water treatment technology in...

BANGALORE WATER SUPPLY

AND SEWERAGE BOARD

Water Treatment Technology

in BWSSB

Dr PN Ravindra

Executive Engineer

Water Sources for Bangalore City

Glimpses of Water Treatment History

Till 1895 Unfiltered Water in Karanjee System from a

Number of Tanks such as Dharmambudhi, Sampangi,

Ulsoor, Sankey etc.,

Supplemented by Local Wells and Stepped Ponds.

Hessarghatta Reservoir

From 1896, First Protected Water Supply From Hessarghatta

Lake Across River Arkavathy

Designed for Population of 250,000 at 55 Lpcd.

Chamarajendra Reservoir is 20 kms from Bangalore having

capacity of 747.7 mcft.

Jewel Filters at Malleshwaram

Received Raw Water for Treatment.

http://www.flickr.com/photos/distra/2647600056/in/photostream/

Water Treatment Principle

• Clarification

• Filtration

• Disinfection

Aerator

FM

Flash Mixer

Flocculation

Clarifier

Filter

Disinfection

Chlorine

FLOW DIAGRAM

IMPURITIES IN WATER :

• DISSOLVED SALTS

• SETTLABLE SOLIDS

• SUSPENDED SOLIDS

Treated Water

Hessarghatta Raw water qualities

Parameter Minimum Average Maximum

Turbidity (NTU) 20 45 3000

pH 7.0 8.2 8.73

Alkalinity as CaCO3 (mg/L) 20 145 190

Total hardness as CaCO3

(mg/L)40 125 190

Flocculator

Settling Tanks

Jewell Filter

Jewell Filter Features

Diameter – 5.30 m

Filter Depth – 2.5 m

Media depth – 1.05 m

Numbers – 5

Capacity – 2.5 MLD Each

Filtered Water Reservoir

From Time To Time There Were Shortages.

TG Halli Reservoir was Built as per Suggestion of a

Committee Headed by Sir M Visvesvaraya across River

Arkavathy, about 40 Kms from Bangalore and

Commissioned in 1932.

Capacity 55 mcmt later Increased to 95 mcmt

Designed to Provide 72 lpcd later Increased to 90 lpcd

Supply initially 75 MLD, later Increased to 112.5 MLD

and later Upgraded for 140 MLD Capacity.

Existing Raw water qualities

Parameter Minimum Average Maximum Std Devt

Turbidity (NTU) 15 55 4500 2200

pH 7.2 7.8 7.5 0.15

Alkalinity as CaCO3 (mg/L) 30 121.9 190 39.5

Electrical Conductivity

(µmhos/cm)120 400 600 140


(mg/L)80 140 210 30

Hydraulic Flocculator and Settling Tanks

No. of Chambers -2

Size – 51.2 * 25.6 *4.5 m

Detention time – 6hrs

Weir loading –

80 m^3/m-day

Surface Loading –

24 m^3/m^2-day

Hydraulic Flocculator

Clariflocculator

Filter Houses

Filter House – 1933

10 nos – 10 MGD

Fitration rate – 3.6 m/hr


Filter House – 1958

8 nos – 12 MGD

Fitration rate – 4.8 m/hr


TG Halli Water Treatment Complex

Cauvery Water Supply Stages

River Cauvery, about 100 Kms from Bangalore and

Manometric Head is 450 metres

Cauvery Water

Supply Stages

Commissioning

year

Capacity ,MLD

I Stage 1973 135

II Stage 1982 135

III Stage 1993 270

IV Stage Phase I 2002 270

IV Stage Phase II March 2012 * 500

Total 1310 MLD

94% 0f the time the raw water turbidity is less

than 20 NTU for years 2004 and 2006. In year

2005 when unusual rainfall occurred the raw

water turbidity is still less 20 NTU for 90% of the

time.

Existing Raw water qualities

Parameter Minimum Average Maximum Std Devt

Turbidity (NTU) 1.2 7.7 88.8 9.7

pH 7.0 8.2 8.73 0.25

Alkalinity as CaCO3 (mg/L) 30 121.9 190 39.5

Electrical Conductivity

(µmhos/cm)91.4 345.4 496 115.8


(mg/L)29 105.3 158 35.5

Calcium as Ca (mg/L) 4.8 18.7 33.6 5.5

Magnesium as Mg (mg/L) 2.9 14.2 26.9 5.9

Chloride as Cl (mg/L) 10 20.9 32 5.0

Existing/Proposed Water Treatments Plants

Stages Processes Capacities

Stage IConventional Clariflocculator

with Rapid Sand Filters135 MLD

Stage II Conventional Clariflocculator

with Rapid Sand Filters

135 MLD

Stage III Conventional Clariflocculator

with Rapid Sand Filters

270 MLD

Stage IV,

Phase IPulsator Clarifier with Aquazur

Filters

270 MLD

Stage IV,

Phase

II

Dissolved Air Flotation with

Aquazur Filters500 MLD

Direct Filtration

RAPID

MIX

Media

FILTRATION

Clearwell

Chlorine

To

Distribution

Coagulant (alum

or PACL)

Chlorine

During low turbidity period water is

directly applied to the filters

During high turbidity period water is

passed through sedimentation basins

before applied to filters

THANK YOU

Existing WTPs

Aeration (optional)

Pre- Chlorination

Coagulant Addition

Flash Mixing

Flocculation

Clarification

Filtration

Disinfection

Treatment Process is Solid contact followed by Aquazur filters

Water Treatment Plant

Existing WTP Stage IV Phase I

THE PULSATOR TECHNOLOGY

•Pulsating Sludge Blanket Clarifier

•Flat Bottom RCC Tank

•Even water distribution over entire floor

•Sludge withdrawal across width of tank

PRINCIPLE OF FILTRATION

• SAND FILTRATIONSAND MEDIA FUNCTION

GRADED / UNIFORM

• MEDIA CLOGGINGFACTORS AFFECTING

TURBIDITY, FLOW RATE,

GRAIN SIZE

• FEATURES OF

•AQUAZUR-VDEEP FILTER BED

POSITIVE PRESSURE IN BED

AIR/WATER BACKWASH + SWEEP

Filters

AQUAZUR - FALSE FLOOR

Existing Water Treatments Plants – Unit Process

Parameter Stage I Stage II Stage III

Stage IV,

Phase

I

Flocculator retention time

(min)30 33 29 41

Clarifier retention time

(min)100 167 171 58

Clarifier surface loading

rate (m3/m2/h)1.98 1.63 1.60 2.65

Weir loading rate (m3/m/h) 15.9 15.1 15.1 -

Existing Water Treatment PlantsBasis of Design for Filtration Process

Parameter Stage I Stage II Stage III Stage IV Ph I

Filtration rate (m/h) 6.0 6.0 6.0 7.58

Air scour rate (m/h)

Duration (min)

None

-

36

2 to 3

Not known

4 to 5

55

1

Combined air-water

rate (m/h)

Duration (min)

55.0 (air )

7.5(water)

5

55.0 (air )

7.5 (wate)

5

55.0 (air )

7.5 (water)

5

55.0 (air )

7.5 (water)

5

Waterwash ratem/h)

Duration (min)

19.7

20

24

4 to 5

20

4 to 5

15

5

Cross waterwash

m/h)

Duration (min)

7.5 to 9.0

8+

7.5 to 9.0

8+

7.5 to 9.0

8+

7.5 to 9.0

8+

Backwash frequency

(Once in--)24 hrs 24 hrs 24 hrs 72 hrs

Existing Raw Water Frequency distribution of turbidity

Year

Number of days per year Max

turbidity

(NTU)T≤5 5<T≤10 10<T≤20 20<T≤30 30<T≤40 T>40

2003246 23 2 2 0 0

22.1190.1% 8.4% 0.7% 0.7% 0.0% 0.0%

2004216 54 73 21 1 1

44.3859.0% 14.8% 19.9% 5.7% 0.3% 0.3%

2005193 59 71 26 9 7

115.852.9% 16.2% 19.5% 7.1% 2.5% 1.9%

2006208 95 45 12 3 2

84.857.0% 26.0% 12.3% 3.3% 0.9% 0.5%

2007 up

to May

151 0 0 0 0 04.18

100.0% 0.0% 0.0% 0.0% 0.0% 0.0%

2003-071014 231 191 61 13 10

115.866.7% 15.2% 12.6% 4.0% 0.9% 0.7%

Year Range

Raw

water

Turbidity

(NTU)

Settled water Turbidity

(NTU)

Stage I Stage II Stage III

2005

minimum

mean

maximum

1.20

8.90

88.80

0.98

5.14

29.30

1.00

6.23

28.00

1.09

5.60

38.00

2006

minimum

mean

maximum

1.20

6.50

71.30

1.10

4.52

14.20

1.10

5.16

20.70

1.20

4.68

17.20

2007

minimum

mean

maximum

1.29

6.76

78.18

1.20

5.52

22.20

1.25

6.06

24.10

1.20

4.68

17.20

Raw and Settled Water Turbidity

Year Range Raw water

Turbidity

(NTU)

Filtered Water Turbidity (NTU)

Stage I Stage II Stage III

2005 minimum

mean

maximum

1.20

8.90

88.80

0.60

3.21

19.50

0.66

4.27

21.00

0.48

2.46

16.00

2006 minimum

mean

maximum

1.20

6.50

71.30

0.90

2.47

10.00

0.90

3.26

14.00

0.80

2.25

13.00

2007 minimum

mean

maximum

1.29

6.76

78.18

1.20

3.84

11.50

1.00

3.05

16.50

0.80

2.84

14.50

Raw and Filtered Water Turbidity

Treated Water Qualities, Phase I

Sample Parameters Performance Requirement

Settled water Turbidity, NTU Less than 5 for 90% of time

Combined

filtrate

Turbidity, NTU

Aluminium, mg/L

pH

Colour, Pt/Co scale

Iron, mg/L

Less than 1 for 100% of time

Up to 0.03

7.0 to 8.5

Less than 5 units

Less than 0.1

Filtrate from

individual filters

Turbidity

Aluminium, mg/L

Same as above

Less than 0.03, 95% at any time

Clearwater

reservoir outlet

Faecal Coliforms

Total Coliforms

0/100 mL

0/100 mL

Cauvery Stage IV Phase I/II

270/500 MLD WTP

The Project Scope for WTP Consists of:

Review of Existing WTP and

Raw Water Quality

• Raw water quality with statistical analysis:

increase in levels of TOC, EDCs, Planktons

• Unit processes and their design parameters

• Alum dose and Alum feeding system

• Removal efficiency of settled water and Filtration

unit along with related problems attributed to low

removal efficiency

Proposed Water Treatment Plant Design Treated Water Parameters

Sample Performance Requirement

Combined filtrate Turbidity : Less than 1 NTU for 100% of

time and less than 0.5 NTU

95% of the time

Settled Water : Less than 5 NTU for 90%

of time

Al : Up to 0.03 mg/L

pH: 7.0 to 8.5

Colour: Less than 5 units Pt/Co scale

Iron: Less than 0.1 mg/L

Filtrate from individual filters Turbidity: Same as above

Al: Less than 0.03 mg/L 95% at any time

Clearwater reservoir outlet Faecal Coliforms: 0/100 mL (Nil)

Total Coliforms: 0/100 mL (Nil)

Aeration

Pre- Chlorination

Coagulant Addition

Flash Mixing

Flocculation

Claification/Sedimentation

Filtration

Disinfection

Water Treatment Plant Operation

Scheme of Treatment Process

Direct Filtration

Clariflocculator (existing)

Rectangular Clarifier with plate

settlers

Solid Contact Clarifiers

Dissolved Air Flotation

Enhanced Coagulation

Low Pressure Membrane Filtration

Clarification/Sedimentation

High Rate Clarification

Rectangular

Sedimentation

Basins

a

Inclined Plates

Clari-Flocculator

Pulsator (Solids Blanket Clarifier)

Collection laterals

Vacuum pump

Vent valveVacuum chamber

Collection channel

Sludge drawoff lines

Sludge concentrator

Distribution channelDistribution lateralsParallel plates

NEW TRENDS - DAF

HIGH PERFORMANCE DISSOLVED AIR FLOTATION CLARIFIER. VELOCITIES

10-12 TIMES HIGHER THAN CONVENTIONAL CLARIFIER.

MAIN AREA OF APPLICATION – LOW TURBIDITY ( ~ 30 PPM SS) WATERS

T = 10 à 20

mnT = 5 à 10 mnU F =25 à 40

m/h

10% RECYCLEAIR

Primary difference between conventional and

dissolved air flotation

Gravity Settlement

Buoyancy Flotation

Air bubble

Attachment of bubblesto flocs

Typical DAF Arrangement

Ballasted Flocculation

Actiflo Process

Or Ballasted

Flocculation

FILTRATION

Chlorine

Clearwell

To

Distribution

Raw

Water

Chlorine

Coagulant (alum

or PACL)

Ballasted Flocculation

1.

2.

3.

4.

5.

6.

7.

Raw Water Inlet

Injection of Microsand

Flash Mixing Zone (Coagulation)

Gentle Mixing Zone (Flocculation)

Inlet to Settling Zone

Lamella Modules

Collecting Troughs or Pipes

8.

9.

10.

11.

12.

13.

Treated Water Outlet

Sludge Scraper and Trough

Sludge and Sand Outlet Sump

Recycling Pump

Hydrocyclone for Microsand Recovery

Sludge Outlet

Membrane Process

Micro or Ultra

FILTRATION

Chlorine

Clearwell

To

Distribution

Reject Stream

Raw

Water

Chlorine

Membrane

Chemical

Cleaning Tank

Membrane Filtration

Submerged type

Filtered Water

Process Tank(Influent)

X-Section

Membrane

Layer

Inner Reinforcing

Structure

Common sludge treatment process flow for all

Water Treatment Plants

Waste

Water

Collectio

n

Tank

Thickner

Pump

House

Thickner

Sludge

Sump &

pump

House

Centrifuge

Sludge

for

Disposal

To raw

Water

Channel

To raw

Water

Channel

Sludge

Dewatering

Waste

Water

Collection

Tank

Sludge water from

Clarifier

Footprint for New WTP

No.5

No.4

No.3

No.2

No.1

PretreatmentBasins – (conventional or

Solids contact basins)

ClearWell

BackwashBasins

FilterBuilding

PumpStation

ServiceBuilding

Conventional

Treatment Plant

(with our without

plates)

No.5

No.4

No.3

No.2

No.1

Actiflow or DAFUnits

ClearWell

BackwashBasins

FilterBuilding

PumpStation

ServiceBuilding


High Rate –

Clarification

Plant

No.5

No.4

No.3

No.2

Membrane Units

FilterBuilding

PumpStation

ServiceBuilding


Membrane

filtration PlantBackwash

Basins with CIPs

ClearWell

5

4

2

1

3

Process Comparison

• Treatment Process

– Conventional (with plates)

– Solids Blanket type

– Direct Filtration

– DAF

– Ballasted Flocculation

– Membranes

Solids Blanket includes –

upflow clarifiers and Pulsators

• Equipment Availability

– Within India

– Within India

– Within India

– Imported (ancillary equipment locally)



Operational issues

Process Effect of influent water characteristic on filter effluent turbidities

(less than 1 NTU 100 % or less than 0.5 NTU 90% of the time

Conventional High to moderate –Susceptible to change of influent turbidity and

affects filter operations and filter effluent quality

Conventional + Plates Moderate –Less susceptible to change of influent turbidity and do

not affects filter operations and filter effluent quality.

Solids Blanket / Pulsator Moderate to low -More susceptible to change of influent turbidity

and affects filter operations and filter effluent quality.

Direct Filtration High - In absence of coagulant. More filter control are required

affecting the filter effluent quality.

Dissolved Air Flotation (DAF) Moderate to low -Less susceptible to turbidity shock load and

filter operations are controlled with ease of air/solid ratio .

Ballasted Flocculation None

Membrane Filtration None

Operational issues

Process Chemicals Required O & M issuesExpansion feasibility

Conventional Low to moderate Coagulant

dose + Disinfectant

Low to Moderate – can be

expanded with plates

Conventional + Plates Low to moderate Coagulant

dose + Disinfectant

Moderate

No expansion feasibility

Solids Blanket / Pulsator High Coagulant dose +

Disinfectant

High

No expansion feasibility

Direct Filtration Low Coagulant dose + filter

aid polymer + Disinfectant

Moderate to High - Operation of

Filters is Critical – Plant can be

expanded

Dissolved Air Flotation

(DAF)

Moderate Coagulant dose +

Disinfectant

High

plant can not be expanded

Ballasted Flocculation Moderate Coagulant dose +

Disinfectant + Micro-sand

High

plant can be expanded with

increase in overflow rate - limited

Membrane

Pressure

Vacuum

Disinfectant and Membrane

cleaning chemicals

Moderate

plant can be expanded with

modular approach

CAPITAL COST, O & M COST (Annual / 30 years)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Conventional

Plant with SS

Plate Settlers

Conventional

Plant with PVC

Plate Settlers

Solids Blanket

Clarifiers

Direct Filtration Dissolved Air

Flotation

Ballasted

Flocculation

Membrane

Filtration

Capital Cost

O & M (Annual Cost)

O & M (30 years)

Selected Option

Breakdown of Cost Components (budgetary estimates)

Process Civil Mechanical +

Piping

Electrical &

Instrumentation

Percent of overall capital costs

Conventional Plant 50% 29% 19%

Conventional Plant

with Plate Settlers50% 29% 19%

Solids Blanket

Clarifiers45% 36% 22%

Direct Filtration 38% 35% 24%

Dissolved Air

Flotation31% 42% 26%

Ballasted

Flocculation28% 43% 26%

Membrane

Filtration13% 66% 24%

-20%

0%

20%

40%

60%

80%

100%

Conventional

Plant with

Plate Settlers

Solids Blanket

Clarifiers

Direct

Filtration

Dissolved Air

Flotation

Ballasted

Flocculation

Membrane

Filtration

CAPEx % Higher with Direct Filtration

OPEx % higher with Direct Filtration – 30 Yr.

scenario

Selected Option

Comparison of Capex and Opex

Cost Comparison

Process Capital

Costs

O&M

costs (7

years)

O&M

costs

(30 Yr

scenario)

Millions of Rupees

Conventional

Plant with Plate

Settlers with SS

2250 61 265

Solids Blanket

Clarifiers2380 66 286

Direct Filtration 1515 51 151

Dissolved Air

Flotation2300 45 224

Ballasted

Flocculation2493 88 291

Membrane

Filtration2465 106 185

CAPEx %

Higher with

Direct

Filtration

48%

57%

52%

65%

62%

OPEx %

higher with

Direct

Filtration – 30

Yr. scenario

75%

89%

48%

92%

22%

Final Words

• BWSSB has moved along with advancement in

technology

• Gradual increase of Planktons, TOC, EDCs

and THM precursors in Raw water, posing

challenge for tackling such contaminants

• Analysing water for 33 critical parameters as

per BIS 10500

water treatment technology in...

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