practices that created the problem.
3.2.14 Radionuclides
Radionuclides are radioactive elements that enter the water cycle and surface
waters from nuclear power plants, fallout from atomic blasts, releases from
military facilities, and other facilities involved in the metallurgical processing
of radioactive materials. Natural sources of radionuclides in receiving streams
are extremely rare.
Ordinary chemical reactions consist of molecules or atoms of chemicals
exchanging or sharing the electrons surrounding their atomic nuclei, while the
nuclei remain unchanged. The reaction products are the new chemical form and
energy emitted or absorbed in the form of heat or other output. With radioactive
materials, the powerful nucleus is affected, resulting in the emission of strong
nuclear particles (protons, neutrons, and/or electrons) and energy (heat and
electromagnetic radiation).
Surface water radionuclides from nuclear reactions are measured as alpha,
beta, and gamma radiation, and as specific elements and their isotopes, such as
thorium, technetium 99, uranium 238, etc. Very strong nuclear radiation has
been released to the environment in the form of sunken nuclear piles in nuclear
submarines and high level nuclear wastes dumped into the ocean by various
countries. The measurement for radionuclides of concern in water quality
management is the picocurie (pCi).
3.2.15 Heavy Metals
Heavy metals find their way into aquatic ecosystems from a variety of natural
and human sources. Heavy metals of most concern include antimony, arsenic,
beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium,
Other Pollutants 37

silver, thallium and zinc. These metals are included on the Priority Pollutant list
(see 40 CFR Part 423, Appendix A).
3.2.16 Pesticides and Herbicides
Pesticides comprise a large class of compounds of concern. Typical
pesticides and herbicides include DDT, Aldrin, Chlordane, Endosulfan,
Endrin, Heptachlor, and Diazinon. Pesticides and herbicides derive from urban
as well as agricultural runoff and contribute to surface as well as ground water
pollution. In addition to toxic effects, pesticides are often bioaccumulative (that
is, they are found in increasing concentrations in the tissues of organisms as one
moves up the food web). Pesticides can also exert teratogenic and mutagenic
effects in aquatic organisms and animals that feed on them.
3.2.17 Polynuclear Aromatic Hydrocarbons
Polynuclear aromatic hydrocarbons (PAH or PNA—also called polycyclic
aromatic hydrocarbons) include a large family of semi-volatile organic
pollutants such as naphthalene, anthracene, pyrene, and benzo(a)pyrene.
Phenanthrene, pyrene, and fluoranthene are products of the incomplete
combustion of fossil fuels. Naphthalene is found in asphalt and creosote. PAHs
from combustion products have been identified as a source of some cancer risk
for people eating seafood.
3.2.18 Polychlorinated Biphenyls
Polychlorinated biphenyls (PCBs) are organic chemicals that formerly had
widespread use in electrical transformers and hydraulic equipment. Members
of this class of chemicals are extremely persistent in the environment and has
been proven to bioconcentrate (i.e., bioaccumulate) in the food web. PCBs
have been distributed world wide and have been found in polar bear flesh, fish
taken from the every ocean, and in the milk of nursing human mothers in urban
American cities. Because of this potential to accumulate in the food web, PCBs
were intensely regulated and prohibited from manufacture by the Toxic
Substances Control Act (TSCA) of 1976. PCBs have been identified as a
potential carcinogenic agent through ingestion of seafood.
3.2.19 Priority Pollutants
Section 307(a) of the Clean Water Act was enacted in 1977. It addressed
toxic water pollutants and required the EPA to list 65 toxic pollutants for the
purpose of regulating their discharge into surface waters (see 40 CFR §
401.15). The original list included several generic classes of chemicals. The
38

EPA then developed a list of 129 chemicals, with no generic classes of
chemicals, in order to provide a list of organics, pesticides, and metals to be
regulated. This list has been termed the 129 Priority Pollutant List. The list was
subsequently modified and the current list includes 126 chemicals, although the
list ends in the number 129. (No chemicals are assigned the numbers 17, 49, and
50.) The list is contained in 40 CFR § 423, Appendix A.
3.2.20 Xenobiotic Compounds
In recent years, researchers have increased investigative efforts in the
occurrence and fate of man-made chemical compounds. These chemicals have
been termed xenobiotic compounds (to indicate that they do not normally occur
in aquatic ecosystems to any significant degree) or anthropogenic chemicals (to
indicate that they are made by man). They derive from the release of
pharmaceuticals and personal care products (PPCPs), and releases from
agricultural (especially animal feeding operations), industrial and domestic
sources.
Xenobiotics include ubiquitous compounds such as caffeine and nicotine,
estrogen products from birth control pills, antibiotics, steroids, detergent
metabolites, disinfectants, chemicals from aquatic and animal husbandry,
fragrances, antioxidants, plasticizers, insect repellents, prescription and
non-prescription drugs and many thousands of other types of chemical
compounds.
The number of xenobiotic compounds (including degradation and
transformation products) released into receiving streams has not been
determined, in part because of the difficulty of analyzing for them. Most of
these chemicals are found in low concentrations in the natural environment; in
the parts per billion to parts per trillion range, and lower. However, we do not
know the long-term effects of exposure to xenobiotics, even at low levels, on
behavior, genetic integrity, or physical impairment of aquatic organisms. Some
researchers believe the long-term effects will be found to be considerable, and
potentially catastrophic, in some locations.
Other Pollutants 39

Kim Ferguson, Great Smokey Mountains National Park, NC

CHAPTER 4
Wastewater Pre-Treatment Technologies
IN previous sections of this chapter, the principal categories of pollutants and
their effects were identified. This section will discuss the various methods
employed to treat the pollutants to produce cleaner wastewater discharges to
surface waters.
4.1 WASTEWATER TREATMENT UNIT OPERATIONS
Nearly 16,000 wastewater treatment plants are currently in operation in the
United States. They range in size from the 1 billion gallon per day (GPD)
Chicago main wastewater treatment plant to smaller package plants with flow
rates in the vicinity of 5,000 GPD or less. For all facilities, whatever the size,
wastewater is treated in a train of sequential treatment processes.
Primary treatment (or pre-treatment) involves unit operations such as
screening, equalization, neutralization, sedimentation, air stripping,
coagulation and precipitation, chelation, oxidation, oil removal, flotation, and
temperature reduction. Primary treatment removes many of the gross
contaminants such as grit, solids, and oil. Primary treatment may also include
unit operations that condition or process wastewater (such as ammonia or
sulfide stripping, or metals removal) so that it will be more suitable for
secondary treatment and to protect downstream equipment.
Most of the types of primary treatment discussed below are employed to treat
municipal wastewater or industrial process wastewater. Certain of these
treatment processes can also apply to treating contaminated groundwater that
has been extracted from the earth.
Secondary treatment (or biological treatment) involves biological oxidation
of organic and inorganic pollutants. The bulk of pollutant removal occurs
during secondary treatment.
Tertiary treatment is applied to secondary effluents to improve effluent
quality beyond the 30/30 (BOD/TSS) general secondary treatment standard. In
41

Figure 4.1. Unit Operations for a Tertiary Wastewater Treatment Facility [15].
42

some locales, tertiary treatment standards have specific numeric values for
BOD, TSS, N, P and other parameters. Tertiary treatment is provided to reduce
TSS, nutrients and refractory compounds.
Figure 4.1, Alternative Wastewater Treatment Technologies, illustrates an
integrated system of sequential treatment processes capable of treating a variety
of plant wastewaters.
The first unit operations are engaged in removing or modifying the physical
properties of the wastewater, such as the removal of grit, rocks, cans and other
large solids in a grit chamber or bar screen. These primary treatment unit
operations are illustrated in Figure 4.2.
4.2 SCREENING AND GRIT REMOVAL
Industrial and municipal wastewater treatment facilities generally employ
some method of screening and/or grit removal to protect downstream
equipment from physical damage or abrasion. For many industries, grit
removal is not a problem, but for Publicly Owned Treatment Works (POTWs),
grit removal is a necessity.
Almost all wastewater treatment plants employ some form of screening to
remove large solids. This can range from a simple manual screen with 2 inch
spacing to sophisticated traveling bar screens and mechanical sieves. Most
screening operations are installed to remove junk and debris from the waste
stream to protect pumps, aerators, clarifier drive rakes, and other devices from
damage.
Figure 4.2. Typical Pretreatment Unit Operations [15].
Screening and Grit Removal 43

4.3 EQUALIZATION
Equalization basins or tanks are installed to minimize severe fluctuations in
wastewater characteristics such as pollutant concentrations, pH, and flow rate.
In some industrial treatment plants, the equalization basin is accompanied by a
parallel spill basin to capture highly concentrated spillage. Equalization basins
are also used to store wastewater to feed biological plants in times of
interruption of wastewater flow. These interruptions occur during process
shutdowns, on holidays (especially Christmas), and during planned plant
maintenance shutdowns.
Figure 4.3 illustrates the equalization and load balancing effects of a
pharmaceutical wastewater influent COD in a variable-volume/flow
equalization basin. With no equalization, the COD concentration fluctuates
widely, with a peaking factor of approaching 2.5 for the highest concentration.
By providing a 24-hour detention time, COD variability is reduced
dramatically, as indicated in Figure 4.3 (note the elimination of frequent spikes
in COD concentration).
Industrial facilities that periodically manufacture high strength batch loads
of wastewater and facilities subject to spills should install a spill basin with an
automatic bypass activated by a chemical monitor upstream of the equalization
basin, as indicated in Figure 4.4.
An equalization basin is a large tank or basin located after gross screening
operations and upstream of other pretreatment processing units. Equalization
basins may be equipped with mixers to promote blending and minimize solids
settling. As intermittent flows containing high concentrations of pollutants or
extreme fluctuations in pH enter the basin, they become diluted with
wastewater already in the basin, thereby equalizing or dampening wastewater
variability.
Figure 4.3. Equalization Load Balancing Analysis [15].
WASTEWATER PRE-TREATMENT TECHNOLOGIES
44

Figure 4.4. Use of High-Strength Holding Pond for Spills [15].
Figure 4.5. Equalization Basin Types [15].
45

TABLE 4.1. Settling Characteristics Of Pulp And Paper-Mill Wastes [15].
Type of waste
Flow, million
gal/day
Raw SS,
Ppm
Raw BOD,
Ppm Temp., ∞F
Removal %
Detention
time, h
OR,
gal/ (d ft2)
SS BOD
Paperboard 4.5
0.75
1.36
2.5
31
30
3.3
0.25
0.301
35
2,500
136
10,000
1,185
524
850
2,000
50
1,150
4,000
450
360
395
195
250
100
250
200
85
85
62
110
95
90
100
110
100
90
90
85
96.1
42
80
85
80
98
90
67
50
24
19
25
25
25
50
10–15
5.35
1.15
5.4
5.3
9.4
0.5
2.6
4.5
1.5
504
940
430
525
438
1910
1028
39
90
374
Specialty 9.4
2.2
1.8
50
203
6,215
665
120
97
120
620
85
81
120
95
100
94
91
91
80
86
90
58
16
2.56
1.5
0.5
18.2
832
157
406
477
Fine Paper 6
6.0
9.9
3.5
7.5–9.0
200
254
500
300
560
235
364
250
126
65
90
70–100
65
65
95
50
90
95
80
90
34
35
48
42
3.9
2.2
2.4
6.0
4.0
695
890
1120
372
670
Miscellaneous 7
14
25
17
0.5
1.0
430
1, 000
75
100
200
1,000
250
330
100
425
200
900
70
73
85
100
70
65
90
95
90
20
60
0
50
95
1.8
6.9
5.9
1.9
2.9
505
911
17
846
1590
509
46

Figure 4.5 illustrates the operation of three types of equalization basins. The
three types shown are: (a) constant flow/mixed, (b) variable flow/mixed, and
(c) constant flow/aerated. If the wastewater flow rate is constant, a constant
volume basin can be employed to equalize pH or contaminant concentrations. If
both flow and concentration are variable, a variable volume basin with a
constant withdrawal rate is employed to equalize mass discharge. If the
wastewater is readily degradable, oxygen should be provided to avoid septic
conditions and the generation of odors.
Equalization basins are a requirement for most chemical manufacturing
plants with multiple processing trains, plants that produce toxic wastewaters,
plants with high variability in organic loading or pH, and plants that are indirect
dischargers and must control discharges to municipalities by discharging
during the evening or on weekends.
Typical design parameters for equalization basins are summarized in Table
4.1.
4.4 PRIMARY CLARIFICATION
Primary clarification, or sedimentation, is employed to remove suspended
solid materials from influent wastewaters. For municipal wastewaters, a
well-designed primary clarification system should remove 50 to 70 percent of
the suspended solids and 25 to 40 percent of the incoming BOD. Some influent
suspended solids exert high BOD, and it is more cost effective to remove them
instead of attempting to treat the BOD in secondary treatment systems. Some
influent suspended solids, such as metal hydroxides, can contaminate
secondary sludges or interfere with secondary unit operations, and must be
removed.
Primary sedimentation is accomplished in settling lagoons or primary
clarifiers. In a clarifier, it is necessary to reduce the mixing and velocity of the
wastewater such that solids with a specific gravity greater than 1.0 (the specific
gravity of water) can be allowed to settle to the bottom of the tank.
At the bottom of the tank, the settled particles form a sludge blanket that
begins to compress and thicken as the incoming sludge packs the older sludge.
Sludge rakes travel along the bottom of the tank to help thicken the blanket and
to assist in sludge removal. The sludge is siphoned or pumped off the bottom
along the length of the rakes or is plowed to the center of the clarifier to a sludge
hopper and pumped away. The sludge is then removed, digested, stabilized,
dewatered, recycled, incinerated, composted, or landfilled. Some primary
clarifiers are equipped with surface skimmers to remove floatable solids,
grease, and oils.
Clarifiers come in two configurations: circular and rectangular. Figure 4.6,
Circular Clarifier, is a section drawing of a circular clarifier and illustrates its
operation. In this illustration, influent enters the unit from the center or influent
Primary Clarification 47

well and immediately encounters a circular baffle or center cage, which serves
to distribute the hydraulic force vectors radially, to minimize short circuiting
and to direct the flow downward. As the influent flows downward, settling
occurs and the settled sludge is moved to a center sludge sump by rotating
sludge plows. The clarified effluent then flows over a weir into an effluent
launder after being skimmed for floatable solids by a scum skim.
Primary clarification can be highly effective in removing some
contaminants. Table 4.1 provides primary clarification data for pulp and
paper-mill wastewaters, and shows substantial TSS removal at different
clarifier surface loading rates.
4.5 NEUTRALIZATION
Many industrial wastewaters contain basic (caustic) or acidic materials
requiring pH adjustment prior to treatment. Adequate pH control is essential to
most waste treatment operations. Biological treatment plants require influent
pH in the 6.5 to 8.5 range. Chemical precipitation units often require pH
adjustment approaching the extremes of the pH scale. As noted in the earlier
discussion on equalization, pH can be adjusted rather simply by equalization;
i.e., allowing large volumes of wastewater to mix and thus dampen pH
fluctuations. Where equalization is insufficient or impractical for adequate pH
adjustment, further adjustment can be accomplished by addition of alkaline or
acid materials through a process called neutralization. Alkaline wastes can be
neutralized with any strong acid, sulfuric acid being the most widely used. Acid
wastes can be neutralized with lime products such as limestone (CaCO3),
quicklime (CaO), hydrated lime [Ca(OH2)], sodium bicarbonate, sodium
hydroxide, or other caustic material.
Neutralizing agents are usually added in relatively small sequential reactors
and agent addition is controlled by instrumentation or computer control. Figure
48
Figure 4.6. Circular Clarifier [15].

4.7, illustrates a typical neutralization system. A pH probe is located in each
reactor and feeds back a 4 to 20 milliamp signal to an electronic controller that
calculates the response needed and sends a signal to a control valve that opens
and closes as necessary to dose neutralizing agents to maintain pH within the
desired set points.
This stepwise addition of chemicals promotes the conservation of
neutralizing agents and provides optimum pH control and response to wide
fluctuations in influent pH. The multistage system also provides better control
when wastewater flow rates increase or decrease quickly. One alternative is to
build a single, large, well-mixed neutralization tank. While this alternative is in
wide use in potable water treatment plants and is used at wastewater facilities
with very stable influent pH readings, it is not practical for wastewater
treatment plants that have to cope with significant variations in pH and/or flow
rate. For these facilities, the installation of an equalization basin (a large surface
impoundment) may be in order.
4.6 OIL REMOVAL
Industries involved in processing basic petrochemical stocks, steel mills,
machine shops, slaughter houses, certain food processing plants, tire plants, and
many other facilities are required to remove oil prior to discharge. Effluents
Figure 4.7. Multistage Neutralization Process (Courtesy of Envirex, Inc.).
Oil Removal 49

from these operations vary a great deal in oil content, ranging from 10 to
100,000 mg/l or more. Oil may be classified as free, emulsified, or soluble. Free
oils are usually not uniformly dispersed within the water, readily float to the
surface and appear as sheens, sheets, or globules. Emulsified oil is usually
dispersed in the water to form a stable non-homogeneous mixture. Soluble oil is
defined as a very fine emulsion in which the oil particle has become chemically
bonded to the water to form a single stable liquid.
Oil removal is accomplished by decantation, flow-through gravity
separators, (e.g., API type separators), skimmers, coalescers, centrifuges,
dissolved and induced air flotation, filtration, membrane technologies, and
chemical and biological treatment.
Most oils found in wastewater have a specific gravity of less than 1.0, so they
float to the water surface where they can be removed by skimming.
Conventional oil skimmers work by removing the free oil and grease (O & G)
that has floated to the surface, preventing it from building up in the separator.
For these conventional skimmers and separators to work effectively, a
quiescent zone must be established in the flow path to allow free oil globules to
float to the surface in order to be skimmed. This skimmer-separator
combination can reduce the free oil concentrations to about 25 to 100 mg/l,
provided the influent concentration is less than 10,000 mg/l.
Other types of separators have been developed to enhance separation by
promoting the formation of larger oil globules from smaller globules. In these
higher efficiency separators, the smaller globules are caused to agglomerate in
Figure 4.8. Oil and Solids Separation on a Corrugated Coalescing Plate (Courtesy of AquaTrend,
Inc.).
50

a common location where they attach and coalesce to form larger globules that
tend to rise much faster to the surface. Such designs include inclined plate,
vertical tube, and vertical plate separators.
Inclined plate separators work by stacking a set of plates at an angle with
respect to the flow. The number and size of these plates is usually calculated by
Stoke’s Law. The oil globules rise to the plate immediately above, collect at the
bottom of each plate, coalesce with other globules and rise to the surface.
Figures 4.8 and 4.9 illustrate the operation of a typical corrugated plate oil
separator. Figure 4.8, Oils and Solids Separation on a corrugated Coalescing
Plate, shows how oil globules are positioned to coalesce into larger globules
and float to the liquid surface, while solids are separated from the oil and water
and fall to the bottom of the unit.
Figure 4.9 illustrates how a typical slant-plate separator works. Oily influent
enters the CPI in a large chamber that serves to slow the fluid entrance velocity
and promote the settling of solids into the grit hopper. The influent then passes
Figure 4.9. Corrugated Plate Separator (Courtesy of Hoffland Environmental, Inc.).
Oil Removal 51

through a distribution baffle to the inclined plate pack. Inside the pack the oil
droplets are encouraged to rise (see Figure 4.8) along the bottom surfaces of the
plates to the top of the unit. Solids slide to the bottom, as indicated in the
schematic. Water passes through the plate pack and rises over the effluent weir
to the discharge pipe. The effluent pipe is positioned below the layer of floating
oil. Oil must be removed either manually or automatically, so that the oil layer
does not extend down to the effluent water pipe.
The vertical tube separator relies on placing a number of closely packed
perforated tubes in the flow path. The tube material is usually an oleific or oil
attracting substance. As the oil/water mixture is pushed through the
perforations, the oil particles that contact the tube material tend to adhere to it
until enough oil is collected to slide along the tube to the surface.
The vertical plate separator relies on forming long and narrow channels by
placing a number of vertical plates parallel to each other and in the direction of
the flow. The height of the plates and the distance between them are such that
the flow is laminar and practically two-dimensional. This creates a parabolic
velocity profile between the plates. Due to the nature of the velocity profile, an
oil bubble is subjected to a velocity gradient across its diameter causing it to
spin. The spin weakens the surface tension bond between the smaller oil
52
Figure 4.10. The HYDRASEP
®
Principle (Courtesy of GNESYS, Inc.).

TABLE 4.2. Typical Efficiencies Of Oil Separation Units [15].
Oil Content Oil
Oil removed,
% Type
COD
removced,
%
SS
removed,
%
Influent, mg/l Effluent, mg/l
300 40 87 Parallel Plate – –
220 49 78 API – –
108 20 82 Circular – –
108 50 54 Circular 16 –
98 44 55 API – –
100 40 60 API – –
42 20 52 API – –
2000 746 63 API 22 33
1250 170 87 API – 68
1400 270 81 API – 35
Figure 4.11. Example Of General Arrangement For API Separator (Courtesy of the American
Petroleum Institute).
53

particles and the water and subjects them to induced lift forces that cause the oil
globules to agglomerate, coalesce and rise. Figure 4.10 illustrates the parallel
plate design of the HYDRASEP® oil/water separator.
To reduce oil concentrations further, specialized equipment must be used. To
achieve oil concentrations of less than 1 mg/l, membrane technologies (such as
reverse osmosis), special solvent extractors, oleofilters, paper media filters,
resin or ceramic adsorbers, activated clays, and specialized biological or
chemical systems may be used. All of the above devices can be preceded by an
emulsion breaking step such as the addition of acids, polymers, or other
chemicals.
Oil/water separators are used frequently in groundwater remediation
projects, especially UST cleanups. Oil/water separators are used typically for
light non-aqueous phase liquid (LNAPL) chemicals or oils (i.e., floaters).
The API separator, illustrated in Figure 4.11, is widely used in the petroleum
industry. Table 4.2 provides data on the performance of oil removal for API,
parallel plate and circular oil/water separators.
4.7 FLOTATION
Air flotation systems are employed to remove and thicken suspended solids
as well as to remove oil. Flotation involves introducing air into a wastewater
stream contained in a tank, in the form of a froth (induced air flotation) or tiny,
discrete bubbles (dissolved air flotation).
Induced air flotation (IAF) systems beat wastewater into a froth using a high
speed, mechanical surface aerator/mixer, or a venturi-type air inducer (see
54
Figure 4.12. Dissolved Air Flotation System (Drawing courtesy Pan American Environmental).

below). The froth collects oil and solids and is displaced into a surface trough
separating the oil and solids from the wastewater.
In dissolved air flotation (DAF), compressed air and recycled water is
blended with wastewater at a pressure of about 60 pounds per square inch (psi).
The mixture is released at atmospheric pressure near the bottom of the flotation
tank. The air, which was dissolved in solution at 60 psi, is suddenly released to
atmospheric pressure, forming millions of tiny bubbles that rush to the surface
to find equilibrium with ambient atmospheric pressure. These bubbles trap and
lift solids and O & G and bring them to the surface where a thick, spongy float
or supernatant is formed and removed by a mechanical skimmer. Figure 4.12
illustrates a typical DAF system, and 4.13 depicts one type of air flotation
system.
Dissolved Air Flotation performance data for several widely dissimilar
wastewaters are presented in Table 4.3
TABLE 4.3. Air Flotation Treatment Of Oily Wastewaters [15].
Wastewater Coagulant, mg/l
Oil Concentration, mg/l
Influent Effluent
Removal,
%
Refinery 0
100 alum
130 alum
0
125
100
580
170
35
10
68
52
72
90
88
70
Oil tanker ballast
water
100 alum + 1 mg/l polymer 133 15 89
Paint manufacture 150 alum + 1 mg/l polymer 1900 0 100
Aircraft maintenance 30 alum + 10 mg/l
activated silica
250–700 20–50 >90
Meat packing 3830
4360
270
170
93
96
Flotation 55
Figure 4.13. Induced Air Flotation System (Wemco Envirotech Company).

Eckenfelder, w. wesley hansard, william ney understanding water quality management - technology and applications-de-stech publications (2004)

Eckenfelder, w. wesley hansard, william ney understanding water quality management - technology and applications-de-stech publications (2004)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Eckenfelder, w. wesley hansard, william ney understanding water quality management - technology and applications-de-stech publications (2004)

Similar to Eckenfelder, w. wesley hansard, william ney understanding water quality management - technology and applications-de-stech publications (2004) (20)

More from Wilder Vicente Rosales Yanac

More from Wilder Vicente Rosales Yanac (19)

Recently uploaded

Recently uploaded (20)

Eckenfelder, w. wesley hansard, william ney understanding water quality management - technology and applications-de-stech publications (2004)