Standard Methods for Examination of Water & Wastewater_1 ppt

Constituents of Water
and Wastewater

Given a wastewater, what process should be applied to treat it: biological, chemical,
or physical? Should it be treated with a combination of processes? These questions
cannot be answered unless the constituents of the wastewater are known. Thus,
before any wastewater is to be treated, it is important that its constituents are
determined. On the other hand, what are the constituents of a given raw water that
make it unfit to drink? Are these constituents simply in the form of turbidity making
it unpleasant to the eye, in the form of excessive hardness making it unfit to drink,
or in the form bacterial contamination making it dangerous to drink? Water and
wastewater may be characterized according to their physical, chemical, and micro-
biological characteristics. These topics are discussed in this chapter.

2.1 PHYSICAL AND CHEMICAL CHARACTERISTICS

The constituent physical and chemical characterizations to be discussed include the
following: turbidity (physical), color (physical), taste (physical) temperature (phys-
ical), chlorides (chemical), fluorides (chemical), iron and manganese (chemical),
lead and copper (chemical), nitrate (chemical), sodium (chemical), sulfate (chemi-
cal), zinc (chemical), biochemical oxygen demand (chemical), solids (physical), pH
(chemical), chemical oxygen demand (chemical), total organic carbon (chemical),
nitrogen (chemical), phosphorus (chemical), acidity and alkalinity (chemical), fats
and oils and grease (chemical), and odor (physical). The characterization will also
include surfactants (physical), priority pollutants (chemical), volatile organic com-
pounds (chemical), and toxic metal and nonmetal ions (chemical). These constituents
are discussed in turn in the paragraphs that follow.

2.1.1 T

URBIDITY

Done photometrically,

turbidity

is a measure of the extent to which suspended matter
in water either absorbs or scatters radiant light energy impinging upon the suspen-
sion. The original measuring apparatus that measures turbidity, called the

Jackson
turbidimeter

, was based on the absorption principle. A standardized candle was
placed under a graduated glass tube housed in a black metal box so that the light
from the candle can only be seen from above the tube. The water sample was then
poured slowly into the tube until the candle flame was no longer visible. The turbidity
was then read on the graduation etched on the tube. At present, turbidity measure-
ments are done conveniently through the use of photometers. A beam of light from
a source produced by a standardized electric bulb is passed through a sample vial.
2

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Physical–Chemical Treatment of Water and Wastewater

The light that emerges from the sample is then directed to a photometer that measures

the light absorbed. The readout is calibrated in terms of turbidity.
The unit of turbidity is the turbidity unit (TU) which is equivalent to the turbidity
produced by one mg/L of silica (SiO

2

). SiO

2

was used as the reference standard.
Turbidities in excess of 5 TU are easily detected in a glass of water and are
objectionable not necessarily for health but for aesthetic reasons. A chemical, for-
mazin, that provides a more reproducible result has now replaced silica as the
standard. Accordingly, the unit of turbidity is now also expressed as formazin
turbidity units (FTU).
The other method of measurement is by light scattering. This method is used
when the turbidity is very small. The sample “scatters” the light that impinges
upon it. The scattered light is then measured by putting the photometer at right angle
from the original direction of the light generated by the light source. This measure-
ment of light scattered at a 90-degree angle is called

nephelometry

. The unit of
turbidity in nephelometry is the nephelometric turbidity unit (NTU).

2.1.2 C

OLOR

Color is the perception registered as radiation of various wavelengths strikes the
retina of the eye. Materials decayed from vegetation and inorganic matter create this
perception and impart color to water. This color may be objectionable not for health
reasons but for aesthetics. Natural colors give a yellow-brownish appearance to
water, hence, the natural tendency to associate this color with urine. The unit of
measurement of color is the platinum in potassium chloroplatinate (K

2

PtCl

6

). One
milligram per liter of Pt in K

2

PtCl

6

is one unit of color.
A major provision of the Safe Drinking Water Act (SDWA) is the promulgation
of regulations. This promulgation requires the establishment of primary regulations
which address the protection of public health and the establishment of secondary
regulations which address aesthetic consideration such as taste, appearance, and
color. To fulfill these requirements, the U.S. Environmental Protection Agency
(USEPA) establishes maximum contaminant levels (MCL). The secondary MCL for

color is 15 color units.

2.1.3 T

ASTE

Taste is the perception registered by the taste buds. There should be no noticeable
taste at the point of use of any drinking water.
The numerical value of taste (or odor to be discussed below) is quantitatively
determined by measuring a volume of the sample

A

(in mL) and diluting it with a
volume

B

(in mL) of distilled water so that the taste (or odor) of the resulting mixture
is just barely detectable at a total mixture volume of 200 mL. The unit of taste
(or odor) is then expressed in terms of a threshold number as follows:
(2.1)TON or TTN
AB+
A

=

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Constituents of Water and Wastewater

127

where
TON

=

threshold odor number
TTN

=

threshold taste number

2.1.4 O

DOR

Odor is the perception registered by the olfactory nerves. As in the case of taste,
there should be no noticeable odor at the point of use of any drinking water. The
secondary standard for odor is 3.
Fresh wastewater odor is less disagreeable than stale wastewater odor but,
nonetheless, they all have very objectionable odors. Odors are often the cause of
serious complaints from neighborhoods around treatment plants, and it is often
difficult for inspectors investigating these complaints to smell any odors in the
vicinity of the neighborhood. The reason is that as soon as he or she is exposed to
the odor, the olfactory nerves become accustomed to it and the person can no longer
sense any odor. If you visit a wastewater treatment plant and ask the people working

there if any odor exists, their responses would likely be that there is none. Of course,
you, having just arrived from outside the plant, know all the time that, in the vicinity
of these workers, plenty of odors exist. The effect of odors on humans produces
mainly psychological stress instead of any specific harm to the body. Table 2.1 lists
the various odorous compounds that are associated with untreated wastewater.
The determination of odors in water was addressed previously under the discus-
sion on taste. Odors in air are determined differently. They are quantitatively mea-
sured by convening a panel of human evaluators. These evaluators are exposed to
odors that have been diluted with odor-free air. The number of dilutions required to
bring the odorous air to the minimum level of detectable concentration by the panel is
the measure of odor. Thus, if three volumes of odor-free air is required, the odor of the
air is

three dilutions

. It is obvious that if these evaluators are subjected to the odor
several times, the results would be suspicious. For accurate results, the evaluators

TABLE 2.1
Malodorous Compounds Associated with Untreated Wastewater

Compound Formula Threshold (ppm) Odor Quality

Ammonia NH

3

18 Odor of ammonia
Butyl mercaptan (CH

3

)

3

CSH — Secretion of skunk
Crotyl mercaptan CH

3

(CH

2

)

3

SH — Secretion of skunk
Diamines NH

2

(CH

2

)

4

NH

2

, NH

2

(CH

2

)

5

NH

2

— Decayed fish
Ethyl mercaptan CH

3

CH

2

SH 0.0003 Decayed cabbage
Hydrogen sulfide H

2

S

<

0.0002 Rotten eggs
Indole C

8

H

7

N 0.0001 —
Methyl amine CH

3

NH

2

4.6 Fishy
Methyl mercaptan CH

3

SH 0.0006 Decayed cabbage
Methyl sulfide (CH

3

)

2

S 0.001 Rotten cabbage
Phenyl sulfide (C

6

H

5

)

2

S 0.0001 Rotten cabbage
Skatole C

9

H

9

N 0.001 Fecal matter

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Physical–Chemical Treatment of Water and Wastewater

should be subjected only once, to avoid their olfactory nerves becoming accustomed
to the odor thus making wrong judgments.

2.1.5 T

EMPERATURE

Most individuals find water at temperatures of 10–15

°

C most palatable. Groundwaters
and waters from mountainous areas are normally within this range. Surface waters
are, of course, subject to the effect of ambient temperatures and can be very warm
during summer.
The temperature of water affects the efficiency of treatment units. For example,
in cold temperatures, the viscosity increases. This, in turn, diminishes the efficiency

of settling of the solids that the water may contain because of the resistance that the
high viscosity offers to the downward motion of the particles as they settle. Pressure
drops also increase in the operation of filtration units, again, because of the resistance
that the higher viscosity offers.

2.1.6 C

HLORIDES

Chlorides in concentrations of 250 mg/L or greater are objectionable to most people.
Thus, the secondary standard for chlorides is 250 mg/L. Whether or not concentra-
tions of 250 mg/L are objectionable, however, would depend upon the degree of
acclimation of the user to the water. In Antipolo, a barrio of Cebu in the Philippines,
the normal source of water of the residents is a spring that emerges along the
shoreline between a cliff and the sea. As such, the fresh water is contaminated by
saltwater before being retrieved by the people. The salt imparts to the water a high
concentration of chlorides. Chloride contaminants could go as high as 2,000 mg/L;
however, even with concentrations this high, the people continue to use the source
and are accustomed to the taste.

2.1.7 F

LUORIDES

The absence of fluorides in drinking water encourages dental caries or tooth decay;
excessive concentrations of the chemical produce mottling of the teeth or dental
fluorosis. Thus, managers and operators of water treatment plants must be careful
that the exact concentrations of the fluorides are administered to the drinking water.
Optimum concentrations of 0.7 to 1.2 mg/L are normally recommended, although
the actual amount in specific circumstances depends upon the air temperature, since

air temperature influences the amount of water that people drink. Also, the use of
fluorides in drinking water is still controversial. Some people are against its use,
while some are in favor of it.

2.1.8 I

RON



AND

M

ANGANESE

Iron (Fe) and manganese (Mn) are objectionable in water supplies because they
impart brownish colors to laundered goods. Fe also affects the taste of beverages
such as tea and coffee. Mn flavors tea and coffee with a medicinal taste. The SMCLs
(secondary MCLs) for Fe and Mn are, respectively, 0.3 and 0.05 mg/L.

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129

2.1.9 L

EAD



AND

C

OPPER

Clinical, epidemiological, and toxicological studies have demonstrated that lead
exposure can adversely affect human health. The three systems in the human body
most sensitive to lead are the blood-forming system, the nervous system, and the
renal system. In children, blood levels from 0.8 to 1.0

µ

g/L can inhibit enzymatic
actions. Also, in children, lead can alter physical and mental development, interfere
with growing, decrease attention span and hearing, and interfere with heme synthesis.
In older men and women, lead can increase blood pressure. Lead is emitted into the
atmosphere as Pb, PbO, PbO

2

, PbSO

4

, PbS, Pb(CH

3

)

4

, Pb(C

2

H

5

)

4

, and lead halides.
In drinking water, it can be emitted from pipe solders.
The source of copper in drinking water is the plumbing used to convey water
in the house distribution system. In small amounts, it is not detrimental to health,
but it will impart an undesirable taste to the water. In appropriate concentrations,
copper can cause stomach and intestinal distress. It also causes Wilson’s disease.
Certain types of PVC (polyvinyl chloride) pipes, called CPVC (chlorinated polyvinyl
chloride), can replace copper for household plumbing.

2.1.10 N

ITRATE

Nitrate is objectionable for causing what is called

methemoglobinemia

(infant cyanosis
or blue babies) in infants. The MCL is 10 mg/L expressed as nitrogen.
Before the establishment of stringent regulations, sludges from wastewater treat-
ment plants were most often spread on lands and buried in ditches as methods of
disposal. As the sludge decays, nitrates are formed. Thus, in some situations, these
methods of disposal have resulted in the nitrates percolating down the soil causing
excessive contaminations of the groundwater. Even today, these methods are still
practiced. In order for these practices to be acceptable to the regulatory agencies, a
material balance of the nitrate formed must be calculated to ascertain that the
contamination of the groundwater does not go to unacceptable levels.

2.1.11 S

ODIUM

The presence of sodium in drinking water can affect persons suffering from heart,
kidney, or circulatory ailments. It may elevate blood pressures of susceptible individuals.
Sodium is plentiful in the common table salt that people use to flavor food to their
taste. It is a large constituent of sea water; hence, in water supplies contaminated by
the sea as in the case of Antipolo mentioned earlier, this element would be plentiful.

2.1.12 S

ULFATE

The sulfate ion is one of the major anions occurring naturally in water. It produces
a cathartic or laxative effect on people when present in excessive amounts in drinking
water. Its SMCL is 250 mg/L.

2.1.13 Z

INC

Zinc is not considered detrimental to health, but it will impart an undesirable taste
to drinking water. Its SMCL is 5 mg/L.

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Physical–Chemical Treatment of Water and Wastewater

2.1.14 B

IOCHEMICAL

O

XYGEN

D

EMAND

Biochemical oxygen demand (BOD) is the amount of oxygen consumed by the organ-
ism in the process of stabilizing waste. As such, it can be used to quantify the amount
or concentration of oxygen-consuming substances that a wastewater may contain.
Analytically, it is measured by incubating a sample in a refrigerator for five days at a
temperature of 20

°

C and measuring the amount of oxygen consumed during that time.
The substances that consume oxygen in a given waste are composed of carbon-
aceous and nitrogenous portions. The carbonaceous portion refers to the carbon
content of the waste; carbon reacts with the dissolved oxygen producing CO

2

. On
the other hand, the nitrogenous portion refers to the ammonia content; ammonia
also reacts with the dissolved oxygen. Even though the term used is nitrogenous,
nitrogen is not referred to in this context. Any nitrogen must first be converted to
ammonia before it becomes the “nitrogenous.”
Generally, two types of analysis are used to determine BOD in the laboratory:
one where dilution is necessary and one where dilution is not necessary. When the
BOD of a sample is small, such as found in river waters, dilution is not necessary.
Otherwise, the sample would have to be diluted. Table 2.1 sets the criteria for
determining the dilution required. This table shows that there are two ways dilution
can be made: using percent mixture and direct pipetting into 300-mL BOD bottles.
Normally, BOD analysis is done using 300-mL incubation bottles.
Because BOD analysis attempts to measure the oxygen equivalent of a given waste,
the environment inside the BOD bottle must be conducive to uninhibited bacterial

growth. The parameters of importance for maintaining this type of environment are

TABLE 2.2
Ranges of BOD Measurable with Various Dilutions
of Samples

Using Percent Mixtures
By Direct Pipetting into

300-mL Bottles
% mixture Range of BOD

5

mL Range of BOD

5

0.01 35,000–70,000 0.01 40,000–100,000
0.03 10,000–35,000 0.05 20,000– 40,000
0.05 7,000–10,000 0.10 10,000–20,000
0.1 3,500–7,000 0.30 4,000–10,000
0.3 1,400–3,500 0.50 2,000–4,000
0.5 700–1,400 1.0 1,000–2,000
1.0 350–700 3.0 400–1,000
3.0 150–350 5.0 200–400
5.0 70–150 10.0 100–200
10.0 35–70 30.0 40–100
30.0 10–35 50.0 20–40
50.0 5–10 100 100

100 0–5 300 0–10

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Constituents of Water and Wastewater

131

freedom from toxic materials, favorable pH and osmotic pressure conditions, optimal
amount of nutrients, and the presence of significant amount of population of mixed
organisms of soil origin. Through long years of experience, it has been found that
synthetic dilution water prepared from distilled water or demineralized water is best
for BOD work, because the presence of such toxic substances as chloramine, chlorine,
and copper can be easily controlled. The maintenance of favorable pH can be assured
by buffering the dilution water at about pH 7.0 using potassium and sodium phosphates.
The potassium and sodium ions, along with the addition of calcium and magnesium
ions, can also maintain the proper osmotic pressure, as well as provide the necessary
nutrients in terms of these elements. The phosphates, of course, provide the necessary
phosphorus nutrient requirement. Ferric chloride, magnesium sulfate, and ammonium
chloride supply the requirements for iron, sulfur, and nitrogen, respectively.
A sample submitted for analysis may not contain any organism at all. Such is
the case, for example, of an industrial waste, which can be completely sterile. For
this situation, the dilution water must be seeded with organisms from an appropriate
source. In domestic wastewaters, all the organisms needed are already there; conse-
quently, these wastewaters can serve as good sources of seed organisms. Experience
has shown that a seed volume of 2.0 mL per liter of dilution water is all that is needed.

Laboratory calculation of BOD.

In the subsequent development, the formu-
lation will be based on the assumption that the dilution method is used. If, in fact,
the method used is direct, that is, no dilution, then the dilution factor that appears
in the formulation will simply be ignored and equated to 1.
The technique for determining the BOD of a sample is to find the difference in
dissolved oxygen (DO) concentration between the final and the initial time after a
period of incubation at some controlled temperature. This difference, converted to
mass of oxygen per unit volume of sample (such as mg/L) is the BOD.
Let

I

be the initial DO of the sample, which has been diluted with seeded dilution
water, and

F

be the final DO of the same sample after the incubation period. The
difference would then represent a BOD, but since the sample is seeded, a correction
must be made for the BOD of the seed. This requires running a blank.
Let

I

′

represent the initial DO of a volume

Y

of the blank composed of only the
seeded dilution water; also, let

F

′

be the final DO after incubating this blank at the
same time and temperature as the sample. If

X

is the volume of the seeded dilution
water mixed with the sample, the DO correction would be (

I

′ −

F

′

)(

X

/

Y

). Letting

D

be the fractional dilution, the BOD of the sample is simply
(2.2)
In this equation, if the incubation period is five days, the BOD is called the

five-
day biochemical oxygen demand

, BOD

5

. It is understood that unless it is specified,
BOD

5

is a BOD measured at the standard temperature of incubation of 20

°

C. If
incubation is done for a long period of time such as 20 to 30 days, it is assumed
that all the BOD has been exerted. The BOD under this situation is the ultimate;
therefore, it is called

ultimate BOD

, or BOD

u

.
BOD
IF–()I′ F′–()X/Y()–
D

=

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132 Physical–Chemical Treatment of Water and Wastewater
BOD
u
, in turn, can have two fractions in it: one due to carbon and the other due
to nitrogen. As mentioned before, carbon reacts with oxygen; also, nitrogen in the
form of ammonia, reacts with oxygen. If the BOD reaction is allowed to go to
completion with the ammonia reaction inhibited, the resulting ultimate BOD is called
ultimate carbonaceous BOD or CBOD. Because Nitrosomonas and Nitrobacter, the
organisms for the ammonia reaction, cannot compete very well with carbonaceous
bacteria (the organisms for the carbon reaction), the reaction during the first few days
of incubation up to approximately five or six days is mainly carbonaceous. Thus,
BOD
5
is mainly carbonaceous. If the reaction is uninhibited, the BOD after five or

six days of incubation also contains the nitrogenous BOD. BOD is normally reported
in units of mg/L.
Experience has demonstrated that a dissolved oxygen concentration of 0.5 mg/L
practically does not cause depletion of BOD. Also, it has been learned that a
depletion of less than 2.0 mg/L produces erroneous results. Thus, it is important
that in BOD work, the concentration of DO in the incubation bottle should not fall
below 0.5 mg/L and that the depletion after the incubation period should not be
less than 2.0 mg/L.
Example 2.1 Ten milliliters of sample is pipetted directly into a 300-mL
incubation bottle. The initial DO of the diluted sample is 9.0 mg/L and its final DO
is 2.0 mg/L. The initial DO of the dilution water is also 9.0 mg/L, and the final DO
is 8.0 mg/L. The temperature of incubation is 20°C. If the sample is incubated for
five days, what is the BOD
5
of the sample?
Solution:
2.1.15 NITRIFICATION IN THE BOD TEST
The general profile of oxygen consumption in a BOD test for a waste containing
oxygen-consuming constituents is shown in Figure 2.1. As mentioned previously,
because the nitrifiers cannot easily compete with the carbonaceous bacteria, it takes
about 5 days or so for them to develop. Thus, after about 5 days the curve abruptly
rises due to the nitrogenous oxygen demand, NBOD. If the nitrifiers are abundant
in the beginning of the test, however, the nitrogen portion can be exerted immediately
as indicated by the dashed line after a short lag. This figure shows the necessity of
inhibiting the nitrifiers if the carbonaceous oxygen demand, CBOD, is the one
desired in the BOD test.
The reactions in the nitrification process are mediated by two types of autotrophic
bacteria: Nitrosomonas and Nitrobacter. The ammonia comes from the nitrogen
content of any organic substance, such as proteins, that contains about 16% nitro-
gen. As soon as the ammonia has been hydrolyzed from the organic substance,

Nitrosomonas consumes it and in the process also consumes oxygen according to
BOD
IF–()I′ F′–()X/Y()–
D

92–()98–()300 10–[]/300()–
10/300

==
183 = mg/L
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Constituents of Water and Wastewater 133
the following reactions:
(2.3)
(2.4)
Adding Eqs. (2.3) and (2.4) produces
(2.5)
Equation (2.4) is called an electron acceptor reaction. Equation (2.3) is an elector
donor reaction, that is, it provides the electron for the electron acceptor reaction.
Together, these two reactions produce energy for the Nitrosomonas.
The produced in Equation (2.5) serves as an electron source for another
genus of bacteria, the Nitrobacter. The chemical reactions when Nitrobacter uses
the nitrite are as follows:
(2.6)
(2.7)
Adding Eqs. (2.6) and (2.7) produces
(2.8)
FIGURE 2.1 Exertion of CBOD and NBOD.
Days of incubation

5 days or more
Oxygen consumed, mg/L
CBOD
NBOD
1
6

NH
4
+
1
3

H
2
O
1
6

NO
2
−
4
3

H
+
e
−
++→+

1
4

O
2
H
+
e
−
1
2

H
2
O→++
1
6

NH
4
+
1
4

O
2
1
6

H

2
O
1
6

NO
2
−
1
3

H
+
++→+
NO
2
−
1
6

NO
2
−
1
6

H
2
O
1

6

NO
3
−
1
3

H
+
1
3

e
−
++→+
1
12

O
2
1
3

H
+
1
3

e

−
1
6

H
2
O→++
1
6

NO
2
−
1
12

O
2
1
6

NO
3
−
→+
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134 Physical–Chemical Treatment of Water and Wastewater
As with Nitrosomonas, the previous reactions taken together provide the energy
needed by Nitrobacter. The combined reactions for the destruction of the ammonium

ion, , (or the ammonia, NH
3
) can be obtained by adding Eqs. (2.5) and (2.8).
This will produce
(2.9)
From Equation (2.9), 1.0 mg/L of is equivalent to 4.57 mg/L of dissolved
oxygen.
2.1.16 MATHEMATICAL ANALYSIS OF BOD LABORATORY DATA
The ultimate carbonaceous oxygen demand may be obtained by continuing the
incubation period beyond five days up to 20 to 30 days. To do this, the nitrifiers
should be inhibited by adding the appropriate chemical in the incubation bottle. The
other way of obtaining CBOD is through a mathematical analysis.
In the incubation process, let y represent the cumulative amount of oxygen
consumed (oxygen uptake) at any time t, and let L
c
represent the CBOD of the
original waste. The rate of accumulation of the cumulative amount of oxygen, dy/dt,
is proportional to the amount of CBOD left to be consumed, L
c
− y. Thus,
(2.10)
where k
c
is a proportionality constant called deoxygenation coefficient.
In the previous equation, if the correct values of k
c
and L
c
are substituted, the
left-hand side should equal the right-hand side of the equation; otherwise, there will

be a residual R such that
(2.11)
At each equal interval of time, the values of y may be determined. For n intervals,
there will also be n values of y. The corresponding Rs for each interval may have
positive and negative values. If these Rs are added, the result may be zero which
may give the impression that the residuals are zero. On the other hand, if the residuals
are squared, the result of the sum will always be positive. Thus, if the sum of the
squares is equal to zero, there is no ambiguity that the residuals are, in fact, equal
to zero.
The n values of y corresponding to n values of time t will have inherent in them
one value of k
c
and one value of L
c
. Referring to Equation (2.11), these values may
be obtained by partial differentiation. From the previous paragraph, when the sum
of the squares of R is equal to zero, it is certain that the residual is zero. This means
that when the sum of the squares is zero, the partial derivative of the sum of the
squares must also be zero. Consequently, the partial derivatives of the sum of R
2
with respect to k
c
L
c
and k
c
are zero. Thus, to obtain k
c
and L
c

, the latter partial derivative
of the sum of the squares must be equated to zero to force the solutions. The method
NH
4
+
1
6

NH
4
+
1
3

O
2
1
6

NO
3
−
1
6

H
2
O
1
3

H
+
++→+
NH
4
−N
dy
dt

y′ k
c
L
c
y–()==
Rk
c
L
c
y–()y′– k
c
L
c
k
c
y– y′–==
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Constituents of Water and Wastewater 135
just described is called the method of least squares, because equating the partial

derivatives to zero is equivalent to finding the minimum of the squares. The corre-
sponding equations are derived as follows:
(2.12)
Solving for k
c
,
(2.13)
(2.14)
In the previous equations, k
c
L
c
and k
c
are the parameters of the partial differen-
tiation. Thus, in Equation (2.14), where the differentiation is with respect to k
c
, the
partial derivative of k
c
L
c
with respect to k
c
is zero, since the whole expression k
c
L
c
is taken as a parameter.
Solving Equation (2.14) for k

c
,
(2.15)
From Eqs. (2.13) and (2.15), L
c
, the ultimate oxygen demand, may finally be
solved producing
(2.16)
(2.17)
The progress of oxygen utilization, y, with respect to time may be monitored by
respirometry. Figure 2.2 shows a schematic of an electrolytic respirometer. As the
waste is consumed, CO
2
is produced which is then absorbed by a potassium hydrox-
ide solution by a chemical reaction. This absorption causes the pressure inside the
bottle to decrease. This decrease is sensed by the electrode triggering the electrolytic
decomposition of H
2
O to produce O
2
and H
2
.
The O
2
is channeled toward the inside of the bottle to recover the pressure and
the H
2
is vented to the atmosphere. The amount of oxygen consumed by the waste
is correlated with the amount of oxygen electrolytically produced to maintain the

pressure inside the bottle.
∑R
2
∂
k
c
L
c
()
∂

0
∑ k
c
L
c
k
c
y– y′–()
2
∂
k
c
L
c
()
∂

2 k
c

L
c
k
c
y– y′–()1()
∑
== =
k
c
∑y′
nL
c
∑y–

=
∑R
2
∂
k
c
∂

0
∑ k
c
L
c
k
c
y– y′–()

2
∂
k
c
∂

2 k
c
L
c
k
c
y– y′–()y()
∑
== =
k
c
∑yy′
∑y
2
L
c
∑y–

=
L
c
∑y′∑y
2
∑y∑yy′–

∑y′∑yn∑yy′–

=
y′
y
m+1
y
m−1
–
t
m+1
t
m−1
–

for 1 mn≤≤=
TX249_Frame_C02.fm Page 135 Friday, June 14, 2002 1:51 PM
© 2003 by A. P. Sincero and G. A. Sincero
136 Physical–Chemical Treatment of Water and Wastewater
Example 2.2 The following data represent the cumulative amount of oxygen
uptake for a river water receiving waste. Calculate L
c
and k
c
.
Solution:
FIGURE 2.2 Electrolytic respirometer for determination of oxygen consumption of a waste.
t (day) 246810
y (mg/L) 10 20 23 25 28
t (day) 2 4 6 8 10

y (mg/L) 10 20 23 25 28 ∑y = 68
b
y′ 3.25
a
1.25 1.25 ∑y′ = 5.75
y
2
400 529 625 ∑y
2
= 1554
yy′ 65 28.75 31.25 ∑yy′ = 125
a
3.25 =
b
68 = 20 + 23 + 25
Hydrogen
electrode
Switch
KOH
CO
2
absorbent
container
Electrolyte
Stirrer
Oxygen electrode
Electrolytic cell
electrode
L
c

∑y′∑y
2
∑y∑yy′–
∑y′∑yn∑yy′–

=
k
c
∑yy′
∑y
2
L
c
∑y–

–=
y′
y
m+1
y
m−1
–
t
m+1
t
m−1
–

for 1 mn≤≤=
23 10–

62–

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© 2003 by A. P. Sincero and G. A. Sincero
Constituents of Water and Wastewater 137

2.1.17 SOLIDS
Solids that find their way into wastewaters include the solids on the kitchen table:
corn, vegetables, crab, rice, bread, chicken, fish, egg, and so on. In short, these are
the solids flushed down the toilet. In addition, there are also solids coming from the
bathroom such as toilet paper and human wastes. In the old combined sewer systems,
solids may include the soils from ground eroded by runoff. Figure 2.3 shows a
pictorial representation of the various components of total solids.
The total solids content of a wastewater are the materials left after water has
been evaporated from the sample. The evaporation is normally done at 103–105°C.
Total solids may be classified as filtrable and nonfiltrable. The filtrable fraction
contains the colloidal particles and the dissolved solids that pass through the filter
in a prescribed laboratory procedure. The nonfiltrable fraction contain the settleable
and the nonsettleable fractions that did not pass through the filter.
The nonsettleable fraction of the nonfiltrable fraction is in true suspension; it is
composed of suspended solids. On the other hand, the settleable fraction does not
suspend in the liquid and, thus, these component solids are not suspended solids; they
are settleable fractions because they settle. Solids retained on the filter (nonfiltrable
solids) are, however, collectively (and erroneously) called suspended solids while those
that pass the filter are collectively (and, also, erroneously) called dissolved solids.
The solids that pass through the filter are not all dissolved, because they also
contain colloidal particles. Also, the solids retained on the filter are not all suspended,
FIGURE 2.3 Components of total solids.
TOTAL SOLIDS
ANY TYPE OF SOLIDS

FILTERABLE
SOLIDS
L
c
5.75 1554()68 125()–
5.75 68()3 125()–

435.5
16

27.22 mg/L===Ans
k
c
125
1554 27.22 68()–
– 0.42 per day==Ans
TX249_Frame_C02.fm Page 137 Friday, June 14, 2002 1:51 PM
© 2003 by A. P. Sincero and G. A. Sincero
138 Physical–Chemical Treatment of Water and Wastewater
because they also contain settleable solids; however, the use of these terms have
persisted. More accurately, the nonfiltrable-nonsettleable fraction should be the one
called suspended solids. Since the nonfiltrable solids are composed of the true sus-
pended solids and the “nonsuspended” suspended solids, nonfiltrable solids are also
called total suspended solids.
The settleable fraction is the volume of the solids after settling for 30 minutes in
a cone-shaped vessel called an Imhoff cone. The volume of solids that settled, in
milliliters, divided by the corresponding grams of solids mass is called the sludge volume
index, SVI. Settleable solids are an approximate measure of the volume of sludge that
will settle by sedimentation. Figure 2.4 shows a photograph of Imhoff cones.
All the types of solids described previously can have fixed and volatile portions.

The fixed portions of the solids are those that remain as a residue when the sample
is decomposed at 600°C. Those that disappear are called volatile solids. Volatile
solids and fixed solids are normally used as measures of the amount of organic
matter and inorganic matter in a sample, respectively. Magnesium carbonate, however,
decomposes to magnesium oxide and carbon dioxide at 350°C. Thus, the amount
of organic matter may be overpredicted and the amount of inorganic may be under-
predicted if the carbonate is present in an appreciable amount.
Example 2.3 A suspended solids analysis is run on a sample. The tared mass
of the crucible and filter is 55.3520 g. A sample of 260 mL is then filtered and the
residue dried to constant mass at 103°C. If the constant mass of the crucible, filter,
and the residue is 55.3890 g, what is the suspended solids (SS) content of the sample?
Solution:
FIGURE 2.4 Imhoff cones.
SS
55.3890 55.3520–
260

g
mL

55.3890 55.3520–
260

1000()1000()==
142.3 mg/L Ans=
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© 2003 by A. P. Sincero and G. A. Sincero
Constituents of Water and Wastewater 139
2.1.18 pH
Even the purest water exhibits ionization. Kohlrausch, a German physical chemist,

demonstrated this property by measuring the electrical conductivity of water using
a very sensitive instrument. The existence of the electrical conductivity is a result
of the chemical reaction between two water molecules as shown below:
(2.18)
The first term on the right-hand side of Equation (2.18) is called the hydronium
ion; the second is called the hydroxide ion. These ions are responsible for the
electrical conductivity of water. The concentrations of these ions are very small. At
25°C, for pure water, there is a concentration of 1 × 10
−7
mole per liter of the
hydronium ion and of the hydroxide ion, respectively. When the water is not pure,
these concentrations would be different. In a large number of environmental engi-
neering textbooks, the hydronium is usually written as H
+
. Also the hydronium ion
is usually referred to as the hydrogen ion. In essence, the hydronium ion can be
looked at as a hydrated hydrogen ion.
Let the symbol {H
+
} be read as “the effective concentration or activity of H
+
”
and the symbol [H
+
] be read as “the concentration of H
+
.” The effective concentration
{H
+
} refers to the ions of H

+
that actually participate in a reaction. This is different
from the concentration [H
+
], which refers to the actual concentration of H
+
, but not
all the actual concentration of this H
+
participate in the chemical reaction. Effective
concentration is also called activity. The effective concentration or activity of a solute
is obtained from its actual concentration by multiplying the actual concentration by
an activity coefficient, f (i.e., {H
+
} = f [H
+
]).
When the concentration of a solute such as H
+
is dilute, the solute particles are
relatively far apart behaving independently of each other. Because the concentration
is dilute (particles far apart), the particles participating in a reaction are essentially
the concentration of the solute. Therefore, for dilute solutions, {H
+
} is equal to [H
+
].
The existence of the hydronium ion is the basis for the definition of pH as
originated by Sorensen. pH is defined as the negative logarithm to the base 10 of
the hydrogen ion activity expressed in gmols per liter as shown below.

(2.19)
The product of the activities of H
+
and OH
−
at any given temperature is constant.
This is called the ion-product of water, K
w
, which is equal to 1 × 10
−14
at 25°C.
Sorensen also defined a term pOH as the negative of the logarithm to the base
10 of the hydroxide ion activity expressed in gmols per liter.
(2.20)
In Equation (2.19), when [H
+
] is equal to one mole per liter, the pH is equal to
zero. When the concentration is 1 × 10
−14
mole per liter, the pH is 14. Although the
pH could go below 0 and be greater than 14, in practice, the practical range is
H
2
OH
2
O  H
3
O
+
OH

−
++
pH log
10
–{H
+
}=
pOH log
10
– {OH
−
}=
TX249_Frame_C02.fm Page 139 Friday, June 14, 2002 1:51 PM
© 2003 by A. P. Sincero and G. A. Sincero
140 Physical–Chemical Treatment of Water and Wastewater
considered to be from 0 to 14. Low pH solutions are acidic while high pH solutions
are basic. A pH equal to 7 corresponds to a complete neutrality. The range of pH
from 0 to 14 corresponds to a range of pOH from 14 to 0.
The ion product of water, K
w
, is
(2.21)
Taking the logarithm of both sides to the base 10,
(2.22)
where
(2.23)
pH is an important parameter both in natural water systems and in water and
wastewater engineering. The tolerable concentration range for biological life in water
habitats is quite narrow. This is also the case in wastewater treatment. For example,
nitrification plants are found to function at only a narrow pH range of 7.2 to 9.0. In

water distribution systems, the pH must be maintained at above neutrality of close
to 8 to prevent corrosion. Above pH 8, the water could also cause scaling, which is
equally detrimental when compared with corrosion.
Example 2.4 10
−2
mole of HCl is added to one liter of distilled at 25°C. After
completion of the reaction, the pH was found to be equal to 2. (a) What is the solution
reaction? (b) What are the concentrations of the hydrogen and hydroxide ions?
Solution:
(a) The solution reaction is acidic.
(b)
2.1.19 CHEMICAL OXYGEN DEMAND
The chemical oxygen demand (COD) test has been used to measure the oxygen-
equivalent content of a given waste by using a chemical to oxidize the organic
content of the waste. The higher the equivalent oxygen content of a given waste,
the higher is its COD and the higher is its polluting potential. Potassium dichromate
has been found to be an excellent oxidant in an acidic medium. The test must be
conducted at elevated temperatures. For certain types of waste, a catalyst (silver
sulfate) may be used to aid in the oxidation.
The COD test normally yields higher oxygen equivalent values than those
derived using the standard BOD
5
test, because more oxygen equivalents can always
{H
+
}{OH
−
} K
w
=

pH pOH+ pK
w
=
pH pK
w
pOH–=
pK
w
log
10
K
w
–=
pH log
10
–{H
+
}= 2⇒ log
10
–{H
+
}=
{H
+
}10
−2
gmol/L Ans= {OH
−
}⇒ 10
2–

gmol/L Ans=
TX249_Frame_C02.fm Page 140 Friday, June 14, 2002 1:51 PM
© 2003 by A. P. Sincero and G. A. Sincero
Constituents of Water and Wastewater 141
be oxidized by the chemical than can be oxidized by the microorganisms. In some
types of wastes, a high degree of correlation may be established between COD and
BOD
5
. If such is the case, a correlation curve may be prepared such that instead of
analyzing for BOD
5
, COD may be analyzed, instead. This is practically advanta-
geous, since it takes five days to complete the BOD test but only three hours for the
COD test. The correlation may then be used for water plant control and operation.
The chemical reaction involved in the COD test for the oxidation of organic
matter is as follows:
(2.24)
From this reaction, chromium as reduced from an oxidation state of +6 to an
oxidation state of +3. The oxidation products are carbon dioxide and water. The
oxidation state is a measure of the degree of affinity of the atom to the electrons it
shares with other atoms. A negative oxidation state of an atom indicates that the
electrons spend more time with the atom, while a positive oxidation state indicates
that the electrons spend more time with the other atom.
2.1.20 TOTAL ORGANIC CARBON
The polluting potential and strength of a given waste may also be assessed by
measuring its carbon content. Because carbon reacts with oxygen, the more carbon
it contains, the more polluting and stronger it is. The carbon content is measured by
converting the carbon to carbon dioxide. The test is performed by injecting a known
quantity of sample into an oxidizing furnace. The amount of carbon dioxide formed
from the reaction of C with O

2
inside the furnace is quantitatively measured by an
infrared analyzer. The concentration of the total organic carbon (TOC) is then
calculated using the chemical ratio of C to CO
2
.
2.1.21 NITROGEN
Nitrogen is a major component of wastewater. People eat meat and meat contains
protein that, in turn, contains nitrogen. Every bite of hamburger is a source of
nitrogen and every fried chicken you buy is a source of nitrogen. Nitrogen in protein
is needed by humans in order to survive which, in turn, produces wastewater that
must be treated.
Protein contains about 16% nitrogen. The nitrogen in protein is an organic nitro-
gen. Organic nitrogen, therefore, is one measure of the protein content of an organic
waste. When an organic matter is attacked by microorganisms, its protein hydrolyzes
into a type of ammonia called free ammonia. Thus, free ammonia is the hydrolysis
product of organic nitrogen. The nitrites and nitrates are the results of the oxidation
of ammonia to nitrites by Nitrosomonas and the oxidation of nitrites to nitrates by
Nitrobacter, respectively. The sum of the organic, free ammonia, nitrite, and nitrate
nitrogens is called total nitrogen. The sum of ammonia and organic nitrogens is called
Organic matter Cr
2
O
7
2−
H
+
catalyst

heat

Cr
3+
CO
2
H
2
O++ ++
TX249_Frame_C02.fm Page 141 Friday, June 14, 2002 1:51 PM
© 2003 by A. P. Sincero and G. A. Sincero
142 Physical–Chemical Treatment of Water and Wastewater
Kjeldahl nitrogen. Of all the species of nitrogen, ammonia, nitrite, and nitrate are
used as nitrogen sources for synthesis. They are to be provided in the correct amount
in wastewater treatment. They also cause eutrophication in receiving streams.
The free ammonia may hydrolyze producing the ammonium ion according to
the following reaction:
(2.25)
At pH levels below 7, the above equilibrium is shifted to the right and the predom-
inant nitrogen species is , the ionized form. On the other hand, when the pH is
above 7, the equilibrium is shifted to the left and the predominant nitrogen species
is ammonia. The unionized form is most lethal to aquatic life. Ammonia is deter-
mined in the laboratory by boiling off with the steam after raising the pH. The steam
is then condensed absorbing the ammonia liberated. The concentration is measured
by colorimetric methods in the condensed steam.
The nitrite nitrogen is very unstable and is easily oxidized to the nitrate form.
Because its presence is transitory, it can be used as an indicator of past pollution
that is in the process of recovery. Its concentration seldom exceeds 1 mg/L in
wastewater and 0.1 mg/L in receiving streams. Nitrites are determined by colori-
metric methods.
The nitrate nitrogen is the most oxidized form of the nitrogen species. Since it
can cause methemoglobinemia, (infant cyanosis or blue babies), it is a very important

parameter in drinking water standards. The maximum contaminant level (MCL) for
nitrates is 10 mg/L as N. Nitrates may vary in concentrations from 0 to 20 mg/L as
N in wastewater effluents. A typical range is 15 to 20 mg/L as N. The nitrate
concentration is usually determined by colorimetric methods.
2.1.22 PHOSPHORUS
Phosphorus can be found in both plants and animals. Thus, bones, teeth, nerves, and
muscle tissues contain phosphorus. The nucleic acids DNA and RNA contain phos-
phorus as well.
The metabolism of food used by the body requires compounds containing
phosphorus. The human body gets this phosphorus through foods eaten. These
include egg, beans, peas, and milk. Being used by humans, these foods, along with
the phosphorus, therefore find their way into wastewaters. Another important
source of phosphorus in wastewater is the phosphate used in the manufacture of
detergents.
In general, phosphorus occurs in three phosphate forms: orthophosphate, con-
densed phosphates (or polyphosphates), and organic phosphates. Phosphoric acid,
being triprotic, forms three series of salts: dihydrogen phosphates containing the
ions, hydrogen phosphate containing the ions, and the phosphates
containing the ions. These three ions collectively are called orthophosphates.
As in the case of the nitrogen forms ammonia, nitrite and nitrate, the orthophosphates
can also cause eutrophication in receiving streams. Thus, concentrations of ortho-
phosphates should be controlled through removal before discharging the wastewater
NH
3
H
2
O  NH
4
+
OH

−
++
NH
4
+
H
2
PO
4
−
HPO
4
2−
PO
4
3−
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© 2003 by A. P. Sincero and G. A. Sincero
Constituents of Water and Wastewater 143
into receiving bodies of water. The orthophosphates of concern in wastewater engi-
neering are sodium phosphate (Na
3
PO
4
), sodium hydrogen phosphate (Na
2
HPO
4
),
sodium dihydrogen phosphate (NaH

2
PO
4
), and ammonium hydrogen phosphate
[(NH
4
)
2
HPO
4
]. They cause the problems associated with algal blooms.
When phosphoric acid is heated, it decomposes losing molecules of water forming
the P–O–P bonds. The process of losing water is called condensation, thus the term
condensed phosphates and, because they have more than one phosphate group in
the molecule, they are also called polyphosphates. Among the acids formed from
the condensation of phosphoric acid are dipolyphosphoric acid or pyrophosphoric
acid (H
4
P
2
O
7
), tripolyphosphoric acid (H
5
P
3
O
10
), and metaphosphoric acid (HPO
3

)
n
.
Condensed phosphates undergo hydrolysis in aqueous solutions and transform into
the orthophosphates. Thus, they must also be controlled. Condensed phosphates of
concern in wastewater engineering are sodium hexametaphosphate [Na(PO
3
)
6
],
sodium dipolyphosphate (Na
4
P
2
O
7
), and sodium tripolyphosphate (Na
5
P
3
O
10
).
When organic compounds containing phosphorus are attacked by microorganisms,
they undergo hydrolysis into the orthophosphate forms. Thus, as with all the other
phosphorus species, they have to be controlled before the wastewaters are discharged.
Orthophosphate can be determined in the laboratory by adding a substance that
can form a colored complex with the phosphate. An example of such a substance is
ammonium molybdate. Upon formation of the color, colorimetric tests may then be
applied. The condensed and organic phosphates all hydrolyze to the ortho form, so

they can also be analyzed using ammonium molybdate. The hydrolysis are normally
done in the laboratory at boiling-water temperatures.
2.1.23 ACIDITY AND ALKALINITY
Acidity and alkalinity are two important parameters that must be controlled in the
operation of a wastewater treatment plant. Digesters, for example, will not operate
if the environment inside the tank is acidic, since microorganisms will simply die
in acid environments. The contents of the tank must be buffered at the proper acidity
as well as proper alkalinity.
Acidity is the ability of a substance to neutralize a base. For example, given the
base and a species , the reaction of the two species in water solution is
Thus, in the previous reaction, because has neutralized , it has acidity
and it is an acid.
Alkalinity, on the other hand, is the ability of a substance to neutralize an acid.
For example, given the acid HCl and the species , they react in solution as
follows:
In the previous reaction, because has neutralized the acid HCl, it has alkalinity.
Alkaline substances are also called bases. From the above two reactions of ,
OH
−
HCO
3
−
OH
−
HCO
3
−
 H
2
OCO

3
2−
++
HCO
3
−
OH
−
HCO
3
−
HCl HCO
3
−
H
2
CO
3
Cl
−
+→+
HCO
3
−
HCO
3
−
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© 2003 by A. P. Sincero and G. A. Sincero
144 Physical–Chemical Treatment of Water and Wastewater

it can be concluded that this species can act both as an acid and as a base. A substance
that can act both as an acid and as a base is called an amphoteric substance.
Alkalinity in wastewaters results from the presence of the hydroxides, carbon-
ates, and bicarbonates of such elements as calcium, magnesium, sodium, and potas-
sium, and radicals like the ammonium ion. Of the elements, the bicarbonates of calcium
and magnesium are the most common. The other alkalinity species that may be
found, although not to a major extent as the bicarbonate, are ,
and . Alkalinity helps to resist the change in pH when acids are produced
during the course of a biological treatment of a wastewater. Wastewaters are normally
alkaline, receiving this alkalinity from the water supply and the materials added
during domestic use. Alkalinity is determined in the laboratory by titration using a
standard concentration of acid. The reverse is true for the determination of acidity
in the laboratory.
2.1.24 FATS, OILS, WAXES, AND GREASE
Organic compounds with the general formula are called organic acids,
where R is a hydrocarbon group. When the compound is a long-chain compound,
it is called a fatty acid. Fatty acids may be saturated or unsaturated. When one or
more carbon bonds is a double bond, the fatty acid is said to be unsaturated. An
example of a saturated fatty acid is stearic acid which has the formula
containing 18 carbon atoms.
Organic compounds with the general formula R
–
OH are called alcohols. An
example of an alcohol is glycerol. It has three OH groups and is called a triol and
has the formula OHCH
2
CH(OH)CH
2
OH. When glycerol reacts with a saturated fatty
acid, fats are typically formed. Fats are solid substances. When the product of the

reaction is not a solid, it is called oil.
When glycerol reacts with unsaturated fatty acids, oils are typically formed. The
reaction is similar to that with the saturated fatty acids. Oils are, of course, liquids.
The fats and oils formed from the reaction of glycerol with the fatty acids are called
triglycerides or triacylglycerides. Fats and oils are actually esters of glycerol and
fatty acids. (Esters have the general formula of , where R′ is another
hydrocarbon group.) Examples of fats are butter, lard, and margarine; and examples
of oils are the vegetable oils cottonseed oil, linseed oil, and palm oil. Fats and oils
are abundant in meat and meat products.
Glycerol may also derive, along with phosphoric acid and the fatty acids, a third
class of compounds called phosphoglycerides or glycerolphosphatides. In these
glycerides, one of the fatty acids is substituted by organic phosphates attaching to
HSiO
3
−
, H
2
BO
3
−
, HPO
4
−2
H
2
PO
4
−
RC
–

OH
||
||
||
||
O
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2

CH
2
CH
2
CH
2
CH
2
CH
2
O
||
C
–
OH
R
O
||
||
||
||
C
–
OR′
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© 2003 by A. P. Sincero and G. A. Sincero
Constituents of Water and Wastewater 145
the glycerol backbone at one of the ends. The organic phosphates are the phosphates
of choline, ethanolamine, and serine. Phosphoglycerides, fats, and oils are collec-
tively called complex lipids. Phosphoglycerides are phospholipids.

Certain alcohols look and feel like lipids or fats; thus, they are called fatty
alcohols. Fatty alcohols are also called simple lipids, which are long-chain alcohols,
examples of which are cetyl alcohol [CH
3
(CH
2
)
14
CH
2
OH] and myricyl alcohol
[CH
3
(CH
2
)
29
CH
2
OH]. Therefore, the two types of lipids are: complex lipids and
simple lipids. Simple lipids do not have the fatty acid “component” of the complex
lipids. The simple lipids can react with fatty acids to form esters called waxes. In
environmental engineering, waxes and complex lipids (fats, oils, and phospholipids)
and mineral oils such kerosene, crude oil, and lubricating oil and similar products
are collectively called grease. The grease content in wastewater is determined by
extraction of the waste sample with trichlorotrifluoroethane. Grease is soluble in
trichlorotrifluoroethane.
Grease is among the most stable of the organic compounds that, as such, is not
easily consumed by microorganisms. Mineral acids can attack it liberating the fatty
acids and glycerol. In the presence of alkali, glycerol is liberated, and the fatty acids,

also liberated, react with the metal ion of the alkali forming salts called soap. The
soaps are equally resistant to degradation by microorganisms.
2.1.25 SURFACTANTS
Surfactants are surface-active agents, which means that they have the property of
interacting with surfaces. Grease tends to imbed dirt onto surfaces. In order to clean
these surfaces, an agent must be used to loosen the dirt. This is where surfactants
come in. Surfactant molecules have nonpolar tails and polar heads. The grease
molecules, being largely nonpolar, tend to grasp the nonpolar tail of the surfactant
molecules, while the polar water molecules tend to grasp the polar head of the
surfactant molecules. Because of the movement during cleansing, a “tug of war”
occurs between the water molecules on the one side and the grease on the other
with the surfactant acting as the rope. This activity causes the grease to loosen from
the surfaces thus effecting the cleansing of the dirt. Detergents are examples of
surfactants. They are surface-active agents for cleaning.
Surfactants collect on the air–water interface. During aeration in the treatment
of wastewater, they adhere to the surface of air bubbles forming stable foams. If
they are discharged with the effluent, they form similar bubbles in the receiving
stream.
Before 1965, the type of surfactant used in this country was alkyl benzene
sulfonate (ABS). ABS is very resistant to biodegradation and rivers were known to
be covered with foam. Because of this and because of legislation passed in 1965,
ABS was replaced with linear alkyl benzene sulfonate (LAS). LAS is biodegradable.
The laboratory determination of surfactants involves using methylene blue. This
is done by measuring the color change in a standard solution of the dye. The
surfactant can be measured using methylene blue, so its other name is methylene
blue active substance (MBAS).
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146 Physical–Chemical Treatment of Water and Wastewater
2.1.26 PRIORITY POLLUTANTS

Before the 1970s, control of discharges to receiving bodies of water were not very
strict. During those times, discharge of partially treated wastewaters were allowed;
but although facilities could be built to treat discharges by, at least, partial treatment,
several communities and industries were discharging untreated wastewaters. This
practice resulted in gross pollution of bodies of water that had to be stopped.
The 1970s show pollution control starting in earnest. Industries were classified
into industrial categories. These resulted in the identification of priority pollutants
and the establishment of categorical standards for a particular industrial category.
These standards apply to commercial and industrial discharges that contain the
priority pollutants identified by the EPA. Since industries are allowed to discharge
into collection systems, these priority pollutants find their way into publicly owned
treatment works (POTWs).
The following are examples of priority pollutants: arsenic, selenium, barium,
cadmium, chromium, lead, mercury, silver, benzene, ethylbenzene, chlorobenzene,
chloroethene, dichloromethane, and tetrachloroethene. The priority pollutants also
include the pesticide and fumigant eldrin, the pesticide lindane, the insecticide
methoxychlor, the insecticide and fumigant toxaphene, and the herbicide and plant
growth regulator silvex. There are a total of 65 priority pollutants.
2.1.27 VOLATILE ORGANIC COMPOUNDS
Generally, volatile organic compounds (VOCs) are organic compounds that have
boiling points of ≤100°C and/or vapor pressures of >1 mmHg at 25°C. VOCs are
of concern in wastewater engineering because they can be released in the wastewater
collection systems and in treatment plants causing hazards to the workers. For
example, vinyl chloride is a suspected carcinogen and, if found in sewers and released
in the treatment plants, could endanger the lives of the workers.
2.1.28 TOXIC METAL AND NONMETAL IONS
Because of their toxicity, certain metals and nonmetal ions should be addressed in
the design of biological wastewater treatment facilities. Depending on the concen-
tration, copper, lead, silver, chromium, arsenic, and boron are toxic to organisms in
varying degrees. Treatment plants have been upset by the introduction of these metals

by killing the microorganism thus stopping the treatment. For example, in the
digestion of sludge, copper is toxic in concentrations of 100 mg/L, potassium and
the ammonium ion in concentrations of 4,000 mg/L, and chromium and nickel in
concentrations of 500 mg/L.
Anions such as cyanides, chromates, and fluorides found in industrial wastes
are very toxic to microorganisms. The cyanide and chromate wastes are produced
by metal-plating industries. These wastes should not be allowed to mix with sanitary
sewage but should be removed by pretreatment. The fluoride wastes are normally
produced by the electronics industries.
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Constituents of Water and Wastewater 147
2.2 NORMAL CONSTITUENTS OF DOMESTIC
WASTEWATER
The normal constituents of domestic wastewater are shown in Table 2.3. The para-
meters shown in the table are the ones normally used to characterize organic wastes
found in municipal wastewaters. As indicated, untreated domestic wastewater is
categorized as weak, medium, and strong.
2.3 MICROBIOLOGICAL CHARACTERISTICS
In addition to the physical and chemical characterization of water and wastewater,
it is important that the microbiological constituents be also addressed. The constituent
microbiological characterizations to be discussed in this section include the follow-
ing: bacteria, protozoa, and viruses. In addition, qualitative and quantitative tests for
the coliform bacteria will also be addressed. The treatment then proceeds to viruses
and protozoa. The treatment on protozoa will include discussion on Giardia lamblia,
Cryptosporidium parvum, and Entamoeba histolytica.
TABLE 2.3
Typical Composition of Untreated Domestic Wastewater
Concentration (mg/L)
Constituent Strong Medium Weak

Biochemical oxygen demand, BOD
5
at 20°C 420 200 100
Total organic carbon (TOC) 280 150 80
Chemical oxygen demand (COD) 1000 500 250
Total solids 1250 700 300
Dissolved 800 500 230
Fixed 500 300 140
Volatile 300 200 90
Suspended 450 200 70
Fixed 75 55 20
Volatile 375 145 50
Settleable solids, mL/L20105
Total nitrogen 90 50 20
Organic 35 15 10
Free ammonia 55 35 10
Nitrites 0 0 0
Nitrates 0 0 0
Total phosphorus as P 18 10 5
Organic 5 3 1
Inorganic 13 7 4
Chlorides 110 45 30
Alkalinity as CaCO
3
220 110 50
Grease 160 100 50
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148

Physical–Chemical Treatment of Water and Wastewater

The basic units of classifying living things are as follows: kingdom, phylum,
class, order, family, genus, and species. Organisms that reproduce only their own
kinds constitute a species. The genera are closely related species. Several genera
constitute a family. Several related families form an order and several related orders
make a class. A number of classes having common characteristics constitutes a
phylum. Lastly, related phyla form the kingdom. Ordinarily, only two kingdoms
exist: plant and animal; however, some organisms cannot be unequivocally classified
as either a plant or an animal. Haeckel in 1866 proposed a third kingdom that he
called

protist

to include protozoa, fungi, algae, and bacteria. Protists do not have
cell specialization to perform specific cell functions as in the higher forms of life.
At present, it is known that the protists bacteria and cyanobacteria are different
from other protists in terms of the presence or absence of a true nucleus in the cell.
This leads to the further division of the protists.
The protists fungi, algae, and protozoa contain a membrane-enclosed organelle
inside the cell called a nucleus. This nucleus contains the genetic material of the
cell, the DNA (deoxyribonucleic acid) which is arranged into a readily recognizable
structure called

chromosomes.

On the other hand, the DNA of bacteria is not arranged
in an easily recognizable structure as the chromosomes are. The former organisms
are called the eucaryotes; the latter, the procaryotes. Therefore, two types of protists

exist: the eucaryotic protists and the procaryotic protists. The eucaryotes are said to
have a true nucleus, while the procaryotes do not.
A third type of structure that does not belong to the previous classifications is
the virus. Although viruses are not strictly organisms, microorganisms, in general,
may be classified as

eucaryotic protists, procaryotic protists

, and

viruses.

2.3.1 B

ACTERIA

Bacteria

are unicell procaryotic protists that are the only living things incapable of
directly using particulate food. They obtain nourishment by transporting soluble
food directly from the surrounding environment into the cell. They are below pro-
tozoa in the trophic level and can serve as food for the protozoa. Unlike protozoa
and other higher forms of life that actually engulf or swallow food particles, bacteria
can obtain food only by transporting soluble food from the outside through the cell
membrane. The nutrients must be in dissolved form; if not, the organism excretes
exoenzymes that solubilize the otherwise particulate food. Because of the solubility
requirement, bacteria only dwell where there is moisture. Figure 2.5 shows a sketch
of the bacterial cell.
Bacteria are widely distributed in nature. They are found in the water we drink,
in the food we eat, in the air we breathe; in fact, they are found inside our bodies

themselves (

Escherichia coli

). Bacteria are plentiful in the upper layers of the soil,
in our rivers and lakes, in the sea, in your fingernails—they are everywhere.
Bacteria are both harmful and beneficial. They degrade the waste-products produced
by society. They are used in wastewater treatment plants—thus, they are beneficial. On
the other hand, they can also be pathogenic. The bacteria,

Salmonella typhosa

, causes
typhoid fever;

Shigella flexneri

causes bacillary dysentery.

Clostridium tetani

excretes
toxins producing tetanus.

Clostridium botulinum

excretes the toxin causing botulism.

Corynebacterium diphtheriae

is the agent for diphtheria.

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Constituents of Water and Wastewater 149
Bacteria come in three shapes: spherical (coccus), rod-shaped (bacillus), and
spiral-shaped (vibrio, spirillum, and spirochete). A vibrio is a spiral organism shaped
like a coma. A spirillum is also a spiral organism whose long axis remains rigid
when in motion; the spirochete is also yet another spiral organism whose long axis
bends when in motion.
The cocci range in size from 0.5
µ
m to 2
µ
m in diameter. The smallest bacillus
is about 0.5
µ
m in length and 0.2
µ
m in diameter. In the opposite extreme, bacilli
may reach to a diameter of 4
µ
m and a length of 20
µ
m. The average diameter and
length of pathogenic bacilli are 0.5
µ
m and 2
µ
m, respectively. The spirilla are

narrow organisms varying in length from 1
µ
m to 14
µ
m.
The shape of the bacteria is maintained by a rigid cell wall. The cytoplasm of
the cell has a high osmotic pressure that, without a rigid cell wall, can easily rupture
by the diffusion of outside water into the cell. The rigidity of the cell wall is due to
its chemical makeup of which the chief component is mucocomplex, a polymer of
certain amino sugars and short peptide linkages of amino acids. Depending upon
the type of bacteria, the bacteria may also contain techoic acid and mucopolysac-
charide, or lipoprotein and liposaccharide.
Directly beneath the cell wall is a membrane called the cytoplasmic membrane
that surrounds the cytoplasm. In the eucaryotes, an organelle called mitochondrion,
and, in the photosynthetic eucaryotes, an organelle called chloroplast are the sites
for the electron-tranport and the respiratory enzyme systems. The bacteria do not
have the mitochondrion nor the chloroplast, but the functions of these organelles are
embedded within the sites in the cytoplasmic membrane. The cytoplasm is the living
material which the cell is composed of, minus the nucleus.
Many bacilli and all spirilla are motile when suspended at the proper temperature
in a suitable medium. The organ of locomotion is the flagella. The bacterium may
have one flagella, few, or many arranged in a tuft. The flagella may protrude at one
end or both ends of the organism. True motility is seldom observed in the cocci.
FIGURE 2.5 Structure of a bacterial cell.
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