Sidney Innerebner, PhD, PE, CWP Indigo Water Group, … Innerebner, PhD, PE, CWP Indigo Water Group,...

Sidney Innerebner, PhD, PE, CWP

Indigo Water Group, LLC

Clarifier Basics Clarifiers have both hydraulic capacity and solids

handling capacity

Use State Point Analysis to predict performance

Secondary Clarifier Capacity

Hydraulic capacity

Detention Time

Surface Overflow Rate

Weir Loading Rate

Pulling down is GRAVITY

Pushing up is CURRENT (surface overflow rate)

Surface Overflow Rate Average,

gpd/sf Peak, gpd/sf

Conventional Activated Sludge

400 - 700 1000 – 1600

Extended Aeration 200 - 400 600 - 800

SOR = Influent Flow to Clarifier Clarifier Surface Area

4 Source: Metcalf and Eddy 4th Edition (2003) – pg 687

Weir Loading Rate Peak, gpd/lf

WWTPs less than 1 mgd 20,000

WWTPs greater than 1 mgd 30,000

WLR = Influent Flow to Clarifier

Linear Feet of Weir

5 Source: Recommended Standards for Wastewater Facilities (2004) pg 70-4

Solids Loading Rate to Clarifier Average, lb/sf*hr

Peak, lb/sf*hr

Conventional Activated Sludge

19.2 – 28.8 38.4

Extended Aeration 4.8 – 24.0 33.6

SLR = (QINF + QRAS)(MLSS, mg/L)(8.34)

Clarifier Surface Area

7 Source: Metcalf and Eddy 4th Edition (2003) – pg 687

State Point Analysis Use State Point Analysis to predict performance

Mathematical model of clarifier

Uses settling data – Sludge Volume Index (SVI)

Some limitations

State Point Analysis Actual or Estimated Settling Characteristics (SVI)

Mixed Liquor Suspended Solids Concentration

Clarifier Surface Area

Influent Flow

Return Activated Sludge (RAS) Flow

10

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d)

Solids Concentration (g/L)

MLSS and RAS/WAS

Concentration

State Point X-Axis

EJWahlberg, April 1996

11

0

5

10

15

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35

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0 5 10 15

Solid

s F

lux

(lb/f

t2d

)


Solids Loading Rate or Flux

State Point Y-Axis


12

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



The State Point

(x,y) coordinates x = SLR, lb/ft2*d = 14 y = MLSS, g/L = 3.5

State Point

13

0

5

10

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20

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35

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0 5 10 15

Solid

s F

lux

(lb/f

t2d

)


Overflow Line

Overflow line slope is equal

to surface overflow rate

(SOR)


14

0

5

10

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35

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0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Overflow Line

Qinfluent = Higher Steeper Slope

15

0

5

10

15

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35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Overflow Line

Qinfluent = Lower Flatter Slope

16

0

5

10

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20

25

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35

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0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line Solids

Loading Rate

17

0

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35

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0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line

Expected RAS/WAS

Conc.

18

0

5

10

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20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line

Slope is the Solids Underflow

Rate - SUR

19

0

5

10

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25

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35

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0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line

QRAS = Higher Steeper Slope

Slope = Underflow Rate

20

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line Higher Flux

Lower RAS/WAS Concentration

21

0

5

10

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35

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0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line

Lower Flux

Higher RAS/WAS Concentration

22

0

5

10

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20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line

Placement depends on the solids concentration entering the clarifier.

23

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line

Higher MLSS moves line up, but slope stays the same.

24

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Underflow Line

Lower MLSS moves the line down.

25

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d)


Settling Curve


Flux Curve built from

SVI or other settling data

Solids Flux Theory Particles cannot move relative to one another

Hindered settling

Interface forms

Interface subsides at a constant velocity

Velocity depends on

Concentration of solids (volume fraction)

Settling characteristics

27

0

5

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35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d)


Settling Curve


LOW SVI = Big Curve

More

Clarifier Capacity

28

0

5

10

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25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Settling Curve

BIG SVI = Small Curve

Less

Clarifier Capacity

Bowling Balls versus Feathers

Concept Applies to Floc Too

Dense, Round Floc Filaments = Feathers! Poor Settling

Reduced Treatment Capacity

31

0

5

10

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25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Clarification Success!

The State Point must be within the Flux Curve for clarification to be possible.

State Point

32

0

5

10

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20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



State Point Analysis

When State Point is outside the settling curve, clarifier has a clarification failure. It can’t settle the incoming solids.

Causes of Clarification Failure MLSS Concentration too High

Influent Flows too High

Poor Settling Characteristics

Using State Point to Set RAS Rate Underloaded Condition – blanket going down

Overloaded Condition – blanket going up

Critically Loaded Condition – stable blanket

RAS should be as LOW as possible while:

Not building a blanket

Preventing denitrification in the blanket

35

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Adjusting RAS Flow

Thickening Failure

36

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Adjusting RAS Flow

Over Pumping RAS

37

0

5

10

15

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25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Adjusting RAS Flow

Critically Loaded

38

0

5

10

15

20

25

30

35

40

0 5 10 15

Solid

s F

lux

(lb/f

t2d

)



Adjusting RAS Flow

Thickening Failure

Critically Loaded

Over Pumping RAS

What Can be Controlled MLSS Concentration (WAS Rate)

RAS Rate

Number of Clarifiers On-Line

SVI (did somebody say polymer?)

Grand Island Examples Three clarifiers

100 foot diameter each

Side water depths of 9 ft (#1 and 2), 12.5 ft (#3)

Average influent flow = 8 mgd

Typical RAS flow = 40% of influent

SVI = 120 mL/g

MLSS = 3000 mg/L

RAS = 9,500 mg/L

Find the surface area of one clarifier

Input conditions and find the State Point

Solids in Effluent (Cloudy) Ashing –small ash-like particles on surface of clarifier

Start of denitrification

High grease content

Pin Floc – small dense particles of floc

Old sludge breaking down

Straggler Floc – Light fluffy sludge particles

Young sludge, low mixed liquor

How do you know?????

43

Clumping

44

Sludge Clumping

45

Ashing

46

Straggler Floc

47

Denitrification or Hydraulics? Look for bubbles

Behind the rake arm

At the clarifier edges

During peak loading

Did sludge go down and come back up?

Possible denitrification

Did it never go down in the first place?

Straggler floc

Pin floc 48

Rising Sludge Behind Rake Arm

51

Solids went under the scum baffle and

came back up. Good indication of

denitrification.

52

My sludge won’t settle! A modification to your settleometer test can tell you if

the problem is in the aeration basin (biology) or in the clarifier (operations)

Thank you Eric, don’t call me doctor, Wahlberg!

Testing Procedure Collect a grab sample of

MLSS

At the same time, get a grab of secondary clarifier effluent

Run the settleometer test as usual

Analyze supernatant AND clarifier samples for TSS

Interpreting the Results You should have two TSS results

Turbidity works well for this test too.

If the TSS for the settleometer test and the clarifier effluent are about equal: IT IS A BIOLOGY ISSUE

If the TSS for the settleometer is much better than the clarifier effluent: IT IS A CLARIFIER ISSUE

Biology Versus Clarifier

Biology Issues

Air on/off cycles

Filaments

Low DO

High VFA

Nutrient limitations

MCRT too low

MCRT too high

Clarifier Issues

Carrying big blankets

Denitrification in the blanket

Sludge in clarifier too long (no DO in here!)

Hydraulic surge

Something wrong with collection mechanism

Sidney Innerebner, PhD, PE, CWP

Indigo Water Group, LLC

Sidney Innerebner, PhD, PE, CWP Indigo Water Group, … Innerebner, PhD, PE, CWP Indigo Water Group,...

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