Handbook of Water and Wastewater Treatment Plant Operations - Chapter 13 ppsx

Untreated water drawn from groundwater and surface waters and used as a drink-ing water supply can contain contaminants that pose a threat to human health.. These guidelines apply to dri

Water Quality

A RE W E TO W AIT U NTIL A LL F ROGS “C ROAK ”?

The earliest chorus of frogs — those high-pitched rhapso-dies of spring peepers, those “jug-o-rum” calls of bullfrogs, those banjo-like bass harmonies of green frogs, those long and guttural cadences of leopard frogs, their singing a prelude to the splendid song of birds — beside an other-wise still pond on an early spring evening heralds one of nature’s dramatic events: the drama of metamorphosis.

This metamorphosis begins with masses of eggs that soon hatch into gill-breathing, herbivorous, fishlike tadpole lar-vae As they feed and grow, warmed by the spring sun, almost imperceptibly a remarkable transformation begins.

Hind legs appear and gradually lengthen Tails shorten.

Larval teeth vanish and lungs replace gills Eyes develop lids Forelegs emerge In a matter of weeks, the aquatic, vegetarian tadpole will (should it escape the many perils

of the pond) complete its metamorphosis into an adult, carnivorous frog.

This springtime metamorphosis is special: this anticipated

event (especially for the frog) marks the end of winter,

the rebirth of life, and a rekindling of hope (especially for

mankind) This yearly miracle of change sums up in a few

months each spring what occurred over 300 million years

ago, when the frog evolved from its ancient predecessor

Today, however, something is different, strange, and

wrong with this striking and miraculous event

In the first place, where are all the frogs? Where have they gone? Why has their population decreased so

dra-matically in recent years?

The second problem: That this natural metamorphosis process (perhaps a reenactment of some Paleozoic drama

whereby, over countless generations, the first

amphibian-types equipped themselves for life on land) now demonstrates

aberrations of the worst kind, of monstrous proportions

and dire results to frog populations in certain areas For

example, reports have surfaced of deformed frogs in certain

sections of the U.S., specifically Minnesota Moreover, the

U.S Environmental Protection Agency (EPA) has received

many similar reports from the U.S and Canada as well as

parts of Europe

Most of the deformities have been in the rear legs and appear to be developmental The question is: Why?

Researchers have noted that neurological abnormali-ties have also been found Again, the question is why?

Researchers have pointed the finger of blame at para-sites, pesticides, and other chemicals, ultraviolet radiation,

acid rain, and metals Something is going on What is it?

We do not know!

The next question becomes: What are we going to do about it? Are we to wait until all the frogs croak before we act — before we find the source, the cause, the polluter — before we see this reaction in other species; maybe in our own?

The final question is obvious: When frogs are forced by mutation into something else, is this evolution by gunpoint?

Is man holding the gun?1

13.1 INTRODUCTION

The quality of water, whether it is used for drinking, irrigation, or recreational purposes, is significant for health

in both developing and developed countries worldwide The first problem with water is rather obvious: A source

of water must be found Secondly, when accessible water

is found it must be suitable for human consumption Meeting the water needs of those that populate earth is an on-going challenge New approaches to meeting these water needs will not be easy to implement: economic and institutional structures still encourage the wasting of water and the destruction of ecosystems.2 Again, finding a water source

is the first problem Finding a source of water that is safe

to drink is the other problem

Water quality is important; it can have a major impact

on health, both through outbreaks of waterborne disease and contributions to the background rates of disease Accordingly, water quality standards are important to pro-tect public health

In this text, water quality refers to those characteristics

or range of characteristics that make water appealing and useful Keep in mind that useful also means nonharmful

or nondisruptive to either ecology or the human condition within the very broad spectrum of possible uses of water For example, the absences of odor, turbidity, or color are desirable immediate qualities There are imperceptible qualities that are also important —the chemical qualities The fact is the presence of materials, such as toxic metals (e.g., mercury and lead), excessive nitrogen and phospho-rous, or dissolved organic material, may not be readily perceived by the senses, but may exert substantial negative impacts on the health of a stream and on human health The ultimate impact of these imperceptible qualities of water (chemicals) on the user may be nothing more than loss of aesthetic values On the other hand, water-containing 13

366 Handbook of Water and Wastewater Treatment Plant Operations

chemicals could also lead to a reduction in biological

health or to an outright degradation of human health

Simply stated, the importance of water quality cannot

be overstated

In regards to water and wastewater treatment

opera-tions, water quality management begins with a basic

understanding of how water moves through the

environ-ment, is exposed to pollutants, and transports and deposits

pollutants The hydrologic (water) cycle depicted by

Figure 13.1 illustrates the general links among the

atmo-sphere, soil, surface waters, groundwaters, and plants

13.2 THE WATER CYCLE

Simply, the water cycle describes how water moves

through the environment and identifies the links among

groundwater, surface water, and the atmosphere (see

Figure 13.1) As illustrated, water is taken from the earth’s surface to the atmosphere by evaporation from the surface

of lakes, rivers, streams, and oceans This evaporation process occurs when the sun heats water The sun’s heat energizes surface molecules, allowing them to break free

of the attractive force binding them together, and then evaporate and rise as invisible vapor in the atmosphere Water vapor is also emitted from plant leaves by a process called transpiration. Every day, an actively growing plant transpires five to ten times as much water as it can hold

at once As water vapor rises, it cools and eventually condenses, usually on tiny particles of dust in the air When it condenses, it becomes a liquid again or turns directly into a solid (ice, hail, or snow)

These water particles then collect and form clouds The atmospheric water formed in clouds eventually falls

to earth as precipitation The precipitation can contain

FIGURE 13.1 Water cycle (From Spellman, F.R., The Science of Water, Technomic Publ., Lancaster, PA, 1998.)

12

11

1

2

14

13

7

3

1 Rain cloud

2 Precipitation

3 Ground water

4 Animal water intake

5 Respiration

6 Excretion

7 Plant absorption

8 Transpiration from plants

9 Return to ocean

10 Evaporation from soil

11 Evaporation from ponds

12 Evaporation from ocean

13 Water vapor

14 Cloud formation

14

13

9

Water Quality 367

contaminants from air pollution The precipitation may

fall directly onto surface waters, be intercepted by plants

or structures, or fall onto the ground Most precipitation

falls in coastal areas or in high elevations Some of the

water that falls in high elevations becomes runoff water,

the water that runs over the ground (sometimes collecting

nutrients from the soil) to lower elevations to form

streams, lakes, and fertile valleys

The water we see is known as surface water Surface

water can be broken down into five categories:

1 Oceans

2 Lakes

3 Rivers and streams

4 Estuaries

5 Wetlands

Because the amount of rain and snow remains almost

constant, and population and usage per person are both

increasing rapidly, water is in short supply In the U.S

alone, water usage is 4 times greater today than it was in

1900 In the home, this increased use is directly related

to an increase in the number of bathrooms, garbage

dis-posals, home laundries, and lawn sprinklers In industry,

usage has increased 13 times since 1900

There are 170,000+ small-scale suppliers that provide

drinking water to approximately 200+ million Americans

by 60,000+ community water supply systems, and to

nonresidential locations, such as schools, factories, and

campgrounds The rest of Americans are served by private

wells The majority of the drinking water used in the U.S

is supplied from groundwater Untreated water drawn

from groundwater and surface waters and used as a

drink-ing water supply can contain contaminants that pose a

threat to human health

approximately 146,000 gal of freshwater

annu-ally, drinking 1 billion glasses of tap water per

day.3

With a limited amount of drinking water available for

use, water that is available must be used and reused or we

will be faced with an inadequate supply to meet the needs

of all users Water use and reuse is complicated by water

pollution Pollution is relative and hard to define For

example, floods and animals (dead or alive) are polluters,

but their effects are local and tend to be temporary Today,

water is polluted in many sources, and pollution exists in

many forms It may appear as excess aquatic weeds; oil

slicks; a decline in sport fishing; and an increase in carp,

sludge worms, and other forms of life that readily tolerate

pollution Maintaining water quality is important because

water pollution is not only detrimental to health, but also

to recreation; commercial fishing; aesthetics; and private,

industrial, and municipal water supplies

At this point the reader may ask: With all the recent publicity about pollution and the enactment of new envi-ronmental regulations, has water quality in the U.S improved recently? The answer is that with the recent pace

of achieving fishable and swimmable waters under the Clean Water Act (CWA), one might think so

In 1994, the National Water Quality Inventory Report

to Congress indicated that 63% of the nation’s lakes, riv-ers, and estuaries meet designated uses — only a slight increase over that reported in 1992

The main culprit is nonpoint source pollution (NPS) (to be discussed in detail later) NPS is the leading cause

of impairment for rivers, lakes, and estuaries Impaired sources are those that do not fully support designated uses, such as fish consumption, drinking water supply, ground-water recharge, aquatic life support, or recreation Accord-ing to Fornter & Schechter, the five leadAccord-ing sources of water quality impairment in rivers are:

1 Agriculture

2 Municipal wastewater treatment plants

3 Habitat and hydrologic modification

4 Resource extraction

5 Urban runoff and storm sewers4 The health of rivers and streams is directly linked to the integrity of habitat along the river corridor and in adjacent wetlands Stream quality will deteriorate if activ-ities damage vegetation along riverbanks and in nearby wetlands Trees, shrubs, and grasses filter pollutants from runoff and reduce soil erosion Removal of vegetation also eliminates shade that moderates stream temperature Stream temperature, in turn, affects the availability of dissolved oxygen (DO) in the water column for fish and other aquatic organisms

Lakes, reservoirs, and ponds may receive water-car-rying pollutants from rivers and streams, melting snow, runoff, or groundwater Lakes may also receive pollution directly from the air

In attempting to answer the original question about water quality improvement in the U.S., the best answer probably is that we are holding our own in controlling water pollution, but we need to make more progress This understates an important point; when it comes to water quality, we need to make more progress on a continuing basis

13.3 WATER QUALITY STANDARDS

The effort to regulate drinking water and wastewater efflu-ent has increased since the early 1900s Beginning with

an effort to control the discharge of wastewater into the environment, preliminary regulatory efforts focused on protecting public health The goal of this early wastewater treatment program was to remove suspended and floatable

368 Handbook of Water and Wastewater Treatment Plant Operations

material, treat biodegradable organics, and eliminate

pathogenic organisms Regulatory efforts were pointed

toward constructing wastewater treatment plants in an

effort to alleviate the problem Then a problem soon

devel-oped: progress Time marched on and so did proliferation

of city growth in the U.S where it became increasingly

difficult to find land required for wastewater treatment and

disposal Wastewater professionals soon recognized the

need to develop methods of treatment that would accelerate

nature’s way (the natural purification of water) under

con-trolled conditions in treatment facilities of comparatively

smaller size

Regulatory influence on water-quality improvements

in both wastewater and drinking water took a giant step

forward in the 1970s The Water Pollution Control Act

Amendments of 1972 (CWA), established national water

pollution control goals At about the same time, the Safe

Drinking Water Act (SDWA) passed by Congress in 1974

started a new era in the field of drinking water supply to

the public

13.3.1 C LEAN W ATER A CT (1972)

As mentioned, in 1972, Congress adopted the Clean Water

Act (CWA), which establishes a framework for achieving

its national objective “… to restore and maintain the

chem-ical, physchem-ical, and biological integrity of the nation’s

waters.” Congress decreed that, where attainable, water

quality “… provides for the protection and propagation of

fish, shellfish, and wildlife and provides for recreation in

and on the water.” These goals are referred to as the

“fishable and swimmable” goals of the act

Before CWA, there were no specific national water

pollution control goals or objectives Current standards

require that municipal wastewater be given secondary

treatment (to be discussed in detail later) and that most

effluents meet the conditions shown in Table 13.1 The

goal, via secondary treatment (i.e., the biological

treat-ment component of a municipal treattreat-ment plant), was set

in order that the principal components of municipal

waste-water, suspended solids, biodegradable material, and

pathogens could be reduced to acceptable levels Industrial

dischargers are required to treat their wastewater to the

level obtainable by the best available technology (BAT)

for wastewater treatment in that particular type of industry

In addition, a National Pollutant Discharge

Elimina-tion System (NPDES) program was established based on

uniform technological minimums with which each point

source discharger has to comply Under NPDES, each

municipality and industry discharging effluent into

streams is assigned discharge permits These permits

reflect the secondary treatment and BAT standards

Water quality standards are the benchmark against

which monitoring data are compared to assess the health

of waters to develop total maximum daily loads in

impaired waters They are also used to calculate water-quality-based discharge limits in permits issued under NPDES

13.3.2 S AFE D RINKING W ATER A CT (1974)

The SDWA of 1974 mandated EPA to establish drinking-water standards for all public drinking-water systems serving 25 or more people or having 15 or more connections Pursuant

to this mandate, EPA has established maximum contami-nant levels (MCLs) for drinking water delivered through public water distribution systems The maximum contam-inant levels of inorganics, organic chemicals, turbidity, and microbiological contaminants are shown in

Table 13.2 EPA’s primary regulations are mandatory and must be complied with by all public water systems to which they apply If analysis of the water produced by a water system indicates that an MCL for a contaminant is being exceeded, the system must take steps to stop pro-viding the water to the public or initiate treatment to reduce the contaminant concentration to below the MCL EPA has also issued guidelines to the states with regard to secondary drinking-water standards These appear in Table 13.3 These guidelines apply to drinking water contaminants that may adversely affect the aesthetic qualities of the water (i.e., those qualities that make water appealing and useful), such as odor and appearance These qualities have no known adverse health effects, and thus secondary regulations are not mandatory However, most drinking-water systems comply with the limits; they have learned through experience that the odor and appearance

of drinking water is not a problem until customers com-plain One thing is certain, they will comcom-plain

13.4 WATER QUALITY CHARACTERISTICS

OF WATER AND WASTEWATER

In this section, we describe individual pollutants and stres-sors that affect water quality Knowledge of the parameters

or characteristics most commonly associated with water and wastewater treatment processes is essential to the

TABLE 13.1 Minimum National Standards for Secondary Treatment

Characteristic

of Discharge

Unit of Measure

Average 30-day Concentration

Average 7-day Concentration

BOD mg/L 30 45 Suspended solids mg/L 30 45 Concentration pH units 6.0–9.0 6.0–9.0

Source: Federal Register, Secondary Treatment Regulations, 40 CFR Part

133, 1988

Water Quality 369

water or wastewater operator We encourage water and

wastewater practitioners to use a holistic approach to

man-aging water quality problems

It is important to point out that when this text refers

to water quality, the definition used is predicated on the

intended use of the water Many parameters have evolved

that qualitatively reflect the impact that various

contami-nants (impurities) have on selected water uses; the

follow-ing sections provide a brief discussion of these parameters

13.4.1 P HYSICAL C HARACTERISTICS OF W ATER

The physical characteristics of water and wastewater we

are interested in are more germane to the discussion at

hand — a category of parameters or characteristics that can be used to describe water quality One such category

is the physical characteristics for water, those that are apparent to the senses of smell, taste, sight, and touch Solids, turbidity, color, taste and odor, and temperature also fall into this category

13.4.1.1 Solids

Other than gases, all contaminants of water contribute to the solids content Classified by their size and state, chem-ical characteristics, and size distribution, solids can be dispersed in water in both suspended and dissolved forms

In regards to size, solids in water and wastewater can be classified as suspended, settleable, colloidal, or dissolved

TABLE 13.2

EPA Primary Drinking Water Standards

3 Maximum Levels of Turbidity

Turbidity reading (monthly average) 1 or up to 5 TUs if the water supplier can demonstrate to the state that the

higher turbidity does not interfere with disinfection maintenance of an effective disinfection agent throughout the distribution system, or microbiological determinants

Turbidity reading (based on average of 2 consecutive

days)

5 TUs

4 Microbiological Contaminants

Individual Sample Basis

Test Method Used Monthly Basis Fewer than 20 samples/month More than 20 samples/month

Number of Coliform Bacteria Not to Exceed:

Membrane filter technique 1/100 mL average daily 4/100 mL in more than 1 sample 4/100 mL in more than 5% of samples Fermentation Coliform Bacteria Shall Not Be Present in:

10-mL standard portions More than 10% of the

portions

3 or more portions in more than

1 sample

3 or more portions in more than 5% of samples

100-mL standard portions More than 60% of the

portions

5 portions in more than 1 sample 5 portions in more than 20% of the

samples

Source: Adapted from U.S Environmental Protection Agency, National Interim Primary Drinking Water Regulations, Federal Register,

Part IV, 1975

Arsenic 0.05 Chlorinated hydrocarbons Barium 1.0 Endrin 0.0002 Cadmium 0.010 Lindane 0.004 Chromium 0.05 Mexthoxychlor 0.1 Lead 0.05 Toxaphene 0.005 Mercury 0.002 Chlorophenoxys

Nitrate 10.0 2,4-D 0.1 Selenium 0.01 2, 4, 5-TP silvex 0.01 Silver 0.05

370 Handbook of Water and Wastewater Treatment Plant Operations

Solids are also characterized as being volatile or

nonvola-tile The distribution of solids is determined by computing

the percentage of filterable solids by size range Solids

typically include inorganic solids, such as silt, sand,

gravel, and clay from riverbanks, and organic matter, such

as plant fibers and microorganisms from natural or

man-made sources We use the term siltation to describe the

suspension and deposition of small sediment particles in

water bodies In flowing water, many of these

contami-nants result from the erosive action of water flowing over

surfaces

Sedimentation and siltation can severely alter aquatic

communities Sedimentation may clog and abrade fish

gills, suffocate eggs and aquatic insect larvae on the

bot-tom, and fill in the pore space between bottom cobbles

where fish lay eggs Suspended silt and sediment interfere

with recreational activities and aesthetic enjoyment at

streams and lakes by reducing water clarity and filling in

lakes Sediment may also carry other pollutants into surface

waters Nutrients and toxic chemicals may attach to

sedi-ment particles on land and ride the particles into surface

waters where the pollutants may settle with the sediment

or detach and become soluble in the water column

Suspended solids are a measure of the weight of

rel-atively insoluble materials in the ambient water These

materials enter the water column as soil particles from

land surfaces or sand, silt, and clay from stream bank

erosion of channel scour Suspended solids can include

both organic (detritus and biosolids) and inorganic (sand

or finer colloids) constituents

In water, suspended material is objectionable because

it provides adsorption sites for biological and chemical agents These adsorption sites provide attached micro-organisms a protective barrier against the chemical action

of chlorine In addition, suspended solids in water may be degraded biologically resulting in objectionable by-products Thus, the removal of these solids is of great concern in the production of clean, safe drinking water and wastewater effluent

In water treatment, the most effective means of remov-ing solids from water is by filtration It should be pointed out, however, that not all solids, such as colloids and other dissolved solids, can be removed by filtration

In wastewater treatment, suspended solids is an impor-tant water-quality parameter and is used to measure the quality of the wastewater influent, monitor performance

of several processes, and measure the quality of effluent Wastewater is normally 99.9% water and 0.1% solids If

a wastewater sample is evaporated, the solids remaining are called total solids As shown in Table 13.1, EPA has set a maximum suspended-solids standard of 30 mg/L for most treated wastewater discharges

13.4.1.2 Turbidity

One of the first things that is noticed about water is its clarity The clarity of water is usually measured by its turbidity Turbidity is a measure of the extent to which light is either absorbed or scattered by suspended material

in water Both the size and surface characteristics of the suspended material influence absorption and scattering Although algal blooms can make waters turbid, in surface water, most turbidity is related to the smaller inor-ganic components of the suspended solids burden, primarily the clay particles Microorganisms and vegetable material may also contribute to turbidity Wastewaters from indus-try and households usually contain a wide variety of turbidity-producing materials Detergents, soaps, and var-ious emulsifying agents contribute to turbidity

In water treatment, turbidity is useful in defining drinking-water quality In wastewater treatment, turbidity measurements are particularly important whenever ultravi-olet radiation (UV) is used in the disinfection process For

UV to be effective in disinfecting wastewater effluent, UV light must be able to penetrate the stream flow Obviously, stream flow that is turbid works to reduce the effectiveness

of irradiation (penetration of light)

The colloidal material associated with turbidity pro-vides absorption sites for microorganisms and chemicals that may be harmful or cause undesirable tastes and odors Moreover, the adsorptive characteristics of many colloids work to provide protection sites for microorganisms from disinfection processes Turbidity in running waters inter-feres with light penetration and photosynthetic reactions

TABLE 13.3

Secondary Maximum Contaminant Levels

Chloride 250 mg/L Causes taste

Color 15 cu a Appearance problems

Copper 1 mg/L Tastes and odors

Corrosivity Noncorrosive Tastes and odors

Fluoride 2 mg/L Dental fluorosis

Foaming agents 0.5 mg/L Appearance problems

Iron 0.3 mg/L Appearance problems

Manganese 0.05 mg/L Discolors laundry

Odor 3 TON b Unappealing to drink

pH 6.5–8.5 Corrosion or scaling

Sulfate 250 mg/L Laxative effect

Total dissolved solids 500 mg/L Taste, corrosive

Zinc 5 mg/L Taste, appearance

a Cu = color unit

b TON = threshold odor number

Source: Adapted from McGhee, T.J., Water Supply and Sewerage,

McGraw-Hill, New York, p 161, 1991

Water Quality 371

13.4.1.3 Color

Color is another physical characteristic by which the

qual-ity of water can be judged Pure water is colorless Water

takes on color when foreign substances such as organic

matter from soils, vegetation, minerals, and aquatic

organ-isms are present Color can also be contributed to water

by municipal and industrial wastes

Color in water is classified as either true color or

apparent color Water whose color is partly due to

dis-solved solids that remain after removal of suspended matter

is known as true color Color contributed by suspended

matter is said to have apparent color In water treatment,

true color is the most difficult to remove

a unique origin Intrinsic color is easy to

dis-cern, as can be seen in Crater Lake, OR, which

is know for its intense blue color The

appear-ance of the lake varies from turquoise to deep

navy blue depending on whether the sky is hazy

or clear Pure water and ice have a pale blue

color

The obvious problem with colored water is that it is

not acceptable to the public Given a choice, the public

prefers clear, uncolored water Another problem with

col-ored water is the effect it has on laundering, papermaking,

manufacturing, textiles, and food processing The color of

water has a profound impact on its marketability for both

domestic and industrial use

In water treatment, color is not usually considered

unsafe or unsanitary, but is a treatment problem in regards

to exerting a chlorine demand that reduces the

effective-ness of chlorine as a disinfectant

In wastewater treatment, color is not necessarily a

problem, but instead is an indicator of the condition of the

wastewater Condition refers to the age of the wastewater,

which along with odor, provides a qualitative indication of

its age Early in the flow, wastewater is a light

brownish-gray color The color of wastewater containing DO is

nor-mally gray Black-colored wastewater usually accompanied

by foul odors, containing little or no DO, is said to be septic Table 13.4 provides wastewater color information

As the travel time in the collection system increases (flow becomes increasingly more septic), and more anaerobic conditions develop, the color of the wastewater changes from gray to dark gray and ultimately to black

13.4.1.4 Taste and Odor

Taste and odor are used jointly in the vernacular of water science The term odor is used in wastewater; taste, obvi-ously, is not a consideration Domestic sewage should have a musty odor Bubbling gas and/or foul odor may indicate industrial wastes, anaerobic (septic) conditions, and operational problems Refer to Table 13.5 for typical wastewater odors, possible problems, and solutions

In wastewater, odors are of major concern, especially

to those who reside in close proximity to a wastewater treatment plant These odors are generated by gases produced by decomposition of organic matter or by sub-stances added to the wastewater Because these subsub-stances are volatile, they are readily released to the atmosphere at any point where the waste stream is exposed, particularly

if there is turbulence at the surface

Most people would argue that all wastewater is the same; it has a disagreeable odor It is hard to argue against the disagreeable odor However, one wastewater operator told us that wastewater “smelled great, smells just like money to me — money in the bank.”

This was an operator’s view We also received another opinion of odor problems resulting from wastewater oper-ations This particular opinion, given by an odor control manager, was quite different His statement was that “odor control is a never ending problem.” He also pointed out that to combat this difficult problem, odors must be con-tained In most urban plants, it has become necessary to physically cover all source areas, such as treatment basins, clarifiers, aeration basins, and contact tanks, to prevent odors from leaving the processes These contained spaces must then be positively vented to wet-chemical scrubbers

to prevent the buildup of a toxic concentration of gas

TABLE 13.4 Significance of Color in Wastewater

Influent of plant Gray None

Red Blood or other industrial wastes Green, yellow, other Industrial wastes not pretreated (paints, etc.) Red or other soil color Surface runoff into influent, also industrial flows Black Septic conditions or industrial flows

Source: Spellman, F.R., The Science of Water, Technomic Publ., Lancaster, PA, 1998.

372 Handbook of Water and Wastewater Treatment Plant Operations

As mentioned, in drinking water, taste and odor are

not normally a problem until the consumer complains The

problem is that most consumers find taste and odor in water

aesthetically displeasing As mentioned, taste and odor do

not directly present a health hazard, but they can cause the

customer to seek water that tastes and smells good, but

may not be safe to drink Most consumers consider water

tasteless and odorless When consumers find that their

drinking water has a taste, odor, or both, they automatically

associate the drinking water with contamination

Water contaminants are attributable to contact with

nature or human use Taste and odor in water are caused

by a variety of substances such as minerals, metals, and

salts from the soil; constituents of wastewater; and end

products produced in biological reactions When water has

a taste but no accompanying odor, the cause is usually

inorganic contamination Water that tastes bitter is usually

alkaline, while salty water is commonly the result of

metallic salts However, when water has both taste and

odor, the likely cause is organic materials The list of

possible organic contaminants is too long to record here,

but petroleum-based products lead the list of offenders

Taste- and odor-producing liquids and gases in water are

produced by biological decomposition of organics A

prime example of one of these is hydrogen sulfide; known

best for its characteristic rotten-egg taste and odor Certain

species of algae also secrete an oily substance that may

produce both taste and odor When certain substances

combine (such as organics and chlorine), the synergistic

effect produces taste and odor

In water treatment, one of the common methods used

to remove taste and odor is to oxidize the materials that

cause the problem Oxidants, such as potassium

perman-ganate and chlorine, are used Another common treatment

method is to feed powdered activated carbon before the

filter The activated carbon has numerous small openings

that absorb the components that cause the odor and tastes

These contained spaces must then be positively vented to

wet-chemical scrubbers to prevent the buildup of toxic concentrations of gas

13.4.1.5 Temperature

Heat is added to surface and groundwater in many ways Some of these are natural, and some are artificial For example, heat is added by natural means to Yellowstone Lake, WY The Lake, one of the world’s largest freshwater lakes, resides in a calderas, situated at more than 7700 ft (the largest high altitude lake in North America) When one attempts to swim in Yellowstone Lake (without a wetsuit), the bitter cold of the water literally takes one’s breath away However, if it were not for the hydrothermal discharges that occur in Yellowstone, the water would be even colder In regards to human heated water, this most commonly occurs whenever a raw water source is used for cooling water in industrial operations The influent to industrial facilities is at normal ambient temperature When it is used to cool machinery and industrial processes and then discharged back to the receiving body, it is often heated

The problem with heat or temperature increases in surface waters is that it affects the solubility of oxygen in water, the rate of bacterial activity, and the rate at which gases are transferred to and from the water

examina-tion of water or wastewater, temperature is not normally used to evaluate either However, tem-perature is one of the most important parameters

in natural surface-water systems Surface waters are subject to great temperature variations Water temperature does partially determine how effi-ciently certain water treatment processes operate For example, temperature has an effect on the rate at which chemicals dissolve and react When water is cold, more chemicals are required for efficient coagulation and floc-culation to take place When water temperature is high, the result may be a higher chlorine demand because of

TABLE 13.5

Odors in Wastewater Treatment Plant

Earthy, musty Primary and secondary units No problem (normal) None required

Hydrogen sulfide (rotten egg odor) Influent Septic Aerate, chlorinate, oxonizate

Trickling filters Septic conditions More air/less BOD Secondary clarifiers Septic conditions Remove sludge Chlorine contact Septic conditions Remove sludge General plant Septic conditions Good housekeeping Chlorine like Chlorine contact tank Improper chlorine dosage Adjust chlorine dosage controls Industrial odors General plant Inadequate pretreatment Enforce sewer use regulations

Source: Spellman, F.R., The Science of Water, Technomic Publ., Lancaster, PA, 1998.

Water Quality 373

the increased reactivity, and there is often an increased

level of algae and other organic matter in raw water

Tem-perature also has a pronounced effect on the solubility of

gases in water

Ambient temperature (temperature of the surrounding

atmosphere) has the most profound and universal effect

on temperature of shallow natural water systems When

water is used by industry to dissipate process waste heat,

the discharge locations into surface waters may experience

localized temperature changes that are quite dramatic

Other sources of increased temperatures in running water

systems result because of clear-cutting practices in forests

(where protective canopies are removed) and from

irriga-tion flows returned to a body of running water

In wastewater treatment, the temperature of

wastewa-ter varies greatly, depending upon the type of operations

being conducted at a particular installation Wastewater is

generally warmer than that of the water supply, because

of the addition of warm water from industrial activities

and households Wide variation in the wastewater

temper-ature indicates heated or cooled discharges, often of

substantial volume They have any number of sources For

example, decreased temperatures after a snowmelt or rain

event may indicate serious infiltration In the treatment

process, temperature not only influences the metabolic

activities of the microbial population, but also has a

pro-found effect on such factors as gas-transfer rates and the

settling characteristics of the biological solids

13.4.2 C HEMICAL C HARACTERISTICS OF W ATER

Another category used to define or describe water quality

is its chemical characteristics The most important

chem-ical characteristics are:

1 Total dissolved solids (TDS)

2 Alkalinity

3 Hardness

4 Fluoride

5 Metals

6 Organics

7 Nutrients

Chemical impurities can be either natural, man-made

(industrial), or be deployed in raw water sources by enemy

forces

Some chemical impurities cause water to behave as

either an acid or a base Because either condition has an

important bearing on the water treatment process, the pH

value must be determined Generally, the pH influences

the corrosiveness of the water, chemical dosages necessary

for proper disinfection, and the ability to detect

contami-nants The principal contaminants found in water are

shown in Table 13.6 These chemical constituents are

important because each one affects water use in some manner; each one either restricts or enhances specific uses

As mentioned, the pH of water is important As pH rises, for example, the equilibrium (between bicarbonate and carbonate) increasingly favors the formation of car-bonate, which often results in the precipitation of carbonate salts If you have ever had flow in a pipe system interrupted

or a heat-transfer problem in your water heater system, then carbonate salts that formed a hard-to-dissolve scale within the system most likely the cause It should be pointed out that not all carbonate salts have a negative effect on their surroundings Consider, for example, the case of blue marl lakes; they owe their unusually clear, attractive appearance to carbonate salts

We mentioned earlier that water has been called the

universal solvent. This is, of course, a fitting description The solvent capabilities of water are directly related to its chemical characteristics or parameters

As mentioned, in water-quality management, total dis-solved solids (TDS), alkalinity, hardness, fluorides, metals, organics, and nutrients are the major chemical parameters

of concern

13.4.2.1 Total Dissolved Solids (TDS)

Because of water’s solvent properties, minerals dissolved from rocks and soil as water passes over and through it produce TDS (comprised of any minerals, salts, metals, cations or anions dissolved in water) TDS constitutes a part of total solids in water; it is the material remaining

in water after filtration

Dissolved solids may be organic or inorganic Water may be exposed to these substances within the soil, on surfaces, and in the atmosphere The organic dissolved constituents of water come from the decay products of

TABLE 13.6 Chemical Constituents Commonly Found in Water

Constituent

Calcium Fluorine Magnesium Nitrate Sodium Silica Potassium TDS Iron Hardness Manganese Color Bicarbonate pH Carbonate Turbidity Sulfate Temperature Chloride

Source:Spellman, F.R., The Science

of Water, Technomic Publ., Lancaster,

PA, 1998.

374 Handbook of Water and Wastewater Treatment Plant Operations

vegetation, from organic chemicals, and from organic

gases

Dissolved solids can be removed from water by

dis-tillation, electrodialysis, reverse osmosis, or ion exchange

It is desirable to remove these dissolved minerals, gases,

and organic constituents because they may cause

psycho-logical effects and produce aesthetically displeasing color,

taste, and odors

While it is desirable to remove many of these

dis-solved substances from water, it is not prudent to remove

them all This is the case, for example, because pure,

distilled water has a flat taste Further, water has an

equi-librium state with respect to dissolved constituents If

water is out of equilibrium or undersaturated, it will

aggressively dissolve materials with which it comes into

contact Because of this problem, substances that are

readily dissolvable are sometimes added to pure water to

reduce its tendency to dissolve plumbing

13.4.2.2 Alkalinity

Another important characteristic of water is its alkalinity —

a measure of water’s ability to neutralize acid or really an

expression of buffering capacity The major chemical

con-stituents of alkalinity in natural water supplies are the

bicarbonate, carbonate, and hydroxyl ions These

com-pounds are mostly the carbonates and bicarbonates of

sodium, potassium, magnesium, and calcium These

con-stituents originate from carbon dioxide (from the

atmo-sphere and as a by-product of microbial decomposition of

organic material) and from their mineral origin (primarily

from chemical compounds dissolved from rocks and soil)

Highly alkaline waters are unpalatable; this condition

has little known significance for human health The

prin-cipal problem with alkaline water is the reactions that

occur between alkalinity and certain substances in the

water Alkalinity is important for fish and aquatic life

because it protects or buffers against rapid pH changes It

is also important because the resultant precipitate can foul

water system appurtenances In addition, alkalinity levels

affect the efficiency of certain water treatment processes,

especially the coagulation process

13.4.2.3 Hardness

Hardness is due to the presence of multivalent metal ions

that come from minerals dissolved in water Hardness is

based on the ability of these ions to react with soap to

form a precipitate or soap scum

In freshwater, the primary ions are calcium and

mag-nesium; iron and manganese may also contribute Hardness

is classified as carbonate hardness or noncarbonate hardness

Carbonate hardness is equal to alkalinity but a

non-carbonate fraction may include nitrates and chlorides

Hardness is either temporary or permanent Carbonate hardness (temporary hardness) can be removed by boiling Noncarbonate hardness cannot be removed by boiling and

is classified as permanent

Hardness values are expressed as an equivalent amount or equivalent weight of calcium carbonate (equiv-alent weight of a substance is its atomic or molecular weight divided by n) Water with a hardness of less than

50 ppm is soft Above 200 ppm, domestic supplies are usually blended to reduce the hardness value The U.S Geological Survey uses the following classification:

The impact of hardness can be measured in economic terms Soap consumption points this out; it represents an economic loss to the water user When washing with a bar

of soap, there is a need to use more soap to get a lather whenever washing in hard water There is another problem with soap and hardness When using a bar of soap in hard water, when lather is finally built up, the water has been softened by the soap The precipitate formed by the hard-ness and soap (soap curd) adheres to just about anything (tubs, sinks, dishwashers) and may stain clothing, dishes, and other items There also is a personal problem: the residues of the hardness-soap precipitate may precipitate into the pores, causing skin to feel rough and uncomfort-able Today these problems have been largely reduced by the development of synthetic soaps and detergents that do not react with hardness However, hardness still leads to other problems, including scaling and laxative effect Scal-ing occurs when carbonate hard water is heated and calcium carbonate and magnesium hydroxide are precipitated out

of solution, forming a rock-hard scale that clogs hot water pipes and reducing the efficiency of boilers, water heaters, and heat exchangers Hardness, especially with the pres-ence of magnesium sulfates, can lead to the development

of a laxative effect on new consumers

There are advantages to be gained from usage of hard water These include:

1 Hard water aids in the growth of teeth and bones

2 Hard water reduces toxicity to many by poison-ing with lead oxide from lead pipelines

3 Soft waters are suspected to be associated with cardiovascular diseases.5

Range of Hardness (mg/L [ppm] as CaCO 3 )

Descriptive Classification

1–50 Soft 51–150 Moderately hard 151–300 Hard

Above 300 Very hard