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)

Why Alum?Introduction

Permissible Values of Turbidity

USA 0.5 – 1 NTU

European Union Inoffensive

Canadian 0.1 – 1 NTU

Indian Standards 10 NTU

An integral step in the Water Treatment Process

Colloidal InteractionsThe DLVO Theory

Electrical Repulsion

Van der Waal’s

Attraction

Energy Barrier

Energy Trap

CoagulationandFlocculationDestabilisation and Agglomeration of Colloids

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.

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.

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.

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.

Alum – How it works.Role of Alum in Coagulation-Flocculation

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

Reaction

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.

ExperimentationDetermination of Alum Requirement

Standard Solution used

Al2(SO4)3.16H2O

10 mg per ml of solution in water

ResultsDiscussions on Observations and Conclusions

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

)

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

)

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

)

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

)

Source

Alum

Dosage

(mg/l)

Lake beside the Cricket field 7

Lake behind the Library 12

Lake Serpentine 12

Brahmaputra 37

Thank You.