Discolouration in potable water distribution systems PODDS ... · PDF...

29
Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water distribution systems PODDS: from theory to practice

Transcript of Discolouration in potable water distribution systems PODDS ... · PDF...

Page 1: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Prof. Joby BoxallPennine Water GroupUniversity of Sheffield

Discolouration in potable water distribution systems

PODDS: from theory to practice

Page 2: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

• Most apparent water quality issue to customers

• A major cause of customer contacts

• Often a ‘mask’ for other water quality issues

• Discolouration incidents prosecuted in UK found ~50% associated with ‘planned works’ (2009 data)

Discolouration

• 146 significant events reported in 2009

• 34% discolouration• ~50% of these due to planned

operations

Page 3: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Sediment deposit or cohesive layers?

∞?

Layer Shear strength , τ (N/m2)

1.2

Dis

colo

urat

ion

pote

ntia

lC

(N

TUm

)

τ’ τa

τexcess

Cplastic

Ciron

CI pipe

Plastic pipe∞

∞?

Layer Shear strength , τ (N/m2)

1.2

Dis

colo

urat

ion

pote

ntia

lC

(N

TUm

)

τ’ τa

τexcess

Cplastic

Ciron

CI pipe

Plastic pipe

0

5

10

15

20

25

30

0.000 -0.004

0.004 -0.008

0.008-0.016

0.016-0.031

0.031-0.063

0.063-0.125

0.125-0.250

0.250 -0.500

bin size ranges (mm)

% c

ount

s

mean

mean + standarddeviationmean - standarddeviation

0

10

20

30

40

50

60

70

80

90

100

00:38 00:46 00:53 01:00 01:07 01:14 01:22 01:29 01:36 01:43Time (hrs:mns)

Turb

idity

(NTU

)

0

2

4

6

8

10

12

14

16

Flow

rate

(l/s

)

FlushIntermediateInletHachFlow rate

Page 4: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

The PODDS approach..

• Proposes that processes in addition to gravitational settling lead to material accumulation and retention within pipes of distribution systems• pipe and fitting corrosion, lining erosion, biological

growth, flocculation, chemical reactions, electrochemical interactions etc

• Specific processes not explicitly considered in PODDS approach, approximated to ‘cohesive forces’

Page 5: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

The PODDS model

• An empirical computational tool to predict the turbidity response of distribution networks to changes in hydraulic conditions• Describes discolouration potential as a function of

normal daily or recent hydraulic forces (shear stress)• Calculates mobilisation by comparison of this with

imposed event hydraulic force (shear stress)• Coded as addin to EPANET – readily applicable to any

1D network modelling software

Page 6: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water
Page 7: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water
Page 8: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Verification for Cast Iron pipes

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000 5000 6000 7000Time (seconds)

Turb

idity

(NTU

)

0

1

2

3

4

5

6

7

8

9

Flow

Rat

e (l/

s)

Measured TurbidityModelled TurbidityFlow Rate

0

20

40

60

80

100

120

140

160

180

200

19500 20000 20500 21000 21500 22000Time(seconds)

Turb

idity

(NTU

)

0

1

2

3

4

5

6

Flow

Rat

e (l/

s)

Measured Turbidity

Modelled Turbidity

Flow Rate

660m 4” CI; 2003 90m 3” CI; 2005

0

100

200

300

400

500

600

700

6740 6940 7140 7340 7540 7740 7940 8140 8340

Time (seconds)

Turb

idity

(NTU

)

0

0.5

1

1.5

2

2.5

3

3.5

4

Flow

Rat

e (l/

s)

Measured TurbidityModelled TurbidityFlow Rate

0

2

4

6

8

10

12

14

16

18

20

2750 3000 3250 3500 3750 4000 4250 4500

Time (seconds)

Turb

idity

(NTU

)

0

2

4

6

8

10

12

14

16

Flow

Rat

e (l/

s)

Measured TurbidityModelled TurbidityFlow Rate

230m 3” CI 2005 360m 12” CI; 2006

Page 9: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Verification for plastic pipes

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

6000 7000 8000 9000 10000Time (seconds)

Turb

idity

(NTU

)

0

2

4

6

8

10

12

14

16

Flow

Rat

e (l/

s)

Measured Turbidity

Modelled Turbidity

Flow Rate

0

10

20

30

40

50

60

70

80

13700 14200 14700 15200 15700 16200Time (seconds)

Turb

idity

(NTU

)

0

1

2

3

4

5

6

7

8

9

10

Flow

Rat

e (l/

s)

Measured TurbidityModelled TurbidityFlow Rate

447m 146mm PE with τultimate limited to

1.2N/m2; 2006 380m 89mm PE with τultimate limited to

1.2N/m2; 2005

0

25

50

75

100

6500 7500 8500 9500 10500Time (seconds)

Turb

idity

(NTU

)

0

2

4

6

8

10

12

Flow

rate

(l/s

)

Measured TurbidityModelled TurbidityFlow Rate

0

20

40

60

80

100

120

140

160

17000 17500 18000 18500 19000 19500Time (seconds)

Turb

idity

(NTU

)

0

1

2

3

4

5

6

7

8

9

10

Flow

Rat

e (l/

s)

Measured TurbidityModelled TurbidityFlow Rate

170m 106mm uPVC with τultimate limited to

1.2N/m2; 2005280m 72mm PE with τultimate limited to

1.8N/m2; 2005

Page 10: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

• Typical operational scenario: increase demand at outlet by 10 l/s

• 100% flow/velocity increase downstream

• 10% flow/velocity increase upstream

• Where is the risk of material mobilization?

Example based on actual discolouration incident in the UK, 2009

100 l/s → 110 l/s

10 l/s → 20 l/s

Material mobilisation: where is the risk?

Page 11: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

110 l/s

20 l/s

Areas of customer

complaints

Discolouration material mobilised in

upstream section

Material mobilisation

Example based on actual discolouration incident in the UK, 2009

Page 12: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

A

B

C

Velocity or Shear Stress?

Page 13: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

PODDS history

• PODDS 1, 2001-2003 EPSRC funded. Detailed research into material characterisation, model formulation and initial field verification

• PODDS II, ‘Realising the potential of the PODDS model for the UK water industry’, 2004-2006. Nation wide validation through extensive field studies

• PODDS III, ‘Managing Discolouration: Research informing practice’, 2007-2009. Risk based computational tools, repeat testing to start exploring asset deterioration.

• PODDS IV, ‘Discolouration in trunk mains’. 2010-2013. Research focused on trunk main applications.

Page 14: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

14

Site Bridgwater Northern Ring

Main

Coker Hill to Maiden Beech

Bowden to Devizes

Properties 4km, 600 to 400mm, various

materials

7km, 450mm AC 6km 350mm Unlined Ductile

IronOriginal proposal & estimated cost

Swabbing £490K

Swabbing£530K

Main replacement £2M

Revised proposal (PODDS mediated) & cost

Overnight flushing of main £227K

Trunk main conditioning

£150K

Trunk main conditioning

£40K

Savings £263K £380K *£2M*Expenditure deferred

Examples of benefits

Page 15: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Trunk Main: PODDS fit / calibration

A

A

B

B

Conditioned layer strength

Page 16: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Prediction Of Discolouration in Distribution Systems

- Quantifying discolouration impact of flow changes

- Maintain TM flexibility by conditioning procedures (maintenance schedules with no water loss)

- Simulate discoloured water event potential

• High impact industry driven research

• New conceptual understanding

• Predictive empirical model• But process knowledge……0

1

2

3

4

5

6

7

8

9

10

0 0.5 1 1.5 2 2.5 3*Conditioned Flow (Ml/d)

Peak

Tur

bidi

ty (N

TU)

*Full pipe conditioning to higher demand requires new flow to be maintained in excess of 24 hours.

0

0.5

1

1.5

2

00:00 12:00 00:00 12:00 00:00

Time (hours)

Turb

idity

(NTU

) Turbidity response curve for 1.5 Ml/d flow conditioned pipe

with 0.5 Ml/d flow increase.

Page 17: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Dec

reas

ing

Laye

r she

ar

stre

ngth

Time

Time

Erosion 1Regeneration

Modes of regeneration

Page 18: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Dec

reas

ing

Laye

r she

ar

stre

ngth

Time

Time

Time

Erosion

2

1Regeneration

Modes of regeneration

Page 19: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Dec

reas

ing

Laye

r she

ar

stre

ngth

Time

Time

Time

Erosion

2

1

3

Regeneration

Time

Modes of regeneration

Page 20: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Dec

reas

ing

Laye

r she

ar

stre

ngth

Time

Time

Time

Erosion

2

1

3

Regeneration

Time

Modes of regeneration

Page 21: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

• Vast surface area, high residence times, uncertain and variable conditions• Physically, chemically and biologically complex and active systems

NG – Nutrient Gradient PI – Protozoan Interaction C – Corrosion E – Erosion S – Sloughing © Kat Fish 2010

Distribution system as reactors, not inert networks of pipes

Page 22: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Unique experimental facility

• Temperature controlled, re‐circulating system• 600m of HDPE pipe, 79mm diameter• Full scale system flows and pressures• Coupons to allow analysis of accumulation directly on the pipe wall      

designed to limit distortion of boundary layer flow

Page 23: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

SEM Images – 28 day biofilm development, 16oC  0.2 l s‐1 

Page 24: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

SEM Images – 28 day biofilm development, 16oC  0.2 l s‐1 

Primary Attachment

Page 25: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

SEM Images – 28 day biofilm development, 16oC  0.2 l s‐1 

Primary Attachment

Developed Biofilm

Page 26: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Quantify the distribution of biofilm (cells) with respect to depthInsight into the impact of environmental conditions (extremes of hydraulic condition and temperature during growth phase shown)Knowledge regarding the stability of the biofilm (change in distribution due to imposed flushing regime)

High varied conditioning shear stress at 8⁰C

0.1 N/m² steady state conditioning shear stress at 16⁰C

Conclusive association of discolouration and

microbiology / biofilms

Biofilm

Page 27: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Summary• PODDS simple, cost effective water 

quality tool

• Management strategies can be developed for:• safe operating flow limits • short term flow increases• long term conditioning and 

operation

• Capital vs. Operational costs can be evaluated

• Accurate flow measurement essential!

• HOWEVER...• Regeneration rates?

• Biofilms/particulates?Water Engineering Research

University of SheffieldDepartment of Civil & Structural Engineering

www.PODDS.co.uk

Water Distribution System Operational Strategies:Implications from PODDS Verified Research

The PODDS concept to Water Distribution Systems (WDS) management is based on scientific research that hasshown discolouration is a predictable response to increases in system shear stress. Applying an hydraulic shear force(τa) above the peak daily (τ’) creates an excess shear (τexcess) leading to discolouration (figure 1). The response is afunction of the strength characteristics and the accumulated discolouration (C) of material layers attached to thepipewalls.

Cohesive material layers develop throughout WDS with asset deterioration primarily being determined by waterquality (amount of particulate material entrained) and conditioning hydraulics. Optimal pro‐active managementstrategies are required to maintain assets yet minimise network interventions, thus saving time, money and limitdiscolouration risk to customers. To achieve this pipe material needs to be considered during operational planningas material accumulation processes, layer strength characteristics and discolouration potential are different inplasticand cast iron pipes

Plasticor smooth-walled

pipes

Cast Ironor rough-walled

pipes

Figure 1 – PODDS model of layer shear strength vs. discolouration potential

1Average UK value; actual deterioration rate variable based on water quality and network hydraulics.Warning: potential discolouration risk can be posed much sooner.

2Value shown based on work in the Netherlands by KIWA.

Prof. Joby Boxall Tel: 0114 2225760email: [email protected]

Dr. Stewart Husband Tel: 0114 2225416email: [email protected]

August 2013

Modelling has shown that a flushing induced force of 1.2 N/m2 is sufficient to

mobilise all material layers and clean pipe. MAINTENANCE

Modelling has shown that for any increase in applied shear force (e.g. flushing), material will continue to be mobilised.

"6/11"4/5"3/3

/6.0/2.1 2

slslsl

smmN TARGET

FLUSHING VELOCITY

Risk based value. Criteria: available flow, pipe discolouration

status and risk of unplanned hydraulic disequilibria.

4 Years 1DETERIORATION

(from clean to maximum risk)

1.5 years surface water 3 years ground water

a) Research suggests a peak daily flow of 20.4m/s will promote “self-cleaning” b) Improving water quality (reduces

deterioration rate).

OPERATION

a) Higher daily flows reduce potential discolouration event magnitude.

b) Improving water quality (reduces deterioration rate).

Biofilms believed integral to cohesive layers formation; liable to ‘slough’ increasing

discolouration risk. NOTES

Corrosion by-products increase pipe deterioration rate and ‘feed’ downstream

pipes (irrespective of material). Implementation of self-cleaning velocity

criteria to maintain residential water quality (networks characterised by a branched structure with

downstream declining diameter)

NETWORK DESIGN Not applicable

∞?

Layer Shear strength , τ (N/m2)

1.2

Dis

colo

urat

ion

pote

ntia

lC

(N

TUm

)

τ’ τa

τexcess

Cplastic

Ciron

CI pipe

Plastic pipe∞

∞?

Layer Shear strength , τ (N/m2)

1.2

Dis

colo

urat

ion

pote

ntia

lC

(N

TUm

)

τ’ τa

τexcess

Cplastic

Ciron

CI pipe

Plastic pipe

Page 28: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

PODDS V Translating laboratory based microbial / biofilm research into practicable field based discolouration knowledge to deliver the next paradigm in discolouration management New directions•Field studies linking biofilm development and discolouration•Develop rapid, cultivation-independent assays to quantify microbial viability•Multivariate analysis to associate asset deterioration and explanatory factors•Develop strategies to manage biofilms and discoloration•Validate and deliver the next generation of PODDS toolsAdditional on-going benefits;•Laboratory based experimental programme•Water network specific sensor technologies•PODDS network, forum and user groups

Page 29: Discolouration in potable water distribution systems PODDS ... · PDF file03.02.2017 · Prof. Joby Boxall Pennine Water Group University of Sheffield Discolouration in potable water

Acknowledgements

• Dr Stewart Husband• All the collaborating companies and

individuals who have supported and enable the research over the years

• For more information, please visit:www.PODDS.co.uk