Environmental Engineering
Laboratory Manual
Compiled By
Shashi Kumar Gupta
Professor and Head
Department of Civil Engineering
K L University, Guntur
1
Certificate of Completion
This is to certify that Mr/Ms ………………………………………………………………………….
Bearing
registration
number
…………………………………,
a
student
of
…………………… section ……….. has completed the laboratory requirements by
executing all the experiments as stipulated in the university syllabus.
Lab Incharge
HOD
Acknowledgement
2
The author wishes to acknowledge with a deep sense of gratitude, the encouragement and
support provided by Dr. Ch. Hanumantha Rao, Professor in the Department of Civil
Engineering, K.L University. The author is also thankful to the Library staff, colleagues and all
those who helped directly or indirectly in updating the laboratory manual. The author also
wishes to acknowledge the support obtained from Dr. K. Rajasekhara Reddy, Assoc.
Professor, Dept. of Civil Engineering, and Mr. K. Venkateswara Rao, Technician,
Environmental Engineering Laboratory. The author is also grateful to Department of Civil
Engineering and K.L University for giving an opportunity as well as providing all necessary
infrastructural support for the preparation of this manual.
Professor Shashi Kumar Gupta
Preface
3
Pollution of surface and ground water resources by intensive industrialization, population
growth and agricultural activities has been on the increase. Before any concrete step for
containing Environmental quality is manifested it is important to figure of the extent of
pollution occurred at a particular source of water, which in many instance is due to
discharge of wastewaters in to water resources. Hence testing and analysis of water and
wastewater become paramount in the area of Environmental Quality Management. This
activity also forms a prerequisite for asserting the adverse effects of pollutants on
environment and treatability studies thereof. This Environmental Engineering manual is
prepared in a comprehensive manner and every experiment is presented with learning
objective, theoretical concepts, significance of the test, precautions and review questions.
Extensive reference has been made to contributions by various authors, which is gratefully
acknowledged.
Any suggestions for the improvement of this issue of the manual are whole-heartedly
welcomed.
Shashi Kumar Gupta
3-10-2012
Contents
4
Page No.
Sl. No
List of the Experiments
1
Determination of pH
7-11
2
Determination of Electrical conductivity
12-16
3
Determination of Turbidity
17-21
4
Determination of Optimum coagulant dose by Jar test
22-26
5
Determination of Hardness
27-32
6
Determination of Acidity
33-36
7
Determination of Alkalinity
37-41
8
Determination of Available Chlorine
42-45
9
Determination of Residual Chlorine
46-48
10
Determination of Fluoride
49-52
11
Determination of Iron
53-56
12
Determination of Total Solids
57-60
13
Determination of Total Dissolved Solids
61-64
14
Determination of Suspended Solids
65-67
15
Determination of Settleable Solids
68-70
16
Determination of Dissolved Oxygen
71-75
17
Determination of Biochemical Oxygen Demand
76-80
18
Determination of Chemical Oxygen Demand
81-86
19
Determination of Chlorides
87-90
5
Competencies expected to acquire through laboratory work:
1. To be able to identify the relevant tests necessary to ascertain the water/wastewater
quality/characteristics.
2. To be able to demonstrate the use of laboratory equipment/gear to perform the
water/wastewater tests independently and/or in a group.
3. To be able to write a report and demonstrate learning.
Projects Identified:
1.
2.
3.
4.
5.
To assess and report the quality of water sample drawn from Buckingham Canal
To assess and report the quality of water sample drawn from KLU Canteen
To assess and report the quality of water sample drawn from Tadepalli
To assess and report the quality of water sample drawn from Nalgonda district
To assess and report the quality of water sample drawn from Vijayawada municipal
supply.
6. To assess and report the characteristics of wastewater sample drawn from KLU canteen.
7. To assess and report the characteristics of wastewater sample drawn from inlet to a
septic tank.
8. To assess and report the characteristics of wastewater sample drawn from outlet from
effluent from a septic tank.
9. To assess and report the characteristics of wastewater sample drawn from inlet to
Vijayawada treatment works.
10. To assess and report the characteristics of treated wastewater sample drawn from
Guntur treatment works.
6
EXERCISE NO. : 1
Determination of pH of a given water or waste water sample
Learning Objectives:
To learn about:




pH of water
use of pH stripes
use of pH meter
Significance of pH in Environmental
Engineering practice
AIM: To determine pH of the given samples of water or waste water
APPARATUS REQUIRED:

pH - strips (papers)

pH-meter

beakers
REAGENTS REQUIRED:
1. Distilled water
2. Standard Buffer solutions: Standard buffer solutions having pH values of 4.0,7.0 and 9.2 are
readily available. Otherwise, they can be prepared easily by dissolving the pH - powder or
tablets completely in 100 ml of distilled water. For example, pH tablet or powder corresponding
to a pH of 4.0, if dissolved in 100 ml of distilled water gives a standard solution of pH 4.0.
Similarly, solutions having pH 7.0 and pH 9.2 can be prepared
THEORY:
PH is the negative logarithm of Hydrogen Ion concentration and thus is the measure of the power
of hydrogen ion concentration. pH = -log (H+) where H+ is the concentration of hydrogen ion
expressed in moles/litre i.e. grams/litre for H+. Thus if pH of a solution is 4.5, its hydrogen ion
concentration = 10-4.5 moles/litre or 10-4.5 grams/litre. pH value indicates whether a solution is
acidic or neutral. Fresh distilled water has a pH of 7. Acidic waters have a pH of 0 to 7, whereas
alkaline waters have a pH of 7 to 14. Ammonia and lime solutions have a pH of about 12
whereas many cold drinks, lemon juice, battery acid etc. have pH of less than 4. As pH is
measured on a logarithmic scale, water having a pH of 6 is 10 times more acidic than neutral
7
water; water having a pH of 4 is 1000 times more acidic than water with pH 7 and a pH of 2 is
100,000 times more acidic than a pH of 7.
Acidic waters can be treated by neutralization with alkalies such as lime/limestone or NaOH.
Alkaline waters can be neutralized by adding acids such as HC1 or H2SO4. pH is an important
parameter to be measured in the laboratory as most of the water and sewage analytical and
treatment processes are a function of pH.
The pH of a solution can be found easily by using pH- strips (papers) or a pH-meter. pH-meter
gives very accurate values whereas pH-strips give approximate values. pH is determined by the
measurement of electromotive force of a cell comprising an indicator electrode responsive to
hydrogen ions (such as glass electrode) immersed in the test solution and a reference electrode
(usually a mercury calomel electrode). Contact between the test solution and the reference
electrode is usually achieved by means of a liquid junction, which forms a part of the reference
electrode. The ' emf ' of this cell is measured with pH meter. This is a high impedance
electrometer calibrated in terms of pH.
Fig.1: Digital pH Meter
PRINCIPLE:
1. pH is measured by a pH meter using a glass electrode which generates a potential varying
linearly with the pH of the solution in which it is immersed.
2. pH paper (similar to the litmus paper) changes colour only particular range and also gives out
an approximate of pH
PROCEDURE:
Using pH Meter:
1. Calibrate the electrode(s) with two standard buffer solutions of pH 4.0 and 9.2. (A buffer
solution is a solution offering resistance to change in pH and whose pH value is known.). Note
8
that each time the electrodes needs to be washed in distilled water and wiped with clean tissue
paper.
2. The sample temperature is determined at the same time and is entered into the meter to allow
for a temperature correction.
3. Dip the electrodes into the sample solution, swirl the solution and wait up to one minute for
steady reading. A pH meter reading within ±0.1 pH unit will be adequate for such work.
4. The reading is taken after the indicated value remains constant for about a minute.
Using pH paper:
1. Dip pH paper strip into the ssample to be tested.
2. Compare the resulting colour with standard colours.
3. The papers in use do not fade during the measuring time.
OBSERVATIONS AND RESULTS:
pH value
Description of sample
Temperature
pH meter
1.
2.
3.
CONCLUSIONS:
9
pH paper
PRECAUTIONS:
1) At pH values above 10, so called alkali errors may occur. In such cases, the use of an
alkali resistant electrode is recommended. Changes in glass structure can occur in older
electrodes, so that errors may appear when measuring in weakly buffered waters. In such
cases, the electrode should be renewed.
2) The sensitivity can be reduced by the presence of oil in the samples. Measurement errors
in oil-containing waters may be prevented by washing the electrode before each
measurement using soap or detergents followed by water, dilute hydrochloric acid and
finally with more water.
SIGNIFICANCE :
1. pH (6.5 to 8.5) has no direct adverse effect on health, however a lower value below 4 will
produce sour taste and higher value above 8.5 a bitter taste.
2. Higher values of pH hasten the scale formation in water heating apparatus and also
reduce the germicidal potential of chlorine. High pH induces the formation of
trihalomethanes which are causing cancer in human beings.
3. pH below 6.5 starts corrosion in pipes, thereby releasing toxic metals such as Zn, Pb,
Cd and Cu etc.
4. According to BIS, water for domestic consumption should have a pH between 6.5 to 8.5.
5. Determination of pH is one of the important objective in biological treatment of the waste
waters. In anaerobic treatment, if the pH goes below 5 due to excess accumulation of
acids, the process is severely affected. Shifting of pH beyond 5 to 10 upsets the aerobic
treatment of the waste waters. In these circumstances, the pH can be adjusted by addition
of suitable acid or alkali to optimize the treatment of the waste waters.
6. pH value or range is of immense value for any chemical reaction. A chemical shall be
highly effective at a particular pH. Chemical coagulation, disinfection, water softening
and corrosion control are governed by pH adjustment.
7. Dewatering of sludges, oxidation of cyanides and reduction of hexavalent chromium
into trivalent chromium also need a favorable pH range.
8. It is used in the calculation of carbonate, bicarbonate, CO2 corrosion, stability index and
acid base equalibria.
REVIEW QUESTIONS:
1. What is the principle involved in pH meter?
2. What is the relation between pH and H+ ion concentration?
3. A decrease of one unit pH measurement represent how much of an increase in
hydrogen ion concentration?
4. What is the pH of a 0.1 N HCl solution?
5. What is the pH of natural rain water?
6. What is the pH of sea water?
10
7. What is the pH index?
8. What is the significance of pH in disinfection by chlorination?
9. What is the permissible range of pH for drinking water?
10. What is the significance of pH in waste water treatment?
11. What is the relationship between (a) pH and hydrogen ion concentration (b) pH and
hydroxide ion concentration?
12. A 50% decrease in hydrogen ion concentration represent how much of an increase in
pH units?
13. What
is
the hydroxide
concentration,
if
hydrogen concentration is 3.0 x
10~2 mole/l?
14. What is the pH of a 0.05 M NaOH solution?
15. What would be the pH of a solution containing 1.008 gm of hydrogen ion per litre?
11
EXERCISE NO. : 2
Determination of Electrical Conductivity of given water sample
Learning Objectives:
To learn about:





Electrical Conductivity
Dissolved salts/solids
Salinity
Estimation of TDS
Relation between EC & TDS
AIM: To determine the electrical conductivity of the given water or soil sample
APPARATUS REQUIRED:
1. Conductivity meter
2. Thermometer
3. Beakers
4. Simple Balance
REAGENTS REQUIRED:
1. Distilled water
2. 0. 1 N KCl
THEORY: Electrical conductivity (EC) is the capacity of the water to carry an electrical current.
Specific conductance is the reciprocal of specific resistance and is usually expressed in
micromhos/cm (or mhos/cm for saline samples). EC is proportional to the concentration of
dissolved solids in the solution and hence can be used for a rapid and practical estimation of total
dissolved solids (TDS) or salinity.
TDS in mg/1 = K x EC in micromhos/cm, where 'K' is the proportionality constant that depends
mainly on the type of the solution and temperature. For most of the surface water sources and
open wells, value of K may be taken as 0.62 to 0.66. For saline waters such as estuarine waters,
sea waters and some deep/tube well waters, value of K may be taken as 0.75 to 0.9.
Usually, double distilled waters have an EC of less than 2 µ mhos/cm; distilled water less than
10 and many surface water sources such as streams, rivers, lakes and ponds possess an EC of
200 to 2000 µ mhos/cm; estuarine waters, sea waters and some deep/tube wells have an EC
range of 4000 to 40000 µ mhos/cm.
12
Fig.2: Digital Electrical Conductivity Meter
PRINCIPLE:
The electrical conductivity is a total parameter for dissolved, dissociated substances. Its value
depends on the concentration and degrees of dissociation of the ions as well as the temperature
and migration velocity of the ions in the electric field
PROCEDURE:
1. First standardize or calibrate the conductivity meter by following the procedure given in the
operation manual supplied by the manufacturer. This is usually done by adjusting the
calibration switch to the standard value. For example, if the knob of the instrument is kept at
2 m mhos/cm, the instrument may read 1.6 or 1.8. Then, adjust the ‘CAL’ i.e. calibrations
switch till the instrument reads 1.99 or 2.00 m mhos/cm (i.e. 1990 or 2000 micro mhos/cm).
Alternatively, calibrate the cell with standard 0.1 N KC1 solution of conductivity 14.12 m
mhos at 30°C. The procedure may differ slightly from instrument to instrument.
2. Take the water sample in a beaker and dip the electrode of the conductivity meter into the
sample. Keep the knob in the suitable range and note down the value of EC in micro mhos/
cm. For example, if the conductivity of the sample taken is 163 micro mhos/cm, then if the
knob is kept in the EC-range 0 to 20,000 ^mhos/cm, the instrument may read the EC value
as 1000; if the knob is kept in the 0 to 2000 range, the instrument may read it as 200; if the
knob is kept in the 0 to 200 range only the instrument can read it as 163 micro mhos/cm and
again when the knob is kept in the 0 to 20 µ mhos/cm range, obviously, the instrument cannot
measure any value.
3. Note down the temperature of the sample also by using a thermometer and mention in result.
13
4. Take out the electrode from the sample; wash it thoroughly and carefully with distilled water,
clean it carefully with tissue paper, dip the cell in the next sample and repeat the procedure
explained above.
CALCULATIONS:
TDS (mg/l) = C x specific conductivity (micro-mhos)
where C is empirical factor which may vary from 0.55 to 0.9 (usually 0.62) depending on the
soluble solids present in water. The above relation holds good only when electrical conductivity
value should be less than 50 m-mhos/cm (50,000 µ mhos/cm)
OBSERVATIONS AND RESULTS:
Description
Temperature
of sample
(oC)
Electrical
Conductivity
(µ mhos/cm)
1.
2.
3.
CONCLUSIONS:
14
Total Dissolved Solids
=EC x K
(mg/l)
PRECAUTIONS:
1. The electrode must be dipped into the sample carefully lest it is broken.
2. Sometimes a 1:2 soil-water ratio may not leave a clear supernatant. In such a case add totally
250 ml of distilled water so that a soil-water ratio of 1:5 is maintained. Never forget to mention
the soil-water ratio and temperature in the result.
3. If the EC falls outside the range of the instrument, dilute the sample, with distilled water and
then estimate the EC.
4. Keep the electrode immersed in distilled water always and at the end of each measurement
wash it thoroughly with distilled water. Organic material coating, if any, can be removed with
alcohol or acetone followed by distilled water.
SIGNIFICANCE:
1. Electrical conductivity measurements are often employed to monitor desalination plants.
2. It is useful to assess the source of pollution. Salinity and TDS can be estimated very quickly
from conductivity.
3. In coastal regions, conductivity data can be used to decide the extent of intrusion of sea water
into ground water.
4. Conductivity data is useful in determining the suitability of water and waste water for disposal
on land. Irrigation waters up to 2 m mhos/cm conductance have been found to be suitable for
irrigation depending on soils and climatic characteristics.
5. If conductivity of a water sample is more than 2000 µ mhos/cm, it may not be considered as
suitable for irrigation. If EC of a wastewater exceeds about 3000 µ mhos/cm i.e. if TDS exceeds
2100 mg/l, it cannot be disposed off without treatment.
6. If TDS is more, water cannot be used for drinking as well as construction purposes. TDS
affects strength and solidity of concrete and palatability of food cooked. It also causes
gastrointestinal irritation.
7. When turbid water in a small, transparent container, such as drinking glass is held upto the
light, an aesthetically displeasing opaqueness or 'milky' colouration is apparent.
8. The colloidal material which exerts turbidity provides adsorption sites for chemicals that may
be harmful or cause undesirable tastes and odors, and for biological organism that may be
harmful. Disinfection of turbid waters is difficult because of the adsorptive characteristics of
some colloids and because the solids may partially shield organisms from disinfectant.
15
9. In natural water bodies, turbidity may impart a brown or other colour to water and may
interfere with light penetration and photosynthetic reaction in streams and lakes.
Turbidity increases the load on slow sand filters. The filter may go out of operation, if excess
turbidity exists.
REVIEW QUESTIONS:
1. Define electrical conductivity of water?
2. What is the relationship between TDS and electrical conductivity?
3. What are the substances that do not exert electrical conductivity?
4. What is unit of measurement of electrical conductivity?
5. Conductivity data is used to assess source of pollution in water distribution. How?
6. What is the value of TDS, if electrical conductivity of water is 2.35 mhos and constant
0.8?
7. What is the importance of measurement of electrical conductivity?
8. What is the value of TDS of sea water?
9. How do you estimate the salinity of ground water?
10. How do you estimate the salinity of soils?
16
EXERCISE NO. : 3
Determination of amount of Turbidity present in the given water sample
Learning Objectives:
To learn about:




Turbidity of water
Measurement of turbidity
Use of Nephelometer
Significance of turbidity measurement
in EE practice
AIM: To find out Turbidity of the given water samples.
APPARATUS REQUIRED:
1. Nephelometric turbidimeter
2. Sample tubes.
REAGENTS REQUIRED:
1. Dissolve 1.0 gm Hydrazine sulphate and dilute to 100 ml.
2. Dissolve 10 gm Hexamethylene Tetramine and dilute to 100 ml.
3. Mix 5 ml of each of the above solution (1 and 2) in a 100 ml volumetric flask and allow to
stand for 24 hours at 25 ± 3°C and dilute to 1000 ml. This solution has a turbidity of 40 NTU.
4. This solution can be kept for about a month.
THEORY:
Turbidity is the measure of transparency or ‘murkiness’ of water. The suspended matter in water
interfering with passage of light is called turbidity. Turbidity may be caused by a wide variety of
suspended matter which range in size from colloidal to coarse dispersions, depending upon the
degree of turbulence. Turbidity in natural waters is caused by clay, silt, organic matter and
partially hydrolyzed metals (fine colloidal), phytoplankton and other microscopic organisms.
Turbidity is measured photo metrically by determining the percentage of light of a given
intensity absorbed or scattered. Jackson turbidimeter and Nephelometric turbidimeter are
generally used to measure turbidity of water samples. Jackson turbidimeter was based on light
absorption and Nephelometric turbidimeter was based on intensity of light scattering.
Now-a-days, most of the turbidimeters are working based on light scattering principle. Jackson
turbidimeter can be used for samples with moderate turbidity whereas Nephelometric
17
turbidimeter for samples with low turbidity. The units of turbidity are J.T.U., N.T.U., F.T.U. and
mg/l (silica scale).
Fig.3: Nephelometric turbidimeter
Fig.4: Schematic diagram of Principle
PRINCIPLE:
When light is passed through a sample having suspended particles, some of the light is scattered
by the particles. The scattering of the light is generally proportional to the turbidity. The turbidity
of sample is thus measured from the amount of light scattered by the sample taking a reference
with standard turbidity suspension
PROCEDURE:
1. Switch on Nephelometric turbidimeter and wait for few minutes till it warms up.
2. Set the instrument at 100 on the scale with a 40 NTU standard suspension. In this case, every
division on the scale will be equal to 0.4NTU turbidity.
3. Shake thoroughly the sample, and keep it for some time to eliminate the air bubbles.
4. Take sample in Nephelometer sample tube and put the sample in sample chamber and find out
the value on the scale using the factor worked out in step 2/
5. Dilute the sample with turbidity free water and again read the turbidity.
18
OBSERVATIONS & RESULTS:
Sample details
Turbidity (NTU)
Remarks
1.
2..
3.
CONCLUSIONS:
PRECAUTIONS:
1. The determination of turbidity is interfered by the presence of debris and other rapidly
settleable matter.
2. The true colour in the sample reduces the values of turbidity.
SIGNIFICANCE:
1. The colloidal material which exerts turbidity provides adsorption sites for chemicals that may
be harmful or cause undesirable tastes and odors, and for biological organism that may be
harmful. Disinfection of turbid waters is difficult because of the adsorptive characteristics of
some colloids and because the solids may partially shield organisms from disinfectant.
19
2. Knowledge of the turbidity variation in raw water supplies along with other information is
useful to determine whether a supply requires special treatment by chemical coagulation and
filtration before it may be used for a public water supply.
3. Turbidity measurements are used to determine the effectiveness of the treatment produced
with different chemicals and the dosages needed.
4. Turbidity measurements help to gauge the amount of chemicals needed from day-to-day in the
operation of water treatment works. Turbidity increases the load on slow sand filters. The filter
may go out of operation, if excess turbidity exists.
5. Measurement of turbidity in settled water prior to filtration is useful in controlling chemical
dosages so as to prevent excessive loading of rapid sand filters.
6. Turbidity measurements of the filtered water are needed to check on faulty filter operation.
7. Turbidity measurements are useful to determine the optimum dosage of coagulants to treat the
domestic and industrial wastes.
REVIEW QUESTIONS:
1. What is Turbidity?
2. What is NTU?
3. What are the causes of turbidity in water?
4. What units are generally used for measuring turbidity?
5. What limit is fixed on turbidity for drinking water by various organizations?
6. What is FTU?
7. What is the difference between visual method and instrument method in
turbidity measurement?
8. Is the one FTU equal to one JTU?
9. Turbidity is not a direct quantitative measurement of suspended solids. Why?
10. What is meant by coefficient of fineness? Mention its importance.
11. What limit is fixed on turbidity for drinking water by various organizations?
12. What is basic difference in principle involved in Jackson turbidimeter and Nephelo
turbidimeter?
13. What is the desirable turbidity in alum coagulated, flocculated and clarified water before
enter into rapid sand filter?
20
14. Name the chemical added to the turbidity standards to prevent the growth of bacteria or
algae.
15. What is the general coagulant used for removal of turbidity in water?
21
EXERCISE NO. : 4
Determination of optimum coagulant dose by Jar test
Learning Objectives:
To learn about:






Removal of turbidity
Coagulation
Flocculation
Coagulants
Sedimentation
Use of Jar test apparatus
AIM: To determine the optimum amount of coagulant required to treat the turbid waters.
APPARATUS REQUIRED:
1. Jar test apparatus
2. Turbidity meter
3. pH meter
4. Beakers
5. Pipettes.
REAGENTS REQUIRED:
1% alum solution.(dissolve 1.0 gram of alum in 100 ml distilled water).
THEORY:
The solids may vary in size from 1 millimicron to 200 millimicrons and broad in characteristics
between the suspended and dissolved solids. They are small enough to exhibit stability by virtue
of the slight residual electrical charge (generally negative), but large enough to interfere with
passage of light and therefore cause turbidity. They will not settle physically unless destabilized,
coagulated and flocculated into larger mass with sufficiently greater densities than water.
Generally, it follows that this is precisely the treatment that is used to remove them from water
and waste water. Coagulants employed are normally those electrolytes possessing strong positive
charges when dissolved in water. For example salts of Al+++ and Fe+++. The coagulant appear to
react simultaneously with the negative hydroxyl ions and the negative colloidal impurities. Both
are reduced substantial by the reaction. Little benefit will be gained by attempting to employ
chemical coagulation to remove solids which are not truly colloidal in nature.
22
Alum is generally used as coagulant for coagulation of water and reactions are as follows:
Al2 (SO4)3 18 H2O + 3 Ca (HCO3)2
----------- 3 CaSO4 + 2Al (OH)3 + 6 CO2 + 18 H2O
Stochiometrically, the alum reaction consumes calcium and magnesium alkalinity. The quantity
of alkalinity required to react with 10 mg/l of alum is
10 mg/1 x (3 x 100 g/mol)/(666.7 g/mol)
= 4.5mg/l
If less than this amount of alkalinity is available, it must be added. Lime is commonly used for
this purpose when necessary, but it is seldom required in the treatment of waste water.
Turbidity varies in surface waters seasonally. The consumption of alum is a function of turbidity
present in water. As such the dose of alum shall be determined on routine basis by using jar test
for the optimum dosage.
Fig.5: Jar Test Apparatus
Fig.6: Jar Test Working Principle
PRINCIPLE:
Metal salts hydrolyse in presence of the natural alkalinity to form metal hydroxides. The divalent
cations can reduce the zeta-potential, while the metal hydroxides are good absorbents and hence
remove the suspended particles by enmeshing them.
PROCEDURE:
1. Take 1 litre of sample into each of the 6 beakers.
2. Switch on the motor and adjust the speed of paddles to 100 rpm.
3. Add varying doses of alum solution i.e., 1 ml, 2 ml, 3 ml, 4 ml or 6 ml to different beakers
simultaneously. (The doses vary with turbidity in water sample.)
4. Allow flash mix (at 100 rpm) for 1-2 minute.
5. Reduce the speed of paddles to 4-6 rpm and continue mixing for 10-15 minutes.
6. Switch off the motor and allow 20 minutes for settling.
23
7. Collect the supernatant without disturbing the sediment and find the turbidity of each.
8. Also record pH, colour, alkalinity and temperature
9. Repeat the experiment to narrow down the optimum dose.
10. Record the ideal (optimum) dose of the coagulant for excellent floc formation.
OBSERVATIONS & RESULTS:
1. Raw water turbidity (NTU) =
2. Raw water pH
=
Sample detail/ Dosage of coagulant
jar no.
Residual turbidity
1
2
3
4
5
6
7
CONCLUSIONS:
24
pH
Ideal Dose of
Coagulant
PRECAUTIONS:
1. RPM for slow and flash mixing must be followed otherwise floc formation may not take
place properly.
2. Experimental set up should not be subjected to unnecessary vibrations, which interfere
with settlement of particles.
3. Coloured samples should not be used because it will be difficult to identify the most clear
sample to get optimum dose of coagulant.
SIGNIFICANCE:
4. This test is useful to identify various natural coagulants.
5. It is useful to estimate optimum dosage of coagulant
6. Excess dosage of alum may contribute excess aluminium in drinking water. According
recent investigation aluminium is neurotoxin. Excess aluminium if present in drinking
water is highly toxic and causes abdominal pain and ‘dementia’.
7. Less dosage of alum do not remove turbidity in water which ultimately increase load on
filters. So, the optimum dosage should be added in coagulation process to prevent the
above problems.
REVIEW QUESTIONS:
1. What is the purpose of rapid mixing in jar test?
2. What is importance of slow mixing in jar test?
3. What is coagulation?
4. What is flocculation?
5. What are coagulants?
6. List some commonly used coagulants.
7. What is the cause of alkalinity reduction in coagulation process?
25
8. Specify the advantages of using a coagulant in water treatment.
9. What do you understand by liquid alum?
10. What is a flocculent aid?
11. Water is to be supplied at the rate of 135 litre/capita/day for a population of 1 lakh. The
dose of alum needs for coagulation is 30 mg/l. Calculate the quantity of alum needed per
day.
12. What are the common methods of removal of turbidity?
13. What is sedimentation?
14. Where do you find sedimentation tanks?
15. What is a clarifier?
EXERCISE NO. : 5
26
Determination of Temporary and Permanent Hardness of Water
Learning Objectives:
To learn about:






Hardness of water
Temporary Hardness
Permanent Hardness
Carbonate Hardness
Testing by EDTA method
Significance in EE practice
AIM: To determine the total Hardness, Temporary and Permanent hardness of the given water
sample.
APPARATUS REQUIRED:
1. Burette
2. Pipette
3. Conical flask
4. Beaker
REAGENTS REQUIRED:
1. Buffer solution
2. Erio Chrome black T indicator
3. Standard EDTA solution 0.01M.
4. Inhibitor
5. Murexide indicator
6. Sodium hydroxide 2N.
THEORY:
Hardness is the resistance of the water for the formation of lather with soap. It is caused mainly
by the multivalent metallic cations like Ca2+, Mg2+, Fe2+, Sr2+, A12+ and Mn2+. Temporary
hardness, also called carbonate hardness is mainly caused by- carbonates and bicarbonates of
calcium and magnesium and can be removed by boiling or by adding lime to water. Permanent
hardness, also known as non-carbonate hardness is due to the presence of sulfates, chlorides and
nitrates of calcium and magnesium. It can be removed only by processes like ion exchange or
Zeolite process.
27
If hardness is less than 50 mg/1 as CaCO3 it may be treated as very soft water; 50-150:
moderately hard; 150-300: hard and if it is more than 300 mg/1 as CaCO3 it is treated as very
hard water. The desirable limit for hardness in drinking water is 300 mg/1 as CaCO3.
Usually surface waters are soft to moderately hard; distilled water and rain water are very soft;
ground waters are generally harder than river waters; deep/tube well waters are harder than
shallow/open well waters and brackish waters may have a hardness of more than l0000mg/1 as
CaCO3 also. Hardness can easily be determined in the laboratory by titration with EDTA.
Table: Classification of water based on Hardness
Degree of hardness
mg/l as CaCO3
Soft
0-75
Moderately hard
75-150
Hard
150-300
Very hard
>300
Fig.7: Burette with stand
Fig.8: Pipettes
PRINCIPLE:
The test is based on the fact that Ca and Mg ions form a weak complex with the blue dye,
Eriochromeblack T and a more stable complex with EDTA. When the dye is added to hard water
28
a wine red complex is formed, and when EDTA is added, the wine red complex is disrupted with
the release of the dye. The end point is wine red to blue in colour.
Ca2+ +Mg + EDTA
--------------------- ca EDTA +Mg EDTA
PROCEDURE:
Total Hardness:
1. Take 100 ml well mixed sample in conical flask.
2. Add 1-2 ml buffer solution followed by 1 ml inhibitor.
3. Add 2 drops of Erio Chrome black T and titrate with standard EDTA (0.01M) till wine-red
colour changes to blue.
4. Note down the volume of EDTA required (A).
5. Run a reagent blank Note the volume of EDTA required for blank (B).
6. Calculate the volume of EDTA required for sample (A-B).
Carbonate Hardness:
1. Take 25 or 30 ml of sample in conical flask.
2. Add 1 ml NaOH to raise pH to 12.0 and a pinch of murexide indicator.
3. Titrate with EDTA till pink colour changes to purple. Note the volume of EDTA used (A1).
CALCULATIONS:
Total Hardness (mg/l) as CaCO3
= {(A-B) x 1000}/(ml of sample)
Carbonate Hardness (mg/l) as CaCO3 = {A1 x 1000}/(ml of sample)
Where A1 = Volume of EDTA used by the sample
Non- Carbonate Hardness = Total Hardness – Carbonate Hardness
OBSERVATIONS & RESULTS:
29
Sample
details
Volume of
Initial burette
sample Taken
reading
Final burette
EDTA Solution
reading
Used
(ml)
(ml)
(ml)
(ml)
Total
hardness
Calcium
hardness
(carbonate)
CONCLUSIONS:
PRECAUTIONS:
30
Hardness
(mg/l)
1. The presence of heavy metals can cause the colour change to be unclear. Hence metal
ions present if any must be removed by adding suitable inhibitors.
SIGNIFICANCE:
1. Absolutely soft waters are tasteless (e.g.distilled water). On the other hand, hardness upto 600
mg/l can be relished if got acclimatized to.
2. Moderately hard water is preferred to soft water for irrigation purposes.
3. Scales are formed as inner coating of pipe lines prevents corrosion.
4. Absolutely soft waters are corrosive and dissolve the metals.
5. More cases of cardiovascular diseases are reported in soft water areas.
6. Hard water is useful to growth of children due to presence of calcium.
7. The precipitate formed by soap and hardness adheres to surfaces of tubs, sinks and utensils
and stains clothes and dishes. The precipitate may remain in the pores and the skin may feel
rough and uncomfortable and may lose its texture. In addition, the excess soap used produce the
required lather may kill the natural antibiotics secreted by the skin and makes it more vulnerable
for infections.
REVIEW QUESTIONS:
1. What are the constituents that cause hardness in water?
2. How do you classify the water based on hardness?
3.
What is meant by pseudo-hardness?
4. What are the salts that cause permanent hardness?
5. What are the methods to be used for removal of temporary hardness?
6. What is non carbonate hardness?
7. What is non carbonate hardness?
8. How do you remove permanent hardness?
9. What is scaling?
10. What are hard waters?
11. Distinguish between hard waters and heavy waters.
12. What is EDTA?
13. What are the disadvantages of hard waters?
31
14. What are the advantages of hard water with respect to human health?
15. Why and how is pH value adjusted to about 10 in softening process?
EXERCISE NO. : 6
32
Determination of Acidity of the given water sample
Learning Objectives:
To learn about:






Acidity of water
Causes for acidity of water
Neutralizing acidity
Determination of Acidity
Mineral Acidity
CO2 Acidity
AIM: To determine the Acidity of the given water sample.
APPARATUS REQUIRED:
1. Burette
2. Conical flask
3. Pipettes
4. Beaker
REAGENTS REQUIRED:
1. Standard Sodium hydroxide (0.02N NaOH)
2. Phenolphthalein indicator,
3. Methyl Orange indicator,
4. Sodium Thiosulfate (0.1N)
5. Carbon dioxide free distilled water
THEORY:
Acidity of given sample is its qualitative capacity to neutralize a base. It is the capacity of a
liquid to donate Hydrogen ions. It is a measure of quantity of the base required to neutralize a
given sample to a designated pH. Acidity in water is mainly due to the mineral acids and carbon
dioxide. As such, it is the measure of the ability of water to neutralize bases.
Types of acidity:
(1) Mineral acidity
33
(2) CO2 acidity.
Mineral acidity is due to the presence of HCI, H2SO4, HNO3 and strong organic acids. It is
expressed in terms of CaCO3 equivalent of the hydroxyl ions neutralized. Mineral acidity is
present in many industrial wastes, particularly those of metallurgically industry and from the
production of synthetic organic materials. Certain natural waters may also contain mineral
acidity. The drainage from abandoned mines, lean ore - dumps and gob - piles will contain
significant amount of sulfuric acid.
Carbon dioxide acidity is due to presence of free CO2 in ground and surface waters. Carbon
dioxide acidity is present in ground water and surface water from the hypolimnion of stratified
lakes and reservoir due to oxidation of organic matter by bacteria
PRINCIPLE:
The test is based on the principle that the hydrogen ions present in the sample are neutralized by
titrating them with a standard alkali. The mineral acidity can be calculated by titrating samples to
pH 4.3. The CO2 and bicarbonates (carbonic acid) present in the sample can be neutralized
completely by continuing the titration to pH 8.3.
PROCEDURE:
1. Take 100 ml of the given sample in a conical flask.
2. Add 1 drop of 0.1N sodium thiosulphate solution to remove the residual chlorine if present.
3. Add 2 drops of Methyl orange. The sample turns pink.
4. Titrate it against alkali (0.02N NaOH) until the colour changes to yellow.
5. Note down the volume of the NaOH added (V1)
6. Take another conical flask containing 100 ml of water sample; add 2 or 3 drops of
Phenolphthalein.
7. Proceed with titration until the sample turns pink.
8. Note down the total volume of NaOH added (V2)
CALCULATIONS:
34
Mineral Acidity due to mineral acids (as CaCO3) in mg/l =
V1 x1000
(ml of sample taken)
CO2 acidity due to CO2 (as CaCO3) in mg/l =
V2 x1000
(ml of sample taken)
OBSERVATIONS AND RESULTS:
Sample
Details
Volume of
Sample
(ml)
Methyl orange indicator
Initial
Burette
reading
Final
Burette
reading
(ml)
(ml
NaOH
used (V1)
(ml)
1.
2.
3.
CONCLUSION:
PRECAUTIONS:
35
Phenolphthalein Indicator
Initial
Burette
reading
Final
Burette
reading
(ml)
(ml)
NaOH
used (V2)
(ml)
1. Colour, turbidity, iron, aluminium or manganese and residual chlorine are prime sources
of interference.
2. Colour and turbidity can be avoided using potentiometric titrations.
3. Iron, aluminium and manganese is prevented by the addition of Na -K tartrate.
SIGNIFICANCE :
1. Acidity interferes in the treatment of water (as in softening).
2. It corrodes pipes (zinc coating of G.I. pipes got dissolved).
3. Aquatic life will be affected.
4. pH is critical factor for bi-chemical reaction. The favorable pH is 6.8 to 7.5.
5. Waters contain mineral acidity are so unpalatable.
6. Waters having acidity more than 50 mg/l cannot be used in R.C.C. works.
7. Most industrial wastes containing mineral acidity must be neutralized before they are
subjected to biological treatment or direct discharge into water courses or sewers. Quantities of
chemicals, size of chemical feeders, storage space and costs are determined from the laboratory
data of acidity
REVIEW QUESTIONS:
1. What is meant by acidity in water and waste water?
2. What are the sources of mineral acidity in water?
3. In acidity and alkalinity measurements, the titrant used (NaOH or H2SO4) is usually N/50.
Why?
4. What is the range of pH where acidity is present in water?
5. Name any four industries which discharge acid effluents.
6. What is the source of acidity for natural pure water?
7. What is the nature of human stomach?
8. What is the effect of acidity on water distribution network?
9. Can you estimate mineral acidity from sample, if added methyl organe indicator to sample
turns to yellow?
10. What are constituents that cause acidity in water?
EXERCISE NO. : 7
36
Determination of Alkalinity of the given water sample
Learning Objectives:
To learn about:





Alkalinity of water
Causes for alkalinity
Neutralizing alkalinity
Determination of alkalinity
Significance of alkalinity in EE
practice
AIM: To determine the Alkalinity of the given water sample.
APPARATUS REQUIRED:
1. Burette
2. Conical flask
3. Pipettes
REAGENTS REQUIRED:
1. Standard sulphuric acid (0.02N)
2. Phenolphthalein indicator
3. Methyl orange
4. Carbon dioxide free distilled water
5. Sodium thiosulphate (0.1 N).
THEORY:
Alkalinity is a measure of the ability of water to neutralize acids. It is a measure of the quantity
of ions that will react to neutralize hydrogen ions. It is caused by CO3-, OH- HPO4- , NH3- etc,
but is mainly due to HCO3- CO3- and OH- It is expressed in terms of CaCO3 equivalent of the
hydrogen ions neutralized. Alkalinity of water is due to presence of the following:
(1)Bicarbonates, carbonates, hydroxides of sodium, potassium, calcium and magnesium.
(2) Salts of weak acids and strong bases as
(a) borates, silicates and phosphates
(b) salts of organic acids as humic acid
37
(c) salts of acetic, propionic and hydro sulfuric acids.
(3) Algae utilize the free and combined carbon dioxide present in natural waters during
photosynthesis.
However, the major portion of the alkalinity In natural waters is caused by carbonates,
bicarbonates and hydroxides which may be ranked in order of their association with high PH
values. Boiler waters always contain carbonates and hydroxide alkalinity. Chemically treated
waters (lime or lime-soda ash softening waters) will be alkaline due to presence of carbonates
and excess hydroxides. High alkalinity in natural waters will favour the growth of producers
(algae and phytoplankton groups).
PRINCIPLE:
The test is performed by neutralizing the hydroxyl ion present in the sample by titrating against
the given standardized acid. Alkalinity of a sample is its quantitative capacity to neutralize a
strong acid to a specific pH.
PROCEDURE:
1. Take 50 ml of the given sample in a conical flask.
2. Add one drop of 0.1N sodium thiosulphate solution to remove the free residual chlorine if
present. This step can be avoided for waters like ground water and sea water, where free residual
chlorine is absent.
3. Add 2 drops of phenolphthalein indicator. The sample turns pink.
4. Run down 0.02 N standard sulphuric acid till the solution turns to colour less.
5. Note down the volume of H2S04 added (V1).
6. To the same sample add 2 drops of methyl orange indicator the sample turns to yellow.
7. Resume titration till the colour of the solution turns to pink.
8. Note down the total volume of H2S04 added (V2).
CALCULATIONS:
1. Phenolphthalein alkalinity (P) (mg/l) as CaCO3 = V1 x normality of H2SO4 x 1000 x 50
volume of sample taken
2. Total alkalinity (T) as CaCO3 mg/l
= V2 x normality of H2SO4 x 1000 x 50
volume of sample taken
38
Value of P and T
Alkalinity due to
OH-
CO3--
HCO3-
P=0
0
0
T
P < 1/2 T
0
2P
T - 2P
P = 1/2 T
0
2P
0
P > 1/2 T
2P - T
2T - 2P
0
T
0
0
P=T
OBSERVATIONS AND RESULTS:
Sample
details
Phenolphthalein
Methyl orange
Volume of
Sample
(ml)
Initial
burette
reading
(ml)
Final . H2S04 Initial Final
burette used burette burette
reading
reading reading
(ml)
(ml)
(ml) (ml)
1.
2.
3.
39
H2S04
used
(ml)
CONCLUSION:
PRECAUTION:
Colour, Turbidity and free chlorine may cause interference and hence must be removed
SIGNIFICANCE:
1. Highly alkaline waters are usually unpalatable and consumer acceptance decreases. Water
having an alkalinity of less than 200 mg/l as CaCO3 is desirable for drinking.
2. Large amount of alkalinity imparts a bitter taste to water.
3. The principal objection of alkaline water is the reactions that can occur between alkalinity and
certain cations in water. The resultant precipitate can foul pipes and other appurtenances of
water distribution systems like valves.
4. To neutralize acids produced during flocculation, the sample should be alkaline, as otherwise,
further floe formation (either Al(OH)3 or Fe(OH)3) slowly ceases. For example, an alkalinity
of about 4.5 mg/l as CaCO3 is essential for every 10 mg/1 dosage of alum.
5. To find out the quantity of lime and soda-ash required for the removal of hardness, alkalinity
should be found out. The purity of lime (i.e. % of CaO in given sample) also can be analysed
by finding alkalinity values .
6. Wastewaters containing excess caustic (hydroxide) alkalinity are not to be discharged into
natural water bodies or sewers. Excess alkalinity in water is harmful for irrigation which leads
to soil damage and reduces crop yields. Water having an alkalinity content of less than 250
mg/1 is desirable for domestic consumption.
7. Excess alkalinity gives a bitter taste to water. It reacts with cations and forms precipitates
which can damage pipes and other appurtenances like valves. However some alkalinity is
required in drinking water to neutralize the acids such as lactic acid and citric acid, produced
in the body. Thus it acts as a buffer. As such, waters having no alkalinity (such as rain water
or distilled water) cannot be used for drinking.
40
REVIEW QUESTIONS:
1. What is meant by alkalinity in water and waste water?
2. What are constituents that cause alkalinity in water?
3. At what pH range the alkalinity is present in water?
4. How is alkalinity removed from water?
5. What is the permissible limit of alkalinity in water to be used for R.C.C. works?
6. What is the significance of determining alkalinity?
7. Why CO2 must be removed from the water used in determination of alkalinity.
8. What is principle used in determination of alkalinity?
9. What is P-alkalinity and T-alkalinity?
10. What is the permissible limit for alkalinity as per BIS?
41
EXERCISE NO. : 8
Determination of Available chlorine in bleaching powder
Learning Objectives:
To learn about:




Available chlorine
Determining available chlorine
Bleaching power’s strength
Significance of available chlorine
AIM: To determine the available chlorine in the given sample of bleaching power.
APPARATUS REQUIRED:
1. Conical flask
2. Burette
3. Pipette
REAGENTS REQUIRED:
1. Concentrated acetic acid
2. Potassium iodide crystals
3. Sodium thiosulphate 0.025N
4. Starch indicator
THEORY:
Chlorine and its derivatives inactivate the enzymatic system of pathogenic bacteria present in
water. It also oxidizes the organic substances and soluble iron and manganese at higher dosage.
For efficient chlorination, water should be intermixed thoroughly with chlorine added and let to
stay in contact with the reagent for at least 30 minutes (60 minutes, when chlorination is
combined with ammonization) before it will be delivered to consumer. Chlorine water contact
can be ensured in a pure water tank or in the pipe line which supplies water to consumer,
provided that this has a sufficient length.
42
Chlorine may be applied in gaseous form (Cl2) or in form of bleaching powder [Ca(OCl2)].
Chlorine combines with water and hypochlorous and hydrochloric acids are formed.
Hypochlorous acid is the most effective disinfectant.
Cl2 + H2O---------- HOCl + HCl
(if pH >5)
The effectiveness of bleaching power depends on the available chlorine present in it.
PRINCIPLE:
Bleaching powder is commonly used as a disinfectant. The chlorine present in bleaching powder
gets rduced with time. So to find the exact quantity of bleaching powder required, the amount of
available chlorine in it must be determined prior to its usage.
Chlorine will liberate from Potassium Iodide solution, when pH is 8 or less.
The iodine
liberated, which is equal to the amount of active chlorine, is titrated with standard sodium
thiosulphate using starch as an indicator.
PROCEDURE
1. Take 1 gm of fresh bleaching powder. Adding small quantity of water to it, prepare fine paste.
Add some more water, stir and allow to settle for a few minutes. Dilute it with distilled water to
make up to 1 litre and put stopper to the container.
2. Take a known volume (V)25 ml of the bleaching powder solution from above in a conical
flask and add about 1 gm of KI crystals.
3. Add 5 ml of conventrated acetic acid and allow the reaction to complete - deep yellow colour
is formed.
4. Titrate the sample with standard sodium thiosulphate solution (0.025N) until the deep yellow
colour of the liberated iodine is almost faded out, and becomes pale yellow..
5. Add 1 ml of starch solution (gives blue colour) and titrate until the blue colour disappears.
6. Note down the quantity of sodium thiosulphate added (V1).
7. Repeat the same procedure for distilled water.
8. Note down the volume of sodium thiosulphate added (V2). (V2=0 for distilled water which is
free from chlorine)
9.Repaet the experiment with at least three different concentrations o bleaching powders e.g. 1, 2
3 gms
43
CALCULATIONS:
Concentration of chlorine =
(V1 - V2) x N x 35.45 x 1000
Vol. of bleaching powder solution
1 gm of bleaching powder contains _______ mg of chlorine.
Percentage of chlorine content in bleaching powder =_________________.
Model calculation:
If 2ml of NA2S2O3 is used to titrate 25ml sample,
available chlorine = (2 x 0.025 x 35.45 x 1000)/25
= 70.9 mg/l i.e. 70.9 mg chlorine is present in 1gm bleaching powder.
Therefore chlorine available = 0.0709gm/gm
or 7.09gm/100gm or 7.09%.
OBSERVATIONS AND RESULTS:
Sr.
No.
Gm of
bleaching
powder
dissolved
per litre,
Vol. of
sample
taken (ml)
Burette reading
Initial
Final
Volume of
Na2S2O3 used
( ml)
CONCLUSION:
44
Available Chlorine
Mg/l
%
SIGNIFICANCE :
1. This test is useful to assess the quality of bleaching powder.
2. It is useful to estimate the amount of bleaching powder required for effective disinfection of
water.
3. If excess chlorine is used, it may irritate Eyes and Nose, bleach hair, cause allergy and cancer,
on the other hand if dosage is smaller, pathogens, that cause several water borne diseases cannot
be killed completely.
4. Chlorine is available in different states, gaseous, liquid and also as a solid. Bleaching powder
is a slaked lime through which chlorine is injected. Hence, it contains calcium, oxygen and
chlorine (CaOCI2). It is hydroscopic (i.e. absorbs moisture from the atmosphere).
This bleaching powder loses its chlorine content if it is exposed to the atmosphere and due to
prolonged storage. Hence, the amount of chlorine contained by it need be decided before
application of bleaching powder to water.
REVIEW QUESTIONS:
1. What do you understand by pre-chlorination and post chlorination?
2. What is the difference between available chlorine and residue chlorine?
3. Specify the optimum chlorine dosage, contact time and pH range for effective
disinfection.
4. What is disinfection?
5. Why chlorination is a very commonly used as a disinfection process?
6. What are the disadvantages with the use of chlorination?
7. What is the chemical formula of bleaching power?
8. What is free chlorine?
9. What is combined chlorine?
10. What is the percentage of chlorine available in bleaching powder?
11. What is the purpose of chlorine gas?
12. Why turbidity must be removed before chlorination?
13. What is hypochlorous acid?
14. When does the hypochlorite ion form?
15. What is the position/location of chlorination in a water treatment and distribution
system? Why?
45
EXERCISE NO. : 9
Determination of Residual Chlorine in water sample
Learning Objectives:
To learn about:




Chlorination
Residual Chlorine
Purpose of residual chlorine
Testing of residual chlorine
AIM: To determine the amount of Residual chlorine available in the given water sample
APPARATUS REQUIRED:
1. Chloroscope (comparator)
REAGENTS REQUIRED:
Orthotolidine reagent
THEORY:
Free residual chlorine is never found in natural surface or ground waters. It is present in treated
waters only if disinfection is done by chlorination. If chlorine is added to water, a part is utilized
in the destruction of pathogens and the rest remains in water as free residual chlorine. Free
residual chlorine is essential to ensure safety against future contamination of water in
distribution pipes, valves etc. During epidemics and in swimming pools, higher residuals of upto
0.5 mg/I are maintained. Excess chlorine can be removed by dechlorinating agents like sodium
thiosulfate, SO2 and activated carbon. Residual chlorine is determined in laboratory by
Orthotolidine test or Starch-iodide test. Orthotolidine is an aromatic organic compound that is
oxidized in acid solution by chlorine, chloramines, and other oxidizing agents to produce an
yellow coloured compound called Holoquinone. Intensity of yellow colour of holoquinone is
proportional to the amount of chlorine present. Chloroscope, a colour comparator is mostly used
to determine residual chlorine.
PRINCIPLE:
Orthotolidine is an aromatic organic compound that is oxidized in acid solution by chlorine,
chloramines, and other oxidizing agents to produce a yellow coloured compound called
Holoquinone. Intensity of yellow colour of holoquinone is proportional to the amount of chlorine
present.
46
Fig.10: Chloroscope
PROCEDURE:
1. Take the water sample under question into one of the cylinders of the comparator and distilled
water into the other.
2. Add 5 drops of Orthotolidine solution to both the cylinders and put them in the comparator.
3. The colour which matches in both the cylinders directly gives the 'residual chlorine'.
OBSERVATIONS AND RESULTS:
Amount of the residual chlorine (mg/l) =
CONCLUSION:
PRECAUTIONS:
Oxidizing agents such as ferric compounds, manganic salts, nitrites etc may cause interference
hence must be removed.
SIGNIFICANCE :
1. Chlorine residuals determination is used to control Chlorination of domestic and industrial
waste waters.
47
2. Determination of chlorine residuals is used universally in disinfection practice to control
addition of chlorine so as to ensure effective disinfection without waste.
3. Determination of chlorine residual in water distribution is useful to find the source of
contamination or leakage points, so as to supply wholesome water to the consumer.
4. Active chlorine (free and combined) should be determined at each stage in the processing of
drinking water and in the water mains in order to guarantee bacteriologically impeccable water.
5. Active chlorine should be present in drinking water within the range 0.1 to 0.2 mg/l. However,
excessive chlorine content may give out bad odour and may change even taste of waters. Further,
chlorine is said to be carcinogenous.
REVIEW QUESTIONS:
1. Why do you determine residual chlorine in water treatment practice and water supply mains?
2. Free available chlorine is more effective than combined available chlorine. Why?
3. Name the instrument used for determination of residual chlorine in water distribution mains.
4. Give the chemical formula of bleaching powder.
5. What is residual chlorine?
6. What happens, if excess chlorine is present in drinking water?
7. What is the major drawback of all other disinfection processes other than chlorination?
8. What is breakpoint chlorination?
9. What are trihalomethanes?
10. What is Orthotolidine test?
11. What is the mechanism of disinfection by chlorination?
12. What happens if bleaching powder is stored for a long time?
13. What factors are affecting disinfection process?
14. What are water borne diseases?
15. Hundred percentage pathogen bacteria is removed in water treatment plant. However 0.1 to
0.2 mg/l residual chlorine is maintained in water distribution main. Why?
48
EXERCISE NO. : 10
Determination of Fluoride in water sample
Learning Objectives:
To learn about:





Fluoride in water
Significance of fluoride
Testing of fluoride
Health effects of fluoride
Permissible limits
AIM: To determine the amount of fluoride in the given water sample.
APPARATUS REQUIRED:
Nessler tubes.
REAGENTS REQUIRED:
1. Standard sodium fluoride solution.
2. Zirconium alizarin solution.
.
3. Mixed acid solution.
4. Acid Zirconium alizarin reagent.
5. Sodium thiosulfate solution.
THEORY:
Waters in contact with natural deposits of fluoride such as fluorspar, CaF2 and criolite, Na3AIF6
and waters contaminated by effluents from glass and aluminium manufacturing industries are
found to contain excess fluoride. Many countries all over the world are suffering from high
concentrations of fluorides in drinking water. In India alone about 30 million people are
suffering from fluorosis. Fluoride is often called a two edge sword. Fluoride in small dosages
has remarkable influence on the dental system by inhibiting the dental caries, while in higher
dosages causes dental and skeletal fluorosis. The unfortunate thing which makes the subject
more complicated is that the margin between its curative and harmful doses is quite narrow.
Presence of large amounts of fluoride(>1.5mg/l) is associated with dental and skeletal fluorosis
and less amounts (<l mg/l) with dental cavities. In young children the disease affects only the
teeth. This is known as dental fluorosis. In aged people the disease affects the bones, tendons and
49
ligaments. This is known as skeletal fluorosis. In Andhra Pradesh alone, there are 1.32 million
people in 1079 villages in 17 districts are consuming water with fluoride more than 1 mg/l of
naturally occurring water. Recent surveys conducted by the A.P. Rural Water Supply
Department has shown that the fluoride content in Yellareddiguda village of Nalgonda Dist. is 20
mg/l as compared to a permissible limit of 1.5 mg/l. Fluoride can be analysed in the laboratory
by colorimetric method.
Fig.11: Nessler Tubes
PRINCIPLE:
The test is based on the fact that fluoride ion combines with zirconium ion to form a stable
complex ion, ZrF6 and this results in bleaching the reddish colour of zirconium and alizarin
combination. The decrease in intensity of colour is directly proportional to fluoride
concentration.
PROCEDURE:
1. The sample should be free from chlorine, if chlorine present, it shall be dechlorinated
with a slight excess of sodium thiosulphate solution before use.
2. If sample contains excess interfering ions, the sample should be appropriately diluted or
distillated before test.
3. Take 0, 3, 6, 9, 12, 15 ml of standard sodium fluoride solution in six Nessler tubes and
dilute each to 100 ml by distilled water. The tube respectively represent fluoride
concentration of 0, 0.3, 0.6, 0.9, 1.2 and 1.5 mg/l respectively
4. Add 5 ml of acid zirconium reagent in each Messier tube.
5. Similarly add 5 ml of acid zirconium reagent into the Nessler tubes containing 100 ml of
sample.
6. Mix thoroughly and compare the colours after standing for one hour .
50
OBSERVATIONS AND RESULTS:
Fluoride(mg/l)
Sample Details
1.
2.
3.
4.
5.
CONCLUSION:
PRECAUTIONS:
Handle Nessler tubes carefully.
SIGNIFICANCE:
Presence of large amounts of fluoride is associated with dental and skeletal fluorosis (> 1.5 mg/l)
and inadequate amounts with dental caries (< 1 mg/l) (WHO 1984).
Dental fluorosis: In young children the disease affects only on the teeth. This is known as dental
fluorosis. The teeth lose their shiny appearance and chalk-white patches develop on them. This is
known as mottled enamel and is an early sign of dental fluorosis. The white patches later become
yellow and turn brown or black. The severe cases loss of enamel is accompanied by pitting
which give the tooth a corroded appearance. Mottling is the best seen on the incisors of upper
jaw. It is almost entirely confined to the permanent teeth and develops only during their period of
formation.
51
Skeletal fluorosis: In aged people, the disease affects the bones, tendons and ligaments. This is
known as skeletal fluorosis. This is followed by pain and stiff of the back and later the joints of
both limbs and limitation of neck movements. Early detection of the disease is difficult until
radiological help is sought.Skeletal fluorosis is reported to be a public health problem in several
district of A.P., Haryana, Karnataka, Kerala, Punjab, Rajasthan and Tamil Nadu.
Genu valgum: Recently scientists working at the National Institute of Nutrition, Hyderabad
found a new form of fluorosis characterised by genu valgum and osteoporosis of the lower limbs
in some districts of Andhra Pradesh and Tamil Nadu. Children below the age of 10 years were
also affected with this deformity in the districts of Nalgonda and Prakasam of Andhra Pradesh. It
was observed that this syndrome was most prevalent among people whose staple diet was
sorghum. Further studies have shown that diets based upon jower promote a higher retention of
ingested fluoride than their based on rice.
REVIEW QUESTIONS:
1. What is the permissible limit of fluoride for drinking water according to B.I.S.?
2. Fluoride is called a two-edge sword. Why?
3. What are the methods available to remove fluoride in drinking water?
4. What are the states facing excess fluoride problem in ground water in India?
5. How can you increase fluoride concentration in drinking water with deficiency of
fluorine?
6. What are geological minerals that contain fluoride?
7. What are the effects of low content of fluoride in drinking water?
8. What are the effects of excess fluoride in drinking water?
9. What is Nalgonda technique?
10. What are different techniques of Defluoridation?
52
EXERCISE NO. : 11
Determination of Iron in water sample
Learning Objectives:
To learn about:






Iron in drinking water
Effects of iron in water
Significance of iron
Testing for iron
Removal of iron
Permissible limit
AIM: To determine the quantity of Iron present in the given sample
APPARATUS REQUIRED:
1. Nessler's tubes (100 ml)
2. Conical flasks – 6 numbers
3. Pipettes
REAGENTS REQUIRED:
1. Hydrochloric acid
2. Hydroxylamine hydrochloride solution
3. Ammonium acetate buffer solution
4. Sodium acetate solution
4. Phenanthroline solution
5. Stock iron solution
6. Standard iron solution (1 ml = 1 µg Fe).
THEORY:
Iron is present mostly as divalent form (ferrous) in both surface and ground waters under
reducing environment. The presence of iron in natural waters can be attributed to the dissolution
of rock and minerals, acid mine drainage, landfill leachates, sewage and industrial effluents. The
permissible limit of iron in drinking water is 0.3 mg/l according to B.I.S.
53
PRINCIPLE:
In the phenanthroline method, the ferric form of iron is reduced to ferrous form by boiling with
hydrochloric acid and hydroxylamine hydrochloride. The reduced iron chelates with 1,10
phenanthroline at pH 3.2 to 3.3 to form a complex of orange-red colour. The intensity of colour
is proportional to the concentration of iron and obeys Beer's law.
PROCEDURE:
1. Pipette 10, 20, 30 and 50 ml of standard iron solution into 100 ml conical flasks.
2. Add 1 ml of hydroxylamine hydrochloride solution and 1 ml of sodium acetate solution to
each flask.
3. Dilute each to about 75 ml with distilled water.
4. Add 10 ml of phenanthroline solution to each flask.
5. Make up the contents of each flask exactly to 100 ml by adding distilled water and allow at
least 10-15 minutes for maximum colour development.
6. For visual comparison, pour the solution in 100 ml Nessler tubes and keep them in a
stand.Four tubes have Fe content of 0., 0.2, 0.3 and 0.5 mg/l of iron contents.
7. Mix the sample thoroughly and measure 50 ml into a conical flask.
8. Add 2 ml of con. HCI and 1 ml of hydroxylamine solution and a few glass beeds.
9. Boil the contents to half of the volume for dissolution of all the iron.
10. Cool the flask to room temperature and transfer the solution to a 100 ml Nessler tube.
11. Add 10 ml of ammonium acetate buffer solution and 2 ml phenanthroline solution and dilute
to 100 ml mark with distilled water. If the sample contains interference of heavy metals, add
10 ml of phenanthroline, instead of 2 ml.
12. Mix thoroughly and allow at least 10 to 15 minutes for maximum colour development.
13. For visual comparison, match the colour of sample with that of the standards prepared in
steps 1 to 6 above.
14. The matching colour standard will give the concentration of iron in the sample.
54
OBSERVATIONS AND RESULTS:
Iron(mg/l)
Sample Details
1.
2.
3.
4.
5.
6.
CONCLUSION:
PRECAUTIONS:
Strong oxidizing agents like cyanide, nitrite, poly-phosphates, chromium, zinc, cobalt, copper
and nickel interfere with the determination of iron.
The boiling of the sample with an acid initially removes interference of cyanide, nitrite and
polyphosphates. Hydroxylamine eliminates the interference caused by strong oxidizing agents.
55
SIGNIFICANCE:
1. Although iron has got little concern as a health hazard but is still considered as a nuisance in
excessive quantities. Long - time consumption of drinking water with a high concentration of
iron can lead to liver diseases (hemosiderosis).
2. Iron rich water exposed to the air, become turbid and highly unacceptable from the aesthetic
view point due to oxidation of soluble iron to insoluble ferric oxide which settles out as a rust
coloured salt. Such water often tastes unpalatable even at low concentration (0.3 mg/l).
3. Iron in excess of 0.3 mg/l causes stains to wash basin and steel containers. They also form red
spot on clothes.
4. Iron also promote the growth of iron-bacteria which derive their energy from the oxidation of
ferrous to ferric. This gives a rusty appearance to the waters. Colonies of these bacteria may also
form a slime which causes problems in water closets, pipes, pumps and distribution systems.
5. High concentration of iron in water is not suitable for processing of food, beverages, ice,
dyeing, bleaching and many other items. Water with higher concentration of iron when used in
preparation of tea and coffee, interacts with tannins giving a black inky appearance with a
metallic taste. Coffee may even become unpalatable at concentration of iron more than 1 mg/l.
6. Iron content of water is important in determining the suitability of water for domestic and
industrial purpose.
7. The ratio of iron to manganese is a characteristic factor that determines the type of treatment
unit used, as well as the amount of organic matter present in the water.
REVIEW QUESTIONS:
1. What is the health effect on human beings due to long time consumption of iron rich
water?
2. What is the reason for iron present in ground water in state of ferrous?
3. What are the methods used for removal of iron in water?
4. What is the permissible limit for iron in drinking water as per B.I.S ?
5. What are the uses of determination of iron in water treatment works?
6. What are Iron- bacteria? How they affect corrosion?
7. What is the colour change of water, by which presence of iron can be predicted?
8. What is the disease caused by the deficiency of iron in human beings?
9. What is deferrization of ground water?
10. What is Hemosiderosis?
56
EXERCISE NO. : 12
Determination of Total Solids in water
Learning Objectives:
To learn about:


Total solids
Determination of total solids


Effects of total solids
Significance
AIM: To determine the Total solids of the given water sample.
APPARATUS REQUIRED:
1. Evaporating dishes (pyrex, porcelain or platinum)
2. Oven
3. Desiccators
4. Water bath.
THEORY:
The term solids refer to the matters either filterable or non-filterable that remain as residue upon
evaporation and drying in oven at 103°C to 105°C. Various kinds of solids present in water and
waste water are shown in fig. below. Gravimetric method is used to measure all types of solids
except total settleable solids by Imhoff cone. Solids are generally expressed in mg/l.
The filterable solids fraction consists of colloidal and dissolved solids. The colloidal fraction
consists of particulate matter with an approximate diameter range from 1 milli-micron to micron.
The dissolved solids consist of both organic molecules and inorganic ions that are present in true
solution in water.
PRINCIPLE: Total solids are determined as the residue left after evaporation and drying of the
unfiltered sample
57
Fig.12: Classification of Solids
Fig.13: Evaporating Dish (porcelain)
Fig.14: Evaporating Pan
Fig.16: Water Bath
Fig.15: Desiccator
58
PROCEDURE:
1. A clean porcelain dish is ignited in a muffle furnace and after partial cooling in the air, it is
cooled in a desiccator and weighed.
2. A 100 ml of well mixed sample (graduated cylinder is rinsed to ensure transfer of all suspend
matter) is placed in the dish and evaporated at 100°C on water bath, followed by drying in oven
at 103°C for 1 hour.
3. Dry to a constant weight at 103°C, cool in a desiccator and weigh.
CALCULATIONS:
Total solids (mg/l) =
(A-B) x 1000
V
A
=
Final weight of the dish in mg.
B
=
Initial weight of the dish in mg.
V
=
Volume of sample taken in ml.
OBSERVATIONS AND RESULTS:
Sample details
Volume of sample Initial weight of
(ml)
the dish (mg)
1.
2.
3.
59
Final weight of
the dish (mg)
Total
(mg/l)
solids
CONCLUSION:
SIGNIFICANCE:
1. Total solids determination is used to assess the suitability of potential supply of water for
various uses. In cases, in which water softening is needed, the type of softening procedure used
may be dictated by the total solids content.
2. Corrosion control is frequently accomplished by the production of stabilized waters through
pH adjustment. The pH at stabilization depends to some extent upon the total solids present as
well as the alkalinity and temperature.
REVIEW QUESTIONS:
1. Define a solid with reference to Environmental Engineering
2. The residue and container must be cooled in desiccators after drying or ignition
operation. Why?
3. What is the normal size of colloid in water?
4. What is the permissible limit for total dissolved solids drinking water?
5. What are suspended solids?
6. How suspended solids are removed?
7. What is the quality of water if it contains high amount of solids?
8. What are fixed solids, and volatile solids?
9. What are the methods available for removal of inorganic dissolved solids from water?
10. What are the methods available for removal of organic dissolved solids from water?
60
EXERCISE NO. : 13
Determination of Total Dissolved Solids in water
Learning Objectives:
To learn about:




Total Dissolved Solids
Determination of TDS
Use of Filter paper, Desiccator
Significance of TDS
AIM: To determine the Total Dissolved Solids of the given water sample
APPARATUS REQUIRED:
1. Evaporating dishes
2. Oven
3. Desiccator
4. Whatman filter paper No. 44
5. Water bath.
THEORY:
In natural waters, dissolved solids consists mainly of inorganic salts such as carbonates,
bicarbonates, chlorides, sulphates, phosphate and nitrates of calcium, magnesium, sodium,
potassium, iron etc. and small amount of organic matter and dissolved gases. The determination
of dissolved solids does not give a clear picture of the kind of pollution.
PRINCIPLE: Total dissolved solids are determined as the residue left after evaporation and
drying of the filtered sample.
61
Fig.17: Whatman Filter Paper
PROCEDURE:
1. A clean porcelain dish is ignited in a muffle furnace and after partial cooling in the air, it
is cooled in a desiccator and weighed.
2. The sample is filtered using the filter paper
3. A 100 ml of filtered sample is placed in the dish and evaporated at 100°C on water bath,
followed by drying in oven at 103°C for 1 hour.
4. Dry to a constant weight at 103°C, cool in a desiccator and weigh.
CALCULATIONS:
Total solids (mg/l) =
(A-B) x 1000
V
A
=
Final weight of the dish in mg.
B
=
Initial weight of the dish in mg.
V
=
Volume of sample taken in ml.
62
OBSERVATIONS AND RESULTS:
Sample details
Volume of sample Initial weight of
(ml)
the dish (mg)
Final weight of
the dish (mg)
Total
Dissolved
Solids (mg/l)
1.
2.
CONCLUSION:
SIGNIFICANCE:
1. Estimation of total dissolved solids is useful to determine whether the water is suitable
for drinking purpose, agriculture and industrial processes.
2. Many dissolved substances are undesirable in water. Dissolved minerals, gases and
organic constituents may produce aesthetically displeasing colour, taste and odor. ,
63
3. Some dissolved organic chemicals may deplete the dissolved oxygen in the receiving
waters and some may be inert to biological oxidation, yet others have been identified as
carcinogens.
4. Water with higher solids content often has a laxative and sometimes the reverse effect
upon people whose bodies are not adjusted to them.
5. High concentration of dissolved solids about 3000 mg/l may also produce distress in
livestock. In industries the use of water with high amount of dissolved solids may lead to
scaling in boilers, corrosion and degraded quality of the product.
6. Water with higher solids content often has a laxative effect.
REVIEW QUESTIONS:
1. What is TDS in water?
2. What is the relation between TDS and Electrical conductivity?
3. How TDS can be removed?
4. What is the %age of TDS present in Sea water?
5. What is a solid with reference to Environmental Engineering?
6. The residue and container must be cooled in desiccators after drying or ignition
operation. Why?
64
EXERCISE NO. : 14
Determination of Suspended Solids in water
Learning Objectives:
To learn about:




Suspended solids
Determination
Significance
Removal of suspended solids
AIM: To determine the total suspended solids of the given water sample.
APPARATUS REQUIRED:
1. Gooch crucible/glass fibre filter
2. Suction apparatus
3. Desiccator.
THEORY:
Suspended solids or matter in surface water may consist of inorganic (silt and others) or organic
matter (plant fibres, algal and phytoplankton, metal chelates etc.). These materials are often
natural contaminants resulting from erosive action of water flowing over land surface. Ground
water contains negligible quantity of suspended solids as these being filtered out by soil strata
through mechanical straining action.
The amount of suspended solids in surface waters increases with input of natural and
man-made contamination. The ratio of weight of suspend solids to turbidity is often referred as
coefficient of fineness.
PRINCIPLE: Total suspended solids are determined as the residue left on gooch crucible or a
glass fibre filter after drying in oven.
PROCEDURE:
1. A clean gooch crucible is ignited in a muffle furnace and after partial cooling in the air, cool in
a desiccator and weigh (W1).
2. Pour 100 ml of well mix sample on gooch crucible or glass fibre filter which is kept on filter
flask and apply suction.
3. Wash the gooch crucible with 100 ml of distilled water to remove all soluble salts.65
4. Carefully remove the glass fibre filter paper or gooch crucible and dry in an oven at 105°C for
one hour.
5. Cool in a desiccator and weigh (W2).
6. Ignite gooch crucible in a muffle furnace at 600°C for 15-20 minutes.
7. Cool the crucible partially in air until most of heat has been dissipated and then in a desiccator
and record final weight (W3).
CALCULATIONS:
Total suspend solids (mg/l)
=
(W2 - W1) x1000
ml of sample taken
Suspended volatile solids (mg/l)
=
(W2 - W3) x 1000
ml of sample taken
W1, W2 or W3 are recorded weights in mg.
OBSERVATIONS AND RESULTS:
Sample
details
Volume
of Empty weight of gooch Final weight of gooch Solids mg/l
sample taken crucible (mg)
crucible (mg)
(ml)
Total
suspended
solids
Volatile
suspended
solids
CONCLUSION:
66
SIGNIFICANCE :
1. The suspended solids parameter is used to measure the quality of the waste water influent and
effluent.
2. The suspended solids determination is extremely valuable in the analysis of polluted waters.
3. It is used to evaluate strength of domestic waste water.
4. It is used to determine the efficiency of treatment units.
REVIEW QUESTIONS:
1. What is a suspended solid?
2. Why the suspended solids must be removed?
3. What are the methods of removal of suspended solids?
4. What is meant by floc?
5. What is coagulation?
6. What is destabilization?
7. What is Zeta potential?
8. What are the principles of agglomeration?
9. What is the use of ALUM?
10. Why should we remove suspended solids?
67
EXERCISE NO. : 15
Determination of Settleable Solids of a given sample
Learning Objectives:
To learn about:




Settleable solids
Use of Imhoff cone
Removal of Settleable solids
Significance of settleable solids
AIM: To determine the amount of settleable solids present in the given water sample
APPARATUS REQUIRED:
1. Imhoff cone
2. Holding stand
THEORY & PRINCIPLE:
A particle in suspension whose specific gravity is greater than that of water will settle under
quiescent conditions. The test is usually conducted in an Imhoff cone which is a graduated glass
cone of at least 1ltre capacity with a narrow angle at its apex.
PROCEDURE:
1. Gently fill the Imhoff cone with the thoroughly well mixed sample usually one litre and allow
it to settle.
2. After 45 minutes, gently rotate the cone between hands to ensure that all solids adhering to the
sides are loosened.
3. Allow the solids to settle for 15 minutes more, to make up for a total period of 1 hour.
4. Read the volume of the sludge which has settled in the apex.
5. Express the results in ml settleable solids per litre of sample per hour.
CALCULATIONS:
Total settleable solids = ml of solids x 1000
ml of sample
68
OBSERVATIONS AND RESULTS:
Sample details
Volume of sample taken
(ml)
Total settleable solids
ml /l /hour
1.
2.
3.
4.
PRECAUTIONS:
1. The Imhoff cones must be cleaned with a strong soap and hot water using a brush.
2. Wetting the cone with water before use, helps in preventing adherence of the solids to the
sides.
3. The method is subjected to considerable in accuracy if the solids contain large fragments.
4. The determination of total settleable solids should be carried out soon after sampling in
order to avoid errors through flocculation.
SIGNIFICANCE :
1. The settleable solids determination is used extensively in the analysis of industrial wastes to
determine the need for and design of plain settling tanks in plants employing biological treatment
processes.
2. It is also widely used in waste water treatment plant operation to determine the efficiency of
sedimentation units.
REVIEW QUESTIONS:
1. What are settleable solids?
2. What is the apparatus to measure settleable solids in laboratory?
3. What is the sp.gravity of settleable solids?
4. How to remove settleable solids from water?
5. What is the significance of settleable solids?
69
6. What is the principle of settlement of solids?
7. What is the principle on which sedimentation tank works?
8. What is sludge?
9. How much % age of sludge can be removed in primary sedimentation tank?
10. What is a clariflocculator?
70
EXERCISE NO. : 16
Determination of Dissolved Oxygen present in the water
Learning Objectives:
To learn about:




Dissolved oxygen in water
Significance of DO in water
Testing for DO
Significance of the test for DO
AIM: To determine the quantity of Dissolved oxygen present in the given sample.
APPARATUS REQUIRED:
1. BOD bottles (capacity 300 ml)
2. Sampling device for collection of samples
3. Burette
4. Pipettes.
REAGENTS REQUIRED:
1. Manganous sulphate
2. Alkali iodide-azide reagent
3. Starch indicator
4. Standard sodium thiosulphate (0.025 N)
5. Concentrated sulphuric acid.
THEORY:
The presence of oxygen is essential for the survival of aquatic life in water. This is also true for
the metabolic pathways of aerobic bacteria and other micro-organisms which are responsible for
the degradation and stabilization of organic constituents in waste water. The oxygen serves as an
electron acceptor in metabolic activities mediated by group of decomposers. Non-polluted
surface waters are normally saturated with dissolved oxygen.
A rapid fall of DO level in river waters is one of the first indication of organic pollution. The DO
level in natural water depends on physical, chemical and biological activities prevailing in the
water body. Thus, it is one of important parameters for assessing the quality of water bodies and
also plays key role in water pollution control activities.
71
The major inputs of dissolved oxygen to natural waters are from atmosphere and photosynthetic
reaction. Where the algae and phytoplankton production is high, the over saturation of oxygen
can occur during day time. The solubility of oxygen in waters depends on temperature, pressure,
altitude and chloride concentration. The solubility of atmospheric oxygen decreases with
increase in temperature in fresh water and rate of biological oxidation increase with temperature.
In summer season, polluted streams have higher oxygen demand than winter. The solubility of
atmospheric oxygen in fresh waters vary from 14.6 mg/l at 0°C to about 7 mg/l at 35°C under 1
atmospheric pressure. The solubility of oxygen is lesser in salt containing water than in clean
water.
Low dissolved oxygen in water can kill fish and many other organisms in water have specific
requirements of oxygen, for e.g. game fish requires at least 5 mg/l and coarse fish about 2 mg/l
of minimum dissolved oxygen in water. The minimum dissolved oxygen should maintain in
stream, rivers and other water bodies to survive aquatic life. The concentration of oxygen will
reflect whether processes of oxidation undergoing are aerobic or anaerobic and also degree of
contamination.
PRINCIPLE:
Oxygen present in sample oxidizes the divalent manganous to its higher valence which
precipitates as a brown hydrated oxide after addition of NaOH and Kl. Upon acidification,
manganese reverts to divalent state and liberates iodine from Kl equivalent to D.O. content in the
sample. The liberated iodine is titrated against Na2S2O3 (0.25N), using starch as an indicator. If
oxygen absent in sample, the MnSO4 react with the alkali to form white precipitate Mn (OH)2.
PROCEDURE:
(Winkler method):
1. Take the BOD bottle, Fill it with water. Put the lass stopper. Remove the stopper and find
measure the volume of ater to assess the capacity of the bottle in ml. (say this is X ml)
2. Fill the bottle up to brim with the water sample. Put the stopper again. Remove the stopper.
Add 2 ml of manganous sulphate and 2 ml of alkali iodide-azide solution to the BOD bottle. The
tip of the pipette should be below the liquid level, while adding these reagents.
3. Restopper with care to exclude air bubbles and mix by repeatedly inverting the bottle 2 to 3
times.
4. If no oxygen is present, the manganous ion reacts with hydroxide ion to form white precipitate
of Mn(OH)2. If oxygen is present, some Mn++ is oxidized to M++++ and precipitates as a brown
coloured manganic oxide.
Mn++ + 2(OH)- ------------ Mn(OH)2 (white)
Mn++ 2(OH)- + ½ O2------ MnO2 (brown) + H2O
5. After shaking and allowing sufficient time for all oxygen to react, the chemical precipitates are
allowed to settle leaving clear liquid within the upper portion.
72
6. Add 2 ml of concentrated sulphuric acid
7. The bottle is restoppered and mixed by inverting until the suspension is completely dissolved
and yellow colour is uniform throughout the bottle.
MnO2 + 2I- + 4H+ -------- Mn++ + I2 + 2H2O
8. A volume of. 203* ml is taken into the conical flask and titrated with 0.025N sodium
thiosulphate solution until yellow coloured iodine turns to a pale straw colour.
9. Since it is impossible to accurately titrate the sample to a colourless liquid, 1 to 2 ml of starch
solution is added.
10. Continue titration to the first disappearance of the blue colour.
{
*200 x X
= 203 ml
}
(X - 4)
CALCULATIONS:
1 ml of 0.025 N Na2S2O3 is equivalent to 0.2 mg of O2, since the volume of the sample is
200 ml.
1 ml of sodium thiosulphate is equivalent to
(0.2 x 1000)/200 mg/l = 1 mg/l
73
OBSERVATIONS AND RESULTS:
Sample
details
Temp, of Volume of Initial
sample
burette
sample °C
taken (ml) reading
(ml)
Final
burette
Reading
(ml)
Ml of
D.O. in
Na2S2O3
mg/l
used
SIGNIFICANCE:
1. It is necessary to know D.O. levels to assess quality of raw water and to keep a check on
stream pollution.
2. D.O. test is the basis for BOD test which is an important parameter to evaluate organic
pollution potential of a waste.
3. D.O. test is necessary for all aerobic biological waste water treatment processes to control the
rate of aeration.
4. Oxygen is an important factor in the corrosion of iron and steel. D.O. test is used to control
oxygen in boiler feed waters.
5. D.O. test is used to evaluate the pollution strength of domestic and industrial wastes.
6. Determination of D.O. in waste waters is useful to identify the nature of biochemical reactions
whether aerobic which gives out stable end products (H2O and C02) and do not produce any foul
smells or anaerobic whose end products are unstable and produce foul smells (H2S).
REVIEW QUESTIONS:
1. What is the minimum dissolved oxygen required for survival aquatic life?
2. What processes affect the D.O. content in the water?
74
3. When do you say the water is polluted?
4. What methods are used to determine dissolved oxygen?
5. Explain the reasons for take'203 ml' sample instead of 200 ml sample in D.O. test.
6. What is the value of saturated DO under STP conditions?
7. What happens to the amount of DO if temperature rises?
8. What are the ill effects of discharge of thermal effluents on streams?
9. What is the function of the NaOH sometimes used in preparing the thiosulphate solution
used for dissolved oxygen determination?
10. What processes affect the D.O. content in the water?
11. Two water samples are collected in two different sources A and B and tested for D.O. Source
A and B gives D.O. levels 1.2 mg/l and 8 mg/l respectively. Comment on results.
12. Two samples were collected simultaneously at the same spot in the river for dissolved
oxygen analysis. One sample was fixed immediately after collection and the other was
treated later in the laboratory. Indicate two possible factors that could cause lower results to
be obtained in the second sample.
13. What is the role of algae in DO test?
14. What happens if toxins present in the sample, in DO test?
15. How can you improve the DO content of waater?
75
EXERCISE NO. : 17
Determination of BOD of waste water
Learning Objectives:
To learn about:




Biochemical Oxygen Demand
Significance of BOD
Measurement of BOD
Removal of BOD
AIM: To determine the Biochemical oxygen demand (BOD) exerted by the given waste water
sample.
APPARATUS REQUIRED:
1. BOD bottles
2. Incubator to control temperature at 20o C
Reagents Required:
1. Distilled water
2. Phosphate buffer solution
3. Magnesium sulphate solution
4. Calcium chloride solution
5. Ferric chloride solution
6. Sodium thiosulphite solution.
THEORY: The biochemical oxygen demand (BOD) is a measure of the oxygen utilised by
micro-organisms during biological oxidation of organic matter contained in the liquid waste
under a specified experimental conditions.
Organic matter + O2
microorganism
> CO2 + new bacteria + H2O
On an average basis, the demand for oxygen is directly proportional to the amount of
biodegradable matter in waste water under aerobic condition. Hence, BOD is a direct measure of
oxygen requirements and an indirect measure of biodegradable organic matter.
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Biochemical oxidation is a slow process and theoretically takes an infinite time to go to
completion. Within 20 days period, the oxidation of organic matter is about 95% to 99%
complete and in the 5 days period used for the BOD test, oxidation is from 60% to 70%
complete. The 20°C temperature used is an average value for slow moving streams in
temperature climates and is easily duplicated in incubator. It is long period to conduct 20 days
BOD test. Hence the BOD test is standardized for 5 days incubation at 20°C in incubator.
The BOD is an empirical biological test in which the water conditions*such as temperature,
oxygen concentration or type of bacteria play a decisive role. These and other factors therefore
cause the reproducibility to be much less than that of pure chemical tests. In spite of this
disadvantage, the BOD test has a special importance in the assessment of pollution of surface
waters.
The biochemical decomposition in waste waters normally takes place in two almost distinct
phases. In the first phase or carbonaceous phase, carbonaceous matter is decomposed finally
yielding CO2 and H2O. In second phase, known as the nitrification phase, ammonium is
oxidized to nitrite and then to nitrate by the action of Nitrosomanas and Nitrobacter respectively.
Despite the presence of ammonium, this nitrification does not take place in every water or waste
water so that the test result can be very uncertain. Nitrification is mainly observed in waste water
of sewage works, since here a large number of the slowly reproducing nitrifying bacteria are
present.
In many cases of waste water analysis, the nitrification can be prevented by the action of
inhibitors in order to allow greater comparability between sample series. However, such
inhibitors should not be employed when investigating river waters, since environmental
information is required the oxygen consumption by all substances contained in the water and not
only organic components. In BOD test, light must be excluded from the incubator to prevent
algae growth that may produce oxygen in the BOD bottle.
The first stage equation of BOD reaction is as follows:
Yt = L0 (1-10-kt) when k is base 10.
Yt = L0 (1-e-kt) when k is base e.
Yt = Amount of BOD utilised or exerted at anytime/.
L0 = Ultimate BOD (the original concentration of the organic matter before any biological action
has occurred).
k = Deoxygenation constant per day.
The amount of BOD remaining at any time t equals Lt = L0 (10-kt)
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PRINCIPLE:
The BOD is an empirical biological test. This BOD test may be considered as wet oxidation
procedure in which the living organisms serve as the medium for oxidation of the organic matter
to carbon-dioxide and water.
On the basis of the above principle, it is possible to interpret BOD data in terms of organic
matter as well as the amount of oxygen used during its oxidation.
PROCEDURE:
1. Place the desired volume of distilled water in a 5 litre flask. Aeration is done by bubbling
compressed air through water.
2. Add 1 ml of phosphate buffer, 1 ml of magnesium sulphate solution, 1 ml of calcium chloride
solution and 1 ml of ferric chloride solution for every litre of distilled water (dilution water).
3. In the case of the waste waters which are not expected to have sufficient bacterial population,
add seed to the dilution water. Generally, 2 ml of settled sewage is sufficient for 1000 ml of
dilution water.
4. Highly acidic or alkaline samples are to be neutralized to a pH of 7.
5. Add 2 or 3 ml of sodium thiosulphite solution to destroy residual chlorine if any.
6. Take the sample as follows: Strong wastes: 0.1, 0.5 or 1% Settle domestic sewage: 1, 2.5 or
5% Treated effluents: 5, 12.5 or 25% River water 25% to 100%.
7. Dilute the sample with the distilled water and mix the contents well.
8. Take diluted sample into 3 BOD bottles.
9. Fill another three BOD bottles with diluted (distilled) water alone.
10. Immediately find D.O. of a diluted waste water and diluted water (distilled water).
11. Incubate the other three BOD bottles at 20°C for 5 days. They are to be tightly stoppered to
prevent any air entry into the bottles.
12. Determine D.O. content in the incubated bottles at the end of 5 days (120 hours).
CALCULATIONS:
Let initial D.O. of diluted sample
= D0
D.O. at the end of 5 days for the diluted sample
= D5
Initial D.O. of distilled water (blank)
= C0
DO. at the end of 5 days for the distilled water (blank)
= C5
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D.O. depletion of dilution water
= C0- C5
D.O. depletion of the diluted sample
= D0 - D5
D.O. depletion due to microbes
= (D0 - D5) – (C0- C5)
BOD at 20°C of the sample
=
{ (D0 - D5) x Vol of bottle} - C0- C5
ml of sample
OBSERVATIONS AND RESULTS:
Sr. Volume of Dilution Initial D.O. Final D.O.
Initial
Final D.O.
of sample of sample D.O. of
of blank
No. sample (ml) ratio
mg/l
mg/l
blank mg/l
mg/l
1.
2.
CONCLUSION:
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5 days BOD
at 20°C
(mg/l)
SIGNIFICANCE :
1. BOD is essential to determine strength of domestic and industrial sewage.
2. The determination of BOD is used in studies to measure the self purification capacity of
streams and serves regulatory authorities as a means of checking on the quality of effluents
discharged to such waters.
3. BOD of wastes is useful in the design of treatment facilities.
4. It is a factor in the choice of treatment method and is used to determine the size of certain
units, particularly trickling filters and activated sludge units.
5. It is used to evaluate the efficiency of various treatment units.
6. It is useful to estimate population equivalent of any industrial wastes which is useful to collect
cess from industrialist for purification industrial wastes in municipal sewage treatment plant.
7. It is only the parameter to give an idea of the bio-degradability of any sample and self
purification capacity of rivers and streams.
REVIEW QUESTIONS:
1. What is meant by BOD?
2. What do you understand by 200 mg/l of BOD5 at 20°C?
3. Why was the 5 day incubation period been selected for BOD determination?
4. What factors affect the rate of biochemical oxidation of organic matter in the BOD test?
5. Light must be excluded from the incubator in BOD test. Why?
6. What solution is added to BOD test samples to prevent undesirable oxygen consumption
through nitrification?
7. List five requirements which must be complied with in order to obtain reliable BOD data
8. What should be the composition of a 'good dilution water' for BOD determination?
9. What significant part do protozoa play in the BOD test?
10. Which type of organic matter is measured in BOD5 test?
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EXERCISE NO. : 18
Determination of COD of Waste water
Learning Objectives:
To learn about:




Chemical oxygen demand
Significance
Measurement of COD
Removal of COD
AIM: To determine the Chemical oxygen demand (COD) of given waste water sample
COD of wastewaters is measured in the laboratory normally by two methods:
1 REFLUX METHOD
2 DIGESTION VIAL METHOD
Each of these methods are described below one after the other
1. REFLUX METHOD
APPARATUS REQUIRED:
1. Reflux apparatus
2. Hot plate/heating mantle
3. Burette.
Reagents Required:
1. Standard potassium dichromate 0.25 N
2. Sulphuric acid with reagent (Conc.H2SO4 + Ag2SO4)
3. Standard ferrous ammonium sulphate 0.25 N
4. Ferroin indicator
5. Mercuric sulphate
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THEORY:
Chemical oxygen demand is the oxygen required for chemical oxidation of organic matter by
strong chemical oxidant (K2Cr2O7) under acidic condition. The degree of oxidation depends
upon the type of substance, pH value", temperature, reaction time and concentration of oxidizing
agent as well as the type of added accelerators, if any.
The main disadvantage of the test is that oxygen is also consumed by the oxidation of inorganic
substances such as nitrites, chlorides, sulphides, reduced metal ions etc. and some organic
materials are not oxidized by dicromate such as some amino acids, ketones or saturated
carboxylic acids, benzine pyridine etc. Consequently the test is a poor measure of strength of
organic wastes unless these factors are taken into consideration.
COD test indicates the total oxidizable organic material present in the sample and does not
differentiate between biologically oxidizable and biologically inert organic matter.
The COD test is much more useful than BOD for estimating strength of certain industrial wastes
both organic (pesticide industries) and inorganic (metallurgical industries) which are contained
toxic chemicals. The major advantage of the COD test is the short time required for evaluation.
The determination can be made in about 3 hours rather than 5 days required for the measurement
of BOD. Further the test is relatively easy, gives reproducible results and is not affected by
interferences as in BOD test.
PRINCIPLE:
The organic matter present in sample geJts oxidized completely by K2Cr207 in the presence of
H2SO4 to produce CO2 and H2O. The excess K2Cr2O7 remaining after the reaction is titrated
with Fe(NH4)2 (S04)2 . The dicromate consumed gives the O2 required to oxidation of the
organic matter.
PROCEDURE:
1. Place 0.4 gm of H2SO4 in the reflux flask.
2. Add 20 ml of sample (or an aliquot diluted to 20 ml)
3. 10 ml of more concentrated dichromate solution are placed into flask together with glass
beeds.
4. Add slowly 30 ml of H2SO4 containing Ag2SO4 and mix thoroughly.
5. Connect the flask to condenser. Mix the contents thoroughly before heating. Improper mixing
results in bumping and the sample may be blown out.
6. Reflux for a minimum period of 2 hours. Cool and wash down the condenser with distilled
water.
7. Dilute the sample to make up 150 ml and cool.
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8. Titrate excess K2Cr2O7 with 0.25 N Fe(NH4) SO4 using ferroin indicator. Sharp colour change
from blue green to wine-red indicates the end point.
9. Reflux the blank in the same manner using distilled water instead of sample.
CALCULATIONS:
Quantity of Fe(NH4)2 (SO4) added for blank = A ml.
Quantity of Fe(NH4)2(SO4) added for the sample = B ml.
COD =
(A-B) x normality Fe(NH4)2 (SO4) x 8 x 1000
Quantity of sample(ml)
OBSERVATIONS AND RESULTS:
Sample
details
Volume
of Initial burette Final burette Vol of
sample taken reading (ml)
Reading (ml) Fe(NH4)2
(ml)
(SO4)
Used (ml)
COD of the
sample
mg/l
1.
SIGNIFICANCE:
1. The COD test is used extensively in the analysis of industrial wastes.
2. It is particularly valuable in surveys designed to determine and control losses to sewer
systems.
3. The test is widely used in the place of BOD in the operation of treatment facilities because of
the speed with which the results can be obtained.
4. It is useful to assess strength of wastes which contain toxins and biologically resistant organic
substances.
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5. The ratio of BOD to COD is useful to assess the amenability of waste for biological treatment.
Ratio of BOD to COD greater than or equal to 0.8 indicates that waste waters are highly
amenable to the biological treatment.
2 DIGESTION VIAL MEHOD
1. Take 1.5 ml of wastewater sample into 4-vials and take 2-vials for blank also.
2. Add 2.00 ml of Potassium dichromate solution in each vial.
3. Add 3.00 ml of concentrated sulphuric acid in each vial.
5. Keep these 4+2 vials in the digestio apparatus for two hours and digest them for 2-hrs at 150
degree celcius.
6. After coolong dilute the sample to make up 150 ml in a titration flask and cool.
7. Titrate excess K2Cr2O7 with 0.25 N Fe(NH4) SO4 using ferroin indicator. Sharp colour change
from blue green to wine-red indicates the end point.
9. Average the values of vials 1-4, and 5-6 separately for calculation the COD value.
CALCULATIONS:
Quantity of Fe(NH4)2 (SO4) added for blank = A ml.
Quantity of Fe(NH4)2(SO4) added for the sample = B ml.
COD =
(A-B) x normality Fe(NH4)2 (SO4) x 8 x 1000
Quantity of sample(ml)
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OBSERVATIONS AND RESULTS:
Sample
details
Volume
of Initial burette Final burette Vol of
sample taken reading (ml)
Reading (ml) Fe(NH4)2
(ml)
(SO4)
Used (ml)
COD of the
sample
mg/l
SIGNIFICANCE:
1. The COD test is used extensively in the analysis of industrial wastes.
2. It is particularly valuable in surveys designed to determine and control losses to sewer
systems.
3. The test is widely used in the place of BOD in the operation of treatment facilities because of
the speed with which the results can be obtained.
4. It is useful to assess strength of wastes which contain toxins and biologically resistant organic
substances.
5. The ratio of BOD to COD is useful to assess the amenability of waste for biological treatment.
Ratio of BOD to COD greater than or equal to 0.8 indicates that waste waters are highly
amenable to the biological treatment.
REVIEW QUESTIONS:
1. What is meant by COD of waste water?
2. The waste water sample has higher BOD than COD. Can you interpret?
3. What organic compounds are not oxidized in COD test?
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4. What major limitations are of the COD test?
5. Why do COD analysis and BOD analysis usually give different results for the same waste
water?
6. What are the parameters to be measured to determine the strength of waste water?
7. What is the test preferred to estimate strength of pollution from industrial waste water?
8. Why COD test does not differentiate between biodegradable and non degradable organic
matter?
9. What are the strong acids used in COD test?
10. What is the purpose of strong acids in COD test?
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EXERCISE NO. : 19
Determination of Chlorides in water
Learning Objectives:
To learn about:




Chlorides in water
Significance of chlorides
Testing of chlorides
Removal of chlorides
AIM: To determine the content of Chlorides in the given water sample..
APPARATUS REQUIRED:
1. Burette
2. Pipettes
3. Conical flask.
Reagents REQUIRED:
1. Chloride free distilled water
2. Potassium chromate indicator
3. Standard silver nitrates (0.014 1 N)
4. Standard sodium chloride (0.014 1 N).
THEORY:
Chloride is present in all natural waters at greatly varying concentration depend on the
geochemical conditions. Chlorides in natural waters can be attributed to leaching of chloride
containing rock and soils, discharges of effluents from chemical industries, ice cream plant
effluents, edible oil mill operations, sewage disposal, irrigation drainage, contamination from
refuse Leachate and sea water intrusion in coastal regions. Each of these source may result in
local contamination of both surface and ground water.
Large amounts of chlorides reach to the receiving water through leaching of domestic sewage. A
man discharges 8 to 10 gm per day of NaCI through both urine and excreta. As such, domestic
sewage contains more chlorides than domestic water supply. Due to this chloride can often serve
as a chemical — pollution indicator of domestic sewage contamination when considered together
with other parameters and a natural geological origin does not apply.
87
When chlorides concentration of 250 mg/l is present along with sodium ions, a salty taste can be
observed. The salty taste may be absent in waters in absence of sodium ions, even concentration
of chlorides is as high as 1000 mg/l.
Chlorides are highly soluble with most of naturally occurring cations except with silver.
Chlorides can only be removed by reverse osmosis process and electrolysis. Sea water has
chlorides content of 19,000 to 20,000 mg/l.
PRINCIPLE:
Chloride ion is determined by Mohr's method, titration with standard silver nitrate solution in
which silver chloride is precipitated at first. The end of titration is indicated by formation of red
silver chromate from excess AgN03 and potassium chromate used as an indicator in neutral to
slightly alkaline solution.
AgNO3 + Cl ——————> AgCl + NO3 (white)
2AgN03 + K2CrO4 ——————> Ag2CrO4 + 2 KNO3 (red)
PROCEDURE:
1. Take 100 ml of the sample in conical flask.
2. Adjust its pH to be between 7.0 and 8.0 either with sulphuric acid or sodium hydroxide
solution. Otherwise, AgOH is formed at high pH level or CrO2 is converted Cr2O2 at low pH
levels.
3. Add 1 ml of potassium chromate to get light yellow colour.
4. Titrate with standard silver nitrate solution till colour change from yellow to brick red.
5. Note the volume of silver nitrate added (A).
6. If more quantity of potassium chromate is added, Ag2CrO4 may form too soon or not soon
enough.
7. For better accuracy, titrate distilled water in the same manner.
8. Note the volume of silver nitrate added for distilled water (B).
CALCULATIONS:
Chloride in (mg/l) = (A-B) x normality of AgNO3 x 35.46 x 1000
volume of the sample taken
88
OBSERVATIONS AND RESULTS:
Sample
details
Volume of
Observations
sample taken
Initial burette Final burette AgNO3 solution Chlorides mg/l
(ml)
reading (ml)
reading (ml)
used (ml)
1.
2.
CONCLUSION:
SIGNIFICANCE:
1. Chlorides determination in natural waters is useful in the selection of water supplies for human
use.
2. Chlorides determination is used to determining the type of desalting apparatus to be used.
3. The chloride determination is used to control pumping of ground water from locations where
intrusion of sea water is a problem.
4. Chlorides interfere in the determination of chemical oxygen demand (COD). A correction
must be made on the basis of the amount of chlorides present.
89
REVIEW QUESTIONS:
1. What is the need for pH adjust to 7 to 8 sample in chlorides estimation?
2. What is the effect of temperature on the determination of chlorides?
3. How does the presence of NH4 ions in the sample affect the chlorides determination?
4. What are the reasons for non-salty taste of water, even chlorides concentration more than
1000 mg/l?
5. What process is to be used to remove excess chlorides in waste?
6. What is meant by indicator blank correction?
7. Would the analytical results by the Mohr method for chlorides be higher, lower, or the
same as the true value if an excess of indicator were accidentally added to the sample?
Why?
8. What is the permissible limit for chloride in drinking water as per BIS?
9. What is the colour of the precipitate formed by AgCl?
10. What is the colour of the precipitate formed by Ag2CrO4?
11. What is the relation between salinity and chlorides?
12. What are the ill effects of excess chlorides on concrete?
90