CH2 water treatment

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CHE 262 CHEMICAL PROCESSES AND SUSTAINABILITY Prepared by: Mohd Shahrul Nizam Bin Salleh

Transcript of CH2 water treatment

Page 1: CH2 water treatment

CHE 262CHEMICAL PROCESSES AND

SUSTAINABILITY

Prepared by: Mohd Shahrul Nizam Bin Salleh

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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.

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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.

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Content must be removed from the water source

Waste

Solid material / Colloidal particles

Pathogen

Heavy Metal

Exceed dissolved salt

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FACTORS CONTRIBUTE TO THE

SELECTION OF TREATMENT METHOD :

Sources of water intake

Characteristic of water

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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

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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

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Typical treatment plant for groundwater :

1) Aeration

2) Flocculation/precipitation

3) Sedimentation

4) Recarbonation

5) Filtration

6) Disinfection

7) Solids processing

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Water IntakeWater Intake ScreeningScreening

FlocculationFlocculation

Pre-SedimentationPre-SedimentationAerationAeration

pH AdjustmentpH Adjustment

CoagulationCoagulation

SedimentationSedimentation

DistributionDistribution DisinfectionDisinfection

Pump HousePump House

Filtration Filtration

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The selection criteria for water intake location: must have the best available quality far from strong current that can 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 and possess adequate space

and facilities for maintains works.

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Surface water often has large debris, such as sticks, leaves, fish, and trash, floating in it.

These objects can damage the water treatment system and others mechanical devices.

It must be removed before the water enters the treatment plants.

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After screening, the finer but denser, mainly inorganic suspended matter is removed by allowing the water to pass slowly through a chamber where it settles down to the bottom.

The aim being to remove grit sa as to prevent wear of machinery and unwanted accumulation of heavy inert matter in pumps sumps or in flocculation/ sedimentation tanks

It is usual to design these grit chambers to settle out only those suspended particles that are larger than 0.2 mm in diameter and have a specific gravity greater than 2.65.

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- Used to control the growth in water of micro-organisms which

release taste and odor, producing substances or of those organisma

which when killed, may decompose and produce taste and odor

- 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.

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Provide oxygen from the atmosphere for the oxidation of dissolved iron and manganese to their insoluble form and to liberate carbon dioxide and hydrogen sulphide thereby reducing corrosiveness and removing odour

it can increase the dissolved oxygen content in water thereby causing it to have a sparkling appearance and water freshness.

The efficiency depends on the amount of surface contact between air and water, their time contact and the type of aerator and is generally measured by the decrease in the concentration of carbon dioxide in the water

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Raw Water

Aerated Water

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principally preparation of water for sedimentation and filtration at economically high rates of flow

The purpose of this process is to destabilize colloidal particles and enable them to become attached to other particle, so that they may be removed in subsequent process

Form particles large enough to be removed by the subsequent settling or filtration process.

Coagulant chemicals are added to water, rapid mixing ; causing a reduction of the forces tend to keep particles apart.

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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

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The floc that is formed is made up of small particles (micro floc) which still have a positive charge from the coagulant added.

They continue to neutralize negatively charged particles like those of colour and turbidity.

Finally, the micro floc particles begin to collide and stick together to form larger settleable floc particles.

There are many physical and chemical factors that affect the success of a particular coagulant, including mixing condition, pH, alkalinity, turbidity and temperature of the water.

the optimum pH range for coagulation of turbidity waters is usually 5.7 to 6.5.

Both alum and ferric sulphate are affected by the alkalinity of the raw water.

An effective floc will not form if the alkalinity in the water is not high enough. Increase in turbidity, temperatures and mixing energy can also improve coagulation.

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Sedimentation is the process of deposited the floc and thus reduces the amount of suspended particles that must be removed by the filters

create conditions in which the flow is as possible for a long enough period to permit the maximum practicable amount of floc to be settled before the water reaches the outlet end of the tanks

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process of separating suspended impurities from water by passage through a bed of granular materials – the filter media

The purpose of filtration process is to remove the particulate impurities and fine floc that still not settle during the sedimentation process from the water being treated

These impurities consist of suspended particles (fine silts and clays), colloids and biological forms (bacteria and plankton). The type of media filter used here are rapid sand and dual media

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Final step of treating the water. The purpose of disinfection process is making

water safe for consumption by destroying harmful organisms.

The disinfectant chemical that is used here is chlorine gas.

Chlorine gas is easily obtained, relatively cheap and most importantly, it leaves residual chlorine that can be measured.

Chlorine must be dosed within the range of 1.8 to 2.0 to ensure that water at the last place still contains at least 0.2 ppm of chlorine.