29103542 Water Treatment Technology Tas 3010 Lecture Notes 9a Water Intake Screening Aeration...

TAS 3101 : WATER TREATMENT TECHNOLOGY

CHAPTER 9a : Water Treatment Process : Water Intake, Screening, Aeration, Coagulation SHAHRUL ISMAIL, DESc. Izan Jaafar, Engineering Science, FST, UMTUniversity College of Science and Technology Malaysia

CHAPTER 3: Environmental Microbiology

Menu1) Introduction 2) Water Intake 3) Water Treatment Process 4) Screening 5) Pre-Sedimentation 6) Aeration 7) CoagulationIzan Jaafar, Engineering Science, FST, UMT

IntroductionCharacteristic 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.Izan Jaafar, Engineering Science, FST, UMT

ObjectivesObjectives : 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.Izan Jaafar, Engineering Science, FST, UMT

Water Treatment - PollutantContent must be removed from the water source Waste Solid material / Colloidal particles Pathogen Heavy Metal Exceed dissolved salt

Izan Jaafar, Engineering Science, FST, UMT

Water Treatment SelectionFACTORS CONTRIBUTE TO THE SELECTION OF TREATMENT METHOD : Sources of water intake Characteristic of water Cost


1 Water IntakeSELECTION 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 SourcesSOURCES OF WATER INTAKE : SURFACE WATER GROUNDWATER : Particle Removal : Removal of dissolved inorganic contaminants WATER STORAGE - High content of Fe & Mn - Algal Bloom


Surface Water TreatmentTypical 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) DisinfectionIzan Jaafar, Engineering Science, FST, UMT

Surface Water Treatment


Groundwater TreatmentTypical treatment plant for groundwater : 1) Aeration 2) Flocculation/precipitation 3) Sedimentation 4) Recarbonation 5) Filtration 6) Disinfection 7) Solids processing


Groundwater Treatment


Water Treatment ProcessWater Intake Pump House Screening

Coagulation

Aeration

PrePre-Sedimentation

Flocculation

Sedimentation

DistributionIzan Jaafar, Engineering Science, FST, UMT

pHDisinfection Adjustment

Filtration

Intake StructurePipes 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 facilitiesIzan Jaafar, Engineering Science, FST, UMT

Pump House - Storage- Water from rivers may be stored in bankside reservoir for periods between a few days 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. months to allow natural


Tower Water Intake

Gate controls

Water Surface

Open Port

Entry Port

Closed port

Outlet


Tower Water Intake


Screening-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


Traveling Water Screen


Screening


Pre-Sedimentation- 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.


AerationPurpose : 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 CondPurpose : 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 MechanismOxidation 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 MechanismThe 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 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 removedIzan Jaafar, Engineering Science, FST, UMT

result in decrease water pH

Aeration Types1) 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 airIzan Jaafar, Engineering Science, FST, UMT

Cascade Aerator

Raw Water

Aerated Water


Multiple Platform Aerator

latf r s

Wat r asi


Venturi Aerator

Perforated Pipe

Air Supply

Throat

Venturi

Raw Water

Aerated Water


Draft Tube AeratorAir Aerated Water

Raw Water

Sludge


Aeration Mechanism


Coagulation1) 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 Colloidal Particles- 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


4 - CoagulationFactors Affecting Coagulation Process : - Chemical Coagulant Dosage - pH Adjustment - Turbidity


Coagulation - ChemicalsMost commonly used coagulants : Chemicals Alum (Aluminium Sulphate) Ferric Chloride Ferric Sulphate Cationic Polymers Description Often used in conjuction with cationic polymers May be more effective than alum in some application Effective in some waters and more economical in some location Can be used alone as the primary coagulant or in conjunction with aluminium or iron coagulant

Others : Sodium aluminateIzan Jaafar, Engineering Science, FST, UMT

Rapid Mix- BasinPhysical 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 Cond 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 p 0.3 - 0.5 times the tank diameter or width Baffles extend 10% of tank diameter or width


Rapid Mix- Basin Designto = V / Q to = detention time, s V = volume of the basin, m3 Q = flow into basin, m3/s


Velocity Gradient, GG = (P / Q V) G = velocity gradient, s-1 P = power input, Watt or Nm/s or J/s V = volume of water, m3 Q = dynamic viscosity, N.s/m2


G values for rapid mixingto 0.5 (in-line blending) 10 20 20 30 30 40 > 40 G 3,500 1,000 900 800 700


Coagulant - CalculationQUESTION :

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?


Coagulation Jar TestJAR 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.Izan Jaafar, Engineering Science, FST, UMT

Clean WaterColourless Odourless Tasteless No Suspended Solids


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Safe WaterNo pathogen microorganism No dangerous organic/inorganic Less mineral substances


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Coagulation - MixingPurpose : To provide a uniform dispersion of coagulant chemical throughout the water influent


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THANKS FOR YOUR ATTENTION..


29103542 Water Treatment Technology Tas 3010 Lecture Notes 9a Water Intake Screening Aeration...

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