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

09/10/2007 I ADVANCED WATER TREATMENT I PROCESSES

COPYRIGHT © 2003 SUEZ ENVIRONNEMENT I 2

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




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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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).



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++

++ ++ +

++

+

Suspended matter Coagulation Flocculation



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



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



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Coagulation - Flocculation Processes Flocculation chamber - example



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



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



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



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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� Principles







> Densadeg


> Actiflo

� Summary



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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4

5

6

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� easy to convert an existing tank into Pulsator� Buenos Aires, 1 300 MLD� Alexandria, 240 MLD

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Stilling baffles




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)




� Principles







> Densadeg


> 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



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.




� Principles







> Densadeg


> 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



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

4 conventional water treatment - university of...

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