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Poi nts Tio Rem emb er:
1· \Va ter sho uld be filtered before it is
use d for drin kin g, as it con tain s ma ny
nak ed eye. ln order to have
imp unt ies tl1a t can not be easily see n with the
safe dnn kin g wat er, it sho uld be boiled.
wat er tha t goes down the dra ins
2. Ric h in lath er, mixed witl1 oil, blac k bro wn
from sin ks, showers, toilets, laundries is
dirty. It is called wastewater
3. The sludge is transferred to a sep ara te tan
k where it is decomposed by the
the process can be used as fuel
ana ero bic bacteria. The biogas produced in
or can be use d to produce electricity.
is not safe for drinking.
4. Water gets con tam ina ted by hum ans and it
ases suc h as cholera, typhoid
5. Drinking con tam inated water res ults in dise
fatal.
and dia rrh ea. Polluted wat er can also prove
people have to travel several
6. \Vater has become so sca rce tha t ma ny
kilometers to get drin kin g water.
.
7. Ma rch 22n d is cel ebr ated as World Water Day
d in several stages, and this
8. Pol luta nts in was te wat er can be remove
pro ces s is called "sewage treatment".
dissolved impurities, and the
9. This sewage is liquid was te containing
urit ies are call ed con tam ina nts , whi ch con tain ma ny han nfu l
imp
sub sta nce s.
can be reu sed , or released into a
10. Waste wa ter nee ds to be trea ted before it
ies and the se imp urit ies should
wa ter body. Wa stew ate r has ma ny imp urit
be removed by wa ter trea tme nt.
h chemicals like chlorine and
11. it ma y be nec ess ary to disinfect wa ter wit
n system.
ozone before rele asin g it into the dis trib utio
nt euc aly ptu s tree s all along
12. It has bee n sug ges ted tha t we sho uld pla
plu s was tew ate r rapidly and
sewage pon ds. The se tree s abs orb all sur
e
release pur e wat er vap our into the atm osp her
down the dra in. They can har den
13. Cooking oil and fats sho uld not be thro wn
and block the pipes.
mo tor oil, and medicines may
14. Chemicals like pai nts , solvents, insecticides,
kill microbes tha t help purify wa ter
h covered dra ins into a biogas
15. Excreta from the toilet sea ts flow thr oug
rce of energy.
plant. The biogas produced is use d as a sou
re is no dus tbin in sig ht, we
16. We should not sca tter litter anywhere. If the
the dus tbin .
should car ry the litter home and throw it in

NARAYANA GROUP OF SCHOOLS 78

 CBSE CHEMISTRY STUDY MATERIAL CLASS - VII
··-··--· .................................................................................................................... .
·-
2. What is sewage?
industries, agricultural
Ans. The waste water that is being generated at homes,
activities, huma n activities etc. is called sewage.
3. What do you mean by "aewaae treatment"?
before it enter s a
Ans. Sewage treatm ent is a process of removing pollutants
water body or is refused.
4. Name two chemical• uaed to diainfect water.
Ans. Chlorine and ozone
State various uses of water. \
5.
cloii es and utens ils •
Ans. Water is used for: •Drin king • Cooking• Washing
Generating electricity • Bathing
• Habitat for various organisms etc.

Short answer questions

ment plant.
1. Explain the function of bar screens in a wastewater treat
rities. Large size
A. Bar screens clear the wastewater of all the physical impu
the waste wate r
waste like napkins, plastics, cans etc. are removed from
through the bar screens.
Explain.
2. Why should oils and fats be not released in the drain?
harde n the soil
A. Oils and fats should not be released in drains because they
the soil in the
in the pipes and block them. Fats get clogged in holes of
drain and block it. It does not allow the water to flow.
3. What is sludge? Explain how it is treated.
g the
A. Sludge is the collected solid waste from the wastewater durin
in a separ ate
treatment in water treatm ent plant. Sludge is decomposed
manu re.
tank by the anaerobic bacteria. Activated sludge is used as
4. Untreated human excreta is a health hazard. Explain.
d problems. It
A. Untreated huma n excreta can cause a lot of healt h relate
se causi ng
pollutes water, air and soil. The polluted water contain disea
etc.
bacteria which can sprea d epidemics like cholera, meningitis

5. What is waste water?

polythene bags,
A. The dirty water which contains various impurities like dust,
the drain s from
Vegetable peels, kitchen waste, oil & water that goes down
e wate r cann ot be
sinks, showers, toilets, laundries etc. is waste water. Wast
used further.
se.
6. Explain the relationahip between sanitation and disea

NARAYANA GROUP OF SCHOOLS

 ·~

CBSE CHEMISTRY STUDY MAT~'RIAI, CJ,AMl .. \'IJ

·······--· ----- ------------------------~---------------- ······································ ·:·····:·--..i----· ....
A. Sanitation and di~t'HS<' ate H'ln1t•d to (•nch ol h,•r. Sani1:it1<m mvo vc_ pro-J}{....,.
.
d isposal t I I'<' phccs ·, Jf samtatin1J •~
of sewage and I t•fttsl' from house HTH. pu J 1 ,, '
,
there, no disease will occur, but if sn11ilation is no1 there VfJnouo t~pcs of
disease will occur and spread. So snnitntion should be kept to avmd
disease.
7• Outline your role as an active citizen In relation to sanitation.
A. As active citizen we should take care of our personal environmental
sanitation. We should make people aware of the benefits of sanitatifm, We
should help municipal corporations to cover all the open drajns and remove
disease causing substances thrown in open.
8. What is a manhole? Why are manholes made?
A. A manhole is a covered vertical hole in the ground, pavement or road above
the underground sewer pipeline.
If there is any leakage or blockage in the underground sewer pipeline, the
sanitary worker can go down, up to these sewer pipelines for cleaning or
any repair.
9. Why should not chemicals be released in the drain?
A. Chemicals like paints, solvents, insecticides should not be thrown down the
drain as it may kill the useful microbes that help to decompose the waster
present in the sewage & purify water.
10. Why should used tea leaves, solid food remains, etc. not be released in
the drains?
A. Used tea leaves, solid food remains etc. should not be thrown down the
drain as they may choke the drain.
11. What do you understand by the term "sewerage"?
A. Sewerage is like a transport system that carries sewage from the point
where it is being generated to the point of disposal i.e. treatment plant.
12. Suggest alternative arrangement for sewage disposal.
A. To improve sanitation, low cost onsite sanitation sewage disposals are
being made. For example: septic tanks, composting pits etc.

13. Why are bacteria used in sewage treatment plants?

A. The bacteria decompose the s1:15pended waste that includes domestic wastes
& other undesirable organic substances present in the clarified water.
The activity of bacteria produces decomposed organic material from which
solid waste is separated. This solid waste is used as manure.

NARAYANA GROUP OF SCHOOLS

CBSE CHEMISTRY STUDY MATERIAL CLASS VII
.... ··--------
.................................................... ···•··•···· -

14. What are tlie harmful effect, of aewerage?

Ans. Accumulation of sewerage leads to:
a) spread of various diseases.
b) Water pollution.
LONG ANSWER QUESTIONS
1. Explain the various types of sewage.
A: There are various types of sewage, depending upon its colour and odour.
Some sewage is black and has a very bad odour.
Sullage water: Waste water released from the kitchen is called sullage water.
The contaminants in sullage water are mild detergents, oils and food
particles. Moreover, it contains lots of water released when utensils are
washed.
Foul waste: Waste water released from toilets is termed as foul waste. It
consists of human waste and a lot of bacteria that release gases and bad
odour. It is highly infectious.
Trade waste: Waste released from industries and commercial organizations
is called trade waste. It consists of acids and strong chemicals that are toxic
in nature.
2. List five ways to control sewage generation.
A. Ways to control sewage generation are:
• Leakage in sewer lines should be checked & repaired regularly.
• Do not defecate, spit or scatter litter in public places.
• Used tea leaves, solid food remains, toys, towels etc. should not be thrown
in water pipe because these materials may choke the pipe.

3. Describe the step, involved in getting clarified water from wastewater.

A. Following steps are involved in the purification of water:
(i) Firstly all the physical impurities like stones, plastic bags, cans etc. are

NARAYANA GROUP OF SCHOOLS

 CBSEcttEM1
--------~\' Sl'UD\ MATIERIAL

to be Temo\ ~ 1~ ;~ d · ..... . ..... . ·····-··········-~-~~-~:.~11

{ii) lb one b) passmg the \\atcr through bar screens. ··-
en Water is take t
~erno\ ed b) sed1mentatton.
°
n gnt and sand removal tank where impuritie
s are
(iii) Sohd Lm u ·
lbes . P nties a nd feaccs etc. are collected from bottom of water.
. e tmpuriues collected are called sludge.
(n) Clarified w t · 1
a er is c eaned of other impurities by aerator. All disease
cau ·
sing bacteria are removed by chlorination.

WORKSHEET- 1
l. \\by are open drains a concern?
2
· Sta.te whe ther the following statements are True or False.
In case a statement is false, write the correct statement.
(a) Sewage is a s 0 lid ·
waste which causes water pollution and soil pollution.
12/04/2018 95
(b) Used water is wastewater.
(c) Vilastewater could be reused.

(d) Where underground sewerage systems and refuse disposal systems are not
available, the high cost on-site sanitation system can be adopted.
3. How are open drains harmful for human health?
4. Name two inorganic impurities present in sewage. 15. Animal waste, oil and
urea are some of the organic impurities present in sewage. Name two more
organic impurities present in sewage.
5. Name two alternative arrangements for sewage disposal where there is no
sewerage system.
6. A man travelling in a train threw an empty packet of food on the platfonn.
Do you think this is a proper waste disposal method? Elaborate.
7. Why should we not throw (a) used tea leaves into sink? (b) Cooking oil and
fats down the drain?

WORKSHEET- 2
1. • and orgaruc
What are the different types of inorgaruc · unpun
· 'ties generally
present in sewage?

NARAYANAGROUP OF SCHOOLS