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SOUTH MOUNTAIN SCHOOL LIBRAR1 - --~ ;- :. MILLBURN, N. ,. , ,_
l ' OLLUT .i,D
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?-I any years :'l,_;- o ,fl1en y o ur fc1. t he r
was in your ar;e ,
he c ou l d g o t o a ri v er near a bic_; cit y f or s wi mn iin c;
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?-; ow , you
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a big ci ty .
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c<1.rrn ot sw i m or p l a y
Do y ou kn o w why
?
in a
If y o u
w i l l t e l l you .
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The wa t e r
of
a riv e r
n ear a b i g ci t y ha s bad s me ll
and ma n y ge r ms wh ich ma ke you sick .
d i r t y 1¡,a ter " po ll uted wa ter ".
We call t h is
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The water of t r1e river be c ame d irty bec a us e
peop l e have dumped many d i rty was t e into th e r i ver.
Ma ny factories a lso dump t he i r d i r ty wa st e into the
river .
We c a ll t h is d irty waste "s e wage ".
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The g e r ms in a d irty wa ter make fis he s si c k .
If you eat a sick fi sh, you wi l l be c ome sick also .
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Do you k n ow h ow we c a n cle a n t he s ewag e ?
I will tell you the answer.
First, we must mea s u r e
how many germs are in the sewage.
The g erms are so
small that we cannot see them with our e yes.
Therefore,
we measure the amount of oxygen the g e rms e a t up.
large amount of oxygen is eaten up, we can tell that
there are many germs in the sewage.
l>y
We call the
amount of oxyg en eaten up/'--the germs "the biochemical
oxygen d emand".
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Second , if the r e are many g erms in t he sewage , we
must k ill t h em be for e we dump t he s e wage into t h e
river.
It is very difficult, and take s lots of
money to clean the sewage.
But, we must do it in
order to have clean rivers.
sewage "the s ewage treatment".
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We c all this cleaning of
8
Step One :
screen .
and rags .
The sewag e wa ter pa sses through a
This catch es lar ge objects such as sticks
SEWAGE TREATMENT
There are t wo st eps i n sew age tr ea tment.
We
c a ll t h ese the pri mary treatment and t h e secondary
treatment.
By the primary treatment, we re move all
of solids such as sticks, g ravel, and sands.
7
9
Step Two:
Next the sewage water f lows slowly
This allows
through a tank called "grit chamber".
sand, g ravel, and oth er h eavy objects to settle.
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The s e wage wa t e r
S te p T h r e e :
a l a r g e t a nk c a l l e d
" pr i mary settli ng t a n k " wh ere
T h e s o l i ds are d ivided
it st a nd s for a l ong t ime .
On e g roup s e ttl e s to t h e b ottom
into t wo g roup s .
of t he t a nk .
group r i se s
t hen flo ws i nto
1·ve c a l l t h is " sludg e" .
We c a l l
t o t h e top .
Th e other
th i s "scum" .
The
wa t e r b e t ween t h ese two gr ou ps is drain e d off .
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When t he sewa~e 1vat er l eav e s th e primary tr ea t me nt ,
it may b e d i s c har ge d into a river if it is clean .
If it ne e d s more cleaning , we pass t he m t h r ou gh the
secondary tre a t ment .
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S t ep One :
The sewag e water is spr a yed over stone s
in a tank and a llowed to trickle d own through them .
We call t h i s tank "t r ickling fi lter".
c atch t h e ge r ms in the sew age water .
The stones
13
Step Two :
The sewage wa t er may t h en be s e nt to
another tank whe re it is allowed t o st a nd while
Thi s tank is c a lled "th e
remaining s o lids settle .
secondary settling tank" .
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S t ep T hr e e :
F inally 1ve may
add a gas c a l l ed
" chl or ine" to he l p k i l l g e rms.
"chlorina ti o n ".
We c a l l t his
The wa t er i s
then d ischarged into
a lake or a rive r.
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Now, many c i ti es a nd factories d o not have s u ch
This is why we h ave
sewag e treatment p lants.
such a dirty river ne a r
cities a nd factories.
It
is our job to b uil d such a sewage treatment plant
in order to h ave a clean river where we can swim
and fish.
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Date Due
00011! MOUNTAIN SCHOOL LIBRARYMILLBU:RN, N. J.
00 Printed In U.S.A.