clarifying settling tank capacity: 2d and 3d clarifier cfd

Clarifying Settling Tank

Capacity: 2D and 3D

Clarifier CFD Modeling

Will Martin, PE

Agenda/Outline

Clarifier modeling background

- What’s the purpose?

- What types of models are available/used?

- What’s the use for each level/type of model?

2D/3D Modeling

- Current state of the industry – historic uses

- Recent developments

Case studies

Processes

in Secondary

Settling Tanks

• Hydrodynamics

• Settling

• Turbulence

• Sludge Rheology

• Flocculation

• Heat Exchange

and Temperature

Settling Tank Models

Empirical Design Criteria

• Surface overflow rate (SOR)

• Solids loading rate (SLR)

Solids Flux Theory

• State point analysis (SPA)

One-dimensional models

Computational Fluid

Dynamics (CFD)

• Two-dimensional (2D) models

• Three-dimensional (3D)

models

2-D Models

• Includes the major process and

factors affecting clarifier

performance and capacity including

hydrodynamics, turbulence,

flocculation, temperature

Concentration (g/L): 0.01 0.02 0.05 0.11 0.23 0.52 1.14 2.50 5.50

8.5 ft14.8 ft 14 ft

Example: 2Dc Model

Limitation: Complex

inlet configurations

3-D Models

Limitation:

• Cost

• Computational

time

Processes in Secondary Settling Tanks

• Hydrodynamics

• Settling

• Turbulence

• Sludge Rheology

• Flocculation

• Heat Exchange

and Temperature

• Empirical design

• Solids flux theory

• 1-D Modeling

• 2-D Modeling

• 3-D Modeling

Case Study #1 – Marion Water Pollution

Control Center (Ohio)

WRRF background

• 10.5 MGD AADF WWTP

• Conventional activated sludge

treatment process

• Primary, secondary, and tertiary

clarifiers

Long-term control plan

and no feasible alternatives

analysis for wet weather flows

• Increase wet weather peak

flows from 28 MGD to 42 MGD

Planned Wet Weather Improvements

CFD Model: Confirm capacity/performance

Biowin Model: Confirm wet weather performance

CFD Model: Evaluate design improvements

Clarifier Design Loadings

Design Conditions Flow (MGD)

Primary Clarifier

SOR (gpd/sf)

Secondary/Tertiary Clarifier SOR (gpd/sf)

4 Clarifiers 6 Clarifiers 8 Clarifiers1

2014-2017 AA Flows 9.8 560 560 370 280

Design AA Flows10.5 600 600 400 300

2014-2017 Maximum

Month 15.3 870 870 580 430

Design Maximum

Month 16.4 930 930 620 460

2014-2017 Peak Day38.5 (PC’s), 28

(SC’s)2,180 1,585 1,060 790

Design Peak Day51 (PC’s), 42 (SC’s)

2,890 2,380 1,585 1,190

Notes:1. Includes the existing four (4) tertiary clarifiers in service as secondary clarifiers.

Secondary Clarifier Field Testing

Sampling Parameters

• Settling properties of the sludge: zone and

compression rates

• Flocculation parameters

• Flocculated suspended solids (FSS) and

dispersed suspended solids (DSS)

• Discrete settling parameters

• Sludge volume index (SVI)

• Mixed liquor suspended solids (MLSS)

• Flow rate

• Return activated sludge (RAS) flow rate

• SC effluent suspended solids (ESS) concentration

• RAS suspended solids (RAS SS) concentration

• Sludge blanket height (SBH)

Sludge

Properties

Clarifier

Loading

Clarifier

Performance

Secondary Clarifier Field Testing

0

200

400

600

800

1000

1200

0

2

4

6

8

10

12

14

16

3/21/2018 3/22/2018 3/23/2018

SO

R (

gpd/s

f)

ES

S (

mg/L

)

Combined ESS Average Individual Clarifier ESS

Clairifer 3 ESS Clarifier 4 ESS

Clarifier SOR (gpd/sf)

Day 1

Normal Conditions

4 Clarifiers

In Service

Day 2

Stress Testing

4 Clarifiers

In Service

0

200

400

600

800

1,000

1,200

0

1

2

3

4

5

6

3/21/18 12:00 AM 3/22/18 12:00 AM 3/23/18 12:00 AM

SO

R (

gpd/s

f)

Heig

ht

(ft)

Sludge Blanket Heights - Average All Clarifiers

Sludge Blanket + Dispersed Heigths - Average All Clarifiers

SOR

Day 1

Normal Conditions

4 Clarifiers

In Service

Day 2

Stress Testing

4 Clarifiers

In Service

Secondary Clarifier Model Calibration

Data Period SOR (gpd/sf) MLSS (mg/L)

ESS (mg/L) RAS TSS (mg/L) Blanket Height (ft)

Field

Measurement

Model

Prediction

Field

Measurement

Model

Prediction

Field

Measurement

Model

Prediction

March 21, 2018 –

Model Calibration560 3,630 7 11 15,550 13,750 1.1 2.3

March 21, 2018 –

Model Validation860 3,630 101 11.5 14,390 13,900 2.7 2.9

Notes:

1. Combined data set for individual clarifier and combined samples.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

3/22/2018 6:00 3/22/2018 10:00 3/22/2018 14:00 3/22/2018 18:00

ES

S (

mg/L

)

Field Data - ESS Model Results - ESS

Secondary Clarifier Capacity Evaluation

0

500

1,000

1,500

2,000

2,500

3,000

3,500

0

10

20

30

40

50

60

3/30/2014 3/31/2014 4/1/2014 4/2/2014 4/3/2014 4/4/2014 4/5/2014

SO

R (

gpd/s

f)

Flo

w (

MG

D)

5-Year, 24-Hour Storm Hydrograph Flow to Secondary Treatment

Primary Clarifier Loading (gpd/sf) Secondary Clarifier Loading - 4 SC's (gpd/sf)

Secondary Clarifier Loading - 4 SC's (gpd/sf)

Secondary Clarifier Capacity Evaluation

Peak Flow Rate (MGD)

No. of Clarifiers

SOR (gpd/sf) MLSS (mg/L) RAS Rate SVI (mL/g) Polymer? ESS (mg/L) Blanket (ft)

42 8 1,190

2,500 mg/L 40% 100 mL/g Yes <30 mg/L 2-4 ft

2,500 mg/L 40% 135 mL/g Yes<30 mg/L

2-4 ft

2,500 mg/L 40% 100 mL/g Partial<30 mg/L

2-4 ft

2,500 mg/L 40% 135 mL/g Partial<30 mg/L

2-4 ft

2,500 mg/L 40% 100 mL/g No <40 mg/L 2-4 ft

2,500 mg/L 40% 135 mL/g No <40 mg/L 4-6 ft

3,000 mg/L 40% 100 mL/g Yes<30 mg/L

2-4 ft

3,500 mg/L 40% 100 mL/g Yes<30 mg/L

4-6 ft

3,000 mg/L 40% 135 mL/g No >100 mg/L >10 ft

3,500 mg/L 40% 135 mL/g No >100 mg/L >10 ft

Process Model -Contact Stabilization

40% 100 mL/g Yes<30 mg/L

<2 ft


40% 135 mL/g Yes<30 mg/L

<2 ft


40% 100 mL/g Partial<30 mg/L

<2 ft


40% 135 mL/g Partial<30 mg/L

2-4 ft


40% 100 mL/g No<40 mg/L

<2


40% 135 mL/g No<40 mg/L

2-4 ft

Tertiary Clarifier Design Evaluation

0

2

4

6

8

10

12

14

16

18

20

Mo

del

Pre

dic

ted

ES

S (

mg/L

)

6-foot Launder Spacing 7-foot Launder Spacing 8-foot Launder Spacing

9-foot Launder Spacing 10-foot Launder Spacing

0

2

4

6

8

10

12

14

16

18

20

Mo

del

Pre

dic

ted

ES

S (

mg/L

)

10-foot Center Well Radius




10-foot Center Well Radius, Shallower Depth

Case Study #2 – F. Wayne Hill WRC (Georgia)

• F. Wayne Hill Water Resources Center (FWHWRC)

• 60 mgd advanced wastewater facility

F. Wayne Hill

WRC

Lake Lanier

Discharge

Point

Parameter Units

Monthly

Avg. Limits

Flow mgd 60

TSS mg/L 3

COD mg/L 18

Ammonia-N mg/L 0.4

Total Phosphorus mg/L 0.08

Turbidity Ntu 0.5

Fecal Coliform #/100 2

Historic Primary Clarifier Performance

-100%

-80%

-60%

-40%

-20%

0%

20%

40%

60%

80%

100%

% R

em

ova

l

Primary TSS Removal

Pri TSS Removal from Pri Inf (Load) 30 per. Mov. Avg. (Pri TSS Removal from Pri Inf (Load))

Year

Average

Primary TSS

% Removal

2006 -24%

2007 20%

2008 19%

2009 -27%

Approach used to evaluate the

performance of the primary clarifiers

• Evaluation of historical data and sampling location

• Process and mechanical evaluation

• Special sampling events (2 Phases)

• Two-dimensional (2D) and three-dimensional (3D)

Computational Fluid Dynamics (CFD) modeling.

Revised sampling locations and testing

verified poor primary clarifier performance

Modified Influent, PI, and PE sampling locations and

operating configuration to achieve good sampling

ParameterPI Combined

(mg/L)

PE Combined

(mg/L)% Removal

TSS 327 264 19%

COD 503 437 13%

cBOD 229 208 9%

Jar Testing and Column Testing Results

TSS Removal – 50 to 70%

2Dc Modeling

Solids get trapped

in the scum creating

a thick layer of

solids and scum

that eventually is

carried over the

effluent weirs

3D Modeling

Three dimensional modeling using the ANSYS FLUENT

Results from the existing conditions revealed shortcircuiting from the influent flow into the sludge hopper

Flow Field Inlet Detail

PC Modifications

Before After

Primary Clarifier

% TSS

Removal

Primary 9 – Baffle Installed 48%

Primary 10 – As Is 31%

Primary clarifier performance before

and after proposed modifications

After proposed operational and physical modifications, that included the installation of a canopy baffle, the PSTs showed a significant improvement in performance

0

100

200

300

400

500

600

700

800

900

7/8/09 8/7/09 9/6/09 10/6/09 11/5/09 12/5/09 1/4/10 2/3/10

Co

nc

en

tra

tio

n (

mg

/L)

PE TSS 14 per. Mov. Avg. (PE TSS)

End Phase 1 Sampling Event

Case Study #3 – Passaic Valley

Sewerage Commission (PVSC)

• 330 MGD AADF secondary

treatment capacity

• 400 MGD secondary

treatment peak flow

capacity

• Long-term control plan –

evaluate alternatives to

expand plant wet weather

flow capacity

• Alternatives include step

feed, solids storage, wet

weather treatment

systems, and others

Clarifier Configuration

Modeling Approach

• Build a model of a 3D

representative clarifier

• Refine baseline with operation

and field data

• Sensitivity runs on a ‘slice’ model

(or 2Dc model)

• Confirmation on full 3D model

• Apply 3D model to alternatives

3D Modeling

Secondary

Bypass

Step Feed

3D Modeling Findings

1 RAS rates at peak flow (based on 130 MGD RAS flow): Bypass = 32%, Other simulations =18%

zQuestions?

Will Martin, PE

clarifying settling tank capacity: 2d and 3d clarifier cfd

Documents