7. Water quality aspects of drinking water networks-01.pdf

7/24/2019 7. Water quality aspects of drinking water networks-01.pdf

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Pumping stations and water

transport

Water quality aspects of drinking water

networksct5550


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CT5550: water quality aspects DW networks

Introduction

Water quality changes during transportthrough the network

Chemical processes: interaction betweenpipe material and water

Biological processes:development/regrowth of bacteria and

invertebrates Physical processes: sedimentation andresuspention


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Material composition network

0

20000

40000

60000

80000

100000

120000

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

kmpi

pe

rest

pvc

nod CI

Cast Iron

ac


4/86CT5550: water quality aspects DW networks

Present material composition

Asbestos cement

33%

Cast iron

11%

pvc

50%

rest

4%

nod CI

2%



Physical processes

Main problem: discoloured water Primarily a customer related problem:

discoloured water is harmless

Although relation with bacteriologicalproblems

Focus because of changing attitude ofboth customer (more critical and outspoken) as water company (more

customer oriented)



Early 90s: red water on the

agenda in the Netherlands

Increased customer complaints more critical attitude more professional registration

Unexpected decrease in cast iron also in new plastic networks

Unsatisfactory results of (costly) cleaningprograms



100 Cast Iron (1900)



Basic questions

What is discoloured water How to measure discoloured water What is the cause and nature of

discolourde water What can we do about it



What is red water?

Water with a turbidity that can be noticedby a customer

Turbidity is the key factor in red water



How to measure red water:

Monitoring SystemMonitor 1 Monitor 2 Monitor 3

flow

pH Oxygen

Turbidity Temperature

Conductivity Pressure

(Velocity)


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Single Monitoring system


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Results monitoring turbidity

Continuous monitoring turbidity

0,0

0,1

0,2

0,3

0,4

0,5

04-jun 05-jun 06-jun 07-jun 08-jun 09-jun

T

urbidity[FTU]

Treatment

Location 1

Location 2


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Closer detail

Continuous monitoring turbidity

0,0

0,1

0,2

0,3

0,4

0,5

05-jun 00:00 05-jun 12:00 06-jun 00:00

T

urbidity[FTU]

Treatment

Location 1

Location 2

Minumum

Maximum


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Turbidity [FTU]

Week days

Continuous monitoring of

turbiditybegin pipe

end pipe

sample

complaint

2

1

0

mo susafrthuwetu


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Cause of discoloured water

Resuspension of sediment Sediment originates from

source/treatment plant network (corroding cast iron, biofilm) mixing different water types

Sedimentation is promoted by low

velocities in the network Sudden changes in velocity promoteresuspension


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Mass balance in a network

Particles

Suspended

solids

Bed load

transport

J.H.G. Vreeburg

Deposition &

resuspention

Biofilm

formation &

sloughing

Corrosion

Formation &

coagulationParticles

Suspended

solids

resu

spen

tion


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Actions to prevent red water:

a three stage rocket

Prevent the sediment from entering thenetwork

Improve the treatment of water

Remove sediment swiftly en effectively Conduct cleaning programmes Prevent sedimentation of suspended

matter Design small diameter pipes: design for

self-cleaning capacity


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Variation of production

capacity and water quality


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Turbidity different pumping

stations

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

22 24 26 28 30 2 4 6 8 10 12 14 16

Time (days, refer ence is location ps A)

Turbidity(FTU)

plant C

plant B

plant A


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First stage: improve treatment

Goal: steady process with low turbidity Tools: demand forecasting and clever

use of balancing reservoirs

But: conventional treatment leavessediment in the water

S d t R


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Second stage: Remove

sediment

Cleaning the network, availabletechniques

Flushing

Water/air scouring Pigging

Measuring method:

Resuspension potential


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Research tools

Continuous monitoring turbidity andParticle counts

Resuspension Potential Method

Experimental pipe test rig Analysis of concentrate MF-installation

R i P t ti l


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Resuspension Potential

Method

Principle resuspension of sediment by sudden increase

of velocity

0,35 m/s on top of normal velocity turbidity monitoring no impact on the customer

R i P t ti l


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MethodMonitor

Q

Cause a sudden increase in velocity

V(m

/s)

Timet1 t2

V = 0.35Normal velocity

Closed valve


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Typical RP curve

Turbidity

Time

High resuspensionpotential indicates

polluted network:

cleaning network, e.g.

flushing

Effect of flushing monitored


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Effect of flushing monitored

with resuspension potentialTurbidity

Time

Before

cleaning

Turbidity

Aftercleaning

Time


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Pictures monitor connection



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Method



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Method

Resuspention potential method


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Resuspention potential method

Sample measuring


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Typical RPM curve

First 5 min Last 10 min

Base level

Disturbance Resettling time

Tu

rbidity[F

TU]


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Relative interpretation RPM

5 aspects determine the RP:

Absolute maximum turbidity first five minutes Average turbidity first five minutes Absolute maximum turbidity last ten minutes

Average turbidity last ten minutes Resetling time

0 to 3 points per aspectFirst 5 min

Disturbance

Last 10 min

Resettling time

BaselevelT

urbidity[FTU]


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Ranking RPM

pointsCategory

0 1 2 3

Absolute max

first 5 min40 ftu

Average first 5 min 40 ftu

Absolute max

last 10 min

40 ftu

Average max

last 10 min40 ftu

Time to clear < 5 min. 5-15 min 15-60 min >60 min

Turbidity Dr Lange, Hydrant measuring

Typical RPM results


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Typical RPM results

Pre and Post cleaningTurbidit y w ith RPM, after cleaning

Disturbance 9:59 - 10:15

0

10

20

30

40

50

09:59 10:02 10:05 10:08 10:11 10:14

Time

Turbid

ity[FTU]

Turbidity w ith RPM, befor e cleaning

Dis tur bance 13:09 - 13:23

0

10

20

30

40

50

13:09 13:11 13:13 13:15 13:17 13:19 13:25

Time

Turbid

ity[FTU]

Score 12 Score 0

Hypothesis effects improved


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Res

uspension

PotentialM

ethod

Par

ticles

Effect cleaning

Cleaning

frequency 1

Critical

level

Hypothesis effects improved

particle load

Effect

Q21 ?

Effect improved

treatment

Cleaning

frequency 2


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Additional research

Particle load present system Large volume sampling Test rig 100 new test rig multiple pipes

Goals: Determine characteristics present drinking

water Develop new measurement methods and

tools

Trigger students


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Test pipe rig 100

Charge with

concentrate

O i i l t t t i


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Original set up test rig

time

layerdevelopment

1

2

3 4 5

time

layerdevelopment

1

2

3 4 5

1

2

3 4 5

P ti l t


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Practical set up

Fi t b ti


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First observations

S b ti


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Some more observations

Iron Chloride 0.06 m/s Kaolinite 0.06 m/s

Iron Chloride 0.14 m/s Kaolinite 0.14 m/s

Drinking water quality aspects:


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g q y p

Remove the sediment

Remo e the sediment


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Remove the sediment

Water flushing is effective if: 1,5 m/s is reached Flush volume is 3 times the pipe content Clear water front

Alternative methods as water/air scouringand pigging only when water flushing

boundaries are not met

Results of cleaning program


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Results of cleaning program

City of Venlo

Red line are CI Rest is PVC/AC

Measuring equipment


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Measuring equipment

RPM results individual location


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RPM results individual location

Turbidity data RPM 100 mm AC

0

20

40

60

80

100

120

140

160

180

200

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

time [minutes]

Turbidity[FTU]

22-10-200115-5-2002

22-10-2002

17-11-2003

10-11-2004

28-11-2005

1-11-2006

RPM data 100 mm AC

0

2

4

6

8

10

12

2001 2002 2003 2004 2005 2006 2007 2008

year

RPM[

-]

RPM results CI location


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RPM results CI-location

Turbidity data 4" CI

0

50

100

150

200

250

300

350

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

Time [min]

Turbidity[FTU]

4-3-2002

9-7-2002

7-5-2003

27-5-2004

26-4-2005

9-5-2006

RPM data 4" CI

0

2

4

6

8

10

12

2001 2002 2003 2004 2005 2006 2007

RPM[

-]

Overall results


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Overall results

Average RPM

0,0

2,0

4,0

6,0

8,0

10,0

12,0

2001 2002 2003 2004 2005 2006 2007 2008

RPM[

-]

cast-iron/steel

non ferrous

Innovative cleaning methods


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Innovative cleaning methods

water direction high velocity low velocity

re-suspension of sediment transport

ballball


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Foto ballcleaning


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Foto ballcleaning


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Water/air scouring


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Water/air scouring

Pigging


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Pigging

Result of aggressive cleaning cast

i ( i i W/A i )


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iron (pigging or W/A scouring)

Post-cleaning turbidity

0,00

0,25

0,50

0,75

1,00

13-06-00 15-06-00 17-06-00 19-06-00 21-06-00

T

urbidity[FTU]

Loc 2 post

Loc 4 post

Loc 5 post

Third stage: prevent


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sedimentation Design drinking water networks instead of fire

fighting networks Main characteristics of drinking water network

Looped transport network

Branched district areas with up to 200 connections Velocity in branches 0,4 m/s once a day

Result: self cleaning network

Large draw back: less fire fighting capacity

Self cleaning network


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g

Looped network

V = 0,07 m/sec

sediment

Looped network (disturbed)

V = > 0,4 m/sec

sediment

Drinking water network (self cleaning)V = > 0,4 m/sec

Conventional network


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Flat house

FlatVP 350 kPa

VP 350 kPa

Hospital

75

110

New network


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VP 350 kPa

VP 350 kPa

Hospital

116 85

64

60 m3/h

6340

110


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Pumping stations and watertransport

Water quality aspects of drinking water

networks

ct5550


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Chemical processes


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Materials used in drinking water transport and

distribution Cast Iron Asbestos Cement Plastics as PVC and PE

Materials used in house plumbing Lead Copper

Plastics, mainly PE Other materials as concrete, (galvanised) steel,GRP act chemically in similar ways

Cast Iron: corrosion products


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2+

Fe

2O2-

3CO

2O

3+

Fe3FeCO

3 4FeOOH Fe O FeOOH

Protective layer bad layer

Cast Iron: corrosion problems


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Graphitisation: weakening of pipe

material and strength Loss of hydraulic capacity due to

voluminous corrosion products

Deterioration of water quality Discolouration

Biofilm formation

100 Cast Iron (1900)


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Cast Iron: prevention of

corrosion


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corrosion

Water composition at pumping station

pH > 7,5 TIC > 2 mmol/l

(Total Inorganic Carbon [HCO3-])

(Cl- + 2SO4)/TIC < 1 Coatings

Cement mortar lining

PE-sleeves

Asbestos Cement


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Corrosion process: Leaching of Calcium

Hydroxide Corrosion problems:

Loss of strength Increase of pH Release of asbestos fibres

Precipitation of calcium carbonate

Prevention AC corrosion

problems


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problems

Water composition

-0,2 < SI < 0,3 TIC > 2 mmol/l

2+ 2-

3

eq2+ 2-

3eq eq

Ca COSI = log = pH - pHCa CO

Plastics


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No chemical processes known at the

moment (limited) Lead destabilisation at the start

of the life time

Lead and copper


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Corrosion process: release of lead

Corrosion problem: public health Prevention

Water composition: pH > 7,8 Coating replacement

Optimal composition of

drinking water


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drinking water

2-

4

2

4

3

7.8 and (0,38 TIC + 1.5 SO 5.3) 8.3

2 0.2 0,3

2 1

(if 7.8 < pH < 8.3)

pH

TICSI

Cl SOTIC

TIC HCO

+ <

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7. Water quality aspects of drinking water networks-01.pdf