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SECTION C
SHORT ANSWER TYPE QUESTIONS
Explain disposal of sewage by dilution, and conditions favoring disposal by01.dilution.
Disposal by dilution i s the process whereby the treated sewage or the effluent rom_Ans:
the treatment plant is discharged into the river, stream or a l a r ~ e b?dy ~ . w a t e r :such as lake or sea. The discharged sewage in due course of time IS pUrified t:>ywhat is known as self purification process of natural waters. The degree
amount of treatmemt given to raw sewage before disposing it of into the nverstream will depend not only on the quality of raw sewage but also on the self
purification capacity of the river streamand the intended use of its water.
Disposal by dilution can be adopted under following conditions:
When sewage is comparatively fresh (4-5 hr.? old) and free from floating a n d ~1.
settable solids. '
When diluting walerhas high dissolved oxygen content. 2.
When diluting a t ~ s are not used for the purpose of navJg.c:I!lQD or ~ t e r supply for3.
at least some reasonable distance on the downstream from the pOint of sewage
disposal. "
Where the flow currents of the diluting a t e n i c m ~ l g ' y Q [ a J ) J e ~ c 9 . 1 l ~ g . n Q . . d e . p _ o I D t i Q n " ,4.
nuisanceor
destructionof
aquatic life. Swift forward currents are helpful as theyeasily carry away the sewage to the points 0: unlimite? d i ~ u t i o n . On the other
slow back currents tend to cause sedimentation resulting In large sludge depOSits.
When the outfall sewer of the city or the treatment plant is situated near some5.
natural waters having large volumes.
What are the different causesofwater pollution?02.
Ans:Pollution in a body of water is caused by the introduction of objectionable ~ ~ ~ r i a l
, n!9.JL Pollution may be n a t u r ~ I . _ 9 ~ r t i f i c i a l Le. caused man. ma?e a c t l v l t l ~ S .-'Natural pollution is related with adverse wea ther condit ions .I.e. ~ n t e n s e rain,
sudden thaws etc. This may consists of run off from land carrying Silt,. vegeta?le
matter manure etc. washed into a watercour se during a storm orfollowmg r ~ s l o nof rive; banks and valley slopes. Natural pollution being intermittent and restricted
in short reaches of river is of little consequence.
Artificial pollution is mainly caused by' wastes from household: ~ n d u s t r i e s . and
03 .
Ans:
04.
Ans:
agricultural lands. The domestic waste include. human excreta, Urine, w a s ~ m g s , __ :
ki.i9hell and laundry which do not receive treatment d l r e c t ~ y :discharged into water course. Industrial waste comP:lse of ?rganlc and I n ~ r g a ~ l c .
05 .chemical substances in minute or colloidal suspension which underg? microbial
decomposition resulting in products odoriferous or unacceptabl7 In . taste or Ans:
appearance or harmful to human beings. ~ r i c u l t u ~ ~ 1 w a s ~ e s ~ r H J 1 a n I Y ~ u . e to
the barnyard drainage or washing in of chemical fertilizers, ! J s e G t l ( ; : ~ ( : : t e s . \ ~ e s t l c l d e s
What are effects ofwater pollution?
The effects ofwater pollution are as follows
1. It depletes the DO content of the receiving water to a point that the
becomes incapableof exercising self purification process.
2. The de oxygenation may be sufficient to destroy practically all the fi
other aquatic life.
3. 9ause stream insanitation by causing suspended solids to deposit
stream bed causing silting, the organic matter undergoing putrefacti
, the solid matter buoyed up by gas riSing to the top and resulting in f
massesof evil smelling and unSightly sludge.
4. The use of polluted water downstream by communities for the
requirements may cause the outbreak of water borne diseases.
5. The industrial discharges upstream of r i v ~ m ' decreases the utility o
watersf or bathing and recreational purposes.
6. Polluted waters are difficult to be easily treated and the treatment plan
to incur increased cost n handling such waters. ' ,
What are preventive measures for water pollution?
Preventive measures include gublic consciousness, industrial cooperati
'legislative control. Sl:lfficient publicity and efforts are needed to educate the
the necessity of keeping ponds and streams flowing nearby clean and unp
Industrial cooperation include adequate pretreatmentof
all such industrialwhich are of toxic nature before being discharged into municipal sewers
water courses. Industries could be given some form of tax incentive s
encourage them to undertake water pollution control measures. On the oth
industries caus ing pollution could be subjected to pollution tax and
penalties.
"[he legislative control is a necessity to counter effectively all possible violat
pollution control practices. With the enactment of the water (Preventi
control of pollution) Act 1974 most of the states in India have establishe
Pollution Control Boards. This has resulted in setting up of waste water rplants in a number of ndustries in order to bring down the pollution level w
acceptable limits prior to disposal. These limits must conform with
modifications to the tolerance limits prescribed already by Indian Sta
Institution for discharge of effluent into different bodies. Besides Central
boards are formulating comprehensive water resources conservation p
and developing practical standards for waste water discharges into differe
basins based on actual river water quality data.
Explain self purification of streams.
When sewage is discharged into a body of water the receiving water gets
due to the waste products borne by sewage. But the conditions do not re
for ever because ih e natural forces of purification Le. dilution, sedime
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oxidation-reduction, sunlight etc. go on acting upon the polluted elements and
bring back the- water into its original state. This principle of self purification of
polluted waters is utilized in the methods of disposal of sewage by dilution.
06. Briefly explain water pollution legislation.
Ans: Water pollution has become a universal problem essentia lly due to the increase in
population and industrial growth. In India about 70% ofthe surface water pollution
is caused from domestic sewage and the rest from other sources. Voluntary
measures to check pollution o f water are neither sufficient nor strictly followed,
therefore the govt. of India has to specify certain laws to control water pollution.
These specified laws have been formed to be implemented at he state and central
level.
To formulate such laws Indian Parliament in 1974 passed a "Water Pollution A0" under article 252 of the constitution to check water pollution. This act makes
provisions forthe following
1. Constitution of central and state water pollution control boards
2. T ~ r m s and conditions of selection and service of the members of these
boards.
3. Meetingofbo ards, disqualification and vacationof seats by its members .
4. Functions and powers ofthewater pollution control boards.
5. Setting of water testing labs, penalties and prosecution of industrial
units/municipalities found flouting the norms ofthe board.
6. Provision offunds and infrastructure by state and center .
The aforesaid act has since been modified and amended in 1975, 1977and
1978. We have a central and state water pollution control boards almost .in
every state ofthe country.
07. What are the differenttechniques used for control of noise pollution?
Ans: The techniques employed for controlling noise pollution can be broadly classified
as
1. Control at source
a. Reducing the noise levels from domestic sectors
b. Maintenance of automobiles
c. Control over vibrations
d. Low voice speaking
e. Prohibition on usage of oud speakers
f. Selection o f machinery
g. Maintenanceofmachines
2. Control in the transmission path
a. Installation of barriers
b. Design of building
c. Installation of panels or enclosures
d. Green belt development
3. Using protective equipment.
a. Job rotation
b. Exposure reduction
c. Hearing protection '
08. Discuss how the adverse impact of noise pollution on the workers can
minimized?
Ans: The noi!?epollution can be controlled by using protection equipments as
Protective equipment usage is the ultimate step in noise' contrQLte.QhnQJQ.9Y,
after noise reduction at source and/or after the diversion or engineered contr
transmission path of noise. The first step in the technique of using protec
equipment s to gauge the intensitybfthe problem, identification of the sufferer
his exposure to the noise levels. The usage of protective equipment and
worker's exposure to the high noise levels can be minimized by
1. Job rotation: By rotating the job between the workers working at a partic
noise source or isolating a person, the adverse impacts can be reduced.2. Exposure reduction: Regulations prescribe that, noise level of 90 dB (A
more than 8 hr continuous exposure is prohibited. Persons who are wor
under such conditions will be exposed to occupational health hazards.
schedule ofthe workers should be planned in such a way that, they shoul
be over exposed to the high noise levels.
3. liear ing protection: Equipment like earmuffs, ear plugsett. are the comm
. used devices fo r hearing protection. Attenuation provided by ear-muffs
widely in respectto their size, shape, seal material etc.
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SECTION 0
LONG ANSWER TYPE QUESTIONS
1.
2.
atmosphere whenever the D.O. content of the water falls below its saturatio
value. Oxygen is also contributed by other factors including green I a n t s u n ~ e r t hinfluence of l 1 n l i g h t . This supply of oxygen is termed as reaeratlon and Its rat
depends upon.
depth of receiving water (rate is more in shallow depth) .'condition of body of water (rate is more in a running stream than In a qUiesce
01. Explain the processl various actions involved in the self purification of running
streams.
Ans: The various actions involved in the self purification of streams are physical,
chemical and biological and may be explained as dueto
1. Dilution: As the putrescib le organic matter is discharged into the flowing water, it is
rapidly dispersed or diluted in it, the action resulting in. diminishing the potential
nuisance of sewage. This process is further accelerated by the joining in with the
main stream of surface tributaries and under ground streams.
2. Sedimentation: This helps by the separation of the settle able solids in sewageJn
form of sludge deposits .Settle able solids are most stable and easily
separated out.
3. Q]<idation: As soon as the organic mat ter meets the water, it starts getting oxidi zed
owing to the developmentof the oxidizing organisms in water. This process goes
on till the organic matter has been completely oxidized, the oxygen demand is then
fully satisfied and the stream is said to havepl,J!jTIed itself. It is therefore essential'
for the stream to have initially dissolved oxygen in it. Oxygen is also contributed
through the dilution received from tributaries, through aeration by the action of
wind or by the action of microscopicorganisms.
4. Reduction: Reduction occurs due to the hydrolysis of organic matter e i t h ~ r,chemically or biologically. Anaerobic organisms liquefy splitting complex organic
constituents of sewage with the evolution of odors and gases and in this way
paving the way for stabilization by oxidization .
5. . Sunlight: Sunlight is effective in the sel f purification t h r o u g h J ~ ~ s t a b i l i z i n g and
bleaching effects on bacteria and through the biological action of certain:-
microorganisms deriving the energy from the sun, converting themselves into food
for other forms of ife, absorbing carbon dioxide and giving off oxygen- a process
known as photosynthesis
02 . Discuss oxygen sag curve.
Ans: As the sewage is discharged into a body of water there is at first a depletion f l h ~ e D.O. content ofthe diluting water n order to meetthe biological requirement (BOD)
of the organic sewage. This is termed as deoxygenation and closely follows the'progress of BOD of polluted water. For the reason it is also sometimes referred as
BOD reaction. The rate of deoxygenation action depends on
1. Volume and BOD of sewage
2. Time available for decomposition and
3. Temperature ofthe diluting water
Due to deoxygenation, the D.O. of water would have been rapidly consumed up,'
but for the fact that oxygen is also absorbed at the water surface from the
11 BC2.5
pond) ' .
saturation deficit or the deficit of DO below the saturation a l u ~ . 3.Both deoxygenation and reaeration are occurring simultaneously in any. pollute
stream exposed to the air. Their rates can b.e formulated into expressions a
curves obtained there from. In order to determine the amount of DO present at ainstant the two can be combined together to give the DO or the oxygen curve,
10010-,-MAX. {)fFICITCll/TICAl POINT
I
TlNlE'.J DAYS
Curves of De oxygenation Re aeration and Oxygen sag
Two distinct points of the oxygen sag curve are
1. The critical point or the point of east oxygen content, when the oxygen d
shall be maximum
2. The point of nflexion, when the rate of recovery is maximum.
What are the different zonesof pollution in a river stream?03 .
A polluted stream undergoing self purification has the following four distinct zAns\
efpollution1 Zone of degradation: This usually occurs below the outfall, sewer
. . discharging its contents into the stream. The zone is characterized by
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becoming dark and turbid with the formation of sludge deposits at the bottom.
D.O. g e t ~ reduced to 40%. There is an increase in the carbon dioxide content,
reaeration occurs but is slower than deoxygenation. C'onditions are favorable
t ~ t h e development of aquatic life, fungi a t higher points and bacteria at 10weT
points, breed small worms which work over and stabilize the sewage sludge:
2. Zone of active decomposition: This is marked by heavy pollution. It is
characterized by the absence of DO, water is greyish and darker with active
anaerobic organic decomposition accompanying and with the evolution of
methane, hydrogen sulphide, carbon dioxide and nitrogen bubbling to .the
surface with masses of sludge forming black scum. Fish life, s practically
absent, fungi and bacteria disappear. As the organic decomposition slackens,reaeration sets in and DO again rises to its original level.
3. Zone of recovery: In this zone the stream tries to recover its former
appearance. Most of the organic matter has been settled as sludge, BOD falls
and the DO content rises above 40%. Microscopic aquatic life reappears,
water becomes clearer, fungi decreases and algae reappear. Mineralization is
active and the products such as nitrates, sulphates and carbonates are
. ormed.
4. Clear water zone: In this the natural stream condition is restored, the DO is
higherthan the BOD. Oxygen balance (DO minus total BOD in the first stage)
is attained and recovery is said to be complete. Water b,ecomes attractive in
appearance. Some pathogenic organisms may however be present.
04 . What are the different factors affecting self purification?
Ans: The following conditions affect the self purification of streams
1. Dilution: When the sewage is mixed with a large volume of water the sewage
always remain in aerobic conditions and DO always remain present in the
water.
2. Current: When there is no current the sewage matter deposits ne(;lr outfall
causing formation of sludge bank and foul odors. In heavy currents the
sewage is thoroughly mixed up with the stream waterpreventing all nuisance.
3. Sedimentation: With slow current the heavier solids settle in the stream bed
and start anaerobic decomposition. The products of decomposition are again
mixed with water by the current. If the dilution is sufficient the anaerobic
condition will not develop and the scouring tendency of streams during floodwill wash the deposits.
4. Temperature: At low temperature organisms activities are slow due to whjch
rate of decomposition is slow and in warm temperature action is reverse.
Therefore in summer the streams will get self purified in less time than in
winter. Butth e quantity of DO is more in cold water than in hot water.
5. Sunlight: The pathogens are killed if they are exposed to sunlight, therefQ[e
sunlight helps in self purification. Algae also grows in sunlight caw:?1ng
production of oxygen.
. 'd' d due t'd t'on' After mixing with water organic matter starts getting OXI Ize
6. OXI a I . . t' the water This prodevelopment of the oxidizing organisms p r e ~ e n In . Em dema
p r e ~ a . i l s till the c o m p t ~ e t e b o y x ~ i ~ ~ O ~ r ~ f y t ~ h e e % T : r : ~ c ~ ~ ~ ~ ~ g : ~ s ~ ~ ~ n d the stsatisfied by the aera Ion
becomes purified. .. .' ccurs due to hydrolysis of the organlGr
7. ~ i ~ ~ ~ ~ i ~ ~ ~ ~ ~ ~ ~ u h ~ ~ ~ C ~ ~ I : . t ~ ~ : ~ o h O b i C o ? a n p i ~ ~ ; u ~ : ~ r t g : : ~ n ; n ~ o : : ~ ~ ~ ~matter present in the sewage, t e ac Ion
stabilization starts.
Whatdo you understand by noise pollution, give the different sources of 05 .
pollution? . . d b 'b
Ans: Noise is unwanted o u n d . s ~ ~ ; ~ ~ ~ : ~ ~ r ~ : f s ~ ~ : ~ r o ~ h ~ ~ ~ : a ~ ~ : ~ h r o ~ ; h v ~body and on reaching . b d' re not audible. The frequency liSounds produced by all Vibrating 0 les a '
audibility are from 20 HZ to 20,000 HZ. "
Anoise problem generally o ~ s i s t s o : ~ r ~ ~ : : t ~ ~ : ~ ~ ~ ~ : s ~ ~ ~ m ; : : ~ - ~ ~ ~ ~receiver and the t r a n ~ m l s s l o n pad" g'ated but can include the statmosphere through which the. s?un IS p r o ~ a ,
materials of any building contalnmg thereceiver..
Noise may be continuous or intermittent. Noise ,may be of high r e q U e n c ~ ; ;f r e q ~ e n c y which is u n ~ e : ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ I n ~ : ~ : ; a g b l : ~ ~ ~ ~ ~ ~ ~ I ~ ~ J ; = ~ n ~ ~ S ia child produces soun , . ' , The discrirnination and differentiation bunwanted sou.nd, we call It n ~ l s e . the habi; and interest of the person/sound and nOIse als? depen upon . t of the sound generated du
receiving it, the ~ m b l e n , t conditions a n d l ~ m : e a ~ n s t a n c e s that, excellently r
particular duration of time. There cou It as noise and exceptional musiy f
, musical concert for example, mia be de ffrequencies less than 20 HZ aduring the course o f the concert. s ounso .
infrasonics and greater than 20,0000 HZ are called ultrasonics.
Sources of noise pollution
1. Road Traffic
2. Use of oudspeakers
3. Bursting of crackers
4. Industrial activities5, Railways
6. Aircrafts
.",-, 7. Radio and Television
, !Discuss the effects of noise pollution on human beings and living, organis
06.Noise induces a severe impact on humans and on living organisms. S
Ans: adverse effects are:
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1. A n n o y ~ n c e : It creates annoyance to the receptors due to sound level
f I ~ c t u a t l o n s . The aperiodic sound due to its irregular occurrences causesdlspreasure to hearing and causes annoyance.
2. Physiological effects: The physiological features like breathing amplitude,
blood pressure, heart-beat rate, pulse rate, blood cholesterol are effected.
3. l o ~ ~ of hearing: L?ng exposure to high sound levels cause loss of hearing.
ThiS IS mostly unnoticed, but has an adverse impact on hearing function.
4. Human performance: The working performance of workers/human will be
affected as they will be losing their concentration.
5. Nervous system: It causes pain, ringing in the ears, feeling of tiredness,
thereby effecting the functioning of human system. .
6. Sleeplessness: It affects the sleeping there by inducing the people to .
become restless and loose concentration and presence of mind during their activities-
7. Damage to material: The buildings and materials may get damaged by
exposure to infrasonic/ultrasonic waves and even get collapsed.
Q7. Discuss control of noise pollution at source.
Ans: The noise pollution can be controlled at the source. of generation itself byemploying techniques like .
1. Reducing the noise levels from domestic sectors: The domestic noise
coming from radio, tape recorders, television sets, mixers, washing mach ines,
c o o k i n ~ operations can be minimiLed by their selective and judicious
operation. By usage of carpets or any absorbing material, the noise generatedfrom fellin'g of items in house can be minimized.
2. Maintenance of automobiles: Regular servicing and tuning of vehicles will
reduce the noise levels. Fixing of silencers to automobiles, two wheelers etc.,will reduce the noise levels.
3. Control over vibrations: The vibrations of materials may be controlled using
proper foundations, rubber padding etc. to reduce the noise levels caused byvibrations. .
4. lo w voice speaking: Speaking at low voices enough for communicationreduces the excess noise levels.
5. Prohibition on usage of loud·speakers: By not permitting the usage ofloudspeakers in the habitant zones except for mportant meetings / u n c t i o n ~ .
6. Selection of machinery: Optimum selection of machinery tools or equipment
reduces excess noise levels. For example selection of chairs, or selection of
certain machinery/equipment which generate less noise (Sound) due to its
superior technology etc. is also an important factor in noise minimizationstrategy.
7. Maintenance of machines: Proper lubrication and maintenance of
machines, vehicles etc. will reduce noise levels. For example, it is a common
experience that, many parts of a vehicle will become loose wh ile on a rugg
path of ourney. If these loose parts are not properly fitted, they will genera
noise and cause annoyance to the driver/passenger. Similarly is the case
machines. Proper handling and regular maintenance is essential not only
noise control but also to improve the life of machine.
Q8. Discuss control of noise pollution during transmission.
Ans: The noise pollution can be controlled during transmission by employ
techniques like
1. Installation of barriers: Installation of barriers between n o i s ~ .. _ ~ < > ' L l r Q . ereceiver can attenuate the noise levels. For a barrier to be effective, its latewidth should extend beyond the line-of-sight at least as much as the heig
The barrier may be either close to the source or receiver, to increase
traverse length for the sound wave. It should also be noted that, the prese
of the barrier itself can reflect sound back towards the source. At very la
distances, the barrier becomes less effective because of the possibilit
refractive atmospheric effects.
2. Design of building: The design of the building incorporating the use
suitable noise absorbing material for wall/door/window/ceiling will reduce
noise levels.
3. Installation of panels or enclosures: A sound source may be enclo
within a paneled structure such as room as a means of reducing the no
levels' at the receiver. The actual difference between the sound presslevels inside and outside an enclosure depends not only on the transmiss
loss of the enclosure panels but also on the acoustic absorption within
enclosure and the details of the panel penetrations which may incl
windows or doors.
4. Green belt development: Green belt development can attenuate the so
levels. The degree of attenuation varies with species of greenbelt.
statutory regulations direct the industry to develop greenbelt four times
built-up area for attenuation of various atmospheric pollutants, inclu
noise.
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SECTION E UNIT - 2 : AIR POLLUTION AND CONTROL
OVER VIEW QUESTIONS SECTION A
1. Define water pollution. MULTIPLE CHOICE QUESTIONS
1. Green house effect is causedby excess of2. Give the significance of BOD in waste water.
a. CO2
3. Name he process by which rivers and streamsget purified naturally. b. H2
c. He4. Name the various actions/ processes involved in self purification of streams.
d. O2
5. Give the importance of oxygen sag curve.
2. Damage to leaf structure by air pollutants causes6. What s the significanceof two distinct points on oxygen sag curve? a. Dead areas of eaf
b.. Chlorophyll reduction7. Name different zones of pollution in river stream.
c. dropping of leaf
8. How does thewater current n rivers affect the self purification process? d. All the above
9. What are the effects of water pollution? 3. Which of the following gas causes ai r pollution
a. nitrogen.10. In whatway will you dispose of the sewage of your town?
b. hydrogen
11. Define noise pollution. c. water vapors
d. carbon monoxide12. Name some sources of noise pollution.
4. Which of the following is not a green house gas
a. CO 2
b. CH4
c. CFC
d. Hz
5. Depletion of ozone layer n 'the outer atmosphere is likely to increase the incideof
a. skin cancer
b. lung cancer
c. bronchitis
d. noneofthem
6. The most significant gaseous pollutant is
a. CO2
b. O2
- C. N2
d. 802
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SECTION C
SHORT ANSWER TYPE QUESTIONS
01. Classify different ypes of air pollutants.
Ans: Air pollutants may be classified as
1. According to origin:
((:)) ~ ~ ~ ~ Z s ~ ~ ~ : n n : o ~ : : , i ~ ~ r ~ ~ e e ~ I ~ ~ ~ : i ~ : , ~ ~ ~ ~ ~ ~ ~ ~ o ~ ~ e a : : ~ ~ ~ ~ ~ ~ ~ ; ~ ~ n a s r eecondary pollutants- Which are derived from th . .
chemical or photochemical reactions in the t m o s p ~ ~ ; ~ : ~ : 6 z ~ ~ U ; ~ ~ ~ N d ~ t ~ . t o2. According to chemical composition:
(a) Organic pollutants ego Hydrocarbons aldehydes, ketonesalcohols ' , amines and
(b) Inorganic pollutants as carbon monoxide carbonates ' .~ ~ ~ ~ ~ ~ , ; : : ~ ; ~ n sU:hide, sulphur dio;ide, s U l p h u r l ~ ~ ~ i ~ ~ ~ : ; r ~ , : g ~ ~ :asbestos dust. uon es, ozone, Inorgamc particles such as fly ash, silica....!
3. According to state of matter:
(a) Gaseous pollutants which get mixed with the airand do n t '1'1·CO, NOx, sulphur dioxide. 0 norma y settle out
(b) ~ ~ : ~ c ~ ~ ~ ! ~ i ~ ~ ~ ~ ~ ~ ~ ~ = : ; ~ : ~ ~ : ~ ~ ~ 7 s ~ ~ f i ~ : ~ i v i : e d s O ~ d s o r I.iquidssmog and sprays . e, umes, ust, mist, fog and
02 . What is meant by smog? Discuss its causes and effects
Ans: Smog is a synchronym of two words smoke ' df ' ,photochemical or coal i og. Smog can be of two types-
motorized area in m e t r o ; o ~ ~ ~ ~ ~ i t : : o ~ o c ~ e m l c a l smog is restricted to highly
m e t ~ o r o l o g . i c a l conditions when the air ~ v e ~ e ~ ~ T s e : : : t r : ~ t ~ ~ C ~ s un?er adverse~ ~ i ~ ~ ~ ; ; : : ~ n ~ ~ : : ~ : : ~ ~ : : : b ~ : t ~ ~ ~ X i d a n t s under the i n f l ~ ~ ; ~ : ~ : ~ ~ ~ ~ g % 'nitrogen oxides PAN hyd Y I.rate (PAN). Its main constit uents are
~ r r i t a t i o n , d a m a ~ e to ~ g e ~ ~ ~ ~ r a ~ ~ ~ ; : ; k ~ n ~ Z ~ f ~ ~ b ~ ~ ~ d U c e svisibility, causes eye
ih e fog t'rrom .burning of coal covers urban areas at night or on cold days wh
empera ure IS below 10 degree centigrade d h enconditions prevail ego London (December 1 9 5 ~ ~ efn calm ~ e t e o r o l o g i c a lsulphur compounds and fly ash. . IS og consists of smoke,
~ ; Z ~ ~ ; ~ ~ : ~ ~ ~ ~ ~ ~ : ~ h ~ n ; , ~ ~ : ~ ~ t ~ ~ ~ ~ t ~ ; c ~ i ~ ~ i ~ ~ : ~ ~ i ~ : ~ e a : : ~ : ~ i : " ~ a m ~ n gpneumoma and other ung and heart disease. ' ronc 0-
BC2 5
Write short note on aerosols.03.
Aerosols refer to the dispersion of solid or liquid particles of microscopic size iAns:
gaseous media such as dust, smoke or mist.
An aerosol can be defined as a colloidal system in which the dispersion medium i
a gas and the dispersed phase is solid or liquid. This term aerosol is used durin
the time it is suspended in the air. After it has settled. either by virtue of its weight, b
agglomeration, or by mpact on a solid or liquid surface, the term no onger applie
Thus particulate matter s an air pollutant only when it s n aerosol. However, it s
nuisance both as an aerosol (visibility reduction) and as settled or deposite
matter (soiling of surfaces, corrosions). Aerosols differ widely in terms of partic
size, particle density and their importance as pollutants.Their diameters genera
range from 0.01 microns or less upto about 100 microns. The following are vario
aerosols dust, smoke, mist, fog, fumes etc. .
Discuss dustas an aerosol.04.Dust s made up of solid particles predominantly larger than those found in collo
Ans: and capable of temporary suspension in air or other gases. They do not tend
flocculate except under electrostatic forces, they do not diffuse but settle under
lnflu·ence of gravity. Dust is produced by the crushing, grinding etc. of organiC
inorganic materials. Generally they are over 20 microns in diameter althou
some are smaller. Fly ash from chimney varies from 80- 3 microns cement fr
150-1Omicrons, foundry dust from 200-1" microns. Most of the dust particles se
to the ground as dust fall, but particles 5 microns or smaller tend to form sta
suspensions. Sources of atmospheric dust are combustion, material handling
processing, earth moving operations such as mining, construction etc.
05. List the sources of atmospheric dust.
Ans: The sources of atmospheric dust are
1. Combustion-
a. Fuel burning
b. Incineration (house and municipal garbage)
c. Others ( open fires, forest fires, tobacco smoking)
2. Material handling and processing-
a. Loading and unloading (sand, gravel, coal, ores, lime cement)
b. Crushing and grinding (ores, stones, cement, rocks, chemicals)
c. Mixing and packaging (chemicals, fertilizers)
d. Food processing (flour, corn starch, grains)
e. Cutting and forming (saW mills, wall boards, plastics)
1. Metallurgical operations (foundries, smelters)
g. Industrial operations (paper, textile, manufacture)
24
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3.
4.
Q6.
Ans:
a.
b.
c.
d.
e.
f.
Q7.
Ans:
.
Earth moving-
a. C ~ ~ s t r u c t i o n (road, buildings, dams, site operations, clearance)b. Mmmg ( blasting)
c. Agriculture (soi lfilling,land preparation)
d. Winds
Miscellaneous-
a. House cleaning
b. Mud road cleaning
c. Crop spraying
d. Poultry feeding
e. Engine exhaust
Identify the various pollution so f th dioxide, sulphide, h Y d r O g e n f l u u ~ ~ : s 0 following c o n t ~ m i n a n t s sulphur hydrocarbons. e, car on monoxide, oXides of nitrogen,.
Sulphur dioxide- Combustion of fuel es .. . metallurgical operations such as smelting teclallY coal, petroleum industry,
plants, and paper manufacturing industries.o
ores, power houses, sulphuric acid
Sui h'd . . . . . P .1 e- Natural emiSSions mclude anaerobic biological d
land, m marshes and oceans, vOlcanoes ecay p r ~ c e s s e s .c>n.hydrogen sulphide. Kraft pulp industry, p e t r o l : ~ ~ ~ ~ ~ r ~ . ' , w ~ t e r . spnngs e m ~ t splants, viscose rayon plants and some ch . I . I re menes, coke oventanning industry. emlca operations, dyes manufacture,
H p l ~ ~ ~ ~ g e p n o f l t t U e O r y r i d & e - f M a n u f a c t u r e of phosphate fertilizers, aluminium industry brick , erro enamel works . d . ,
fumaces, glass,fi bre manufacture. ' zmc oun nes and open hearth steel·
Carbon monoxide- Combustion especiall d . operations such as electric and blast f y ue to automobile :xhaust, industrial
engine emission gas manufacturing l a ~ ~ a ~ ~ : i mP:troleum refimng operations, je to . ' mes., .
l a : ~ ~ e ~ o ~ ; i ~ f a g n ~ : ~ I ~ ~ u : ~ : ~ ~ ; ~ ~ ~ : ~ ~ r ~ g nitric acid, a ~ t o ~ o b i l e exhausts,
industry. . maces, explos ive Industry fertilizer
~ ~ ~ ~ ~ ~ : ~ ~ ~ s b e ~ ~ ~ ~ ~ ~ a ~ ~ ~ : i c a l industries, petroleum refineries, automobile
Explain the mechanism of action of ak pollutants on human beings '
~ : : v e f f e c ~ ~ f air pollution on human health generally occur as a result of contact
SUrfa:: ~ ~ " u t a ~ t s and the body. Normally bodily contact OCcurs at thee s m and exposed membranes. Contact with
membraneous surfaces is of utmost importance because o f t h ~ i r hig·h b e x p o ~ e d
capacity compared to that of the skin. Air bome gases, vapours, fumes, mist
dust may cause irritation of the membranes of the eyes, nose, throat, lar
tracheo-bronchial tree and lungs. Some irritants even reach the mucosa .o
digestive tract.
Q8. What are harmful effects of polluted air on human beings?
Ans: Polluted a ir C8uses
1. Eye irritation
2. Nose and throat irritation
3. Irritationofthe respiratory tract
4. Gases like hydrogen sulphide, ammonia and mercaptants cause o
nuisance even at ow concentrations.
5. Increase in mortality rate and morbidity rate
·6. A variety of particulates particularly pollens, initiate asthamatic attacks
7. Chronic pulmonary diseases like bronchitis and asthama are aggravated
high concentration of sulphur dioxide, nitrogen dioxide, particulate matte
photochemical smog .
8. CO combines with the haemoglobin in the blood and consequently incre
stress on those suffering from cardio vascular and pulmonaryd i s easI .
9. HF causes diseases ofthe bone (fluorosis) and mottling ofteeth.
10. Carcinogenic agents cause cancer11. Dust particles cause respiratory diseases. Diseases like silicosis, asbes
etc. results from specific dust.
12. Certain heavy metals like lead may enter the body through lungs and c
poisoning.
Q9. What are the harmful effects of sulphur dioxide and carbon monoxide on h
beings?
Ans: 1. Sulphur dioxide- Sulphur dioxide is an irritant gas which affects the mu
membranes when inhaled. Under certain conditions some of he air bom
gas is oxidized to S03' Each of these two gases in the presence of
vapour or water forms sulphurous and sulphuric acid respectively. S0
very strong irritant, much stronger than S02' causing severe bronchosp
at relatively low levels ofconcentrations.
2. Carbon monoxide- CO has a strong affinity forcombing with the haemo
of the blood to form carboxy haemoglobin COHb. This reduces the ab
haemoglobin t o carry oxygen to the body tissues. CO has about two hu
times the affinity of oxygen for attaching itself to the haemoglobin so th
levelsof CO can still results in high levelsof COHb. CO also affects the c
nervous system. It is also responsible for heart attacks and a high mo
rate.
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010. W ~ a t are the harmful effects of h drocarbeings? • Y bon vapours and insecticides on human
Ans:Hydrocarbon vapours- Some of the h dh e a l t ~ implications. The effect of o r ~ a ~ ~ ~ ~ r b o n . v a p ~ u r s . in a ~ m o s p ~ e r e havecontributor to eye and respiratory irrit r yde IS primarily Irrltatmg. It .IS a major
Insecticides-. nsecticides are t a, Ion causeg by Photochem. carsmog.no on y harmful for' t
man e,g. DDT ( Dichloro Diphenyl Trichloroeth Insec s but also poisonous fornervous system and may attack other v't I ane ). They can affect the centralaffects domestic livestock The a I' a. organs. In fact Indoor spraying of DDT
to their growing use for ~ r i c u l t u ~ ~ u p m u atJon of pesticides in the environmentabort' d urposes can also caus r. Ion, ueto high concentration ofpesti'd . e premature labour &
. CI es In the bodyofexpectant mothers.Q11.Write short notes on radiation hazards?
Ans: The important radioactive isotopes that ma . . . P h o ~ P h o r u s 32, cobalt 60, strontium 90 / d ~ e a c h ambient air are iodine 131, calCium 45 and uranium The ma' ' alum 226, carbon 14, sulphur 35
. . sources of radioactive pollutants are '. ,a N I uc ear reactors
b. Experimental accelerators
c. S C i ~ n t i f i c and medical use of radioactive isotopes .
d. A g r r ~ u l t u r a l and industrial use ()f radioactive isotopes as tracers
e. Test.,ng of nUclear bombs in the atmosphere
!h e serious health effects are anaemia leukaem' .
I s o t o p e ~ also cause genetic defects and ~ t e r i l i t la aocl. cancer. Radioactivecongenltalrnalformations. It also shortens th I'f y, as well e ~ ? r y o defects and
e I e span of an IndiVidual.012.
List the air pollutants affecting plants and vegetation.Ans:
The pollutants which affect the plants and vegetation are1. Sulphur dioxide
2. Fluoride compounds (HF)
3. Ozone
4. Chlorine
5. Hydrogen chloride
6. Nitrogen oxides (N9, N0 etc)2
7. Ammonia8. Hydrogen sulphide
9. Hydrogen cyanide
10. Mercury
11.' Ethylene
12. PAN
Herbicides ( spray of Weed killers)14. Smog .
,
Q13. Explain necrosis, chlorosis, abscission, epinasty with respect to leaf damage
to air pollution.
Ans: Necrosis-Necrosis is the killing or collapse of tissues ofthe eavelj>.
Chlorosis-Is the loss or reduction of the green plant pigment chlorophyll. The
of chlorophyll usually results in a pale green or yellow patterns. Chlorosis gen
indicates a deficiency of some nutrient required by the plants.
Abscission- Leaf abscission is the dropping of leaves from the tree.
Epinasty- Leaf epinasty is a downward curvature of the leaf due to higher r
growth on the upper surface ofthe leaves.
Q14. Explain the various kinds of injury to plants due to air pollutants.
Ans: Kinds of njury to plants due to air pollutants can be classified as
1: 'Acute injury- It results from short time exposure to relatively
concentrations, such as might occur under fumigation conditions. The e
are noted with in a few hours to a few days and may result in visible mar
E . ~ t h e leaves due to a collapse and death of cells. This leads to ne
patterns Le. areas of dead tissues.
2. Chronic injury-I t results from long term low level exposure and usually ca
chlorosis or eaf abscission.
3. Growth or yield retardation- The injury is in the form of an effect on g
without visible markings (invisible injury).Usually a suppression of grow
yield occurs.
Q15. Explain the effects of sulphur dioxide, ozone, hydrogen fluoride, PAN, Eth
and nitrogen dioxide in air pollutants on plants.
Ans: 1. Sulpt1Ur dioxide- Mild effects are interveinal chlorotic bleaching of l
and severe effects are necrosis in interveinal areas and skeletonized lea
2. Ozone- Mild effects are flecks on upper surfaces, premature aging
suppressed growth. Severe effects are collapse of leaf, necrosis
bleaching of eaf.
3. Hydrogen fluoride- HF has a cumulative effects and causes necrosis
leaf tip.
4. PAN- Pan has a mild effect on leaves. Young leaves are more suscept
causes bronzing of lower leaf surface ( upper surface normal ), s u p p r egrowth.
5. Ethylene-Ethylene has mild effect causes epinasty and leaf abscission
6. Nitrogen dioxide- N0 2 has mild effect and it causes suppressed grow
. leafbleaching.
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Q16.List out various methods of sampling.
SECTION 0ns: T ~ ~ J ? ? r : t i c . u l C ! t E : l ' ! 1 a t ! e f in the air may be sa . . ~ r n o r e ofthe following principles." m p l ~ ~ uSing equipment based on one or
1. SedimentC!tlo.n. ~ " ' ~ ' LONG ANSWER TYPE QUESTIONS
~ _ F i l t r ~ t ; o n 01. What are the objectives of using control equipments? List the various typ~ Impingement method collection equipments for particulates.
4. ~ E i e c t r ~ ~ t i ~ p ; ; ; i p i ; t ; r - \.
Ans: Objectives of using control equipments are.
5. T h ~ ~ , ! , a l precipitat;;-- 1. Prevention of nuisance
6. C e n t r i f u - 9 ~ 1 - ~ ; t h ~ ~ 2. Prevention of physical damage to property
7.s O l u i i ~ ~ i ~ p i ~ g e - ~ ' ~ -
3. Elimination of health hazards to plant, personnel and to the general popu4. Recovery of valuable waste products
5. Minimization of economic osses through the reduction of plant maintena
6. Improvement of product quality
Types of collection equipments forthe particulates are .
1. Settling chambers
2. Inertial separators
3. Cyclones
4. Filters
5. Electrostatic precipitators
6. Scrubbers or wet collectors
02. Explain with neat sketch the principle, construction and working of a se
chamber. How can its efficiency be improved?
. Ans: The settling chamber is the simplest type of equipment used for the collect
solid particles. It consists of a chamber n which the carrier gas velocity is redso as to allow the particulates to settle out of the moving stream under the ac
gravity. The most common form is a long box like structure with an inlet at on
and an outlet at the other, set horizontally, often on the ground. It ca
constructed from brick and concrete. The carrier gas is made to pass at th
velocities. solid particulates h a v i n g ~ i g h e r density the s u r r o u n d i nsettle under the influence of gravity on the base of the chamber from wher
are removed through hoppers
- r ~ - - - - ~ 1\- - . . . . . . - ' 7 \ ~ ~AS. , . . - _GAS¥---......
Settling' Chamber
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The gas velocity should be less than about 3m/sec to prevent re entrainment of he Types of inertial orimpact ~ p > ~ ! ~ t o , ( S , . e of mingement separator. The ga
settled particles and less than ,O.5m/sec for good results. Installation costs are low 1. Baffle separators- T h l ~ I S s l m ~ ' e s ~ ~ ~ WhiC:iS obtained by the insertionbecause ofthe simple structure.The efficiency can be improved by decreasing the stream is made follow a to u . o ~ : e 0: s t r e ~ m , As a result the gas is subjected height to be traveled by the particles and sometimes by incorporating horizontal staggered plates mto the path of f d,g f on with the resulting impaction of th
. rays or shelves in the chambers. a series of s u ~ d ~ n C h a n g e s s , ~ b l ~ r 7 0 ~ ~ e ~ o V i n g particles larger than 20microparticles on solid surfaces. UI a
03. What are the advantages and disadvantages.of the settling chambers? Give 'its in diameter, applications.
Ans: Advantages of settling chambers:
1. Low initial cost
2. Simple construction
3. Low maintenance cost
4. Low pressure drop
5, Dry and continuous disposal of solid particulates
6. Can be constructed of almost any material
7. Temperature and pressure limitations imposed only by materials o f
construction used.
Disadvantages
principle separators? types
separators.
Ans: Inertial separators type of control equipment include all collectors which utilize therelatively greater inertia of the dispersoid to effect the particulate-gas s e p a r a t i o n ~Two types of equipments utilize this fundamental principle. They are inertial or
impact separators nnd cyclonic separators.
Inertial or impact separators- They employ incremental changes of direction of
the carrier gas stream to exert the greater inertial effects of the dispersoid.
Cyclonic s,eparators- They produce a continuous centrifugal force as a means of
~ x e r t i n g the greater nertial effects of he dispersoid, OUST (lf1CUI T
1. Large space requirements (c )
2. Only comparatively large particles ( definitely not less than 10 microns, if very Cd)
dense and 40 microns if of ow density) can be controlled
Applications: Industrial application ofthis equipment is limited. Settling chambers used widely for the removal of large solid particulates from natural draft furnaces,
kilns etc. They are also sometimes used in the process industries, particularly the . ,.' f i vers or mpingement elementsfood and metallurgical industries, as a first step in dust control
2. Louvre type e p a r ~ t o r - I n this a senes t o O ~ a u s e a rapid reversal of the gaBecause of simplicity of construction and low maintenance costs, gravity settling an angle to the carner gas stream so I tes to impinge on the louverschambers have found quite widespread applications as pre cleaners for high d i r ~ f J i . o n and thereby cause the pa the moving gas stream in thefficiency collectors. This reduces the inlet dust loadings to the second stage ' particles thus impinged rebound b a ~ ~ r by a secondary air circuit. Suitacleaner and can remove large highly abrasive materials thus reducing h ochamber and are removed from t e, co ec. , maintenance costs of high efficiency equipments. wnich is more subject to removing particles argerthi::'lO 30mlcrons m diameter. abrasive deterioration. . . .
CLEANED AIR04. What is the of inertial Mention the of inertial
t
- \
._._ ) __ 'I R '
L ~ ~ ' - - - - - - - - - - - - - - - - - - - - - - - - - - ~ - - 1)32
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06.
Ans:
the degree of impaction which occurs. Efficiency is a function of four variables,
number, length spacing and configuration of the baffles. It is widely used forparticulate removal in power plants and rotary kilns.
Louvre type- The advantages of louver type of dust collector are simple and low
cost of construction as well as moderate low pressure drop for the degree of
removal obtained. The disadvantages are clogging of the louver grid with a _
corresponding reduction in efficiency and excessiv e abrasion of 1 0 u v e r ~ L e m e . r l l § .Explain the principle, construction and worki ng ota cyclone separator.
Cyclone separators depend on centrifugal force for its action. A cyclone separ ator
can be defined as a structure with out moving parts in which the velocity of an inlet
gas stream is transformed int o a confined vortex from which centrifugal forces tend
to drive the suspended particles to the wall of the cyclone body. It consists of a
vertically placed cylinder which has an inverted cone attached to its base. The
particulate laden gas stream enters tangentially at the inlet point into the cylinder.
The outlet pipe for the purified gas is a central cylindrical opening at the top. The.
dust particulates are collected at the bottom in a storage hopper. The gas path
33
Q7.
Ans:
.
in gas i s c o ~ i t y or density, cyclone diameter, gas ou
inlet area.
3. Dust trap- In this device dust laden gas is introduced into a central pipe (
cylindrical or tapered) and is made to undergo a change in direction by 180
degree. Dust because of nertia settles in the conical chamber. This i s useful whendust oading is high and quantity of gas to be handled is low.
~ " ' ' ' l"... 'ft.......... _-"" "- .............'"
OUST
Q5.Mention the advantages and disadvantages of baffle type and louver typeseparators.
Ans:
Baffle type separators-It is simpleto
operate. It has no moving parts. It is slightlymore expensive to construct than a simple open settling chamber because of the--. . '-
interior work involved in fabricating and installing the baffles. But oWing,to high. -----.
impaction velocity, abrasion is often severe. The efficiency is totally depen dent on
g e ~ e r a l l y follows 'a ~ ~ ~ ~ ~ : , v o ~ ~ ~ ~ : ~ ~ ~ ! ~ : ; : ~ h s : a i ~ ~ I ~ ~ : : : ~ ~ ~ : ~ ~ ~ ~ n openphery ~ ~ : o ~ . The str:am then moves upwards in a narrower i.nner. p: ~ : ~ r : c with the first and leaves through the o.uffet pipe. Due tohraPld I ~ p ~ r a, t of the gas the dispersoids are projected towards t e wa y~ e ~ ~ ~ ~ e ~ , force and then they drop by ·gravity to the bottom of bOdy,.wh
they ar2 collected In the storage hopper. During cyclonic sepa;atlon, c a r T I e ~r o t a t i o n ~ ' velocity may exceed several times the average Inlet gas ve O
Be:" Oe/i.
DenH c : ~ Del?
I.e =HI :Sc- 0c/6lc · ZOe
Jc =arbitl'Ql'y. USUo.Uy
•
Zc;
OUST OIJTl£T
Cyclone separator
"'t d ending on the diame~ : n ~ : ~ ~ ~ ~ ~ o ~ ~ c ~ : ~ : ~ ~ e 5 g ~ ~ : ~ ~ ~ ~ I : e ~ g ~ ~ ~ ~ P : ~ i . c l e s with diameter o
microns and is about 95% for diameters higher han 20mlcrons.
Enumerate the factors on which the c o l l e c ~ i o n e ~ c i e ~ c y of a cyclone depe
Give the merits and demerits of cyclone and Its apPhcatlons.. .
Increase in collection effici ency will result with an i n c ~ e a . s e In any of follow
dustparticle size, dust particle density, gas nlet velOCity, .lnlet dust oadmg, t ? ~f volutions) and ratio of body diameter to gas ou e
. ~ d ~ ~ ~ ; ? ~ ~ ~ ~ ~ ~ o ~ ~ r ~ ~ collector efficiencywill e ~ e t " ~ ~ ~ ~ : ; e i ~ ~ e ~ n ~ ~ %e . ,
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Merits of cyclone separator
,1. Low initial cost
2. Simple construction and operation
3. Low pressure drop
4. Low maintenance requirements
5. It has no moving parts
6. Continuous disposal of solid particulates
7. They can be constructed of any material which will meet the temperature and
pressure requirements and the corrosion potential o f the carrier gas stream
Demerits:
1. Low collection f f i c i e n ~ i e s for the particles below 5-1 0 microns in diameters
2. Equipment is subject to severe abrasive deterioration
3. Decreasing collection efficiency for decreasing dispersoid concentrations in
the gas stream.
Applications
Cyclones are used widely for the control ofgas borne particulates in such industrial
operations as cement manufacture, feed and grain processing, food and' beverage
processing, mineral processing, paper and textile industries and wood working
industries. In disintegration operations such as rock crushing, ore handling and
sand conditioning in industries. They are also used in the recovery of catalyst
dusts n the petroleum industry and in the reduction of ly ash emissions. .
08. Explain the principle, construction and working of an electrostatic precipitator.
Ans: ESP are particulate collection devices that utilize electrical energy directly to assist
in the removal of the particulate matter. They have been used for the removal of
fine dust from all kinds of waste gases with very high efficiency. The principle on
which this equipment operates is that when a gas containing aerosols is passed
between two electrodes. hat are electrically insulated from each other and
between which there is a considerable difference in electrical potential. Aerosol
particles precipitates on the low potential electrode. Out of the two electrodes one
is a discharging electrode and the other a collecting electrode.
The four steps in the process are
1 Place the charge on the partice to be collected
2. Migrate the particle to the collector
3. Neutralize the charge at the collector
4. Remove the collected particles
An ESP consists of six major components
1. Source of high voltage
2. Discharge and collecting electrodes
3. Inlet and outletfo rthe gas
4. Hopper forthe disposal ofttl e collected material
5 An electronic cleaning system d . I sure around the electro es.
6. An outer casing to form an enco
The entire ESP is enclosed in a casing
. f " ".0 'POWER ---......
SUPPLY , \
iosu le tor - - : ; ; . . -0
I ~ _ d i s ch a r g e elec t ' ro<Je
col lect i l "9 elec;.1rod .
d u s t 01"
p r .... c lp i ta tor w e
~ __ col lec ted dus t
gos: floW
E l ~ c t r o s t a t i c Precipitator
· h' happroaching 100%.PThe collection efficiency of the ES IS, Igof elect
disadvantages and applicationsWhat are advantages
Q9. precipitator?
Advantages:Ans: '1 High collection efficiency d 2'. Particles as small as 0.1 micro meter can be remove
Low maintenance and operating costs3.
' ~ : : : : a : ~ : ~ ~ : ~ : i n g of a large volume of high temperature gas
Treatmenttime is negligible (0.1-1?sec) , . 'tator for mainten6. .' easy by removing Units of the precipi7, Cleaning IS
operation h ' I usageThere is no imit to solid, liquid or corrosive c emlca ,
8.
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___
SECTION C
SHORT ANSWER TYPE QUESTIONS
01. What are vectors? Explain transmission of vector borne diseases.
Ans: Vectors may be defined as arthropods or animals that are capable of carrying
disease pathogens from an, animal, human, etc. (reservoir) to another. Thepathogens are transmitted either mechanically (e.g., trachoma by, non-biting flies)to a susceptible host, or after biological transformation (e.g., malaria parasites by
mosquitoes) to a definitive host, Each emergency situation may be characterized
by different types of vectors and vector-borne diseases. In addition to transmitting
diseases, some vectors may also be considered a nuisance because of theirpainful bites, e.g. mosquitoes, biting flies, fleas, and lice. The most troublesome
vectors in evacuation sites and refugee camps are the non-biting flies. The
following table summarizes the vectors and vector-borne diseases that arecommon among displaced populations
Main Diseases Transmitted by Vectors
-
VECTOR DISEASE TRANSMITTED- - ~ ~ - ' - ~ - ~ - - ~ - - - - - - lMosquitoes
Anopheles Malaria, fi lariasis. Culex Japanese encephalitis, filariasis, other viral diseases. Aedes Yellow fever, dengue fever, filariasis, other viral diseases
Lice Skin infections, epidemic typhus, relapsing fever Fleas prague, murine typhus
Ticks Tick-borne relapsing fever, tick paralysis
Rodents ~ J..i_R_a_t_b_ite fever, l e p t o s p i r o ~ i s , s a l m o n e l 1 o s i s _ ~ ~ ___ ___
02 . Enumerate the common vectors?
Ans: The common vectors are:
1. Mosquitoes
a. Anopheles
b. Andes
c. Culex
2. Non Biting fliesa. House fly
b. Blow fly
c. Flesh fly
3. Biting flies
a. Tsetse flies
b. Sandflies:
c. . Blackflies
4. Rodents and Fleas
5. Other Vectors and Pests
a. Lice
b. Mites
c. Ticksd. Bedbugs
e. Cockroaches
f. Snails
03 . Discuss the mosquito borne diseases.
Ans: Mosquito-Borne Diseases: There are many different species of mosquitoe
living in a specific habitat and capable of transmitting a variety of diseas
most common species are:
1. TheAndpheles mosquito that is a vector for malaria and filariasis
2. The Aedes mosquito that is a vector for yellow fever and dengue.
3. The "nuisance" Culex mosquito that may also be a vector of filariasis
encephalitis virus is generally not a critical vector control issue in
emergencies.
04. Discuss the non biting flies borne diseases.
Ans: The non-biting flies housefly, blow fly, and flesh fly_ These flies usua
around food, carrion, garbage, and human and animal waste. When th
they may either transfer or carry disease pathogens that attach on their
other parts of their bodies. These pathogens may then be mech
transported or transferred to humans, animals. Even though they can
transmitted via fly faeces, pathogens do not undergo biological transform
the flies. In unhygienic conditions, flies have more opportunities to ca
following:
1. Flies are mechanical vectors of intestinal infections such as dysenttyphoid.
2. Flies can transmit poliomyelitis and certain eye infections, such as trachom
3. Large fly populations can be extremely bothersome, interfering with
comfort. In fact, some people think that the word "bother" is derived from a
known as "Bot Fly."
48
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exposure to the disease will lower a population's immunity to vecto
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SECTION D
LONG ANSWERS TYPE QUESTIONS
Q1. Discuss the diseases caused by other vectors.
Ans: Other vectors of concern in displaced population camps those can cause diseases
are:
1. Lice among the species of lice, only body lice are vectors of diseases that can
cause epidemics. Migrating populations easily transpor t body lice from their
places of origin. Body lice are common where a large number of people live in
unclean, crowded conditions and they can transmit pathogens for the following. ,
disease:a. Epidemic typhus is a highly contagious disease, which can be transmitted by
contaminated lice faeces penetrating the skin while scratching
b. Relapsing fever can be transmitted by crushed lice penetrating the skin while
scratching.
c. Bites of body lice can cause skin irritation leading to various skin infections.
2. Mites mites commonly cause scabies and other skin infections in displaced
populations, particularly children. Overcrowding and poor personal hygiene
favour the spread of mites within a refugee population.
3. Ticks ticks are usually not a problem in camp settings. But they can transmit
several diseases, (e.g., Q-fever, hemorrhaegic fever, and tick-borne relapsing
fever).
4. Bedbugs bedbugs can become a great nuisance after displaced population
camps have been established for several months. Bedbug bites cause significant
discomfort and loss of sleep. In heavily infested areas, young children may show
signsof anemia.
. 5. Cockroaches cockroaches contaminate unprotected food and may transmit
various pathogens including poliomyelitis virus, amoebae and intestinal viruses.
6. Snails snails are intermediary hosts for the schistosoma flukes that cause ur inary
schistosomiasis and intestinal schistosomiasis.
Q2. Discuss the factors that make displaced populations more susceptible to vectorborne diseases.
Ans: Displaced populations often have an increased risk of vector-borne diseases,
even for diseases that may not have been present in the area before they arrived.
Therefore, just because there has been no history of a particular disease outbreak
in the area does not mean that it can never occur. Factors that make displaced
populations more susceptible to vector-borne diseases include the following:
1. Immunity and Disease Status: Stress, lack of good nutrition, and lack of previous
diseases. This is especially true for malaria when a non-immune populat
moved from urban or highland areas to lowland areas that are warmer or w
urban or highland areas there may be very little exposure to malaria; whe
warmer climates, there isan increased chance for the disease to be trans
When the weather is wetter than where the non-immune population cam
the vector populations increase rapidly. Displaced populations may also
certain parasites and diseases from their former homes to new locations
they multiply and spread. This makes the vectors and humans at the new
susceptible to diseases they would not normally be subjected to.
2. Increased Exposure to Vectors: Displaced populations may be more exp
vectors because of the following reasons:1. Overcrowding makes it easier for lice and mites to spread from p
perSon. It also increases the chance tha t there is an infectious human
person with circulating yellow fever virus, and a nonimmune susceptib
both living within the 50 meter flight range of the mosquito vector
. aegypti).
2. Poor housing results in Closer contact with sandfly vectors of leishm
flea vectors of rodent borne diseases, or tick-borne relapsing fever.
3. Increased Numberof Breeding Sites
a. Mosquito populations can multiply in great numbers in poorly draine
distribution points. There may be an increased number of breedin
either due to more pools of water or more domestic water containers.
significantly increase the incidence of mosquito-borne diseases, as fo
(i). More water-storage containers increase breeding of the dengue feve
Aedes aegypti.
(ii). More water-filled pit latrines increase breeding of the encephaliti
Culex quinquefasciatus.
(iii). More groundwate r pits, ponds, and footprints increase breeding of the
vector Anopheles gambiae
b. While evacuation sites and newly established camps may have
problems with flies, lice, and mosquitoes, problems with rodent pop
usually takes' some time to build up. Poor storage or disposal of
increase the rodent population. These rodents bring fleas and
diseases.
c. Flies are attracted to areas with food and wastewater disposal p
especially around feeding centres. Fly problems are often severe at
beginning ofthe camp, before sanitation systems can be established.
d. Natural disasters (e.g., EI-Nino floods and hurricanes in 1997-98) ma
the environment and increase the breeding sites of other vectors of e
concern, e.g. ticks, tsetse flies, etc., resulting in less common
outbreaks including viral haemorrhagic fevers.
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c. Dead animals and wastes from slaughter houses should be buried as soon as
possible.
Q5. Explain how biting flies are controlled.
Ans: It is important to control biting flies such as t::;etse flies, sandflies wherever they
cause major disease epidemics
1. Tsetse Fly sleeping sickness There are various ways of controlling tsetse fly
populations.
a. Traps: The biconical trap, pyramidal trap and vavoua trap are made up o f blue
and black cloths and mosquito netting. Flies get attracted to the brightly
colored mosquito netting over the traps and are unable to escape after
entering. Traps are cheap, easy to transport, complete ly safe for the user andvery effective means for control of biting flies. Because they do not require any
specific training to use, they are ideal for use by individuals or communities.
b. Insecticide Treated Targets: these consist of impregnated traps and
screens, which are more effective since they kill any flies that land on them.
They may be impregnated by the same pyrethroids used for impregnating
mosquito nets (may be effective fo r upto 3 months).
c. Insecticide Spraying: Aerial and ground spraying of nsecticides may be the
preferable method of control during acute epidemics of sleeping sickness,
river blindness or leishmaniasis. Daytime resting places such as tree trunks,
twigs and roots should be target, Because of its high cost, need for s p e ~ i a lequipment and trained workers, spraying is not recommended as a routine
control measure.Traps attract more flies than screens and require less handling. Screens are
much cheaper than traps and can cover a larger area. However, traps
continue to be effective in catching flies once the insecticide wears out,
screens are only effective as long as the insecticide is active.
2. Sandflies -leishmaniasis
The infection and spread of eishmaniasis may be controlled in the following ways:
Personal Protection: ' avoid being bitten by keeping away from areas that
sandflies are known to breed or rest, and by using bednets, repellents,
clothing.
Residual Spraying: although spraying the interior and exterior sides of
doorways and windows, and the inner walls is effective against indoor-resting
sandflies, malaria control is the primary reason for spraying whereverleishmaniasis is a problem.
• Control of animal reservoir: controlling the animal reservoir population (e.g.
rock hyrax in Ethiopia, dogs or other domestic animals) may reduce the
incidence of eishmaniasis.
55 BC2.5
Q6. How rodent andfleas vector s controlled?
Ans: When controlling flea-borne diseases such as plague and murine typhus, n
attack the rodents before firs t getting rid of he fleas. Otherwise, when the rats
gone, the fleas will attack humans. The effective ways to get rid of rodents
fleas are:
a. Chemical control: dusting rodent footpaths with insecticide dust/powde
effective for large scale flea control (during outbreaks of typhus or plag
When the rats groom themselves, the dust spreads on their fur, thus killing
fleas.
b. Mechanical Protection and Sanitation: These are the only perma
methods for reducing rodent populations in refugee camps. Efforts shoul
made to store all food in rat-proof containers. The final disposal of solid w
should be done n a location and manner that does not encourage rat bree
or create other environmental health risks. Burial or incineration may be u
to finally dispose of household waste and refuse from markets
slaughtering areas.
c. Traps: Trapping rats is good for publicity but generally catches only the
and the stupid rodents.
d. Poisons: Rodenticides are generall y not recommended for refugee camps
e. Caution to Rodent Trapping! safe handling: Lassa fever is common and
virus is spread through the urine of rats. If trapped, these rats have to
disposed of without direct contact between the human and the rat corp
they urinate wild ly and their bodies become covered in the virus
Q7. Discuss how other pests and vectors are controlled?
Ans: Vectors and pests of ess urgent concern can be controlled through environme
mechanical, biological, o r chemical control,as summarized below:
Possible Vector Control Measures
VECTOR PossmLE CONTROL MEASURES
Lice mass laundering in hot water; mass delousing with insecticpowder
Mites mass laundering; supply adequate water for washing and distrib
soap for
the community
clearing vegetation or insecticide spraying is difficult to applyicks
Bedbugs household and personal hygiene; insecticide sprayingBlack Flies larviciding breeding sites in surrounding rivers
Cockroaches protect food; insecticide powder or spraying
sanitation measures, drain water or speed up water flow, sp
molluscicides
Snails
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SECTION B SECTION C
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TRUE FALSE TYPE QUESTIONS
1. Myriad microbes and toxic substances can contaminate foods
2. The majority of food borne diseases are infectious and are caused by bacteria,
viruses, and parasites.
3. Sanitation is the hygienic meansof promoting health through prevention of human
contact with the hazards ofwastes
Answer key
e = T ~ ~ I ~ ~ ~ C = r - - - \ · = C _ l ~ .. ...---L-\- \ - - " ]
BC2.561
SHORT ANSWER TYPE QUESTIONS
01.·, Howare food borne diseases caused?
Ans: Foodborne illnesses are defined as diseases, usually either infectious or t
nature, caused by agents that enter the body through the ingestion of f
disease caused b y consuming contaminated food or drink. Myriad miCfob
toxic substances can contaminate foods. There are more then 250 k
food borne diseases. Th e majority are infectious and are caused by ba
viruses, and parasites .Other food borne diseases are essentially pois
caused by toxins, chemicals contaminating the food. All foodborne microbe
toxins enter the bo dy through the gastrointestinal tract and often causes th. symptoms there. Nausea, vomiting, abdominal cramps and diarrhea are fre
in food borne diseases.
02. Give the significance of sanitation?
Ans: The importance of sanitation are as follows:
1. It ncreases chances of complying to regulatory requirement
2. It prevents outbreakof food borne diseaseli.
3. It enhances product quality and shelf ife
4. It reduces energy and maintenance cost
5. It improves customer relations
6. It ncreases trust of competence agencies and inspectors
03 . What do you understand by sanitation and hygiene?
Ans: Sanitation within the food industry means to adequate treatment o
contact surfaces by a process that is effective in destroying vegetative c
microorganisms of public health significance, and in substantially re
numbers of other undesirable microorganisms. but without adversely affec
product or its safety for the consumer.. Sanitation is the hygienic me
promoting health through prevention of human contact with the hazardsofw
Hazards can be either physical, microbiological,biological or chemical ag
disease. Wastes that can cause health problems are human and animal
solid wastes, domestic wastewater (sewage, s u l l a g ~ , grey water), ind
wastes, and agricultural wastes.
Hygienic means of prevention can be by using engineering solutionsewerage and was tewater treatment), simple technologies (e.g. latrines
tanks), or even by personal hygiene practices (e.g. simple hand washin
soap). Sanitation as defined by the WHO (World Health Organization); Sa
generally refers to the provision of facilities and services for the safe disp
human urine and faeces. Inadequate sanitation is a major cause of disease
wide and improving sanitation is known to have a significant beneficial im
62
health both in households and across communities. The word 'sanitation' also
refers to the maintenance of hygienic conditions, through services such aspathogenic (disease- causing) organisms to humans. The nutritional compo
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garbage collection and wastewater disposal.
04. What are different typesof sanitation?
Ans: The term "sanitation" can be applied to a specific aspect, concept, location, or
strategy, such as:
1. Basic sanitation - refers to the management of human faeces at the household
level. This terminology is the indicator used to describe the target ofthe Millennium
Development Goal on sanitation.
2. On-site sanitation - the collection and treatment of waste is done where it is
deposited. Examples are the use of pit latrines, septic tanks, and imhoff anks.
3. Food sanitation - refers to the hygienic measures for ensuring food safety.
4. Environmental sanitation - the control of environmental factors that form links in
disease transmission. Subsets of this category are solid waste management,
water and wastewater treatment, industrial waste treatment and noise and
pollution control.
5. Ecological sanitation - a concept and an approach of recycling to nature the
nutrients from human and animal wastes.
05. What is pasteurization?
Ans: Pasteurization is the process of heating liquids or oods to kill microorganisms that
can cause disease. It was developed by Louis Pasteur in 1864, and the practice
became commercialized around the late 1800s and early 1900s. In addition to
improving consumer safety, pasteurization can improve the quality and shelf ife of
foods. Pasteurization destroys most disease producing organisms and limits·
fermentation in milk, beer, and other liquids by partial or complete sterilization. The
pasteurization process heats milk to 161 degrees Fahrenheit (63 degrees
centigrade) for 15 seconds, inactivating or killing organisms that grow rapidly in
milk. Pasteurization does not destroy organisms that grow slowly or produce
spores. While pasteurization destroys many microorganisms in milk, improper
handling after pasteurization can re-contaminate milk. Ultra-high temperature
(UHT) processing destroys organisms more effectively and the milk is essentiaJly
. sterilized and can be stored at room temperature for up to 8 weeks without any
change in flavor.
06. How do microorganisms enter the milk supply?
Ans: Our environment contains an abundance of microorganism,s that find their way to
the hair, udder, and teats of dairy cows and can move up the teat canal. Some of
these germs cause an nflammatory disease of the udder known as mastitis while
others enter the milk without causing any disease symptoms in the animal. In
addition, organisms can enter the milk supply during the milking process when
equipment used in milking, transporting, and storing the raw milk is not properly
cleaned and sanitized. All milk and milk products have the potential to transmit
63 BC2.5
that make milk and milk products an important part of he human diet also su
the growth of t ~ e o r g a . n ~ s m s . D r i ~ k i n g raw milk causes food borne illness, and
producers seiling or giVing raw milk to friends and relatives are putting them a
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houses is when the animals are on grazing. Sunlight and heat act as powerful SECTION E
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disinfectants. Direct sun-rays kill many germs and mitigate the action by their
oxidizing and desiccating properties. Heat, as a disinfectant, may be applied either
in the form of a direct flame or burningor steamof the boiling water.
06. Write short note on live stock management n organic farming;
Ans: In Livestock Management in Organic Farming the live stock should be taken
proper care as:
• Cattle should be regularly washed and groomed once or twice a week. The
cattle should be washed once daily in hot weather, once a week during the
rains, and once or twice a month during the cold weather.
Suckling calves need not be bathed, but should be brushed.
• Feet should receive special attention in all animals, and any arge dirt piecesof
stone or thorn found lodged between the hoofs should be removed and sores
properly cleaned.
OVERVIEW QUESTIONS
1. Name some food borne diseases.
2. . How food borne diseases are caused?
3. How food borne microbes enter the human body?
4. Define sanitation.
5. What do you understand by hygiene?
6. What s basic sanitation?
7. Define pasteurization.
8. Why pasteurization is needed?
9. Comment on I milk is carrierof infection.
10. How and when flash pasteurization is needed?
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TRUE FALSE TYPE QUESTIONS
1. According to IS: 3307-1965, the tolerance l imits for industrial effluents discharged
on land for irrigation purposes quantity of oil and grease should not be more than
30mg/l
2. Neutralization means neutralizing the excessive acidity or alkalinity of the
particular waste water, by adding alkali or acid, respectively, to the waste water
3. Physical treatment consists of separating the suspended inorganic matter by
physical processes, like sedimentation and floatation
.Answer key
]
SHORT ANSWER TYPE QUESTIONS
01. Write short note on industrial effluent standard for disposal on land
Ans: According to IS: 3307-1965, following are the tolerance limits for indus
effluents discharged on land for rrigation purposes:
1 the total dissolved inorganic solids should not exceed 21 OOmgll
2. 5day BOD at 20°C should not exceed 500mgll,
3. its pH-value should be between 5.5 to 9.0
4. .quantity of sulphates. and chlorides should not exceed 100 and 600respectively
5. quantityof oil and grease should not be more than 30mg/l and
6. quantity of boron should not exceed 2mg/l
02. Explain equalization and neutralization process of industrial waste
Ans: Equalization: Equalization consists of holding the waste water for some
determined time in a continuously mixed basin, to produce a uniform wastew
Such an arrangement will, of course be necessary when the waste wate r prod
by the industry varies in characteristics and quantity over the entire day.
Neutralization: Neutralization means neutralizing the excessive acidit
alkalinity of the particular wastewater, by adding alkali or acid, respectively, to
waste water. This may be achieved either in the equalization tank, where possor a separate neutralization tank may be used.
03. What.are the various physical treatment processes used for treating indus
waste?
Ans: Physical treatment consists of separating the suspended inorganic matte
physical processes, like sedimentation and floatation
a. Sedimentation: Sedimentation is employed to separate the heavier settle
solids, and hence sedimentation tank may be provided only when the waste w
contains a high percentage of such heavy norganic solids.
b. Floatation: Floatation consists of creation of fine air bubbles in the waste tan
introduction of air into the tank from the bottom. The rising air bubbles, a
themselves to the fine suspended particles, increasing their buoyancy, and flifting them to liquid surface for consequent removal by skimming.
03 . What are the tolerance limit for industrial effluent discharged into public sewers?
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SECTION D
LONG ANSWER TYPE QUESTIONS
01 . How and in what way the industrial waste can pollute the water?
Ans: Certain types of organic, inorganic and radioactive substances present in the
industrial waste in minute suspended or colloidal for r rnd micro organisms
pollute the source of water, where these are disposed off. The decomposition of
industrial wastes by microorganism results in the products which are odoriferous
or unacceptable in taste and appearance as well as harmful to public health. The
organic impurities give odour colour and taste to the water, whereas inorganic
compounds give foaming, odour, turbidity etc. Various types of bacteria, virusesand plant life also grow in the industrial! trade wastes. Organic compounds such as
proteins, carbohydrates, fats, dyes, tar, detergents etc. present in waste are
objectionable. Keratin from wool industries, proteins from egg albumen, tannin
from tanneries, casein from dairies etc. undergo degradation by bacterial action
resulting in compounds which impart most objectionable colour and pollute the
water. The pollutants add colour, taste and odour in the receiving water, make the
water oily, greasy, corrosive and unfit for industrial, recreational or domestic use.
They also impart hardness, change pH-value, increase temperature and algal
growth, destroy the aquatic ife and increase the insect nuisance.
02. What are the permissible limits of ndustrial effluent to be discharged into streams?
Ans: According to IS: 2490-1963 the industrial effluent allowed for discharge into the
water courses should have the following standards
1. 5day BOD at 20°C of effluent to be discharged into inland surface water as30mg/l.
In exceptional cases the BOD may be allowed up to 100mgll
2. as far as possible and practicable, it should be free from colour and unpleasant
odour
3. its pH-value should be between 5.5 to 9.0
4. from the outlet up to 15m downstream, the temperature should not bemore than
40°C in any sect ion ofthe stream,
5. oil, grease, phenolic compounds, cyanides (as CN) and sulphides (as S) should
not exceed 10.0, 1.0,0 :2 and 2.0mg/l respectively,
6. total suspended solids should not exceed100mg/l
7. presence of arsenic, barium, cadmium, Chromium, copper, mercury, lead,selenium, nickel, silver and zinc should not exceed 1.0mgll individually or
collectively,
8. total residual chlorine and fluorides (as F) should not exceed 1.0 and 2mg/l
respectively, and9
9.. radioactive materials like u and pemitters should not exceed 10
respectively.
8
and 10- jJc/ml,
BC2.5
Ans: ~ c c o r d i ~ g to IS: 3306-1965, the tolerance limit for industrial effluents dischargeInto public sewer are as follows: .
1. its pH-value should be between 5.5 to 9.0
2. 5day BOD at 20°C should not exceed 500mgll,
3. lead, copper and zinc should not exceed 1.0, 3.0 and 15mg/l respectively,
4. effluent temperature should not exceed 45°C '
5. quantity of suspended solids h ~ u l d not exceed 600mg/l
6. Chromium, nickel and cyanide should not exceed 2% each
7. effluent containing s o l i d ~ such as straw, plastic, wood, paint residue, gross so
from cannery wastes, crnder, ash, sand, tar, rag, hair, metal shavings, garbagbroken glass etc. should no t be discharged into public sewers
8. phenolic, compounds, sulphates and total inorganic· dissolved solids should n
exceed 5, 1000 and 2100 mgll respectively
9. chloride and boron should not exceed 600 and 2mg/l respectively
04 . What do you understand by acclimatization in biological treatment of indust
waste? .
Ans: Biological t ~ ~ a t m e n t . of industrial waste waters is necessary, when they cont
large q . u a n t l t l ~ s of bl?degradable substances. Such biological treatment may
used either With or Without acclimatization. Acclimatization cons ists of he grad
exposure of the wastewater in increasing concentration to the seed or nitial mi
biological population under a controlled condition. Most of the waste water do contain sufficient nutrients for microbiological growth, and hence nutrients l
urea (containing nitrogen), super phosphates (containing phosphorus) etc. m
h ~ v e t.o be added to the reactors. For balanced growth of micro organisms i
biological treatment reactor, the ratio of BOD: nitrogen: Phosphorus should
100: 5: 1 for aerobic systems, and 100: 2.5: 0.5 for anaerobic systems.
05 . Write short note on pretreatment of industrial wastes.
Ans: Industrial wastes mainly consists ofthe ollowing:
1. effluents obtained from various industrial processes,
2. industries floor washings
3. condensate water
4. sanitary and faecal wastesIt is always not necessary to treat the entire industry waste. Some in p
measu.res may be adopted to reduce or even eliminate the objectionable mat
Followrng are the common measures used for industries waste pre treatments:
1. Use of soft detergents instead of hard detergents for eliminating the fo
nuisance. This is known as process change'.
74 BC2
2. Recoveryof silver from photographic wastes, which provides a primary treatment.It is known as recovery of material.
synthetic ion exchange resins, where some undesirable cations and anionwaste water get exchanged for sodium or hydrogen ionsof the resin.
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3. Reuse of water in industrial processes, such as collecting cooling waters from
boilers, eliminating its heat and reusing it.
4. Mixing of acidic and alkaline wastes together, for neutralizing each other and
making the mixture more nearer to the normal value of pH. This process is known
as mixing oftrade wastes.
The industrial wastes are usually treated by the following processes:
1. The suspended solids are removed by screening or settling tanks
2. Oil, grease and fats are removed by floatation and skimming. This process can be
aided by chemical treatment fnecessary.
3. Colloidal matter is removed by floatation with coagulation and electrolytesfollowed by sedimentation and filtration
4. excessive alkalinity and acidity is removed by adding chemicals or mixing acidic
waste with alkaline waste or vice-versa
5. Re oxygenation of wastes are done by aeration
6. De colorization of waste is done by chemical treatment with sedimentation or
filtration or both.
Q6. Discuss the various chemical treatment processes used for the treatment of
industrial waste water.
Ans: The chemical treatment is used to recover the dissolved organic matter from the
waste water, and may consistsof
one or moreof
the following processes:1. Reverse Osmosis or hyper filtration: The waste water containing dissolved salts
are filtered through semi permeable membranes at a pressure higher than the
osmotic pressure. Such a treatment requires pre treatments like a) activated
carbon adsorption; or b chemical precipitation followed by some kind offiltration
2. Electro dialysis: In electrodialys is dissolved salts from waste water are separated
by passing an electric current through the waste water tank. This treatment also
requires some pre treatment as i s required in reverse osmosis process.
3. Chemical Oxidation: hi-chemical oxidation, chemicals like chlorine and ozone are
used to reduce substances like ammonia and cyanide, etc. from the waste water,
in addition to reducing BOD load on biological treatments.
4. Chemical coagulation: This is used in treating raw water supplies, and helps in
sedimentation of unsetlleable micro and colloidal impurities, which get absorbedin the gelatinous flocs, formed by the chemical reactions between coagulants, or
between the coagulant and the alkalies present n raw water.
5. Adsorption: Adsorption is used to remove non biodegradable organics ( like
synthetic detergents), color and odour from waste water. The process involves
passing the pre treated waste water through the beds of activated carbon.
6. Deionization: Deionization involves passage of waste water through the beds of
7.Thermal reduction: Thermal reduction requires burning and consequent o
of s o m ~ toxic and refractive substances, like organic cyanide, which present In certain specific industrial waste waters.
8.Air s t r i p P i ~ g : In ai: stripp.ing the liquid waste is poured down through a
tower, eqUipped with an air blower at the bottom. This is a modificat ion of aprocess, used for removal of gases from the waste water.
Q7. D i s c ~ ~ s the effects of industrial effluent disposal on sewers, treatment plareceiving streams.
Ans:Heavier suspended solids deposit in sewers or in receiving streams andC h O k i ~ g t:oubles. They also smoother the fish life in streams. Greasy a
matenal mduces depOSition at above places, causes skimming troubles
~ r e a t m e n t plants and ugly scums and sludge banks in receiving waters. Th
m t e ~ ~ r e w i t ~ t.he rights of riparian owners, and with the natural reaeration in
septlclty. ACidic and corrosive discharges act upon the sewer materials a
treatment p.lant structures and equipment corroding and weakening them a
reduce their useful life and capacities. These along with the toxic meta
chemicals destroy the biological activity in streams .and municipal s
treatment plants and r ~ n d e r receiving waters unfit for further use.
temperature of wasteswill aggrevate the situation by hastening the chemibiological reactions.
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TRUE FALSE TYPE QUESTIONS
All porous rocks possesses enough capacity to store water. and h e n ~ ~ are1.considered as potential source of ground water rrespective of theIr permeabIlity
The intake point should be located upstream of he point of sewage disposal2.
3. Dry intake towers are preferred to wet ntake towers
Surface and ground water get heir supply from rain water4.
5. Intake is a device to draw water
Combined gravity and pumping system is the most common system adopted in6.
most of he cases
Surface reservoirs should be located at high points in the distribution system so7.
that gravity supply can be done directly
Elevated reservoirs are commonly known as overhead tanks8.
Circular and ring system is most suitable for the town having well planned streets9.
and roads
Stand pipes are normally employed whe re the constructionof
a surface reservoir10. would not provide sufficient head.
A mass curve of demand is the cumulative demand curve and is obtained by11.continuously adding the hourly demands and plotting these against time of the
maximum day
12. The methodof distribution depend upon the topography of the area
13. Sump well is the ower portionofthe intake where water enters from the conduits
14. Stand pipes are provided.with single inleta,:,d outlet pipe
15. Generally the heightof stand pipes should be more than 15m
1. F
,11. T~ BC2.5
SHORT ANSWER TYPE QUESTIONS
01. What are the different o u ~ c e s ofwater?
Ans: The different sources of water can be broadly classified as
1. Surface sources
2. Sub surface/ underground sources
1. Surface sources can be further divided as
a. Stream
b. Lakesc. Ponds
d. ' Rivers
e. Impounded reservoirs
f. Stored rain water
2. Subsurface/underground sources can be further divided as
a. Springs
b. Infiltration galleries
c. Porous pipe galleries
D. Wells
02 . Discuss stream as a surface source ofwater.Ans: In mountainous region streams are formed by the run off.
The discharge in the streams is much in rainy season than in an y other sea
Those rivers which dry up in summer and contain water only during rainfa
known as 'Rainy Streams'. The quality of water n streams is normally good
the water of first run off. But sometimes run off water while flowing over grou
mixed with clay, sand and mineral impurities. All the suspended impurities c
removed in settling tanks up to certain extent, but the dissolved impurities r
special treatments. The streams generally flow in valleys and are the main s
of water supply to villages of hills which are situated near them.
03 . Discuss lakes as a surface source ofwater.
Ans: In mountains at some places natural basins are formed with imperviousWater from springs and streams generally flows towards these basins and
are formed. The quantity of water in the lakes depends on its basin ca
catchment area, annual rainfall, porosity of the ground etc. The quality o
lakes is good than that of the small lakes: But lakes which are situated
altitudes contain almost pure water which can be used witho ut any treatmen
water s available only to those towns and cities which are situated nearthem
84
04. Discuss rivers as a surface source ofwater.08. Discuss springs as ground water source.
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Ans: Rivers are born in the hills, when the discharge of large number of springs and
streams combine together. In mountains the quantity of water in rivers remains
small, therefore at such places these are called as small rivers. But as the riv.er
moves forward more and more streams combine in it and it increases Its
discharge. Therefore rivers grow bigger and bigger as they move forward d ue to
increase in .their catchment area. Rivers are the only surface sources of water·
which have maximum quantity of water which can be easily taken. In summer the
quality of river water is better than that in monsoon, because in rainy season
runoff water also carries with it clay, silt, sand etc., which make the wat er tUrbid.
River water should always be used after necessary treatment. Some rivers are
snow fed and perennial, and have water throu ghout the year; therefore they do no t
require any arrangement to hold the water. But some rivers dry up wholly or partly
in summer, therefore they require special arrangements to meet he water demand
during hot weather.
05. Discuss ponds as a surface source ofwater.
Ans: These are depressions in plains like lakes of mountains,in which water c ~ l I e c t e dduring rainy season. Sometimes ponds are formed when much excavation I,S done
for constructing kaccha houses in villages, embankment for road and railways,
and manufacture of bricks. Generally the quantity of water in ponds is very small
and contains large amount of impurities. The water of ponds is used for washing
clothes animals, bathing and drinking. The water of pond cannot be used fo rwater
supplyu r p o s e s
due to its limited quantity and large amount of impurities.
06 . Discuss impounded reservoirs as a surface source ofwater.
Ans: Mostly it is found that there is great variation the q u a ~ t i t y of rive: water ?uring
monsoon and summer season. The discharge.m some rivers remam suffiCient to
meet the hot weather demand, but n some rivers the flow becomes very small and
cannot meet the requirements of hot weather. In such cases it e c ~ m e s es.sential.
to store the water for summer season. The water can be stored m the fiver by
constructing a bund, a weir or a dam across the river at s u c ~ p l a ~ e s w h ~ r eminimum area of land is submerged in the water and the reservOir basm remains
cup-shaped having maximum possible depth of water.
Q7. Discuss stored rain water as a surface source ofwater.
Ans: At some places where neither ground water nor surface water is easily v ~ i I ~ b l e , .the only way is to store the rainwater in cisterns or tanks from roofs of bUlldmgs.
The rain water from roofs and pucca courtyards is collected in water tight tanks
with the help of· channels. Water obtained in this way is extremely soft and
reasonably clean. The water stored in this way should be prevented from
contamination. The quantity ofwater stored in this way is limited and can never be
utilized for water supply schemes on large scale.
Ans: Ground water reappears at the ground surface in the form of springs. S
generally can supply small quantity of water, hence cannot be used as so
water to big towns. Good developed springs can be used as water supply s
for small hill towns. Due to presence of sulphur in certain springs, they dis
hot water. Such hot water springs are only useful for taking dips for the
certain skin disease patients. These are no t useful for public water supply.
09. Discuss porous pipe as ground water source.
Ans: When there is large quantity of ground water existing over a wider area, it
cheaply col/ected by laying porous pipes or pipes with open joints in the fullsome distances. These longitudinal and cross pipes are given a slope su
they bring the water towards a point, where a well is constructed to take
water. These porous pipes are surrounded with gravel and broken stone piincrease the intake capacity.
010. Discuss infiltration gal/eries as ground water source.
Ans: The ground water travels towards lakes, rivers or streams. This water w
traveling can be intercepted by digging a trench or by constructing a tunn
holes on sides at right angles to the direction of flow of underground water.
underground tunnels used for trapping underground water near rivers, la
streams are called 'Infiltration galleries'. Yield from these galleries may be a4
as 1.5 X 10 litres/day/meter length of the infiltration gallery. Galler
surrounded on sides and top with gravel or pebble stones to increase their
capacity. Longitudinal slope is given to the galleries and at the end sump. constructed, from where water s pumped out.
SECTION D
LONG ANSWER TYPE QUESTIONS
03 . What are the various classification of wells?Ans: Depending on the method of construction, wells are classified as follows:
1. Dug wells or percolation wells
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Discuss the suitability of surface water with regard to quant ity and quality.01.Rainfall directly affects the quantity of surface water. As the rainfall is uniformAns:throughout the year, the quantity of surface ~ a t e r ~ I s o large v a r l a t l o ~ ~ . The
discharge in rivers and streams remains m a x ~ m u m In r a l ~ y season and minimum
in summer. If the quantity of water in summer IS not sufficient to meet the demand,
it should be stored in impounded reservoirs. In hilly areas having large lakes, the
construction of artificial reservoirs is not necessary.
Surface waters mostly contains large amount of impurities in both u s p e n d ~ d and
dissolved form. Surface water is contaminated by the impurities while traveling ?nthe ground. The suspended impurities contain disease-producing bacteria,
therefore, surface water should not be used before treatment. l a k ~ s and
reservoirs, the suspended impurities settle down in the bottom, .but In their beds
algae, weeds, vegetable and organic g r o w t ~ takes place, which p r o d u c ~ bad
smell, taste and color in water. Therefore thiS water should also b.e u s e ~ after
purification. The sewage of towns and cities. situated near the n v e ~ s IS also
discharged in the rivers, which pollute the river water up to certain length.
, Therefore while taking water for water supply purposes, intakes should always be
installed in upstream side, which is free from contamination due to e ~ a g e . Whe.n
water s stored for long time in reservoirs it should be aerated and chlOrinated to kill
the microscopic organ isms which are born in water.
Q2. Explain the development of wells.In case of rocks the capacity of well can be !ncreased by explosion in the .wellsAns:which will increase the cracks and passages through which w a t e r e ~ t e r s In the
wells. In the case of sandy stratum the yield can be increased by packing g r ~ v e ~ s around the well. In the beginning when new well is c o n s t r u c t ~ d , t h e ~ a t ~ r which IS
drawn contains large quantity of fine sand. These sand particles w l l ~ stick the
mesh of strainer pipe and will decrease the capacity of the well. ThiS choking of
strainer can be removed by the ollowing methods.
Back washing or back blowing. In this method the water is forced in r e ~ e r s . e 1. '
direction by means of compressed air pressure. All the sand, clay material which IS
sticked around the strainer pipe and choked it is agitated and removed. These are
then removed by means of pumping and bailing.
Surging. In this method the sand particles are r e m ? v ~ d from the filter m ~ s h , by2.lowering a plunger in the well and giving severe agitation of the water inside the
strainer pipe.
Gravel packing. In this method the gravel is packed r o ~ n d the strainer pipe. First3.
the gravel is filled between strainer pipe and outer casing of the tube well. T ~ e ncasing is lifted upward to the top of screen and gravel rema.ins around the strainer
pipe.
87
2. Tube wells
3. Driven well or percussion wells
1. Dug wells or percolation wells: Sometimes these are also known as Draw W
'Open Wells'. These are shallow wells which are usually confined to soft
sand and gravel. The diameter of these wells may be between 1 m to 4m an
may be up to 20m depending on the requirement and geological structur
earth. Thesewells are suitable for small discharge of about 20 cu.m/hr. T
of these wells may be constructed with precast Re e blocks, bricks o
masonry. Dug wells are very cheap in construction, and very popula r in rur
and small towns. Wells should be disinfected frequently to avoid the
contamination, because these wells generally are in poor sanitary conditio
2. Tube wells: The maximum discharge which is available from the ordina
wells, is between 4 to 6 liters/sec. due to their low yield open wells are u
small locality or private dwellings. For small localities or private estates th
be their own source of water supply. It is not economical to install pumps
wells, due to their low yield. For obtaining more yield tube wells are co
used. These wells essentially consists of blind pipes and strainer pipes, a
supply of water is from large number of aquifers. The depth of the tube w
vary from SO to SOOm. and the maximum yield from the tube well may b
200Iiters/sec. The yield of the average tube well i s about SOIiters/sec.
3. Driven wells or percussion well: This is a shallow well constructed by d
casing pipe of 2.S cm to 1Scm in diameter. The lower portion of casing pipe
driven in the water bearing stratum is perforated. The bottom end of casin
pOinted known as drive point or well point. The perforated portion of th
covered with fine wire gauge to prevent the passage of soil and sand
insidethe well. The discharge of these wells is very small and these are su
domestic purpose only. These pipes may be up to 12m deep; after this d
water can be taken out by means of pumps.
04. Discuss the suitability of ground water source with regard to quan tity and q
Ans: Ground water is the wate rwhich percOlates in the ground after rainfall. T
the quantity of ground water directly depends on the rainfall. As the rain
uniformly spread throughout the year, the quantity of ground wate
throughout the year. In monsoon or rainy season yield will be maximusummer it will be minimum. The quantity of ground water also depend
underground storage and geological formation of pervious and im
stratums and the type of source of water. The yield from springs will be m
The yield of water from shallow wells will depend on the depth of wate
stratum and its catchment area, but it is usually less and tempora
decreases in dry weather. The quantity of water from deep wells and tub
much more, because water is trapped from several acquifers into the
88
Therefore supplies of tube wells and deep wells are constant and more reliable
than shallow wells and springs. If we compare the quantity of ground water with
Points to be kept in mind while selecting site for ntake works:
1. The best U ~ l i t y of water should be available at the site so that it can be
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surface water, the more quantity is available from surface sources.
The quality of ground water is much better than surface water, because surface
water contains large amount of suspended impurities, whereas ground water is
free from it. But sometimes ground water dissolves minerals, salts etc which come
in its cOr;ltact while in movement. The strainer action· of soil also removes large
quantity of bacteria. Therefore ground water is mostly free from bacteria but may
be soft or hard depending on the dissolved impurities.· Overall ground water is
good in quality but requires some treatment to remove dissolved impurities and to
improve its chemical characteristics.
Q5. What are the factors which governs the final choice of he source of water supply?
Ans: The choice of source of water supply to a town or city depends on the followingfactors:
1. Location: The source of water should be as near to the town as possible. If there
are both surface and ground sources available to the town the selection will be
decided by considering other factors also. If there is no river, stream or reservoirs,
the city will have to depend on ground source of water only because there is no
other alternative.
2. Quantity of water: The source of water should have sufficient quantity of water to
meet up all the demands of city such as domestic, industrial, fire fighting, public
etc. throughout the year. There should be sufficient extra quantity of water to be
required in u t u r ~ while expansion of city.is done. Source of water should beable to
meet he maximum demand n dry weather also.
3. Quality of water: The quality of water should be good which can be 'easily and
cheaply treated. It should not contain disease germs or other pathogenic bacteria
which may endanger the health of the public. Therefore as far as possible the
water of the source should be wholesome, safe and free from pollution.
4. Cost: The cost of water supply scheme depends on many factors as system of
supply, ground levels of city, distance between source and distribution system etc.
If the water flows under the gravitational force it will be cheap, but if it is to be
pumped it will be costly. Similarly the cost will directly depend on the distance
between the source ofwater and city, if the distance is more it will be costly.
The selection is done based on the above points and the source which will give
good quality and the quantity at ess cost will be selected.
Q6. What are intakes? Mention the points which should be taken into considerat ion in
deciding the location and design of an intake for the water supply?
Ans: Intakes are structures which consists of opening, grating or strainer·through which
the raw water from river, canal o r reservoir enters and is cacried to a sump well by
means of conduits. Wate rfrom the sump is pumped through the rising mains to the
treatment plant. Th e main function of intake works is to collect the water from the
surface source and then discharge water so collected, by means of pumps or
directly to the treatment plants.
and economically purified. . .2. For the a f e t ~ of the intake structures there should not be heavy cur
water at the site. .
3. !h e site should such that intake can draw sufficient quantity of wateIn the worst condition, when the diScharge of the source is minimum.
4. The site should be easiiy approachable i t h ~ u t a n y obstruction.
5. A;' far as pOssible the site should be near the treatment works, it will redcunveyance cost from the source to the water works.
6. At the site sufficient quantity should be available for the future expansiowater works.
7. A.s far as possi blethe intake should not be located in the vicinity ofthe p
disposal s e w a ~ e . If at all it becomes necessary due to unavoidable reto locate Intakes In the close proximity of the sewage disposal, a weir
be c o n ~ t r u c t e d upstream of the disposal point, and the intake sholocated In the upstream side of the weir.
Q7. What are different types of ntakes?
Ans: Depending on the source of water the intake works are classified as follows:
1. Lake intake
2. River intake
3. Reservoir intake4, Canal intake
1. Lake intake: .For obtaining water from lakes mostly submersible intak
used. These Intakes are o n s t r u c t e d in the bed of he lake below the low
level as to draw a t e ~ In season also. It consists of a pipe laid in th
of fiver. One en? which IS In the middle of the lake is fitted with bell
opening c o v e ~ e d wlth.a mesh and protected by timber or concrete cri. w a t ~ r enters In the pipe through the bell mouth opening and flows
gravity to the bank where it is collected in a sump well and then pumped
treatn:ent plants necessary treatment. The advantages of this int
there IS no b ~ t r u c t l o n to the navigation, no danger rom floating bodies atrouble due to Ice.~
= _tClA'!..E ~ ~ . ! E l .
TO 8 § A ; M ; W : ; = = = = ~ ~ ~ INLET PIPELake intake
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4. The distribotion system should be economical and easy to maintain and
operateQ10. Discuss the layout of distribution system.
Ans: Depending upon their layout and direction of supply distribution system
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5. It should be able to transport sufficient quantity of water during emergency
such as fire fighting.
6. It should be reliable so that even during breakdown or repairs of one line water
should reach that ocality from other ine.
7. It should not cause obstruction to traffic during repair work.
8. ·It should be safe against any future pollution.
9. The qualityofthepipe should be good and it should not burst.
10. It should be water tight and the water losses due to leakage should be
minimum as far as possible.
Discuss the methods of distribution system o f water.Q9.For efficient distribution the water should reach to every consumer with requiredAns:rate of flow. Depending upon the methods of distribution, the distribution system is
classified as follows:
1. Gravity system
2. Pumping system
3. Dual system or combined gravity and pumping system.
1. Gravity system: When some ground sufficiently high above the city area is
available this can be best utilized for the distribution system in maintaining
pre9sure in water pipes. This method is suitable when source of supply such
as lake, river or reservoir i s at sufficient height than city. The water flows in themains due to gravitational force. As no pumping is required it is the most
reliable system.
2. Pumping system: in this system water is directly pumped in the mains. Since
the pumps have to work at different rates in a day, the maintenance cost
increases. It is preferred to have number of pumps and only the required
numbers may work at various times to meet the demand, in place of providing
pumps of variable speed. If he power ail s, the whole supply of he town will be .
stopped. During fires the water can be pumped in the required quantity by the
stand by units also. u ~ t h i s is not preferred than other systems.
3. Dual system: This is also known as combined gravity and pumping system.
The pump is connected to the mains as well as to an elevated reservoir. In the
beginning when the demand is small the water is stored in the elevatedreservoir, but when demand increases the flow in the distribution system
comes from both the pumping station as well as elevated reservoir. As this
system has two sources, one from reservoir and the second from pumping
station it is called dual system. This system is more reliable and economical
because it requires uniform rate of pumping but meets low as well as
maximum demand.
classified as follows:
1. Dead end orTree system
2. Grid iron system
3. Circula r or ring system
4. Radial system
1. Dead end system: It is suitable fo r irregular developed towns and cities. In
one main starts from service reservoir along the main road. Sub mains
connected to the mains in both the directions along other roads which
the main road. In street, lanes and other small roads which meet the rocarrying sub-mains, branches and minor distributors are laid and
connected to sub-mains. From these branches service connections are m
to i n d i ~ i d ~ a l h o ~ s e s . . This system is cheap in initial cost and
d e t e r ~ l n a t l o n of pipe diameters, valve size etc. disadvantage is that due t
!ormatlon of dead ends stagnation ofwater takes place, i f pipe breaks do
IS closed for repair the whole locality beyond that point goes without w
because water is reaching at each point from one side only, it cannot mee
fire demand, nor supply can be increased o r diverted from other points.
2. Grid iron system: This is also known as reticulated system and is use
towns having rectangular layout of roads. This is improvement over dea
system, all the dead ends are interconnected with each other and w
c i r c u l a t ~ sfreely
h r o u g ~out the system. Main line is laid along the main sub-mainS are taken In both the directions along other minor roads
streets. From these sub-mains branches are taken out and
interconnected. All disadvantages of dead end system are eliminated.
~ u m b e ~ of valves and longer length of pipe is required in this system, the
increasing the overall cost. .
3. C i r c ~ l a r or Ring system: This is adopted only in well planned locality of c
In this each locality is divided into square or circular blocks and the w
mains are laid around all the four sides of the square or round the circle
branches, sub-mains etc. are laid along the inner roads. All the sub-main
branches are taken off from the boundary mains and are interconnect
this way every point receives its supply from two directions. This is the b
the .other s ~ s t e m s but it requires many valves and more pipe length
deSign of this system is easier. The advantages and disadvantages o
system are also the same that of grid iron system.
4. Radial s y s t ~ m : In this system the roads should be laid out radially fr
center. In this system water flows towards outer periphery from one poin
entire area is divided into various zones and one reservoir is provided for
zone,. whic.h is placed i.n the centerof the zone. The water lines are laid ra
from It. ThiS system gives very quick and satisfactory water supply and
the calculation of pipe sizes is very easy. .
What are the functions of distribution reservoirs?011.
The main functions of the storage and distribution reservoirs are:
successfully. Its.main function is increase pressure on the distr
s y s ~ e m by creattng extra storage In the tank above the elevation re
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Ans:1. To store the treated wate r till it is distributed to the city.
2. To absorb the hourly variation in the water demand, and thus allowing the
treatment units and pumps to workat the average constant rate
3. To maintain the constant pressure in the distribution main, because when the
pressure in the pipe lines decreases due to ncrease in demand at peak hours,
the extra demand of wate r is fed by these reservoirs, and the pumps continue
their work at constant speed.
4. Distribution reservoirs lead to an overall economy by reducing the sizes of
pumps, pipe lines and treatment units. 5. By providing distribution reservoirs, the pumping of water in shifts is possible,
because treated water will continuously flow in these reservoirs.
What are the different ypes of distribution reservoirs?012.
The following types of reservoirs are:Ans:
1 Earth reservoirs
2. Masonry and RCC reservoirs
3. Elevated reservoirs
a. Stand pipes
b. Elevated tanks
1. Earth reservoirs: These reservoirs are used when large quantity of water is tibe stored before the treatment. These are constructed by excavating to the
required depth below the ground surface and the excavated earth is used for
the embankment construction to the required height above the ground. Core
wall may be constructed to make the earthen reservoir impermeable. The
embankment should be keyed down to the bottom. Out let pipes may be
provided in the embankment walls at various places to minimiie seepage of
water. To prevent the loss of water and leakage, the sides and the bottom of
the reservoirs should be properly lined with bricks, stones, asphalts or cement
concrete etc.2. Masonry or RCC ( underground) reservoir: These are constructed on high
natural grounds. It is made of bricks, stones, plain or RCC. While designing
ground water table is kept n mind and the side walls should be able to take upthe pressureofwater, when the reservoir is full, and the earth pressure when i t
is empty. The floors are constructed with RCC slab and bituminous
compounds may be used at all construction joints for water tightness.
3. Elevated Reservoirs: Generally two types of elevated reservoirs are used
a. Stand pipe: These are generally made o f RCC or steel and are circular in
.plan. These are up to 12m in height. If it is possible to locate the stand
pipe on a hill or high ground then its entire capacity can be made use of
give .the necessary pressure for distribution. These are provide
single Inlet outlet pipes terminating at the lower elevation
useful capacity of the tank, scour or drain-pipe to drain out and flu
tank and the overflow pipe to discharge surplus water.
b. E l e v a ~ e d t a n ~ s : T h e s e are popular because they have long life r
very ~ I t t l e maintenance and give good appearance in the l o c ~ l i ttank IS p r o ~ i d ~ d with inlet, outlet, overflow and scour or drain p
depth level Indlcato.r with a float arrangement is provided to measu
depth of the water the t ~ n k . About 60 to 100 cm balcony is pr
around the tank for n s p e c t l o ~ and maintenanceofthe tank and st
steel ladder also .fixed tn the inner walls of the tank. The
~ o v e r e ~ and IS prQvlded with a manhole and ventilating pip
lightening conductors. These are used to store large quantityofwa
013. Discuss how the storage capacity of a distribution reservoir is determined b
curve method.
Ans: Capacity of.the reservoir is determined by the principle of mass diagram Ac ~ ~ e shOWing the rate of demand is drawn with time as abscissa and the oo emand ~ u f l n g ~ e n o d as ordtnate. This is represented by the line
~ h n d s of he P are JOined by a straight line marked 0, then the line 0 rep
e m ~ s s diagram of pumping into the tank and its slope represents the
pumping.
Mass Curve
From graph it be observed that the tank is full at the point a and e
the O l n ~ b, so that ItS tangents are drawn at points a and b parallel to the lin
veftrthlcabl tnl t e r ~ e p t bc on the scale would represent the required capacity of
o e a anclng tank.
SECTION C
SHORT ANSWER TYPE QUESTIONS
Turbine meter is similar to rotary meter, and consists of a turbine wheel wrotated by the moving water. The number of revolutions made by the turbine
will give the discharge as in rotary meters.
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01. What are the requirements of a good water meter?
Ans: Requirements of a good water meter are as follows:
1. It mustrecord the entire water passing through it.
2. Its maintenance and repair should be easy
3. It should work efficiently at all pressures in the mains
4. It should cause minimum hinderance to the flow and therefore cause minimum
head loss in its working
5. Its parts should not be easily affected by the chemicals present in the water
passing through it
6. It should prevent the back flow passing through it and should not be liable to
clogging
7. It should measure the discharge within the maximum limitof 20% error.
02 . Enumerate differenttypes of water meter with exa mple.
Ans: Mainly there are two types of water meters
1. The velocity meters orthe Inferential meters
The various types of nferential meters are rotary meters, turbine meters, and
venturi meters.
2. The positive meters or the Displacement meters
The various types of displacement meters are reciprocating type, oscillating
type, disc type etc.
03. Discuss velocity meters.
Ans:. Velocity meters basically measures the horizontal velocityof water lowing through
them. This measured velocity when multiplied by the area of flow cross section,
will give the discharge through the meter. Automatic arrangements are then made
to record the integrated discharge over a period of time. They are used for
measuring high flows and are used in industries, and water works. Not used f or
measuring small domestic supplies. The various types of inferential meters are
rotary meters; turbine meters, and venturi meters.
The rotary meter consists of radial vanes attached to the shaft, and enclosed in a
casing. When the water passes through the meter the radial vanes are rotated in
clockwise direction, which revolve the shaft. The number of revolution per unit
time, made by shaft depends upon the velocity of flow. The velocity of flow and
therefore, the discharge is thus proportional to the speed of he shaft. The meter s
calibrated to directly read the discharge.
BC2.5103
Venturi meter is based on the principle of Bernoulli's equation. It is us
measuring raw waters and high flows in large pipes with a nominal head loss
04. Discuss displacement meters.
Ans: These meters are accurate because they measure the quantity of passing
by counting the number of times the meter chamber is filled and emptie
capacity of the meter chambe r when multiplied by the number of times it
and emptied will directly give the quantity of flow over the given period of im
various types of displacement meters are reciprocating type, OSCillating typ
type etc. A disc meters are most commonly used for measuring small f
residential houses. It consists of a disc placed inside a chamber, provided
inlet and outlet. The water when enters the chamber, oscillates the disc a
center with a spiral motion. One complete filling and emptying of the c
gives one revolution to the train of gears, and the meter thus record the vo
the water passing through it. These are available in different sizes 16 to 15
diameter with safe operating capacities of 90 to 4500 liters per
respectively.
05. Name the different types of pressure pipes.
Ans: The different types of pressure pipes are:
1. Cast iron pipes
2. Steel pipes
3. Reinforced cement concrete pipes
4. Hume steel pipes
5. Vitrified clay pipes
6. Asbestos cement pipes
7. Miscellaneous types of pipes
06. What are cast iron pipes discuss its advantages and disadvantages?
Ans: Cast iron pipes are used in water supply schemes. They are highly res
corrosion and have long life of about 100 years. They are manufactured fr
grey pig iron. They are manufactured in lengths of 2.50m to 5.50m. The fi
also weighed, coated with tar coal and finally tested. They are joined tog
means of Bell and Spigot, threaded or flanged joints. These pipes h
advantages of easy ointing withstanding high internal pressure, long life
corrosion. But these are very heavy and difficult to transport, because
104
brittleness they break or crack easily. Therefore more suitable as distribution
pipes.RUBBER WASHER
(GASKEn
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07.
Ans:
08 .
Ans:
Explain socket and spigot oint.
This is also known as Bell and spigot joint. These are used to join cast iron pipes.
The cast iron pipes are made in such a way that their one end is enlarged whereas
the other end is normal. The enlarged end is called 'socket' or 'Bell' while the
normal end is called 'spigot'. The spigot is fitted into the socket with few strands of
jute wrapped around spigot. The remaining space between the socket and spigot
is finally filled with molten lead, which gets solidified and tightly caulked into the
joint after cooling and thus makinga water tight joint. These joints are some what
flexible and allows the pipe to be laid on flat curves without the use of specials.
Skilled labour s required for these oints.
Bell or Socket
lead
- - --. . :. .-- --, - - ~ -
Socket and spigot joint
Explain Flanged joint.These are used for pumping stations, filter p l ~ n t s and at other locations where it
may be necessary to occasionally disjoint the pipe. Cast iron pipe lengths to be
joined by this oint are cast in such a way as to have flanges at both ends. In case of
steel pipes to be joined by such joints, flanges are separately cast and then
screwed down or welded at both the ends of the respective pipe lengths. Two
flanges are brought together, keeping a rubber washer ( gasket) in between them
so as to make them water tight. They are then fixed by means of nuts and bolts.
These joints are strong but rigid, and hence cannot be used where deflections or
vibrations are expected. They are expansive and mostly used for indoor works.
BC2.5105
, j
---- ,--
FLANGES
Flanged joint
09. Explain the expansion joint.
Ans: Expansion joints are provided ,at suitable intervals in the pipe lines so
c o u ~ t ~ r a c t the t ~ e r ~ ~ 1 st:esses produced due to temperature v a r i ~ t i o np r ~ v l d l n g e . x p a n ~ l o n jOints In cast iron pipes, the socket end is cast flanged a
s ~ l g o t IS plain. The s?cket end is connected rigidly to an annu lar ring wh
slide easily over the s p l g ~ t end. While making this Joint a small space
~ e t w e e n the face of the spigot and the inner face of the socket, and the sp
filled up by means of a rubber gasket. The flanges are then tightened by me
n u t ~ and bolts. When pipes expand, the socket end moves forward and t
left j U ~ t gets closed. l m l ~ a r I Y , when the pipes contract the socket moves bac
c r e a t l n ~ gap. All the time, the annular ring follows the movements of the
and maintains the gasket n position, thus keeping the oint watertight.
C.\.Fol\owerring
Rubbergasket
Expansion joint
106
010. Explain the flexible joint.
These joints are used whe re large scale flexibilities required, when pipes areAns:laid in rivers with uneven beds, large scale settlements may break the ordinary
SECTION D
LONG ANSWER TYPE QUESTIONS
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About 7Scm
l""' '1
.-Municipalstreet water
8 O : : 8 ~ V
type of oint, while laying pipes on curves etc. the pipes to be provided with such a
joint are cast with special types of ends. The socket is spherical; and the spigot,
though plain, is having a bead at the end. A retainer ring is placed over the bead
which keeps the special rubber gaske t in position. A split cast iron "gland" ring is
then placed over t. They are then tightened by means of nuts and bolts. The spigot
end can be moved to give away the desired deflection and nuts are tightened over
thegland ring.
Sphereol socket end
I Gasket Of Duck
LReta,ner ring
Flexible joint
BC2.5107
01. Explain with a neat sketch as to how municipal water mains are connecte
private buildings and houses for giving water supply connections.
Ans: A typical water connection, connecting the servi,ce pipe with the municipal w
mains is as shown
Street /Road
house
mllin (SECTiON)
~Goose· neck pipe(usually of lead)
I I I -I
.j
The water connection
The water connection consists of 1 Ferrule, 2) a goose neck, 3) a service pipe
stop cock and 5) a water meter.
1. Ferrule: a ferrule is a right angled sleeve made of brass or gun metal and is jo
to a hole drilled in the water mains, to which it is screwed down with a plug. Its
usually varies between 10 to 50 mm diameter. For all other connections of
tha n 50mm a tee branch connection, off he water mains, is used.
2. Goose neck: Goose neck is a small sized cur ved pipe made of a flexible mate
usually lead) and is about 75 cm in length forming a flexible connection bet
the water mains and the service pipe.
3. Service pipe: Service pipe is a galvanized iron pipeof ess than 50mm diame
should be laid underground in a trench in which no sewer or drainage pipe is
The service pipe which supplies water o the building through the municipal m
thus connected to the main through the goose neck and ferrule.
4. Stop cock: The stop cock is provided before the water enters the water meter
house. It is housed in a suitable masonry chamber with a removable cover, a
108 BC
fixed in the street close to the boundary wall in an accessible position. Sometimes
it is provided ust before the water meter inside the house, keeping both of hem in
one chamber.
2. They can be easily assembled without skilled labour
3. 12 degree defle
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5. Water meter: It measures and records the quantity of water consumed in the
house. The domestic type water meter generally employed for houses is fitted into
the service pipe with unions; which enables the meter to be changed where
necessary. The meter is fixed in an iron box fitted in an opening or cavity made in
the boundaryw a" ofthe house, and is covered with a movab le iron cover.
02 . Discuss Ree pipes and their advantages and disadvantages.
Ans: Ree pipes are generally made from 1 2:2 cement concrete with maximum size of
aggregates as 6 mm. They are provided with circumferential reinforcement tocarry hoop tension and a nominal longitudinal reinforcement equal to 0.25% ofthe
gross cross sectional area of concrete. Their thickness varies from 2. 5cm to 6.5 cm
for pipes of diameters varying from 0.1 m to 1.2m. These pipes are joined by
placing the protruding end barsof different engths butting against one another and
welding them and finally filling the gap with rich cement concrete so as to provide a
watertight oint.
Advantages are:
1. They can resist external compressive loads and do not collapse under
nominal vacuums and traffic loads.
2. They are not corroded by normal potable water and soils.
3. They are quite strong and the useful li fe is 75 yearsor so.
4. They are easy to construct either at site or at factories and with localingredients.
5. The coefficient of expansion being low, expansion joints may not be needed
when laid above the ground
6. If laid under water the empty pipesdo not float because of their heavy weights.
Disadvantages are:
1. They are likely to corrode by ground waters due to the presence of acids,
alkalis or sulphur compounds.
2. They are difficult to be repaired
3. They cannot withstand very high pressures.
4. They are heavy and bulky, and hence difficult to transport.
5. Making of connections in them is a little difficult ob
6. Theytendto eaks due to shrinkage cracks and porosity.
03 . Discuss the advantages and disadvantages of asbestos pipes.
Ans: Advantagesofasbestos pipes:
1. They are light and hence easy to transport
laying them around curves
4. Expansionjoints are not required as the coefficient of expansion is low joints are also flexible
5. They are very smooth and are hydraulically efficient pipes. Their ccapacity do not reduce with time
6. They are suitable for small size distribution pipes.
Disadvantages of asbestos pipes:
1. They are costly.
2. These pipes do not have much strength and are brittle and soft. They ar
to get damaged by excavating toolsor during transportation transit.
3. The rubber oint seal may deteriorate if exposed to gasoline or other pet
products, and hence cannot be used for transporting petroleum product
04. Write short note on steel pipes.
Ans: Steel pipes are occasionally used for main line and at such places
pressures are high and pipe diameter is more. These are more strong, hav
weight and can withstand high pressure than cast iron pipes. They are cheap
to construct and can be easily transported. The disadvantage of hese pipes
they cannot withstand external loads. If partial vacuum is created by emppipe rapidly, the pipe may be collapsed or distorted. These are affec
corrosion and are costly to maintain. The life of hese pipes is 25 to 50 years.
are not used in distribution system, owing to the difficulty n making connectio
The joints are made by welding or riveting. Longitudinal lap joints are m
riveted steel pipes up to 120 cm diameter. In case thickness of steel plate ex
15.87mm butt jOints are provided. If the diameter of the pipe is very larg
longitudinal seams may be provided. Welded steel pipes can be used fordiameters up to 2.43m or even more.
05. Name various types of sanitary fittings.
Ans:In buildings various types of sanitary fittings are required to collect the wasteThese all fittings can be broadly classified as:
A. Ablution fittings
1. Wash basins
2. Sinks
3. Bathtubs
4. Flushing cisterns
5. Drinking fountains
B. Soil Fittings
1. Water closets
2. Urinals
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3. Slop sinks
Q6. Write short note on wash basins.
Wash basins or lavatory basin is made of white glazed earthen ware, enameledAns:iron etc. these are of two types- the Flat Back and the Angled Back. Wash basins
are either fixed on brackets secured into the wall or on pedestals rising from the
floor.
Wash basin ( Flat back)
As shown the flat back has an oval shaped bowl with a usual capacity of 5 liters up
to the overflow, and a waste pipe of 32mm bore with a trap in the center. The a s t ~. opening is protected by a metallic strainer. The overflow may be of an open weir
type with a removable grating or ofthe slot type as shown in fig. there are two inlets,
one for cold water usually on the right side of the user facing the fixture and theother for hot water. These inlets are controlled by chromium- plated pillar taps. The
wash when fixed has a height of 75 to 80 cm.
Q7. With the helpof a neat sketch describe flushing cisterns.
This is an appliance used for flushing out water closets, urinals etc. These are ofAns:two types- the valveless siphonic type and the valve fitted siphonic type. The
former s preferred and used in practice.
CIIAIII
•1j DYEHRIJIf
PIPf'U I'QI.I.
Flushing cistern ( Bell type)
The Bell type flushing cistern is a valve-less siphonic type. It consist of c
made of a cast iron or pressed steel, having a suitable cover with a sump form
the center through which the flush pipe of 32mm bore passes. The flush
upper end is projected little above the maximum water evel in the cistern, wh
lower end discharges into the W.C. pan. The flush pipe is covered up in the c
by a C.I. bell to the top ofwhich a lever arm with a chain is attached. On pullin
chain the bell is lifted and on releasing it, it is lowered to its original position. D
the movement the water enclosed is spilled over the top of the flushing
causing siphonic action and thereby emptying the entire. contents of the cis
Waternow enters the cistern the flow being controlled by a ball valve arrang
operated by a float. An overflow pipe is provided as an additional safe
against overflowing in case the ball valve arrangement ceases to function.
Q8. What are traps, discuss differenttypes of traps?
Ans: Traps are fittings placed in drainage pipes, which prevent the passage of fou
gases through drains, waste or soil pipes and thus prevent their entry ininteriorof houses or buildings.
Traps may be classified in two ways:
A. According to their shape as
1. P-trap
2. Q-trap
3. S-trap
CItOWNWEIK
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P-THA!1 Q-TtAP
Traps according to shape
B. According to their use: Intercepting trap
1. Floor trap1. Floor traps: Thes e are used for admitting waste water from floors of bath
2. GullyTrapkitchens. These are provided with cast iron grating at top to exclude coarse
3. Intercepting trap matter, so as to prevent it from passing into the drain along with the waste
and thereby cause blockade. A form of floor trap much used in practice is theCAST/RON trap.GRATING
2. Gully trap: These are used for reception of suI/age from baths, sinks and
basins as well as rain or surface water from house tops and back yards. The
pipes or the rain waste pipes, discharging into drains, are seldom connec
them without such interception. Gully trap may have P- trap or S-trap. The
seal is 50 to 75mm deep. The upper section ofthe trap is covered by a C.1. g
to exclude coarse o r solid matter.
3. Intercepting traps or Interceptors: These are used at the junction of the
drain and the house sewer with the primary object of preventing the foul ga
the public sewer from entering the house drainage system. These gases are
through ventilating columns which are provided at the head of every branch
and at key position in the sewerage systems. The trap has an opening at
called the 'cleaning eye' or rodding arm' and has a tight itting plug. This e
the trap to be periodically cleaned of any obstruction present inside. The wat
is 75mm deep.
09 . Write short note on sinks and urinals.BAI;K INtH Ans: Sinks: It is rectangular receptacle used in kitchen or laboratory for drain
-water. It. is commonly made of glazed earthen ware. Usual s
60cm*45cm*25cm. the sink is provided with a wooden draining board fixed
right of the user. It should be so located as to directly receive light throu
. window. The heigh tfrom the floor to the top edge of the sink is about 90cm.
Urinals; These are usually of two types- the Bowl type and the Slab or Sta
The bowl type has a lipped basin with flushing rim while the slab or sta
comprises of lat wall slab with partitions on sides and floor channel to drain
. WATER
SEAt..
. (!WM
':elJJf i}/CAlJl1 r-----.,.....--....
Floor trap
Gully trap
discharge through a trapped outlet. Both the types are flushed through siphonic
type offlushing cisterns; in the bowl type the cistern may be hand operated andof 5
liters capacity while in the stall type, an automatic flushing cistern with a capacity of
of or
SECTION E
OVERVIEW QUESTIONS
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10 to 15 iters feeds a range three more stall urinals. .
Q10. What are the principle governing the design ofwater supply n building?
Ans: The principle governing the designofwater supply n buildings are
1. There should be absolutely no risk involved in the contaminating of water supply
for domestic purposes. In order to ensure this three things are necessary
a. There should not be any cross connection anywhere between a pipe
containing potable water and pipe containing used or polluted water
b. There should be no back flow from any cistern or appliance towards thesource of supply. An adequate air gap, at east 15cm between the outlet end of
the supply pipe discharging water into the cistern and its Hood level rim
effectively prevents any occurrence of back flow
c. The water supply and the drainage pipes should not be laid very close to each
other.
The pipes and fittings should be thoroughly water-tight in order to protect the
building against possible damage due to leakage. Water tightness of joints
ensures minimum wastage of water and risk of contamination is also considerably
reduced
The pipe work should be amply protected against any possible damage. When laid
underground, as in the case of service pipe, it should have an earth cover of at
least 60cm, when laid above the ground or in exposed situations, it should runclear of the wall with a clearance of 2.5 cm and when crossing wall or floor it should
be contained in suitable sleeves for entire length.
Water supply pipes should carry water inside building under adequate pressure in
the water main. However, where available pressure are insufficient 3nd it becomes
necessary to pump water, as in the case of multi-storeyed buildings separate
storage tanks may be used for providing necessary suction lift. The booster pumps
if used, should not be allowed in the service pipe as its suction lift decreases
pressureof water supply to the adjoining building.
1. What do you understand by intermittent and continuous water supply sys
2. Give the function of sluice valve in water supply ine.
3. Differentiate between air relief and pressure relief valves.
4. Give the necessityofwrought iron main in water supply.
5. What is the use of ferrule and goose neck?
6. Give the necessity oftraps.
7. Where will you recommend gully trap?
8. What is the depth of seal in the trap?
9. What are the causes of breakageof seal in the trap?
10. Where will you use floor trap and intercepting trap?
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These forms may be applied by the following methods1. Dry chlorine gas- It may not be drawn from the liquid chlorine it is directly
applied to the water supplied through submerged diffuser. This method is not
satisfactory because its results in corrosion of pipes.
SEcrlON
D
LONG ANSWER TYPE QUESTIONS
Q1. Classify various types of filters. Differentiate between slow sand and rapi
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2. Chlorine solution or iquid chlorine- Liquid chlorine is applied through the water
supply through a discharge ine. This method is very commonly used.
3. Powder form- In the form of bleaching powder is commonly used in small
water plants and is directly mixed in water.
Q12 .Wha t is the effect of pH on chlorination?
Ans: The pH value of water along with temperature and presence of residual chlorine in
the form of free available or combined available have a definite effect on the
effectiveness of the chlorine. Thus in the pH range of 7.0- 8.5 a minimum of 0.05
mgll free available can be effective with water temperature between 5-22 degree
centigrade. Disinfection proceeds very slowly at lower water temperature and with
pH value above 8.5. Also whereas free available chlorine is effective in
concentration of 0.05mgll for a reaction period of 10- 20 minutes. The combined
available chlorine to be comparatively effective within the reaction period, requires
a higher concentration upto about 1.80mg/l. .
Q13. Explain pre chlorination and post chlorination.
Ans: Pre chlorination-It is the application of chlorine before filtration. It may be added in
the suction pipes or in the mixing basins. It reduces bacterial load on filters, this
results increased filter runs and oxidizes excessive organic matter. This helps in
removing taste and odor and make the water fit for use.Post chlorination- When the chlorine is added in the water after all treatments, it s
known as post chlorination, it is generally done after filtration. The chlorine is
commonly added in clear water reservoir. The minimum contact period should be
half an hour, before use of water.
Q 14. What do you understand by dechlorination of water? What are the chemicals used
for dechlorination?
Ans: The process of removing excess chlorine from water is called dechlorination. It
. must be done in such a way that· some residual chlorine remains in water.
Dechlorinating agents OF chemicals used are
1. Potassium permanganate
2. Sodium bisulphate
3. Sodium thiosulphate
4. Sodium sulphite
5. Sulphur dioxide etc.
filters. . .
Ans. Filters may be classified as follows:
1. . Gravity Filters-
a. Slow sand filters
b. Rapid sand filters
2. Pressure Filters
Comparison between rapid sand filter and slow sand fllterS.No Item Slow sand filter 1 Rapid sand filter
'1 . Rate of filtration 100-2001lhrlsqm of filter area 3000-60001lhrlsqm of filte'.
2. Size of one unit 30m*6Om area varies from 6m*8m to 8m*10m area 1 5OO-2OOOsqm from 40-80sqm
1 I
3. Depth of filter 30cm gravel, 90-105cm 45cm gravel, 75cm or lesmedia sand, sand,
4. Effectiv.e size of 0.25-0.35mm Cu=1.75 0.45-0.8mm Cu =1.6sand
5. Under drainage 1 Open jointed pipes or ! Strainer pipes laterals i system i covered drains . 1 discharging into CI main
9cm initial to 1.2 m final I 0.3m initial to 2.1 m final6. 1Loss of head , .
7. Cleaning period 20- 60 days !24-60 hours
8. Method of Scraping of surface and Scour by back washing a
I
9.
cleaning washing down by hoses
Amount of wash 0.2-0.6% of water filteredwater used incleaning
10. Cost of Higher ILoweri construction
1 11 . iCost of operation ILower IHigher
removal of dislodged paU Wy ra d flow
1-4 % of water filtered
12. Ouality of raw It may not be treated withchemical, but should nothave turbidity more than50ppm
Treatment with coagulant isessential
03. Explain in detail the working of rapid sand filter.Ans:
water
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Size of one unit !30m*60m~ .
02. What do you. understand by oss of head and negative head in a rapid sandfilter? What are the permissible values?
Ans. The loss of head in the 'filter operation is caused by the frictional resistance offered
by the filtering medium and the under drains to the water flow. The value of head
loss is equal to the vertical distance between water evel on the filter bed and the
elevation of the hydraulic grade line at the filter outlet. The loss of head
immediately after washing should not be more than 10- 15 cms. When sand bed
gets choked up with impurities the rate of discharge falls down and it is necessary
to wash it to regain its original clean conditions and the stipulated rate of discharge.
In the filters provided with loss of head indicators this choked up condition is shown
by increase in the loss pf head so that it reaches a certain figure generally
about 1.8 m the filter requires washing.
When the loss in the top layers of the sand becomes greater than the head of water
above the sand bed (due to choking) and the water column below such layers acts
as a draft tube and partial vacuum is created . This condition is known as negative
head. Thus the negative head at point in a filter is equal to the intensity of
vacuum at the point and is usually a maximum at the point where the water entersthe under drainage system.
129 BC2.5
Very large
Simple
Not possible
Not required
!
Efficient in removal of
bacteria and suspendedimpurities
Small area
Complicated
Possible
Most essential
Cannot remove all bacteria,disinfection necessary. Moreefficient in removal of color,odor and taste
6m*8m to 8m*10mI
Coagulationtank
Rapid sand filter
The pretreated water from the coagulation sedimentation tanks through th
valve is admitted into the filter units. It is distributed by the troughs which re
submerged while working over the entire bed area. The water then perc
through the sand and gravel layers and thereby the fine suspended and co
impurities present in it are arrested by the sand layer. After this it enters the la
through the strainers or holes and then leaves the filter unit via the manifold.
In the beginning the loss of head of filter is about 15- 22cm. As the filtering
goes on getting clogged with arrested impurities, the resistance to passa
water and hence the loss of head increases. Usually a maximum loss of h
2.5m is permissible. If it increases further till it may pack the sand so tightly
cause difficulties in back washing or may cause the water to break through
without filtration. The filter unit is then washed, the clogging is removed and nworking resumed
04. Explain in detail the construction and working of slow sand filter.
Ans: Slow sand filter consists of open tanks 2000to 4000sq. m in plan and 3 t
deep, containing 600-900mm thick bed ofsand supported on 300mm thick layer. The effective size of sand is 0.35mm with a uniformity coefficient of
1.75. The top of 150 mm layer ofthe filtering media is of a finer variety 0.25m
gravel size varies from 4.7 to 12mm and is placed in layers with the smallesparticles at the top and the largest on the bottom.
13 I•
14
15.
16
17
!
Area
Construction
Flexibility inoperation
Skilledsupervision
Efficiency
Ozonization is regarded as a natural meansofdisinfecting.water and is particuseful in disinfecting water containing bacterial spores. It is however cos
manufacture, has very little residuals present and is not quite suitable for h
turbid waters.
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Slow sand filter
The sand and gravels are laid over a system of open jointed underdrains placed 3
to 6 m apart on the bottom floor sloping towards a main covered drain constructed
along the center or side of the filter tank.
Settled waterf rom plain- sedimentation tank is distributed uniformly over the filter
bed. It percolates through the sand bed and the gravels and get purified during the
process of filteration. The under drainage system collects the filtered water and
passes it on to the clear water reservoir. As the filter media gets clogged the
resistance to the passage of water .and the head loss increases. The water in the
filter tank is first drained, the thick layer of impurities collected over the surface is
then scrapped and washed clean with wate r jets from hoses. The filter is then put
back into normal operation.
Name various disinfecting methods and explain anyoneofthem in detail.05 .
Ans: Various disinfecting methods are as follows
1. Chlorination
2. Ozonization
3. Ultraviolet ray method
4. Excess lime process
5. Application of silver
6. Iodineor bromine
7. Potassium permanganate
Ozonization-The effectiveness of ozone in the disinfection ofwater ies in its high
oxidizing power. Ozone is an unstable isotope of oxygen containing three atoms of
oxygen which while changing to the stable molecular form O2 releases nascent
oxygen. The nascent oxygen reduces organic matter present in the water without
the production of objectionable tastes and odors as with chlorine. The ozone dose
is 2-3mgll to give a trace of 0.1 mgtl' residual after 1Ominutes contact.
BC2.5131
06. What do you understand by chlorination? Explain its action in killing of bacteri
Ans: The process of applying small quantities of chlorine or chlorine compoun
water is called chlorination. The chlorine dose applied is generally 1ppm so
produce residual chlorine of quantity varying from a trace to about 0.05-0.2
The chlorine demand is defined as the difference between the amount of ch
added and the amount of chlorine remaining at the end of a contact period of
minutes.
Action of chlorine:
Chlorine reacts with water to produce hypochlorous acid (HOCI) and hypoch
ion (OC!), which are together known as free available chlorine. The chemical a
may be represented as
CI 2 + H20 = HOCI + HCI
HOCI =H+ +ocrIf ammonia is also present· in water, the other compounds fonned
monochloramine (NH2CI) and Dichloramine (NHCI2) which are together kno
combined available chlorine. These resulting chlorine compounds either
form of free or combined available chlorine interfere with certain enzymes
bacterial cell wall forming a toxic chloro corn pound thus destroying the ba
completely. The effect of chlorine as a disinfectant is principally dependent
the period of contact and the concentration of chlorine in water.
07. Explain chlorine ammonia t reatment for diSinfecting drinking water. What a
advantages of t.
Ans: Useof chloramines or use of chlorine With ammonia-
Chloramines are the disinfectant compound which are formed by the rea
between the ammonia and chlorine. These compounds are quite stabl
remain in the water as residuals for a sufficient time. Hence they can prod
greater safeguard against future pollution, although they are compara
weaker disinfectants compared to free chlorine. Doses of ammonia and ch
used will depend upon the local characteristics of water. Ammonia shou
properly applied and mixed with water about 20 min to 1-2 hours earlier
applying chlorine.
Advantages:
1. They do not cause bad taste and odor when left as residual as is cau
chlorine alone.
2. They are very useful when phenols are present in water. The reac
phenol with chloramines do not result n bad taste ofwater
3. Can remain in water as residual for sufficient time
132 B