TAS 3101 : WATER TREATMENT TECHNOLOGY
CHAPTER 9a : Water Treatment Process : Water Intake, Screening, Screening, CHAPTER 3: Environmental Microbiology
Aeration, Coagulation © SHAHRUL ISMAIL, DESc.
Menu 1) Introducti ction 2) Water In Intake 3) Wat Water Treat reatm ment ent Process Process 4) Screening 5) PrePre-Se Sedi dime ment ntat atio ion n 6) Aeration 7) Coagulation
Introduction Characteristic from surface sources - unsuitable unsuitable for human human consumption, industrial use, commercial use etc. Characteristics : 1) Turbi rbid 2) Colou olour r 3) Acids, salts and gases – corrosive action – impart hardness hardness of water 4) Bacteria Bacteria – Water Water borne borne disease diseases. s.
Obj ectives ectives 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.
Water Treatment Treatment - Pollutant Content must be removed from the water source
Waste
Solid material / Colloidal particles
Pathogen
Heavy Metal
Exceed dissolved salt
Water Treatment – Selection FACTORS CONTRIBUTE TO THE SELECTION OF TREATMENT METHOD :
Sources of water intake
Characteristic of water
Cost
1 – Water Intake 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 SOURCES OF WATER INTAKE :
SURF SURFAC ACE E WATE WATER R
: Part Partic icle le Remo Remova vall
GROUNDW UNDWAT ATER ER
: Remo Remova vall of dis diss solv olved ino inorg rga ani nic c contaminants
WATER STORAGE - High content of Fe & Mn Mn - Algal Bloom
Surface Water Treatment Typical treatment plant for surface water : 1) Screening Screening and grit removal removal 2) Primary Primary sedimentation sedimentation (settling/clar (settling/clarificat ification) ion) 3) Coagulati Coagulation on (Rapid (Rapid mixin mixing) g) 4) Floc Floccu cula lati tion on 5) Second Secondary ary sediment sedimentati ation on 6) Filt Filtra rati tion on 7) Sludge Sludge proces processin sing g 8) Disi Disinf nfect ectio ion n
Surface Water Treatment
Groundwater Treatment Typical treatment plant for groundwater : 1) Aera Aerati tion on 2) Flocculati Flocculation/pre on/precipit cipitation ation 3) Sedi Sedime ment ntat atio ion n 4) Reca Recarb rbon onat atio ion n 5) Filt Filtra rati tion on 6) Disi Disinf nfect ectio ion n 7) Solids Solids proces processin sing g
Groundwater Treatment
Water Treatment – Process Water Intake
Coagulation
Flocculation
Distribution
Pump House
Aeration
Screening
Pre-Sedimentation
Sedimentation
pHDisinfection Adjustment
Filtration
Intake Structure
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
Pump House - Storage -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.
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 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.
Aeration Purpose : 1) El Elim imin inat ate e 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 – Con’d 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 – Mechanism Oxidation of Soluble Fe (II) and Mn (II) to insoluble Fe (III) and Mn (IV)
-
4Fe2+
+
2Mn2+
+
O2
O2
+ 10H2O
+ 2H 2 O
4Fe (OH)3
2MnO2
+
Appromixately : 0.14 mg/L O 2 will oxidise 1 mg/L Fe (II) 0.29 mg/L O2 will oxidise 1 mg/L Mn (II)
-
+
Produce floc / settled Fe & Mn
8H+
4H +
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
Aeration – Ty pes 1)Cascad 1) Cascade e Aerator 2)Multiple Platform Aerator 3)Vent 3) Venturi uri Aerator Aerator 4)Draft 4) Draft-Tube -Tube Aerator Aerator Objectives of all types of Aeration : “ To maximize the area of contact between the water and the air”
Cascade Aerator
Raw Water
Aerated Wa
Multiple Platform Aerator
Platforms
Water Basin
Venturi Aerator
Perforated Pipe
Air Supply
Throat
Raw Water
Venturi
Aerated Water
Draft Tube Aerator Air
Aerated Water
Raw Water
Sludge
Aeration – Mechanism
Coag ulation ulation 1) Many of suspend suspended ed water particl particles es have a negative negative electrical charge. 2) Coagulatio Coagulation n eliminates eliminates natural natural electrical electrical charge charge so they attrack and stick to each other. 3) Form particles particles large large enough enough to be removed 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.
Coagul ation ation – 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 - Coag ulation ulation Factors Affecting Coagulation Process : - Chemical Coagulant Dosage - pH Adjustment - Turbidity
oag ulation ulation - Chemicals Most commonly used coagulants : Chemicals
Description
Alum (Aluminium Sulphat hate)
Often used in conjucti ction 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
Others : Sodium aluminate
Rapid Mix- Basin • 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 – Con’d • 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 Design t =V/Q o
to = detention time, s V = volume of the basin, m3 Q = flow into basin, m3/s
Velocity Gradient, G G = (P /
V) ½
G = velocity gradient, s-1 P = power input, Watt or Nm/s or J/s V = volume of water, m 3 µ
= dynamic viscosity, N.s/m2
G values for rapid mixing to
G
0.5 (in-line blending)
3,500
10 – 20
1,000
20 – 30
900
30 – 40
800
> 40
700
Coag ulant ulant - Calculation 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?
Coag ulation ulation – Jar Test 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.
Clean Water
Colourless
Odourless
Tasteless
No Suspended Solids
Safe Water
No pathogen microorganism
No dangerous organic/inorganic
Less mineral substances
Coagulation - Mixing Purpose : “ To provide a uniform dispersion of coagulant chemical throughout the water influent “
THANKS FOR YOUR ATTENTION…..
