water treatment processes:- coagulation , flocculation, filtration by kalpesh solanki

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Presented by :-Prof. Kalpesh Solanki

Major Clean Up Water Treatment Processes:-Coagulation , Flocculation, Filtration

Course Content

Introduction

Water treatment process or Methods

Coagulation and flocculation

Filtration

IntroductionWhy it is needed?

To kill all pathogenic germs, which are harmful to human health

To remove the unpleasant and objectionable taste and odours from the water

To remove dissolved gases ,colour of water

To make water fit for domestic, industrial, and commercial uses.

To remove micro organism and colloidal matters

To remove hardness of water05/02/23 water treatment

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Raw water collection

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Initial Stages Screening - the removal of any floating objects like leaves,

branches, fishes , weeds, etc. from the water.

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Sedimentation: Removal of Suspended matters having higher specific gravity than water and also fine suspended matter.

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Aeration – Dissolving oxygen into the water to remove smell and taste, promote helpful bacteria to grow, and precipitate nuisance metals like iron and manganese.

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Spray aerators

Major Clean Up• Coagulation and flocculation - causes the agglomeration

and sedimentation of suspended solid particles through the addition of a coagulating agent (usually aluminum sulfate and/or iron sulfate) to the raw water along with a polymer to help form a floc.

• Filtration- Remove Micro-organism and colloidal matter

• Disinfection---Pre-chlorination and dechlorination - mostly to kill algae that would otherwise grow and clog the water filters. Also kills much of the remaining unprotected bacteria.

• Softening- To remove hardness

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COAGULATION & FLOCCULATION Removal of colloidal substances from water

Potable water requirements: health, aesthetics, economic

Colloids

Size of colloids - light waves

Brownian motion

Stability of colloids

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Theory of coagulationCoagulation is the destabilization of colloids by addition of chemicals that neutralize the negative charges

The chemicals are known as coagulants, usually higher valence

cationic salts (Al3+, Fe3+ etc.)

Coagulation is essentially a chemical process

Ionic layer compression

Adsorption and charge neutralization

Entrapment in a flocculent mass

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Relative coagulating power

Na+ = 1; Mg2+ = 30 Al3+ > 1000; Fe3+ > 1000

Typical coagulants

Aluminum sulfate: Al2(SO4)3.14 H2O Iron salt- Ferric sulfate: Fe2(SO4)3

Iron salt- Ferric chloride: Fe2Cl3

Polyaluminum chloride (PAC): Al2(OH)3Cl3

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Aluminum Chemistry

1 mole of alum consumes 6 moles of bicarbonate (HCO3-)

Al2(SO4)3.14 H2O + 6HCO3- 2Al(OH)3+ 6CO2 + 14H2O + 3SO4

-2

•If alkalinity is not enough, pH will reduce greatly

•Lime or sodium carbonate may be needed to neutralize the acid.

•(Optimum pH: 5.5 – 6.5)

With alum addition, what happens to water pH?

Al2(SO4)3.14 H2O 2Al(OH)3+ 8H2O + 3H2SO4-2

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Alkalinity calculation

Al2(SO4)3.14 H2O + 6HCO3- 2Al(OH)3+ 6CO2 + 14H2O + 3SO4

-2

594 mg 366 mg

If 200 mg/L of alum to be added to achieve complete coagulation. How much alkalinity is consumed in mg/L as CaCO3?

594 mg alum consumes = 366 mg HCO3-

200 mg alum will consume = (366/594) x 200 mg HCO3-

= 123 mg HCO3

-

Alkalinity in mg/L as CaCO3 = 123 x (50/61)

= 101 mg/L as CaCO3

Al3+ species as a function of pH

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Iron ChemistryFeCl3+ 3HCO3

- Fe(OH)3+ 3CO2 + 3Cl-

With iron salt addition, what happens to water pH? (Wider pH range of: 4 – 9; Best pH range of 4.5 – 5.5)

1 mole of FeCl3 consumes 3 moles of bicarbonate (HCO3)

If alkalinity is not enough, pH will reduce greatly due to hydrochloric acid formation. Lime or sodium carbonate may be needed to neutralize the acid. Lime is the cheapest.

Mixing device

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1- Mixing basins with baffle walls2- Mixing basin with mechanical devices (Rapid mixing)

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• Rapid or Flash mixing is the process by which a

coagulant is rapidly and uniformly dispersed through the

mass of water. This process usually occurs in a small basin

immediately preceding or at the head of the coagulation

basin. Generally, the detention period is 30 to 60 seconds and

the head loss is 20 to 60 cms of water. Here colloids are

destabilized and the nucleus for the floc is formed.

Slow mixing brings the contacts between the finely

divided destabilised matter formed during rapid mixing.

Coagulation aim

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What is Flocculation?

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Flocculation is the agglomeration of destabilized particles into a large size particles known as flocs which can be effectively removed by sedimentation or flotation.

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Why coagulation and flocculation? Various sizes of particles in raw water

Particle diameter (mm) Type Settling velocity

10 Pebble 0.73 m/s

1 Course sand 0.23 m/s

0.1 Fine sand 0.6 m/min

0.01 Silt 8.6 m/d

0.00010.0001 (10 micron)(10 micron) Large colloidsLarge colloids 0.3 m/y0.3 m/y

0.000001 (1 nano)0.000001 (1 nano) Small colloidsSmall colloids 3 m/million y3 m/million y

Colloids – so small: gravity settling not possible

G r

a v

I t y

s e

t t l

I n

g

Fe species as a function of pH

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Hydraulic Flocculation• Horizontally baffled tank

Plan view (horizontal flow)• Vertically baffled tank

LIsometric View (vertical flow)

L

W

H

The water flows horizontally. The baffle walls help to create turbulence and thus facilitate mixing

The water flows vertically. The baffle walls help to create turbulence and thus facilitate mixing

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http://www.environmental-center.com/magazine/iwa/jws/art4.pdf

Hydraulic Flocculation

Hydraulic flocculators

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Hydraulic flocculators: simple technology

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Flocculators integrated with settling

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Flocculators integrated with settling

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Flocculators both sides of settling

Clarifier• After Flocculation Water enters the settling tank which is

commonly called Clarifier.

Clariflocculator

In modern practice, flocculator and clarifier are provided in one unit called Clariflocculator in which chamber is provided in the center and clarifier compartment is formed by the periferical space.

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Filtration

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The process of passing the water through the bed of such granular materials is known as filtration.

Types of filter

1- The slow sand gravity filter

2- Rapid sand filter

Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 metres deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water.

Filter through a 3 to 5 foot deep bed of unstratified sandflow rate 0.05 gallons per minute per square foot. Biological growth develops in the upper surface of the sand is primarily responsible for particle and microbe removal.Effective without pretreatment of the water by coagulation‑flocculation.

Periodically clean by removing, cleaning and replacing the upper few inches of biologically active sand.

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Microbial Reductions by Slow Sand Filtration

• Effective in removing enteric microbes from water. • Virus removals >99% in lab models of slow sand filters.

– Up to 4 log10; no infectious viruses recovered from filter effluents

• Field studies: – naturally occurring enteric viruses removals

• 97 to >99.8 percent; average 98% overall; • Comparable removals of E. coli bacteria.

– Virus removals=99‑99.9%; – high bacteria removals (UK study)

• Parasite removals: Giardia lamblia cysts effectively removed– Expected removals ~ 99%

 Rapid sand filters

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Rapid sand filtration is a purely physical

drinking water purification method. Rapid sand filters (RSF)

provide rapid and efficient removal of relatively large

suspended particles. Two types of RSF are typically used: 

Rapid gravity

  Rapid pressure sand filters

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•The biggest disadvantages of slow sand filter is that it

requires large area due to slow filtration rate.

•This Requirement make it uneconomical for places where

land is very costly in urban area. In order to reduce

requirement of space and to increase the rate of filtration , a

lot of research conducted which finally led to the developed

of rapid sand filter.

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Rapid sand filters have filter rates 40 times those of slow sand filters. The major parts of a rapid sand filter are:

• Filter tank or filter box

• Filter sand or mixed-media

• Gravel support bed

• Under drain system

• Wash water troughs

• Filter bed agitators

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PRESSURE FILTERS Pressure filters fall into two categories:

pressure sand and diatomaceous earth filters. Pressure

filters are used extensively in iron and manganese removal

plants. A pressure sand filter is contained under pressure in

a steel tank, which may be vertical or horizontal, depending

on the space available. As with gravity filters, the media is

usually sand or a combination of media, and filtration rates

are similar to gravity filters. Groundwater is first aerated to

oxidize the iron or manganese, and then pumped through the

filter to remove the suspended material.

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Construction rapid sand filter

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1- Enclosure tank

2- Filter Media

3- Base material

4- Under Drainage system

5- Other appurtenances

Enclosure tank

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Rectangular in plan

Constructed either of masonary or of concrete , coated with water proof material

Depth- 2.5 to 3.5 m

surface area- 10 to 50 m2

length to width ratio 1.25 to 1.35

Filter media

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It consist sand layer -60 to 90 cm in depth

Effective size of sand varies from 0.35 to 0.6 mm

finer sand be used

Base material

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Graded gravel

total depth varies from 45 to 60 cm

Divided in to 4 to 5 layers

Size (mm) Depth (cm)

2 to 5 5-8

5 to 12 5-8

12 to 20 8-13

20 to 38 8-13

38 to 65 13-20

Under drainage system

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Purpose: It collect the filtered water uniformly over the area of gravel bed.

It provides uniform distribution of backwash water without disturbing the gravel bed and filter media.

Types of under drainage system

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1- Manifold and lateral System

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Wheeler system

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Leopald system

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THANK

YOU