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Chapter 4A
Wastewater Treatment: Characteristics and Systems
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Learning Outcomes
At the end of this learning session
students should be able to1! "nderstand what causes water pollution
#! $ecogni%e the sources of wastewater
&! State the characteristics of wastewater
4! Appreciate the importance of w'w treatment
(! Apply systems used to treat the wastewater
#
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What is water pollution)
* Water pollution is any chemical+ physical orbiological change in the ,uality of water that
has a harmful effect on any li-ing thing thatdrin.s or uses or li-es /in0 it!
* When humans drin. polluted water it often
has serious effects on their health! Waterpollution can also ma.e water unsuited forthe desired use!
&
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The Sources of ollution
Water pollution occurs when a
body of water is ad-ersely
affected due to the addition oflarge amounts of materials to the
water! When it is unfit for its
intended use+ water is considered
polluted!
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2omestic and 3ndustrial Sewage+ which
contains decomposable organic matter and
pathogenic agents! 3ndustrial and trade wastes+ which contain
toic agents ranging from metal salts to
comple synthetic organic chemicals!
Agricultural pollutants+ which comprisefertili%ers and pesticides!
hysical pollutants+ such as thermal pollution
and radioacti-e substances!
Sources of Water ollution
(
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A heavily polluted stream in Guiyu, China. Along side domestic
rubbish the water is badly polluted with toxic waste from the e-
waste recycling yards in the town. 5
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Example of water pollution
Citarum River (West Java) –
Most polluted in the world
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olluted $i-er in 3ndia
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yoto $i-er
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1#
Clean river and
drainage channels in
Kyoto (ug !""#)
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1&
A River in Seoul,Korea
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;ur.y lang $i-er in L
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A River in KL,
Malaysia
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What is Wastewater)
* Wastewater is any water thathas been ad-ersely affected in,uality by anthropogenic influence!
* 3t comprises li,uid wastedischarged by domesticresidences+ commercialproperties+ industry+ and'oragriculture and can encompassa wide range of potentialcontaminants andconcentrations!
* 3n the most common usage+ it refers to the municipalwastewater that contains a broad spectrum of contaminantsresulting from the miing of wastewaters from differentsources!
1(
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Wastewater Contaminants
* Suspended solids < can causesludge deposits and anaerobicconditions in the en-ironment
* Biodegradable organics < cancause anaerobic conditions in
the en-ironment* Pathogens < transmit disease
* Nutrients < can causeeutrophication
* Heavy metals < toicity to biotaand humans
* Refractory organics < toicity tobiota and humans
* Dissolved solids < interferewith reuse
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Characteristics of Wastewater
* Physical < The physical characteristics of waste water
include its solid content==suspended organic
matter+ floating matter and dissol-ed matter+its temperature+ color+ odor'smell+ density+conducti-ity+ specific gra-ity+ transmittanceand specific weight!
< Septic sewage is blac. /due to precipitation ofiron sulfide0
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* Chemical < ;unicipal wastewater also contains a -ariety of inorganic
substances from domestic and industrial sources+ including a
number of potentially toic elements such as arsenic+ cadmium+
chromium+ copper+ lead+ mercury+ %inc+ etc!
< Among the organic substances present in sewage arecarbohydrates+ lignin+ fats+ soaps+ synthetic detergents+ proteins
and their decomposition products+ as well as -arious natural and
synthetic organic chemicals from the process industries!
< >umber of chemicals found in w'w is limitless
< ;easure of w'w strength often use CO2 and ?O2
* CO2 < Chemical Oygen 2emand
* ?O2 < ?iological Oygen 2emand
Characteristics of Wastewater
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Characteristics of Wastewater
* Biological < athogenic bacteria will be present in wastewater
at much lower le-els than the coliform group of
bacteria+ which are much easier to identify and
enumerate /as total coliforms'199ml0!
< Escherichia coli are the most widely adopted
indicator of faecal pollution and they can also be
isolated and identified fairly simply+ with theirnumbers usually being gi-en in the form of faecal
coliforms /@C0'199 ml of wastewater!
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Characteristics of 2omestic
Wastewater
#9
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;unicipal Wastewater
Treatment Systems
* retreatment < remo-es materials
that can cause operational
problems+ e,uali%ation optional
* rimary treatment < remo-e 59B
of solids and &(B of ?O2
* Secondary treatment < remo-e
7(B of ?O2 and solids* Ad-anced treatment < -aries: 8(
B of ?O2 and solids+ >+
#1
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retreatment of 3ndustrial
Wastewaters
* 3ndustrial wastewaters must be pretreated
prior to being discharged to municipal
sewer system* Approach is to remo-e materials that will
not be treated by municipal system
* Local authority must monitor and regulateindustrial discharges
* retreatment re,uirements set by the law
##
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#&
Primary reatment
Secondary
reatment
!"#$%$&'$(NPrimary reatment
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#4
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#(
Sewage
Tunnels
in 2e-elopedCountries
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Treatment lant
#5
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The Stic.ney WWT+ located on (69 acres in Cicero+ 3llinois+
southwest of Chicago+ ser-es #!4 million people li-ing in Chicago
and 4& suburban communities! Capacity: 1!44 billion gallons per
day! #6
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Screens
* Coarse screens < @unction to remo-e
large obDects such as
pieces of wood+ plastic
bottles+ rags+ tetileetc
< Si%e of opening up to
6(=199 mm
< Cleaned eithermanually or
mechanically
#7
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Screens* @ine Screens
< @unction is to remo-efine contaminants+
debris+ plastics that
are not hang on
coarse rac. screen! < Opening si%e small up
to only 1& mm
< ;ost fine screens are
mechanically cleaned
#8
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Erit Chambers
* urpose: remo-e inertdense material+ such as
sand+ bro.en glass+ silt
and pebbles! These
materials is called FgritG
* Erit will cause abrasion
of pumps and other
mechanical de-ices if
not remo-ed
* Erit chambers can be of
rectangular or circular
shape /-orte0
&9
>ote : All design and calculation are the
same as water supply grit chamber
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Horte Erit Chamber * The screened influent enters
tangentially and flows around the
upper chamber
* AdDustable+ rotating paddles or Det of
air augment the spiraling flow to
create an induced -orte which
settles the grit+ transports it to the
center opening of the fied floor plate
for collection in the lower chamber
* The grit solids are remo-ed from the
lower chamber by an air lift or
recessed impeller pump for further
washing and dewatering!
&1
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Ind of Chapter 4A
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