11

STATE POINTSTATE POINTANALYSISANALYSIS

WesTech Engineering, Inc.WesTech Engineering, Inc.Salt Lake City, Utah, USASalt Lake City, Utah, USA

22

Simplified Activated Simplified Activated Sludge Flow SheetSludge Flow Sheet

Q + RAS Q

WAS

Q

RAS

Aeration Basin Clarifier

State Point Analysis

33

Key Parameters used in Key Parameters used in State Point AnalysisState Point Analysis

Factor / Parameter SymbolInfluent flow rateInfluent flow rate QQReturn activated sludge flow rateReturn activated sludge flow rate RASRASMixed liquor concentrationMixed liquor concentration XXmlssmlss

Sludge settling characteristicsSludge settling characteristics VVoo, k, kClarifier surface areaClarifier surface area AA

44

State Point DiagramState Point Diagram

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr

Solids Concentration Axis

Solids Flux Axis

55

What is Solids Flux?What is Solids Flux?

Solids flux is the movementof solids through a clarifier

Solids Flux = mass per unit area per unit time

kg / m2 - hr

Solids Loading Rate (SLR) is one type of solids flux

66

State Point DiagramState Point DiagramWe will plot three elements

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr

- Underflow rate line- Settling flux curve

- Overflow rate line

77

State Point DiagramState Point Diagram

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr Overflow rate line

Slope = SOR = Q/A

88

State Point DiagramState Point Diagram

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr

Underflow rate line

Slope = SUR = RAS/A

Solids loading rateXmlss(Q+RAS)

AState Point

mlssconcentration

Expected underflow conc.

99

Settling FluxSettling Flux

Settling Flux, Gs = X Vs

Where: X = Solids concentration

Vs = Settling velocity at that concentration

Determine Vs with settling tests

1010

Settling FluxSettling Flux

Interface height

We record interface height

vs time

Settling tests at various solids concentrations

1111

Settling CurveSettling Curve

Time (min)

Inte

rfac

e H

eigh

t (m

m)

600

00 5

200400

1510 20

1200

800

1000

14001600

503025 35 4540

Vs is the slope of the straight section of the settling curve

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Settling FluxSettling Flux

Now that we have the settling velocity Vs we can calculate Gs

Gs = X Vs

This gives us one (1) point on the flux curve.

To get more points we need to run more tests at different solids concentrations.

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Settling FluxSettling FluxFor most activated sludge there exists the following relationship

Vs = Vo e-kX

Substitution givesGs = X Vo e-kX

With a few settling tests we can solve for Vo and k and define the whole flux curve.

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VeslundVeslund RelationshipRelationship

X, g/l

lnV

s

-0.5

-2.00.0

-1.5-1.0

1.0 2.0

1.0

0.00.5

1.52.0

5.03.0 4.0

Vo = y intercept k = line slope

1515

State Point DiagramState Point Diagram

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr Now we plot the

three elements together to form the State Point Diagram

1616

Thickening FailureThickening Failure

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr Thickening failure

1717

Inventory ShiftInventory Shift

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr

21

1818

Clarification FailureClarification Failure

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr Clarification failure

1919

Flow IncreaseFlow Increase

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr Overflow line gets steeper

State point moves up

2020

Change Settling PropertiesChange Settling Properties

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr

2121

Optimizing RAS RateOptimizing RAS Rate

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr

RAS rate too high

Underflow conc. too low

2222

Optimizing RAS RateOptimizing RAS Rate

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr

Lower RAS pumping, higher RAS concentration

2323

State Point AnalysisState Point Analysis

8.07.06.05.04.03.02.01.00.0

0 2 4 6 8 10 12 14 16 18 20X, g/l

G, K

g/m

2-hr State Point Analysis is a useful

tool for both designers and operators to graphically understand the dynamics of an activated sludge clarifier.

2424

State Point AnalysisState Point Analysis

Questions ?