4 Conventional Water treatment - University of...
Transcript of 4 Conventional Water treatment - University of...
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CONVENTIONAL DRINKING WATER TREATMENT PROCESSES
Conventional Drinking Water Treatment Processes
2nd French-Serbian Summer School
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Clarification Topics covered
� Coagulation-Flocculation
� Settling
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Coagulation – Flocculation: Principles Objective of treatment
Rawwater
10 microns 0,1 micron 0,01 micron 0,001 micron 0,0001 micron
Treated water
dissolved salts
(nitrates...)
bivalent dissolved salt
(calcium, Fe, Mn)
organic compounds(solvents, pesticides)
virus
organic macromolecule
colloidsred
corpuscle bacteria
nitrogenpollution
hair
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Coagulation – Flocculation: Principles Objective of treatment
Diameter Settling time (m -1)in mm Sp. gravity 2,65 Sp. gravity 2,0 Sp. gravity 1,1
Gravel 10,0 0,013 s 0,02 s 0,20 s
Thick sand 1,0 1,27 s 2,09 s 20,90 s
Fine sand 0,1 2,11 min. 3,48 min. 34,83 min.
Clay 0,01 3,52 hours 5,80 hours 2,42 days
Bacteria 0,001 14,65 days 24,19 days 241,9 days
Colloids 0,000 1 4,12 years 6,66 years 66,59 years
Colloids 0,000 01 412,2, years 665,9 years 6659 years
Colloids 0,000 001 41222,7 years 66590 years 665990 years
TYPE OF PARTICLE
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Coagulation – Flocculation: Principles Objective of treatment
The purpose of coagulation and flocculation is to destabilize suspended solids in water to increase the size of these particles (essentially colloidal) and promote the formation of flocs by adsorption and agglomeration.
Flocculant aids also increase the volume, weight and cohesion of the flocs.
These treatments favor the removal and extraction of particles and other organic matter in downstream processes (clarification, filtration).
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Coagulation – Flocculation: Principles Definitions
Destabilization of suspended solids and colloids ���� neutralization of the negative charges that naturally surround these and keep them apart in ord er to favor the formation of micro flocs.
Characteristics:rapid mixingrapid injectionshort contact time (from a few seconds to ~ 2 minutes)use of coagulants (iron salts, aluminum salts)
Flocculation:
Formation of larger flocs from colloids previously d estabilized by coagulation; Aggregation of particles and colloids due to collisions induced by the motion of water (hydraulic or mechanical flocculation)
Characteristics :slow mixingrapid injectioncontact time from 10 to 30 minutesuse of flocculant aids (polymers)
Coagulation:
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Coagulation – Flocculation: Principles Mechanisms
Coagulant++
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Suspended matter Coagulation Flocculation
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Coagulation – Flocculation: Principles Conventional water treatment chain
Cl2
Pre oxidationCl2, O3, ClO2
pretreatment
Disinfection
Biological inactivation stage
TreatedWater
Raw water
CoagulationFlocculation
Settling orFlotation
Sand or activatedcarbon filtration
Clarification
Separation stageFloc formation
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Factors influencing coagulationType and dose of reagent
� the JAR-TEST is applied to a sample of the raw water entering the WTP to determine:� the type of coagulant � the dose of coagulant
� the coagulation pH� the properties of the sludge produced
� the final choice of coagulant is made based on treatment targets and costs
� it is important to consider local restrictions on sludge production and disposal
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Coagulation - Flocculation ProcessesProcess sequence in WTP
Injection of coagulant
Mixing energy: 500 - 1000 S-1
Time lag between injections
FlocculationCoagulation
Raw water
Injection• Cl2• KMnO4• Cal
minimum contact time5 – 10 minutes
Injection of flocculant
Coagulant contact time
30 sec. – 5 minutes
Duration of flocculation
10 – 30 minutes
Mixing energy: 300 - 800 S-1
Mixing energy: 40 - 80 S-1
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Coagulation - Flocculation Processes Flocculation chamber - example
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Clarification Topics covered
� Coagulation-Flocculation
� Settling
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Clarification Integrating clarification in WTP
correction pH
Settling
storage
Filtration
Raw water
Inlet storagetank
FiltrationGAC
Contact basin
PAC
Pre-treatment• Cl2• KMnO4• Lime
Chlorine
Injection ofpolymer
Injection of coagulant
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ClarificationFactors that affect settling and flotation processe s
Settling or Flotation
Flow rate & variations
Flow velocity & variations
Water quality
Effectiveness of coagulation –flocculation
Floc properties and quantity
Sludge
Properties Extraction
Pressurized water quality
(flotation)Compliance
with clarification water quality
targets:turbidity,
coag. residual,UV abs,TOC…
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Settling: PrinciplesDefinition and objective
� Settling is the processes in which particulate matter – flocs formed during coagulation-flocculation, suspended matter, precipitates – is separated from water by forces of gravity.
� The goal is to remove particles responsible for turbidity and color as well as removing microorganisms
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Clarification: SettlingContents
� Principles
� Settling: Processes
� Static settling tanks
� Sludge blanket clarifiers
> Flat bottom clarifier
> Pulsator / Superpulsator
� Sludge recirculation clarifiers
> Densadeg
> Accelerator / Circulator
> Actiflo
� Summary
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Settling: Static settling tanks Horizontal flow tank with sludge collector
Treated water
Raw water
Sludge extraction
Collector/Scraper
Weir trough
Main characteristics :� length/width ratio: 3 to 6
� depth: 2.5 to 4 m� slope of floor: 1%� collector to facilitate sludge
extraction and avoid high floor slopes
Aguas Argentinas, Bernal WTP
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Settling: Static settling tanks Circular settling tank with sludge collector
Main characteristics :�central flocculation chamber
with mixing� large diameter�depth: 2 to 3,5 m�slope of floor: 4 - 10% �sludge collector
Raw water
Treated water
Treated water
Sludge extraction
Collector / Scraper
Flocculation chamber
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Clarification: SettlingContents
� Principles
� Settling: Processes
� Static settling tanks
� Sludge blanket clarifiers
> Flat bottom clarifier
> Pulsator / Superpulsator
� Sludge recirculation clarifiers
> Densadeg
> Accelerator / Circulator
> Actiflo
� Summary
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Sludge blanket clarifiers Principles
� The objective is to promote continued coagulation and flocculation by increasing the chances of collision among particles
� This is achieved by placing the water in contact with the concentrated sludge containing particles and coagulant reagent
� Two types of processes :� Sludge blanket clarifiers� Sludge recirculation clarifiers
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Sludge blanket clarifiersPULSATOR
1 – Raw water2 – Treated water3 – Sludge extraction4 – Stilling baffles5 – Upper level of sludge
blanket6 – Vacuum chamber 7 – Vacuum pump 8 – Automatic vacuum
breaker valve9 – Perforated pipe for raw
water distribution10 – Sludge concentrators
� flexible process� sludge blanket has a filtering effect
PULSATOR
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Sludge blanket clarifiersPULSATOR
� easy to convert an existing tank into Pulsator� Buenos Aires, 1 300 MLD� Alexandria, 240 MLD
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Sludge blanket clarifiersPULSATOR
Stilling baffles
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Sludge blanket clarifiersPULSATOR
Settled water outlet
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Sludge blanket clarifiersSUPER PULSATOR – Lamellar settling
ULTRAPULSATOR
• Improved water quality
• Increased settling velocity from 4 to 8 m/h (= increased flow rate)
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Clarification: SettlingContents
� Principles
� Settling: Processes
� Static settling tanks
� Sludge blanket clarifiers
> Flat bottom clarifier
> Pulsator / Superpulsator
� Sludge recirculation clarifiers
> Densadeg
> Accelerator / Circulator
> Actiflo
� Summary
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Sludge recirculation clarifiers Principles
� Compact design� high treatment rates: 20 – 40 m/h
� Production of thickened sludge� 30 -150 g/l and potentially more with soft water
� Clarified water of high quality (lamellar settling)
� Mostly unaffected by variations in hydraulic load
� Modular equipment
� Inadequate for colored water and low levels of suspended solids
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Sludge recirculation clarifiers DENSADEG
Eau traitée
Eau brute
CoagulantPolymère
Raw water
CoagulantPolymer
Treated water
Coagulation Flocculation Settling
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Sludge recirculation clarifiers ACTIFLO®Raw water is admitted into a flash mix chamber where coagulant is introduced. It then transits through an injection chamber where polymer and micro-sand are added. The floc is fixed to the micro-sand with the polymer in a flocculation chamber, where it acquires weight and volume.
Finally, the flocculated water passes through the lamellar clarifier, where the ballasted flocsettles and the clarified water overflows to the filters.
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Clarification: SettlingContents
� Principles
� Settling: Processes
� Static settling tanks
� Sludge blanket clarifiers
> Flat bottom clarifier
> Pulsator / Superpulsator
� Sludge recirculation clarifiers
> Densadeg
> Accelerator / Circulator
> Actiflo
� Summary
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Settling Processes: Summary Comparing different clarifiers
Type Example Flocculation
Apparent settling velocity
at surface (m/h)
Concentration of extracted
sludge (g/l)
Static settlingtanks
horizontal orvertical flow
prior or integrated
0,5-2 1-5
Sludgerecirculation
clarifiers
without lamella(Accelerator)
integrated 2-3 5-10
Sludgeblanket clarifiers
without lamellae(Pulsator)
integrated 3-5 2-10
with lamellae(Superpulsator) integrated 6-10 2-10
Densadeg integrated 20-30 30-150
Flat bottom clarifier
integrated 2-4 2-10
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Settling Processes: Summary How to choose clarifiers based on raw water SS
Raw Water Turbidity, NTU
Chl
orop
hyll-
a, µ
g/L,
g/L
10
25
10 20 50 100
SettlingSettling or
DAF
Dissolved Air Flotation
(DAF)
Two-stage Direct
Filtration
One-stage Direct
Filtration