alum requirement for surface water
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STUDY OF ALUM DOSAGE REQUIREMENT FOR VARIOUS SURFACE WATER SOURCES IN AND AROUND IIT GUWAHATI CAMPUS
Ankur Bansal (09010408)Doshi Param (09010415)
Gagandeep Singh (09010417)Md. Qamaruddin Khan (09010433)Minakhi Prasad Misra (09010435)
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Why Alum?Introduction
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Permissible Values of Turbidity
USA 0.5 – 1 NTU
European Union Inoffensive
Canadian 0.1 – 1 NTU
Indian Standards 10 NTU
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An integral step in the Water Treatment Process
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Colloidal InteractionsThe DLVO Theory
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Electrical Repulsion
Van der Waal’s
Attraction
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Energy Barrier
Energy Trap
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CoagulationandFlocculationDestabilisation and Agglomeration of Colloids
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Ionic Layer Compression
Addition of ionic Salts brings about an ionic compression.
Ionic compression squeezes the repulsive energy curve reducing its influence. Further compression would completely eliminate the energy barrier.
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Charge Neutralisation
Coagulant addition lowers the surface charge and drops the repulsive energy curve. More coagulant can be added to completely eliminate the energy barrier.
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Inter-particle Bridging
Bridging occurs when a coagulant forms threads or fibers which attach to several colloids, capturing and binding them together.
Inorganic primary coagulants and organic polyelectrolytes both have the capability of bridging.
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Colloid Entrapment
Colloid entrapment involves adding relatively large doses of coagulants. Some charge neutralization may occur but most of the colloids are literally swept from the bulk of the water by becoming enmeshed in the settling hydrous oxide floc. This mechanism is often called sweep floc.
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Alum – How it works.Role of Alum in Coagulation-Flocculation
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When aluminum sulfate is added to water, hydrous oxides of aluminum are formed.
The simplest of these is aluminum hydroxide (Al (OH)3), which is an insoluble precipitate.
But several, more complex, positively charged soluble ions are also formed, including:
Addition in water
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Reaction
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Alum based Coagulation and Flocculation
The mechanism of coagulation by alum includes both charge neutralization and sweep floc.
One or the other may predominate, but each is always acting to some degree. It is probable that charge neutralization takes place immediately after addition of alum to water.
Simultaneously, aluminium hydroxide precipitates will form. The precipitate grows independently of the colloid population, enmeshing colloids in the sweep floc mode.
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ExperimentationDetermination of Alum Requirement
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Standard Solution used
Al2(SO4)3.16H2O
10 mg per ml of solution in water
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ResultsDiscussions on Observations and Conclusions
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0 2 4 6 8 10 12 14 16 18 20 22 240
1
2
3
4
5
6
7
8
9
10
Source 1: Lake near Cricket Field
Alum Dose (in mg/l)
Turb
idity
(in
NTU
)
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0 1 2 3 4 5 6 7 8 9 10 110
1
2
3
4
5
6
7
8
9
Source 2: Lake Behind the Library
Alum Dose (in mg/l)
Turb
idity
(in
NTU
)
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0 2 4 6 8 10 12 14 16 18 20 220
2
4
6
8
10
12
14
Source 3: Serpentine Lake
Alum Dose (mg/l)
Turb
idity
(in
NTU
)
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10 15 20 25 30 35 40 45 50 55 600
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
Source 4: River Brahmaputra
Alum Dose (mg/l))
Turb
idity
(NTU
)
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Source
Alum
Dosage
(mg/l)
Lake beside the Cricket field 7
Lake behind the Library 12
Lake Serpentine 12
Brahmaputra 37
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Thank You.