water supply practical all

8/7/2019 water supply practical all

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(Affiliated to

T.U.)

A PRACTICAL

REPORT

ON

WATER SUPPLY

ENGINEERING

SUBMITTED BY:

SUBMITTED

TO :

Name: Rabindra

Subedi

Department

of

Class: BCE

III/I

C

Civil

Engineering

Roll no:

62109

Er.

Arun

Prasad

Parajuli


2/17


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1

Submitted by: Rabindra Subedi Water Supply Engineering Practical Submitted to: Department of BCE 62109C Civil Engineering

Er. Arun Prasad Parajuli

EXPERIMENT NO: 1 1st May TURBIDITY

TEST

1.1.

OBJECTIVE: TO DETERMINE THE TURBIDITY OF GIVEN WATER SAMPLES AND CHECK WHETHER IT CAN BE USED

FOR DRINKING OR NOT AS PER THIS TURBIDITY VALUE.

1.2.

APPARATUS REQUIRED:

The apparatus for the turbidity test consists of following: a)

Digital Turbidity Meter: We are using digital turbidity meter of model 331E. It has dimensions of 275 mm 195 mm 105 mm and consists of a tungsten lamp light source, digital display, a photodiode detector and a power supply cable. It has a range of 0 to 1000 NTU. It has further test tube holder to keep the test tube containing solution and sample to be tested and a test tube holder cover to prevent external light to enter while sample is under test. It has a range switch to select the probable turbidity range of the sample, a set zero switch to set zero for the blank solution (distilled water), a calibration switch to calibrate the instrument while having standard solution understand and on off switch to on off the instrument.

b)

Standard Test Tubes: Clear test tubes to keep samples and standard solution under test. c)

Electronic balance: For accurate weighing of chemicals.

d)

Temperature stabilizing device: To maintain test temperature.

e) Volumetric flasks: To prepare standard solution of known turbidity.

f)

Membrane filter having holes of 0.2 mm: To filter the distilled water. g)

Measuring jars etc.

1.3.

CHEMICALS AND

SAMPLES

REQUIRED:

a.

Hydrazine Sulphate [(NH2 )2H2SO4] b.

Hexamamethylenetetramine [ (CH2)6N4)]

c.

Distilled water d.

Water samples to be tested.

The sample should be true representative of the actual water. In taking out samples, care should be taken that no further contamination or purification can be placed after collection and

before the analysis is completed. Well cleaned bottle should be used and it is cleaned by the same water.

1.4.

THEORY: Water in not important for drinking and cooking only but also used for human consumable manufacturing processes as breweries, food processing etc. quality of water is the degree of goodness of characteristics (physical, chemical & biological) of water in all aspects.

Condensation of water vapor make rainfall but this water initially is pure containing two parts of hydrogen and one part of oxygen only by volume. On the way of falling, it absorbs different gases, dust & other impurities. Also during surface runoff, this water carries large number of impurities such as silt, organic, non organic, minerals impurities, suspended matters etc. while moving on earth surface. These substances not always be harmful but may be useful to human life. Again ground water contains both harmful & useful gases and minerals. Before using water for drinking, water treatment is needed. Total purification is difficult & costly and pure water only is not good for our health hence treatment to some extent is done. To ensure whether the water from any selected source is drinkable (wholesome) or not and to ensure the treatment needs water should be tested.

All undesirable substance containing in water in any form is called impurities in water. Water from any source may have following three types of impurities. a)

Suspended Impurities:


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These are those impurities, which normally remains in suspension due to same specific gravity as that of water. E.g. Clay, algae, fungi, organic & inorganic matters & minerals etc. It causes turbidity and suspended impurity is measured in terms of turbidity. It is measured by turbidity test can be removed by sedimentation & filtration.

b)

Colloidal Impurities: These are the small, non visible with naked eye and electrically charged particles, which remain

in, continue motion. Their size is between 10 3 to 10 6 mm. the charge is due to absorbed ions on the solid particles. E.g. Acids or neutral materials as silica glass & most organic matters have

negative charge in neutral water & basic materials as Al2O3 & Fe2O3 are positively charged. Particles of similar charged materials repel each other which cause movement of the particles. It causes color in water and these impurities cause epidemics because the organic matters contain bacteria. It is measured by color test and difficult to remove by ordinary filters.

c)

Dissolved Impurities: Some solid, liquid and gas dissolves in the water when it moves over the rocks and soil etc

because water is the good solvent. Eg: non visible organic compounds, inorganic salts & gases etc. It makes bad taste, hardness and alkalinity. Its concentration is measured in PPM (parts per million) or mg/l and obtained by weighing the residue after evaporation of the water sample from a filtered sample. Due to the presence of stated impurities in water, water should be analyzed to classify, prescribe treatment, control treatment and purification processes and maintains public supplies of a standard of organic quality and palatability. Examination of water may be divided into three as: a.

Physical Examination,

b.

Chemical Examination & c.

Microbiological Examination. Turbidity is the physical characteristics of water and this test comes in the physical

examination of water. It is caused by the suspended as well as colloidal impurities. Turbidity is the degree of clarity of water and is the measure of the resistance to the passage of the light through it. Turbidity is measured in terms in Silica Scale. One milligram of silica in one liter of distilled water gives one PPM (Parts per million) or one mg/l or one JTU (Jackson Turbidity Unit) or One NTU (Nephelometer Turbidity Unit) of turbidity.

The permissible turbidity for domestic water for ideal and safe supply may be between

5 to 10 NTU & as per W.H.O. standard, 2.5 NTU is accepted and rejected if value is greater than 25 NTU.

It can be tested using Turbidity Rod, Jackson Turbidimeter, Baylis Turbidimeter, Nephelometer and Digital Turbidity Meter. Among them the recent technology is Digital Meter.

Turbidity in the lab is determined on the principle that a light passing through a substance is scattered by the particles in the water. In the digital Turbidity Meter, a beam of light is sent to the sample and suspended matter scatter the light and this scattered light is received on the photoelectric cell and amplified to the electronic pulse and can be seen in the digital display.

1.5. PROCEDURE: The procedure was done in three steps are as follows: Step1: Preparation of Reagent:

a)

Preparation of Turbidity free distilled water: Turbidity free water is difficult to obtain but the following method was adopted to make turbidity free water. i.

The distilled water was passed through a membrane filter having holes of 0.2 mm.


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ii.

The collecting flask was rinse twice with the filtered distilled water and discard the next 200 ml filtered distilled water.

b)

Preparation of standard turbidity suspension: i.

Preparation of solution I: 1 gm Hydrazine Sulphate [(NH2)2H2SO4) was dissolved in 100 ml of filtered distilled water in a volumetric flask.

ii.

Preparation of solution II: 10 gm of Hexamamethylenetetramine [(CH2)6N4] was dissolved in 100 ml of filtered distilled water in a volumetric flask.

iii.

Mix 5 ml of solution I and 5 ml of Solution II in the flask and let them stand for 24 hours at

253

C. This suspension has turbidity of 400 NTU. Standard Solution of other known turbidity Values can be made by mixing the following amount of distilled water to the following amount of this 400 NTU solution. S.No. To make standard

solution of Mix

Amount of 400 NTU Solution

Filtered distilled water

1 200 NTU 50 ml 50 ml 2 100 NTU 25 ml 75 ml

Step 2: Calibration of Instrument: i.

The instrument was switch on and kept in on for 10 minutes.

ii. Appropriate

range

was

selected

depending

upon

the

excepted

turbidity

of

the

sample.

iii.

Filtered distilled water was put in the standard test tube and put it in the test tube holder of the machine then cover it and adjust to 000 with the set Zero knob.

iv.

Now in another test tube, appropriate standard solution was just prepared before was taken and place it in the machine as before and set the values on the display of the same standard solution using Calibrate knob.

v.

Calibration was checked by removing and replacing the same test tube. Then the instrument was ready to use.

Step 3: Testing the sample: i.

The sample was place in the test tube and was placed into the machine and it was fully covered.

ii.

The reading on the display for turbidity of that sample was taken. iii.

The test was similarly repeated for other samples.

1.6.

OBSERBATIONS: Name and place of sample collection: Kathmandu Engineering College, Kalimati, Kathmandu

Source of water: Boring Water and Tap Water inside K.E.C. Date and time of sampling: S.No. Sample No. Sampling

Date and time

Sampling Place

Water Source

Measured Turbidity value (NTU)

Average Turbidity Value (NTU)

1 A. 2065 01

18/12:15 pm

K.E.C.

Kalimati Boring

water 20.8 20.8

2 B. 2065 01 18/1pm

K.E.C. Kalimati

Tap Water 4.0 4.0


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1.7.

RESULT: Hence from the experiment we found that the turbidity of water sample taken from boring water

is 20.8 ppm or NTU or mg/l and the turbidity of tap water is 4.0 ppm or NTU or mg/l (silica scale).

1.8.

CONCLUSION &

DISCUSSION:

By using digital turbidity meter we found the turbidity of the sample A and B i.e. 20.8 and 4.0 ppm respectively. And according to W.H.O. Maximum permissible limit of turbidity of the drinking water should be 5 ppm (silica scale). The turbidity of the water sample taken from tap source i.e.

sample B is less than 5 ppm so it is safe for domestic water for ideal and safe supply only considering the Turbidity of the sample. For the standard quality of the sample B only measurement of turbidity is not sufficient but we should examine its all the physical, chemical and biological impurities and if the value obtained is within the permissible limit according to W.H.O. then we can say that the water is safe for drinking purpose.

Considering the turbidity value of water sample A taken from boring water which is 20.8 ppm i.e. more than 5 ppm according to W.H.O. Hence this water is not safe for drinking water supply project, it needs purification to turbidity of water and other test is necessary for the good water supply project.

Hence we conclude that the water sample B is safe in turbidity value and water sample A is not safe according to turbidity value consideration. Sample A needs further purification for turbidity but

purification

of

sample

B

is

not

necessary

for

turbidity

but

on

testing

its

other

impurities,

it

may

needs

purification.

1.9.

PRECAUTIONS:

The following precaution should be taken during experiment: a)

Environment should be free from dust and instrument should be placed in vibration free bench. Room temperature should be 5 C to 45 C and humidity shouldnt be greater than 90%.

b)

Inhalation, ingestion and skin contact to chemicals and standard solutions should be avoided.

c)

Suspension should be prepared weekly. d)

Dirty glassware should not be used. They should be cleaned both inside and outside. The sides of the test tube should not be touch.

e)

Appropriate range should be selected. f)

Allow sufficient time for test tube containing solution and sample to be air bubble free.

g)

Since the instrument is dust sensitive, so it should be kept covered with dust cover when it

is not in use.


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EXPERIMENT NO. 2 1 st May

PH TEST

2.1.

OBLECTIVE:

TO DETERMINE THE PH OF GIVEN WATER SAMPLES AND CHECK WHETHER IT CAN BE USED FOR DRINKING OR NOT AS PER THIS PH VALUE.

2.2. APPARATUS

REQUIRED:

The apparatus for the pH test consists of following: a.

Digital pH Meter: We were using Digital pH Meter of Model 101E. It has dimensions of 275mm 75 and a power supply cable.

The front panel of this instrument consists of following parts: 1.

A slope control

2.

A digital display 3.

A calibration control

4.

Temperature knob 5.

A functional control switch: it consists: a.

ATC (auto temperature control ) mode

b.

pH mode c.

Stand by mode

d.

mV mode The back panel of this instrument consists of following parts:

1.

A input socket for PH & mV 2.

A input socket

3.

A output when a recorder is used 4.

On/off switch

5.

A fuse. b.

Combined pH electrode

c.

Temperature probe. d.

Electrode stand and clamp

e.

Volumetric flasks

f. Measuring jars, Buffer bottles, beakers etc

2.3.

CHEMICALS AND

SAMPLES

REQUIRED:

a.

Buffer tablets (Glaxo make) or powder pack (Ranbaxy make). It may be of 4 pH and 7 pH. b.

KCL (Potassium Chloride) to make saturated solution of KCL for electrode.

c.

Distilled water. d.

Water samples to be tested. The sample should be true representative to the actual water. In taking out samples, care should be taken that no further contamination or purification can be placed after collection and before the analysis is completed. Well cleaned bottle should be used and it is cleaned by the same water.

2.4. THEORY:

In water, pH is the chemical characteristic and this test comes in the chemical examination of water. The water found in nature may be acidic or basic depending on the nature of dissolved salts and minerals. The acidity and alkalinity is measured in terms of pH value because pH value indicates the hydrogen ion concentration in water.


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Water (H2O) is the combination of positively charge of hydrogen ions (H+) or cations and

negatively charged Hydroxyl ions (OH ) or anions. In pure water the concentration of H+ ions and OH ions are equal. When some substances is dissolved in pure water, the solution formed ionized (i.e. splits up into H+ and OH ions) and the balance between the concentration of the same are disturbed. If concentration of H+ ion is greater then the water is acidic and alkaline if that of OH ion is greater. For example, if HCL is added, the water becomes acidic and if NaOH is added it becomes alkaline.

Acidic, if: Alkaline, if: H2O H

+ + OH H2O H

+ + OH

HCL H+

+ Cl

NaOH Na+

+ OH

Applying the law of Mass action in physical chemistry, in a pure water solution, the hydrogen ion concentration is found to be 10 7 moles/liter. [Moles = molecular wt. in gram]. Also, the pH is defined as the logarithm of the reciprocal of hydrogen ion concentration. Mathematically,

pH = log10 H

1 = log 10 [H

+] 1 = log10 [10 7] =7

The pH scale explains variation of types of alkalinity and acidity. The following fig explains it.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Max. Acidity Acidity Alkalinity Max. Alkalinity

Neutral

Water

Fig. A PH Scale Acidity in water is caused by the presence of minerals acids, free carbon dioxide; sulphates of iron,

aluminum etc, whereas alkalinity is caused by the presence of bicarbonates of calcium and magnesium or carbonates of hydroxide of sodium, potassium, calcium and magnesium. As per W.H.O. standard, a pH value of 6.5 to 8.5 should be acceptable and rejected if pH is < 6.5 to > 9.2 for public water supply. Hence pH value should be as closer to 7. The lower value of pH (acidic) causes corrosion and the higher value (alkalinity) may produce sediment deposits, difficulty in chlorination etc.

The pH value of water can be measured by colorimetric method or by Electrometric method using pH meter. Here we are using pH meter and it measures pH directly or in terms of mV (milivolts0. We are concerned here with measurement of pH directly after calibration of instrument.

The principle of pH meter is that if two solutions are separated with pH sensitive glass (i.e. the bulb of glass pH electrode, an electrode, an electrical potential will be developed across the membrane. If the solution inside the bulb contains hydrogen ion concentration, the membrane potential will change as the hydrogen ion concentration of the other solution varies. If electrical connections are made to these solutions inside the glass bulb by the electrodes internal element and outside the glass by a reference electrode the membrane potential can be measured and displayed in the display as pH directly or as mV(millivolts).

2.5.

PROCEDURE: Procedure was done in four steps are as follows:

1.

Connecting the electrode:

I. First the electrode stand was set up and pH electrode was fitted into it.

II.

The protective rubber cap was carefully removed from the filling hole of electrode. The level of KCL solution was made few mm below the hole and refilled with the standard KCl solution and the rubber cap was placed back.

2.

Preparation of Buffer Solutions: I.

To make solution of 7 pH, we dissolve one buffer tablet of 7 pH in 100 ml distilled water.

II.

Similarly, to make solution of pH 4, we dissolve one buffer tablet of pH 4 in 100 ml distilled water. 3.

Calibration of Electrode:


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i.

The pH electrode was connected into the input socket, it was washed with the distilled water and switch on the instrument then dipped the electrode in 7 pH Buffer solution.

ii.

Sated the temperature knob to the buffer solution temperature and sated the instrument to pH mode using functional selector switch and adjust with Calibrate switch till the digital display shows the precise pH value of the buffer at that temperature.

iii.

Now using function selector switch to standby mode. iv.

Them we remove the electrode from the buffer solution and washed it with the distilled water.

v.

Then, dipped the electrode into another buffer solution (4 pH).

vi. Sated the temperature knob to the buffer solution temperature and set the instrument to pH mode using

Functional Selector switch and adjust with slope correction switch until the digital display shows the precise pH value of the buffer at that temperature.

vii.

Now we check the correct readings obtained with both the buffer solutions without further adjustment. (If the function Selector Switch is selected as ATC mode, there is no need to set Temperature knob. At this time connect the temperature probe at Temperature input terminal and immerse it into the solutions along with pH electrode for auto temperature compensation.) Then the instrument was ready to check pH of sample.

4.

Testing the Sample: a.

The electrodes were washed with distilled water and dipped the electrode (Temperature probe ifATC mode is selected) in the sample under test.

b.

The temperature knob was set to the sample temperature (not required if ATC mode is selected), the display give the pH value of the sample in pH units.

c.

The procedure was repeated for other samples.

2.6.

OBSERVATIONS: Name and place of sample collection: Kathmandu Engineering College, Kalimati, Kathmandu

Source of water: Boring water and Tap water Date and time of Sampling: 2065 01 18/12:00pm

S.No. Sample No. Sampling time

Water source

Measured pH value

Average pH value

1 A 12:55 pm Boring water 6.75 6.75 2 B 12:15 pm Tap water 7 7

2.7.

RESULT: From the experiment we found that the pH of Tap water is 7 and the pH of boring well

water is 6.75.

2.8.

CONCLUSION &

DISCUSSION:

The pH vale 7 means that the water is neutral neither acidic nor basic which is safe for drinking purpose. A pH value of 6.5 to 8.5 should be acceptable and rejected if pH is 9.2 for public water supply. According to W.H.O. pH value should be within 6.5 to 8.5. On considering the sample B whose pH value is 7 which is safe for drinking purpose on considering PH. And on considering sample A whose pH is 6.75 and it is also suitable for drinking purpose.

The lower the pH value more the water is acidic and higher the pH value more the alkalinity in the water. Alkalinity is caused by hydroxides, carbonates and bicarbonates but natural alkalinity is due to bicarbonates, which are produced by the action of ground water on limestone or chalk. Acidity in water is caused by the presence of minerals acids, free carbon dioxide, sulphates of iron, aluminum etc. The pH value should be as closer to 7. The lower the


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value of pH (acidic) causes the corrosion and the higher value (alkalinity) may produce sediment deposits, difficulty in chlorination etc.

Hence we conclude that the pH value of both the sample is good so it is suitable for drinking water supply project on considering pH only.

2.9.

PRECAUTIONS: Following precautions should be kept in mind while measuring pH:

a)

Strong acids and base are dangerous so should avoid inhalation, ingestion and skin contact to

chemicals. b)

The electrode should be soaked in distilled water for some hours before use it.

c)

Mixing should be properly done by using two buffers and careful should be taken not to cross contamination.

d)

Dirty glassware should not be used. They should be cleaned both inside and outside. e)

The instrument is dust sensitive so it should be kept covered with dust cover when it is not in use.


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EXPERIMENT NO: 3 15 thMay DISSOLVED

OXYGEN

(DO)

TEST

3.1.

OBJECTIVE:

TO DETERMINE THE DISSOLVED OXYGEN (DO) CONTENT IN THE GIVEN SAMPLE OF WATER.

3.2. APPARATUE REQUIRED: The apparatus for the DO test consists of following: a)

Digital

DO

Meter:

It consists of a power

input cable, power switch, input socket for temperature probe,

DO electrode in the back panel. Magnetic stirrer power output in the some instruments may be available. The front panel consists of a digital display on C for temperature in temperature mode and DO on PPM in DO mode. A function (mode selector) switch, zero knob, calibration knob and temperature adjusting knob are also available in the front panel.

b)

DO electrode:

It consists of silver and gold electrode cells and an electrolyte tube with a ring so that DO membrane and electrolyte can be kept. The electrode has a provision to fit in the DO socket at back panel.

c)

Temperature probe:

It can be fitted in the temperature socket of the DO meter back panel for temperature measurement in temperature mode. d)

Magnetic

stirrer

with

capsule:

It is used for stirring. The capsule is kept in the BOD bottle and the BOD

bottle is kept on the stirrer for stirring sample. Stirrer can get power either from DO meter or separate power supply line.

e)

DO membrane:

f)

Electronic balance:

For accurate weighing of chemicals.

g)

Volumetric flasks: To prepare standard solution of known turbidity.

h)

BOD bottles

i)

Measuring jars

etc.

3.3.

CHEMICALS

AND

SAMPLES

REQUIRED:

a. Potassium chloride [KCl]

b.

Sodium sulphate [Na2SO3] c.

Distilled water

d.

Water samples to be tested.

3.4.

THEORY: Dissolved oxygen is the content of oxygen in water. Surface water gets the dissolved oxygen either

from (i) Diffusion of oxygen from air, which is a physical phenomena depends upon solubility of oxygen and (ii) Photosynthesis activity in water, which is the biological phenomena happened due to the activities of algae, tiny aquatic plants etc.

The solubility of oxygen depends upon the temperature, water movement, and presence of oxygen

demanding

organic

matters.

The

organic

wastes

cause

rapid

depletion

of

DO

from

water.

At

higher

temperature water can hold smaller amount of DO. The presence of oxygen in water is necessary to keep it fresh and sparkling. The quantity of 6 ppm of

dissolved oxygen is essential in water to be used for drinking purpose and 4 ppm for fish and aquatic life. Excess of dissolved oxygen create corrosion of pipe material due to the oxidation.

3.5.

PROCEDURE: The procedure was done in four steps are as follows:


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1.

Preparation of

reagent:

a.

7.5% potassium chloride (KCL) solution (i.e. mix of KCl in 100 ml of distilled water). It was used in electrode as electrolyte.

b.

Then we prepare 2% sodium sulphate (Na2So3) solution (i.e. mix of 2 gm of Na2So3 in 100 ml of distilled water). It has zero DO.

2.

Making instrument

ready:

a.

First the power leads was connected into the power socket and the instrument was put in switched

on condition at 15 minute for warm up. b.

Then the ring of the electrolyte tube was removed and fitted the DO membrane and then fixed the ring to the tube to tighten the membrane.

c.

The electrolyte tube was opened and filled with 7.5% KCL solution and then inserted the electrode and screwed it tightly.

d.

The terminals of electrode were connected to sockets at the back panel of the DO meter. e.

Connected the socket of temperature probe in the temperature input terminal at the back panel of DO meter.

f.

The calibration knob was set to extreme right position and zero knob to extreme left position. Then the instrument was ready.

g.

Then connected the power supply to magnetic stirrer.

3.

Calibration of

instrument:

a.

The instrument was kept in temperature mode and 2% of Na2SO4 solution was taken in a flask then dipped the temperature probe in this solution then noted the temperature after stability of reading and set temperature knob for this temperature.

b.

Then removed the temperature probe and kept instrument in DO mode then inserted DO electrode in the 2% Na2SO4 solution. Being no DO for this solution adjusted reading to 0 using zero knob.

c.

250 ml of flask was taken and filled 2/3 rd of it with distilled water and putting stopper shake it for 20 seconds. Removed the stopper and swirl the water back and repeat this procedure 4 times for the same. Magnetic stirrer used. Kept magnetic capsule in the flask and put in on the stirrer and then switch it on.

d.

Kept the function switch to temperature mode and measured the temperature of this sample as

described above after cleaning probe with distilled water then adjusted the temperature knob for the same temperature. The value of DO for distilled water for 25 C temperature was read from table i.e. 8.2 ppm.

e.

Then the function switch was set to the DO mode and inserted cleaned DO electrode in the flask and set reading to 8.2 ppm using calibrate knob.

f.

Then the instrument was ready for measuring DO of water sample.

4.

Testing the

sample:

a.

The probe and electrode were cleaned with tap water and then with distilled water. b.

Water sample was taken in the flask and measured the temperature as described above and set the temperature knob at the measured temperature then taken the instrument in DO mode.

c. Water

sample

was

taken

in

cocked

BOD

bottle

(to

avoid

absorbing

oxygen

from

atmosphere)

then

shaken it well using magnetic stirrer and carefully un cock it and inserted the DO electrode into it. d.

The reading on display gave the DO content in ppm.

e.

The procedure was repeated for other samples of water.

3.6.

OBSERVATIONS: Name and place of sample collection: K.E.C. Kalimati, Kathmandu

Source of water: Boring water and Tap water


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Date and time of Sampling: 2065 02 01 Lab. temperature: 25 C

Sample DO(ppm) Source A 2.6 Boring water B 8.21 Tap water

3.7. RESULT: Hence from the experiment we found that the DO value for Sample A i.e. Boring water is 2.6 ppm

and for Tap water is found to be 8.21 ppm.

3.8.

CONCLUSION &

DISCUSSION:

It is necessary to determine D.O. in natural water and water to be used for water supply. Aquatic life depends upon the dissolved oxygen. It is vital for maintaining aerobic conditions. From the experiment we found that the DO value for boring water is 2.6 mg/l whereas DO value for tap water is 8.21 mg/l, it signifies that the boring water has less amount of oxygen than tap water. For the aquatic life DO value should be 4ppm at least on considering this condition the boring water is unsafe for aquatic and fish life. For the drinking water Do value should be 6 ppm. So the boring water is not suitable for drinking purpose. Tap water has DO value

greater than 6 ppm which is suitable for both aquatic and drinking purpose. 8.21 ppm DO value of tap water signifies that the water is fresh but on considering the corrosion and oxidation effect it is not so good. The pipe should be PVC type instead of metallic for the distribution of tap water sample because it is highly vulnerable to corrosion effect on metallic pipe.

3.9.

PRECAUTIONS: a.

The BOD bottle should be cleaned, sterilized and airtight.

b.

Great care is required in collection of water samples for D.O. analysis special precautions are required to avoid entrainment or dissolution of atmospheric oxygen.

c.

The electrolyte tube shouldnt contain air bubbles otherwise reading fluctuates and if other salts are present in KCl solution, it may damage the electrode.

d. Magnetic

stirrer

shaking

is

efficient

than

hand

shaking

for

diffusion

process

for

distilled

water.

e.

As the reagents used are strong base and strong acid, the handling of these should be very careful. f.

There should be no delay in the determination of D.O. on all samples that contain an appreciable oxygen or iodine demand.


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EXPERIMENT NO: 4 15 th May JAR

TEST

4.1.

OBJECTIVE:

TO DETERMINE THE OPTIMUM DOSE OF COAGULANT (ALUM) FOR A GIVEN WATER SAMPLE.

4.2.

APPARATUS

REQUIRED:

The apparatus for the optimum dose of coagulant (alum) test consists of following: a.

Jar

Test

Apparatus:

An electrically operated jar test apparatus consists of six stirring paddles of non

corrosive metal which can be rotated at any desired speed by gear and spindle system. b.

Six

test

beakers:

Beakers of 1 to 2 liter capacity to keep water sample.

c.

Electronic balance:

For accurate weighing of coagulants.

d.

Measuring cylinder:

To measure water sample.

4.3.

CHEMICAL REQUIRED:

Alum or aluminum sulphate [Al2 (SO4)3.18 H2O]

4.4.

SAMPLE

REQUIRED:

Water sample for which optimum dose of coagulant to be tested should be free from oil grease etc. and taken after plain sedimentation so that suspended materials are removed from plain sedimentation.

4.5.

THEORY: After physical, chemical and biological examination of water, the degree of treatment required

and hence treatment process required is known. Different impurities can be removed by different process as shown in table below.

A D

If water contents suspended impurities, it can be removed by plain sedimentation but very fine suspended particles such as silt


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suspended and colloidal impurities then sedimentation can be done. This process also removes color, odour and test in water. The chemicals added are called coagulants.

Coagulants feeding Mixing Flocculation Sedimentation (In row water) (In mixtures) (In flocculators) (Sedimentation tanks)

It is generally done after plain sedimentation. In this process, the coagulants (chemicals like alum etc.) are added in water by feeding devices then thoroughly mixed with mixing devices and send to flocculators (a slow

stirring mechanism which helps to produce floc) to produce precipitate or floc then send to the sedimentation basin so that the floc may settle down due to force of gravity and it is then removed without disturbance. In fact the sedimentation with coagulation requires the following processes.

Coagulation:

A chemical process that involves the formation of chemicals flocs, which absorb, entrap & bring together the suspended matters.

Sedimentation:

The process to allow the particles settles down. Aluminum hydroxide or alum [Al2 (SO4)3.18 H2O] is insoluble precipitate. Alum is found to be

most effective between pH ranges of 6.5 to 8.5. Its dose depends upon various factors such as turbidity, color, pH, temperature etc. The common test, which is performed to determine optimum quantity of coagulant, is known as jar test and it is the trial and error method.

4.6. PROCEDURE:

Following procedure was done for the jar test: a.

Six beakers with one liter of water sample were taken first.

b.

Then chemical coagulant (alum) was added in each beaker in increasing quantity i.e. 2mg, 4mg, 6 mg, 8 mg, 10 mg, 12 mg.

c.

The beakers was arrange in the apparatus containing stirrer in order. d.

Then mixed the chemicals at the speed of high speed (about 100 rpm) for 2 minutes and reduce the speed 20 rpm for 10 to 15 minutes and stop the rotation.

e.

The allow the floc to settle down for about 20 minutes. f.

Then we visualize the floc formed in each jar and we choose the beaker with minimum turbidity which gives the best floc the clear water. The dose of coagulant on that beaker gives the optimum dose of coagulants.

4.7.

OBSERVATIONS: Name and place of sample collection: Kathmandu Engineering College, Kalimati, Kathmandu Source of water: Boring water inside KEC. Date and time of sampling: 2065 02 01, 12.00 pm Volume of sample taken: One liter in each beaker Optimum dose of alum: Less than 2 mg/l (ppm)

4.8.

RESULT: Hence from the experiment we found that the optimum dose of alum is less than 2 mg/l (ppm).

4.9.

CONCLUSION &

DISCUSSION:

From the jar test we found that the optimum dose of coagulant alum is less than 2 mg/l. while observing the beakers after floc settle we found that no beaker with the particles with zero velocity it shows that the coagulant for each beaker is more than the optimum dose. For the correct dose analysis we should further repeat the process by adding less than 2 mg alum in each beaker and we should visualize the beaker again and when the beaker shows no particle movement and clear water with best floc formation which is the optimum dose of coagulant.


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4.10.

PRECAUTIONS: Following precaution should be taken in mind while doing jar test:

a.

pH value of sample should be known before selection of coagulant. b.

The mixing of coagulant should be proper and through.

c.

The turbidity of coagulated water should be measured accurately for the exact coagulant dose determination.

d.

The speed of paddles must be constant at the speed of 100 rpm up to 2 minutes and then should be reduced to 20 minutes up to next 15 minutes.

e. Visualization should be accurately done so that correct jar with optimum dose can be

obtained.


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Fig. Jar

test

Apparatus

setup

water supply practical all

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