Standard Methods for Examination of Water & Wastewater_1 ppt

Constituents of Water and WastewaterGiven a wastewater, what process should be applied to treat it: biological, chemical, or physical?. 2.1 PHYSICAL AND CHEMICAL CHARACTERISTICS The cons

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 questionscannot be answered unless the constituents of the wastewater are known Thus,before any wastewater is to be treated, it is important that its constituents aredetermined On the other hand, what are the constituents of a given raw water thatmake 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 andwastewater 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 thefollowing: 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), fatsand oils and grease (chemical), and odor (physical) The characterization will alsoinclude surfactants (physical), priority pollutants (chemical), volatile organic com-pounds (chemical), and toxic metal and nonmetal ions (chemical) These constituentsare discussed in turn in the paragraphs that follow

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 sion The original measuring apparatus that measures turbidity, called the Jackson turbidimeter, was based on the absorption principle A standardized candle wasplaced under a graduated glass tube housed in a black metal box so that the lightfrom the candle can only be seen from above the tube The water sample was thenpoured slowly into the tube until the candle flame was no longer visible The turbiditywas 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

suspen-a source produced by suspen-a stsuspen-andsuspen-ardized electric bulb is psuspen-assed through suspen-a ssuspen-ample visuspen-al

2

126 Physical–Chemical Treatment of Water and Wastewater

The light that emerges from the sample is then directed to a photometer that measuresthe light absorbed The readout is calibrated in terms of turbidity

The unit of turbidity is the turbidity unit (TU) which is equivalent to the turbidityproduced by one mg/L of silica (SiO2) SiO2 was used as the reference standard.Turbidities in excess of 5 TU are easily detected in a glass of water and areobjectionable not necessarily for health but for aesthetic reasons A chemical, for-mazin, that provides a more reproducible result has now replaced silica as thestandard Accordingly, the unit of turbidity is now also expressed as formazinturbidity units (FTU)

The other method of measurement is by light scattering This method is usedwhen the turbidity is very small The sample “scatters” the light that impingesupon it The scattered light is then measured by putting the photometer at right anglefrom 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 ofturbidity in nephelometry is the nephelometric turbidity unit (NTU)

Color is the perception registered as radiation of various wavelengths strikes theretina of the eye Materials decayed from vegetation and inorganic matter create thisperception and impart color to water This color may be objectionable not for healthreasons but for aesthetics Natural colors give a yellow-brownish appearance towater, hence, the natural tendency to associate this color with urine The unit ofmeasurement of color is the platinum in potassium chloroplatinate (K2PtCl6) Onemilligram per liter of Pt in K2PtCl6 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 regulationswhich address the protection of public health and the establishment of secondaryregulations which address aesthetic consideration such as taste, appearance, andcolor To fulfill these requirements, the U.S Environmental Protection Agency(USEPA) establishes maximum contaminant levels (MCL) The secondary MCL forcolor is 15 color units

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:

Constituents of Water and Wastewater 127

where

TON= threshold odor number

TTN= threshold taste number

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 Thesecondary 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 ofserious complaints from neighborhoods around treatment plants, and it is oftendifficult for inspectors investigating these complaints to smell any odors in thevicinity of the neighborhood The reason is that as soon as he or she is exposed tothe odor, the olfactory nerves become accustomed to it and the person can no longersense any odor If you visit a wastewater treatment plant and ask the people workingthere 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 producesmainly psychological stress instead of any specific harm to the body Table 2.1 liststhe 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 toodors that have been diluted with odor-free air The number of dilutions required tobring the odorous air to the minimum level of detectable concentration by the panel isthe measure of odor Thus, if three volumes of odor-free air is required, the odor of theair is three dilutions It is obvious that if these evaluators are subjected to the odorseveral times, the results would be suspicious For accurate results, the evaluators

TABLE 2.1

Malodorous Compounds Associated with Untreated Wastewater

Butyl mercaptan (CH 3 ) 3 CSH — Secretion of skunk Crotyl mercaptan CH3(CH2)3SH — Secretion of skunk Diamines NH 2 (CH 2 ) 4 NH 2 , NH 2 (CH 2 ) 5 NH 2 — Decayed fish Ethyl mercaptan CH3CH2SH 0.0003 Decayed cabbage Hydrogen sulfide H 2 S < 0.0002 Rotten eggs

Phenyl sulfide (C6H5)2S 0.0001 Rotten cabbage

128 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

Most individuals find water at temperatures of 10–15°C most palatable Groundwatersand waters from mountainous areas are normally within this range Surface watersare, of course, subject to the effect of ambient temperatures and can be very warmduring 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 thehigh viscosity offers to the downward motion of the particles as they settle Pressuredrops also increase in the operation of filtration units, again, because of the resistancethat the higher viscosity offers

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 ofacclimation 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 theshoreline between a cliff and the sea As such, the fresh water is contaminated bysaltwater before being retrieved by the people The salt imparts to the water a highconcentration 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 sourceand are accustomed to the taste

The absence of fluorides in drinking water encourages dental caries or tooth decay;excessive concentrations of the chemical produce mottling of the teeth or dentalfluorosis Thus, managers and operators of water treatment plants must be carefulthat 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, althoughthe actual amount in specific circumstances depends upon the air temperature, sinceair temperature influences the amount of water that people drink Also, the use offluorides in drinking water is still controversial Some people are against its use,while some are in favor of it

Iron (Fe) and manganese (Mn) are objectionable in water supplies because theyimpart brownish colors to laundered goods Fe also affects the taste of beveragessuch 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

Constituents of Water and Wastewater 129

Clinical, epidemiological, and toxicological studies have demonstrated that leadexposure can adversely affect human health The three systems in the human bodymost sensitive to lead are the blood-forming system, the nervous system, and therenal system In children, blood levels from 0.8 to 1.0 µg/L can inhibit enzymaticactions Also, in children, lead can alter physical and mental development, interferewith 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 theatmosphere as Pb, PbO, PbO2, PbSO4, PbS, Pb(CH3)4, Pb(C2H5)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 polyvinylchloride), can replace copper for household plumbing

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 ment plants were most often spread on lands and buried in ditches as methods ofdisposal As the sludge decays, nitrates are formed Thus, in some situations, thesemethods of disposal have resulted in the nitrates percolating down the soil causingexcessive contaminations of the groundwater Even today, these methods are stillpracticed In order for these practices to be acceptable to the regulatory agencies, amaterial balance of the nitrate formed must be calculated to ascertain that thecontamination of the groundwater does not go to unacceptable levels

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 theirtaste It is a large constituent of sea water; hence, in water supplies contaminated bythe sea as in the case of Antipolo mentioned earlier, this element would be plentiful

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 drinkingwater Its SMCL is 250 mg/L

Zinc is not considered detrimental to health, but it will impart an undesirable taste

to drinking water Its SMCL is 5 mg/L

130 Physical–Chemical Treatment of Water and Wastewater

Biochemical oxygen demand (BOD) is the amount of oxygen consumed by the ism in the process of stabilizing waste As such, it can be used to quantify the amount

organ-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 atemperature 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 carboncontent of the waste; carbon reacts with the dissolved oxygen producing CO2 Onthe other hand, the nitrogenous portion refers to the ammonia content; ammoniaalso 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 toammonia 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 theBOD 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 fordetermining the dilution required This table shows that there are two ways dilutioncan 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 bacterialgrowth 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

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, BOD5 It is understood that unless it is specified,

BOD5 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 BODu

BOD (I–F)–(I ′ F′– ) X/Y( )

D

-=

132 Physical–Chemical Treatment of Water and Wastewater

BODu, 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,

BOD5 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 BOD5 of the sample?

Solution:

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 (I–F)–(I ′ F′– ) X/Y( )

D

- (9–2)–(9–8) 300 10([ – ]/300)

10/300 -

183

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

16 -NH4+ 1

3 -H2O 1

6 -NO2− 4

3 -H+ e−

→+

14 -O2 H+ e− 1

2 -H2O

→

16 -NH4+ 1

4 -O2 16 -H2O 1

6 -NO2− 1

3 -H+

→+

NO2−

16 -NO2− 1

6 -H2O 1

6 -NO3− 1

3 -H+ 13

-e−

→+

112 -O2 13 -H+ 13

-e− 1

6 -H2O

→

16 -NO2− 1

12 -O2 1

6 -NO3−

→+

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, NH3) 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 dissolvedoxygen

The ultimate carbonaceous oxygen demand may be obtained by continuing theincubation period beyond five days up to 20 to 30 days To do this, the nitrifiersshould be inhibited by adding the appropriate chemical in the incubation bottle Theother 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, theleft-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 residualsare squared, the result of the sum will always be positive Thus, if the sum of thesquares 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 R2with 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

NH4+

16 -NH4+ 1

3 -O2 16 -NO3− 1

6 -H2O 1

3 -H+

→+

NH4−N

dy dt

- = y′ = k c(L c–y)

R = k c(L c–y ) y′– = k c L c–k c y–y′

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 sponding equations are derived as follows:

corre-(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

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 thewaste is consumed, CO2 is produced which is then absorbed by a potassium hydrox-ide solution by a chemical reaction This absorption causes the pressure inside thebottle to decrease This decrease is sensed by the electrode triggering the electrolyticdecomposition of H2O to produce O2 and H2

The O2 is channeled toward the inside of the bottle to recover the pressure andthe H2 is vented to the atmosphere The amount of oxygen consumed by the waste

is correlated with the amount of oxygen electrolytically produced to maintain thepressure inside the bottle

∂

k c

∂ - ∑2 k( c L c–k c y–y′) y

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

KOH

CO2absorbent container Electrolyte

Stirrer

Oxygen electrode

Electrolytic cell electrode

∑y∑yy′

–

∑y′∑y n∑yy′– -

-2.1.17 S OLIDS

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 arethe solids flushed down the toilet In addition, there are also solids coming from thebathroom 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 apictorial 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 iscomposed of suspended solids On the other hand, the settleable fraction does notsuspend in the liquid and, thus, these component solids are not suspended solids; theyare settleable fractions because they settle Solids retained on the filter (nonfiltrablesolids) are, however, collectively (and erroneously) called suspended solids while thosethat pass the filter are collectively (and, also, erroneously) called dissolved solids.The solids that pass through the filter are not all dissolved, because they alsocontain colloidal particles Also, the solids retained on the filter are not all suspended,

FIGURE 2.3 Components of total solids.

TOTA L S O L I D S

FILTERABLE SOLIDS (Total suspended solids)

NON-SETTLEABLE (Imhoff) SETTLEABLENON- COLLOIDAL DISSOLVED

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

k c

125

1554–27.22 68( ) -

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 pended solids and the “nonsuspended” suspended solids, nonfiltrable solids are also

sus-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 organicmatter 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 predicted if the carbonate is present in an appreciable amount

under-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 theresidue 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?

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 hydroniumion; the second is called the hydroxide ion These ions are responsible for theelectrical 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 thehydronium 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 belooked 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 differentfrom the concentration [H+], which refers to the actual concentration of H+ , but notall the actual concentration of this H+ participate in the chemical reaction Effectiveconcentration 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 arerelatively far apart behaving independently of each other Because the concentration

is dilute (particles far apart), the particles participating in a reaction are essentiallythe 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 asoriginated by Sorensen pH is defined as the negative logarithm to the base 10 ofthe 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 tozero 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

H2O+H2O
H3O++OH−

pH = –log10{H+}

pOH = –log10{OH−}

considered to be from 0 to 14 Low pH solutions are acidic while high pH solutionsare basic A pH equal to 7 corresponds to a complete neutrality The range of pHfrom 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 andwastewater engineering The tolerable concentration range for biological life in waterhabitats 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 Inwater 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 isequally 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)

The chemical oxygen demand (COD) test has been used to measure the equivalent content of a given waste by using a chemical to oxidize the organiccontent 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 dichromatehas been found to be an excellent oxidant in an acidic medium The test must beconducted at elevated temperatures For certain types of waste, a catalyst (silversulfate) may be used to aid in the oxidation

oxygen-The COD test normally yields higher oxygen equivalent values than thosederived using the standard BOD5 test, because more oxygen equivalents can always

be oxidized by the chemical than can be oxidized by the microorganisms In sometypes of wastes, a high degree of correlation may be established between COD andBOD5 If such is the case, a correlation curve may be prepared such that instead ofanalyzing for BOD5, 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 theCOD 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 organicmatter is as follows:

(2.24)

From this reaction, chromium as reduced from an oxidation state of +6 to anoxidation 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 theelectrons spend more time with the atom, while a positive oxidation state indicatesthat the electrons spend more time with the other atom

The polluting potential and strength of a given waste may also be assessed bymeasuring 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 byconverting the carbon to carbon dioxide The test is performed by injecting a knownquantity of sample into an oxidizing furnace The amount of carbon dioxide formedfrom the reaction of C with O2 inside the furnace is quantitatively measured by aninfrared analyzer The concentration of the total organic carbon (TOC) is thencalculated using the chemical ratio of C to CO2

Nitrogen is a major component of wastewater People eat meat and meat containsprotein that, in turn, contains nitrogen Every bite of hamburger is a source ofnitrogen 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 thatmust 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 Cr2O72− H+ catalyst

heat Cr3+ CO2 H2O

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 tothe following reaction:

(2.25)

At pH levels below 7, the above equilibrium is shifted to the right and the inant nitrogen species is , the ionized form On the other hand, when the pH isabove 7, the equilibrium is shifted to the left and the predominant nitrogen species

predom-is ammonia The unionized form predom-is most lethal to aquatic life Ammonia predom-is mined in the laboratory by boiling off with the steam after raising the pH The steam

deter-is then condensed absorbing the ammonia liberated The concentration deter-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 pollutionthat is in the process of recovery Its concentration seldom exceeds 1 mg/L inwastewater 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

Phosphorus can be found in both plants and animals Thus, bones, teeth, nerves, andmuscle tissues contain phosphorus The nucleic acids DNA and RNA contain phos-phorus as well

The metabolism of food used by the body requires compounds containingphosphorus The human body gets this phosphorus through foods eaten Theseinclude egg, beans, peas, and milk Being used by humans, these foods, along withthe phosphorus, therefore find their way into wastewaters Another importantsource of phosphorus in wastewater is the phosphate used in the manufacture ofdetergents

In general, phosphorus occurs in three phosphate forms: orthophosphate, 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 phosphatescontaining the ions These three ions collectively are called orthophosphates

con-As in the case of the nitrogen forms ammonia, nitrite and nitrate, the orthophosphatescan also cause eutrophication in receiving streams Thus, concentrations of ortho-phosphates should be controlled through removal before discharging the wastewater

NH3+H2O
NH4++OH−

NH4+

PO43−

into receiving bodies of water The orthophosphates of concern in wastewater neering are sodium phosphate (Na3PO4), sodium hydrogen phosphate (Na2HPO4),sodium dihydrogen phosphate (NaH2PO4), and ammonium hydrogen phosphate[(NH4)2HPO4] They cause the problems associated with algal blooms.

engi-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 (H4P2O7), tripolyphosphoric acid (H5P3O10), and metaphosphoric acid (HPO3)n.Condensed phosphates undergo hydrolysis in aqueous solutions and transform intothe orthophosphates Thus, they must also be controlled Condensed phosphates ofconcern in wastewater engineering are sodium hexametaphosphate [Na(PO3)6],sodium dipolyphosphate (Na4P2O7), and sodium tripolyphosphate (Na5P3O10).When organic compounds containing phosphorus are attacked by microorganisms,they undergo hydrolysis into the orthophosphate forms Thus, as with all the otherphosphorus species, they have to be controlled before the wastewaters are discharged.Orthophosphate can be determined in the laboratory by adding a substance thatcan form a colored complex with the phosphate An example of such a substance isammonium molybdate Upon formation of the color, colorimetric tests may then beapplied The condensed and organic phosphates all hydrolyze to the ortho form, sothey can also be analyzed using ammonium molybdate The hydrolysis are normallydone in the laboratory at boiling-water temperatures

Acidity and alkalinity are two important parameters that must be controlled in theoperation 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 thebase and a species , the reaction of the two species in water solution is

Thus, in the previous reaction, because has neutralized , it has acidityand 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 asfollows:

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 ,

HCO3−

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, 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 calciumand magnesium are the most common The other alkalinity species that may be

and Alkalinity helps to resist the change in pH when acids are producedduring the course of a biological treatment of a wastewater Wastewaters are normallyalkaline, receiving this alkalinity from the water supply and the materials addedduring domestic use Alkalinity is determined in the laboratory by titration using astandard concentration of acid The reverse is true for the determination of acidity

in the laboratory

2.1.24 F ATS , O ILS , W AXES , AND G REASE

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 Anexample 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 OHCH2CH(OH)CH2OH 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 Thereaction 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 anotherhydrocarbon 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 oilsare 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

R

O

||||||||

C–OR′

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 [CH3(CH2)14CH2OH] and myricyl alcohol

[CH3(CH2)29CH2OH] Therefore, the two types of lipids are: complex lipids andsimple 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 intrichlorotrifluoroethane

Grease is among the most stable of the organic compounds that, as such, is noteasily consumed by microorganisms Mineral acids can attack it liberating the fattyacids 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

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 cleanthese surfaces, an agent must be used to loosen the dirt This is where surfactantscome in Surfactant molecules have nonpolar tails and polar heads The greasemolecules, being largely nonpolar, tend to grasp the nonpolar tail of the surfactantmolecules, while the polar water molecules tend to grasp the polar head of thesurfactant 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 otherwith the surfactant acting as the rope This activity causes the grease to loosen fromthe surfaces thus effecting the cleansing of the dirt Detergents are examples ofsurfactants 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 Ifthey are discharged with the effluent, they form similar bubbles in the receivingstream

Before 1965, the type of surfactant used in this country was alkyl benzenesulfonate (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 Thesurfactant can be measured using methylene blue, so its other name is methyleneblue active substance (MBAS)

2.1.26 P RIORITY P OLLUTANTS

Before the 1970s, control of discharges to receiving bodies of water were not verystrict 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 Thispractice resulted in gross pollution of bodies of water that had to be stopped.The 1970s show pollution control starting in earnest Industries were classifiedinto industrial categories These resulted in the identification of priority pollutantsand the establishment of categorical standards for a particular industrial category.These standards apply to commercial and industrial discharges that contain thepriority pollutants identified by the EPA Since industries are allowed to dischargeinto collection systems, these priority pollutants find their way into publicly ownedtreatment 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 alsoinclude the pesticide and fumigant eldrin, the pesticide lindane, the insecticidemethoxychlor, the insecticide and fumigant toxaphene, and the herbicide and plantgrowth regulator silvex There are a total of 65 priority pollutants

Generally, volatile organic compounds (VOCs) are organic compounds that haveboiling 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 wastewatercollection systems and in treatment plants causing hazards to the workers Forexample, vinyl chloride is a suspected carcinogen and, if found in sewers and released

in the treatment plants, could endanger the lives of the workers

Because of their toxicity, certain metals and nonmetal ions should be addressed inthe design of biological wastewater treatment facilities Depending on the concen-tration, copper, lead, silver, chromium, arsenic, and boron are toxic to organisms invarying degrees Treatment plants have been upset by the introduction of these metals

by killing the microorganism thus stopping the treatment For example, in thedigestion of sludge, copper is toxic in concentrations of 100 mg/L, potassium andthe ammonium ion in concentrations of 4,000 mg/L, and chromium and nickel inconcentrations of 500 mg/L

Anions such as cyanides, chromates, and fluorides found in industrial wastesare very toxic to microorganisms The cyanide and chromate wastes are produced

by metal-plating industries These wastes should not be allowed to mix with sanitarysewage but should be removed by pretreatment The fluoride wastes are normallyproduced by the electronics industries

2.2 NORMAL CONSTITUENTS OF DOMESTIC

WASTEWATER

The normal constituents of domestic wastewater are shown in Table 2.3 The meters shown in the table are the ones normally used to characterize organic wastesfound in municipal wastewaters As indicated, untreated domestic wastewater iscategorized as weak, medium, and strong

para-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 constituentmicrobiological characterizations to be discussed in this section include the follow-ing: bacteria, protozoa, and viruses In addition, qualitative and quantitative tests forthe 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)

Biochemical oxygen demand, BOD5 at 20 °C 420 200 100

Chemical oxygen demand (COD) 1000 500 250

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 ownkinds constitute a species The genera are closely related species Several generaconstitute a family Several related families form an order and several related ordersmake a class A number of classes having common characteristics constitutes aphylum Lastly, related phyla form the kingdom Ordinarily, only two kingdomsexist: 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 hecalled protist to include protozoa, fungi, algae, and bacteria Protists do not havecell 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 differentfrom 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 organelleinside the cell called a nucleus This nucleus contains the genetic material of thecell, the DNA (deoxyribonucleic acid) which is arranged into a readily recognizablestructure called chromosomes. On the other hand, the DNA of bacteria is not arranged

in an easily recognizable structure as the chromosomes are The former organismsare called the eucaryotes; the latter, the procaryotes Therefore, two types of protistsexist: the eucaryotic protists and the procaryotic protists The eucaryotes are said tohave a true nucleus, while the procaryotes do not

A third type of structure that does not belong to the previous classifications isthe 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 ofdirectly using particulate food They obtain nourishment by transporting solublefood 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 protozoaand other higher forms of life that actually engulf or swallow food particles, bacteriacan obtain food only by transporting soluble food from the outside through the cellmembrane The nutrients must be in dissolved form; if not, the organism excretesexoenzymes that solubilize the otherwise particulate food Because of the solubilityrequirement, 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 bodiesthemselves (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 Onthe other hand, they can also be pathogenic The bacteria, Salmonella typhosa, causestyphoid fever; Shigella flexneri causes bacillary dysentery Clostridium tetani excretestoxins producing tetanus Clostridium botulinum excretes the toxin causing botulism

Corynebacterium diphtheriae is the agent for diphtheria

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 µm to 2 µm in diameter The smallest bacillus

is about 0.5 µm in length and 0.2 µm in diameter In the opposite extreme, bacillimay reach to a diameter of 4 µm and a length of 20 µm The average diameter andlength of pathogenic bacilli are 0.5 µm and 2 µm, respectively The spirilla arenarrow organisms varying in length from 1 µm to 14 µm

The shape of the bacteria is maintained by a rigid cell wall The cytoplasm ofthe 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 toits chemical makeup of which the chief component is mucocomplex, a polymer ofcertain amino sugars and short peptide linkages of amino acids Depending uponthe 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 nothave 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 mayhave one flagella, few, or many arranged in a tuft The flagella may protrude at oneend or both ends of the organism True motility is seldom observed in the cocci

FIGURE 2.5 Structure of a bacterial cell.

Cell wall prevents

destruction by outside

shear forces; may be

10-50% of cell weight.

Cytoplasmic membrane regulates transport of food into and waste production out of cell.

Cytoplasm containing RNA controls anabolism, manufactures and recycles enzymes, stores food

Flagella, a hairlike appendage that provides motility Slime layer of organic polymers varies in thickness with age of the cell and other environmental conditions; stores food and binds food and other bacteria into food.

The bacteria may be motile in one medium and nonmotile in another; also, it

may be motile at one temperature but nonmotile at another Salmonella typhosa, a

bacillus that causes typhoid fever, moves at a rate of about 2,000 times its length inone hour

Under unfavorable conditions, some species of bacteria, mostly bacillus such as

the Bacillus and Clostridium, assume a form within the cytoplasm that is resistant

to environmental influences adverse to bacterial existence This form is called spores.

The cocci and spirilla rarely exhibit this behavior—this form being confined only

to about 150 species of the bacilli The most important pathogenic, spore-formingbacteria are those causing tetanus, gas gangrene, botulism, and anthrax

Only two members of the procaryotic protists exist: the regular bacteria and theblue-green algae Although the blue-greens possess chlorophyl, their characteristics

are those of bacteria possessing no true nucleus Blue-greens are called cyanobacteria

and are true bacteria, the procaryotic protists

According to body surface reaction, bacteria are classified into Gram-positiveand Gram-negative bacteria This method of classification was introduced by HansChristian Gram, a Danish physician working in Berlin The reaction of the bacterialsurface to staining by crystal violet or gentian violet treated with iodine characterizesthis method For the Gram-positive bacteria, the stain cannot be removed by floodingwith alcohol, acetone, or aniline; for the Gram-negative bacteria, on the other hand,the stain is removed by these solvents

Bacteria reproduce by binary fission The cell elongates and a constriction isformed; genetic materials are pushed through the constriction and the genetic blue-print is transcribed creating a new daughter cell The bacterium divides at the constric-tion It requires from 15 to 30 minutes for the newborn cells to attain adulthood andrestart the cycle of the binary division

Starting with one cell, let N be the number of cells resulting from the binary

fission of one cell at any time Then

(2.26)

where n is the number of generations.

Application of the above equation will show that one bacterium will reproduce to4.7(1021) bacteria in one day assuming a generation time of 20 minutes Using thedimension of a bacterium of 2 µm diameter by 12 µm length, the volume of onebacterium is equal to 3.77(10−17) cubic meter Thus, assuming that the density of thebacteria is the same as that of water, one bacterial cell will reproduce to (1000)(3.77)(10−17)(5)(1021) = 188,500,000 kg in 24 hours! This mass is, of course, impossible to

be obtained from one bacterium in a day What this means, though, is, that in a world situation, the bacterium does not divide unrestricted, but is influenced by otherenvironmental factors such as crowding and exhaustion of the food supply

The coliform group of microorganisms is defined as all aerobic and anaerobic, negative, nonspore-forming, rod-shaped bacteria that ferment lactose with gas and acidformation within 48 hours at 35°C The group belongs to the genera Escherichia,

Gram-N = 2n