WATER TREATMENT TECHNOLOGY (TAS 3010) LECTURE NOTES 9a -Water Intake, Screening, Aeration, Coagulation

Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT© SHAHRUL ISMAIL, DESc.University College of Science and Technology Malaysia

CHAPTER 3:Environmental Microbiology

CHAPTER 9a : CHAPTER 9a : CHAPTER 9a : CHAPTER 9a :

TAS 3101 : WATER TREATMENT TECHNOLOGY

Water Treatment Water Treatment

Process :Process :

Water Treatment Water Treatment

Process :Process :

Water Intake, Water Intake,

Screening, Screening,

Aeration, CoagulationAeration, Coagulation

Water Intake, Water Intake,

Screening, Screening,

Aeration, CoagulationAeration, Coagulation

Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT

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1) Introduction

2) Water Intake

3) Water Treatment Process

4) Screening

5) Pre-Sedimentation

6) Aeration

7) Coagulation


Characteristic from surface sources - unsuitable for human

consumption, industrial use, commercial use etc.

Characteristics :

1) Turbid

2) Colour

3) Acids, salts and gases – corrosive action – impart hardness of

water

4) Bacteria – Water borne diseases.

Introduction


Objectives :

“ To remove harmful microorganisms or chemicals, thereby preventing the

spread of disease in order to supply clean and safe water for public demand”

Good water source :

Raw water with a coliform count of up to 5000/100mL and turbidity up to 10

units

Poor water source :

Raw water with coliform counts that frequently exceed 20,000/100 mL and

turbidities that exceed 250 units.

Objectives


Content must be removed from the water

source

Waste

Solid material / Colloidal particles

Pathogen

Heavy Metal

Exceed dissolved salt

Water Treatment - Pollutant


FACTORS CONTRIBUTE TO THE SELECTION

OF TREATMENT METHOD :

Sources of water intake

Characteristic of water

Cost

Water Treatment – Selection


SELECTION CRITERIA FOR WATER INTAKE LOCATION :

Must have the best available water quality

Far from strong current – adverse affect water intake

potential

Quantity of water demand can be achieved even at a

very low water flow rate

Near to water treatment plant

Easily accessible & possess adequate space and facilities

for maintenance works

1 – Water Intake


SOURCES OF WATER INTAKE :

SURFACE WATER : Particle Removal

GROUNDWATER : Removal of dissolved inorganic

contaminants

WATER STORAGE

- High content of Fe & Mn

- Algal Bloom

1 – Water Intake Sources


Typical treatment plant for surface water :

1) Screening and grit removal

2) Primary sedimentation (settling/clarification)

3) Coagulation (Rapid mixing)

4) Flocculation

5) Secondary sedimentation

6) Filtration

7) Sludge processing

8) Disinfection

Surface Water Treatment


Surface Water Treatment


Typical treatment plant for groundwater :

1) Aeration

2) Flocculation/precipitation

3) Sedimentation

4) Recarbonation

5) Filtration

6) Disinfection

7) Solids processing

Groundwater Treatment


Groundwater Treatment


Water IntakeWater Intake ScreeningScreening

FlocculationFlocculation

Pre-SedimentationPre-SedimentationAerationAeration

pH AdjustmentpH Adjustment

CoagulationCoagulation

SedimentationSedimentation

DistributionDistribution DisinfectionDisinfection

Pump HousePump House

Water Treatment – Process

Filtration Filtration


Pipes design must take into account the

quantity of water to be sucked out

Pipes position must consider the water level

during dry season

Must be fenced for security purposes

Must have screens on pipe or intake

structure – prevent entry of objects that might

damage pumps and treatment facilities

Intake Structure


-Water from rivers may be stored in bankside

reservoir for periods between a few days – months to

allow natural biological purification.

-Provide buffer against short periods of drought or to

allow water supply to be maintained during transitory

pollution incidents in the source river.

-Blending water source.

Pump House - Storage


Gate controls

Water Surface

Open Port

Closed port

Outlet

Entry Port

Tower Water Intake


Tower Water Intake


-With grit removal, remove suspended debris, sand, grit, large

and hard floating huge and hard materials

- Settles very rapidly

- Prevent from damaging pumps & other mechanical devices

- Most deep groundwater does not need screening before

purification steps

Screening


Traveling Water Screen


Screening


- Required if the raw water is too dirty.

- Store the raw water temporarily before proceed to the main

process.

- Removes the particles that will settle out by gravity alone

within few hours.

- Sedimentation basin/clarifier – circular/rectangular tank

holds water for suspended solids settlement.

- Equipped with bottom scraper and hopper that removes

collected sludge.

Pre-Sedimentation


Purpose :

1) Eliminate unneeded dissolved gases

- Remove unpleasant taste and odour-causing substances

- Increase water pH.

- Remove substances that interfere with or add to the cost

of subsequent water treatment processess.

Aeration


Purpose :

2) Increase DO level in water

- Oxidation of Fe2+ to Fe3+ and Mn2+ to Mn4+ respectively

- Increase the water freshness

3) Remove VOC

- Hazardous to public health e.g. gassoline elements

(benzine, xylene etc)

Aeration – Con’d


Oxidation of Soluble Fe (II) and Mn (II) to insoluble Fe (III) and Mn (IV)

4Fe2+ + O2 + 10H2O 4Fe (OH)3 +

8H+

2Mn2+ + O2 + 2H2O 2MnO2 + 4H+

- Appromixately : 0.14 mg/L O2 will oxidise 1 mg/L Fe (II)

0.29 mg/L O2 will oxidise 1 mg/L Mn (II)

- Produce floc / settled Fe & Mn

Aeration – Mechanism


- The production of 1 meq/L H+ will destroy 1 meq/L alkalinity.

- If sufficient alkalinity is present, H+ ion concentration will increase

during the oxidation process – result in decrease water pH

- Effectiveness :

Depends on pH and the reaction time

- Chloride and Potassium Permanganate are also commonly used

oxidizing agent

- Physically, to force O2 to attached to one another. Therefore, Do

level is increased

- Water will settle as Fe (OH)3, indirectly Fe & Mn will be removed



1)Cascade Aerator

2)Multiple Platform Aerator

3)Venturi Aerator

4)Draft-Tube Aerator

Objectives of all types of Aeration :

“ To maximize the area of contact between the water

and the air”

Aeration – Types


Raw Water

Aerated Water

Cascade Aerator


Water Basin

Platforms

Multiple Platform Aerator


Perforated Pipe

Air Supply

ThroatVenturi

Aerated WaterRaw Water

Venturi Aerator


Air

Raw Water

Sludge

Aerated Water

Draft Tube Aerator




1) Many of suspended water particles have a negative

electrical charge.

2) Coagulation eliminates natural electrical charge so they

attrack and stick to each other.

3) Form particles large enough to be removed by the

subsequent settling or filtration process

How ?

- Coagulant chemicals are added to water, rapid mixing ;

causing a reduction of the forces tend to keep particles

apart.

Coagulation


- Particles in water sources that contribute to colour and

turbidity

- Mainly clays, silts, viruses, bacteria, fulvic and humic acids

and organic particulates

- At pH levels above 4.0, particles or molecules are generally

negatively charged

- Have a very large ratio of surface area to volume

Coagulation – Colloidal Particles


Factors Affecting Coagulation Process :

- Chemical Coagulant Dosage

- pH Adjustment

- Turbidity

4 - Coagulation


Most commonly used coagulants :

Others :

Sodium aluminate

Chemicals Description

Alum (Aluminium Sulphate) Often used in conjuction with cationic polymers

Ferric Chloride May be more effective than alum in some application

Ferric Sulphate Effective in some waters and more economical in some location

Cationic Polymers Can be used alone as the primary coagulant or in conjunction with aluminium or iron coagulant

Coagulation - Chemicals


• Physical operation affecting coagulant dose efficiency.

• Chemical addition and quick/uniform mixing• Design criteria

– Detention time between 10 and 30 seconds– G, velocity gradient of 600 - 1000 s-1

– V < 8 m3

Rapid Mix- Basin


• Design liquid depth– 0.5 - 1.1 times basin diameter or width– 1.1 - 1.6 times basin diameter or width (dual

impeller)• Impeller diameter 0.3 - 0.5 times the tank

diameter or width• Baffles extend 10% of tank diameter or width

Rapid Mix- Basin – Con’d


to = V / Q

to = detention time, s

V = volume of the basin, m3

Q = flow into basin, m3/s

Rapid Mix- Basin Design


G = (P / V) ½

G = velocity gradient, s-1

P = power input, Watt or Nm/s or J/s

V = volume of water, m3

= dynamic viscosity, N.s/m2

Velocity Gradient, G


to

0.5 (in-line blending)

10 – 20

20 – 30

30 – 40

> 40

G

3,500

1,000

900

800

700

G values for rapid mixing


QUESTION :

A Water treatment plant designed for a flow 20, 000

m3/day is expected to use alum at a rate of 20 mg/l.

Determine the quantity of alum required for a month’s

supply?

Coagulant - Calculation


JAR TEST :

- Must be performed on each water is to be coagulated

- Must be repeated with each significant change in the

quality of a given water

- Used to calculate the quantity of coagulant to be used

in the water treatment plant.

- Jar Test equivalent to Chemical mixing, coagulation,

flocculation and sedimentation of unit processes in

WTP.

Coagulation – Jar Test


Colourless

Odourless

Tasteless

No Suspended Solids

[BACK]

Clean Water


No pathogen microorganism

No dangerous organic/inorganic

Less mineral substances

[BACK]

Safe Water


Purpose :

“ To provide a uniform

dispersion of coagulant

chemical throughout the

water influent “

[BACK]

Coagulation - Mixing


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WATER TREATMENT TECHNOLOGY (TAS 3010) LECTURE NOTES 9a -Water Intake, Screening, Aeration, Coagulation