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Rocky Mountain Water Environment Association 65 th Annual Meeting September 17, 2002. Folklore in Activated Sludge Treatment Plant Operations. Eric J. Wahlberg. Folklore Defined. Folklore Defined. “An unsupported notion, story, or saying that is widely circulated.”. Learning Objectives.

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Presentation Transcript
slide1

Rocky Mountain Water Environment Association

65th Annual MeetingSeptember 17, 2002

Folklore in Activated Sludge Treatment Plant Operations

Eric J. Wahlberg

folklore defined
Folklore Defined

Folklore Defined

“An unsupported notion, story, or saying that is widely circulated.”

slide3

Learning Objectives

  • Myth 1
  • Myth 2
  • Myth 3
  • Myth 4
  • Myth 5
folklore defined5
Folklore Defined

Where Did I Get This Title?I Stole It.

Richard I. Dick (1976). “Folklore in the design of final settling tanks,” Journal Water Pollution Control Federation, 48, pp. 633-644.

slide6

Myth 1

Blankets are necessary for secondary clarifiers to work properly.

how often has it been said
How Often Has It Been Said

Activated sludge secondary clarifiers perform two functions:

1. Clarification of the overflow

2. Thickening of the underflow

how often has it been said8
How Often Has It Been Said

Activated sludge secondary clarifiers perform two functions:

1. Clarification of the overflow

2. Thickening of the underflow

Yuk!

thickening role is root cause of many problems
Thickening Role is Root Cause of Many Problems
  • Operators try to achieve unachievable RAS concentrations
  • Denitrification
  • Phosphorus release
  • Deterioration in sludge quality
just say no
Just Say No

Thickening

in secondary

clarifiers

slide19

Truth 1

Blankets are not necessary for secondary clarifiers to work properly, and better performance will result when no blankets are kept in secondary clarifiers.

myth 2
Myth 2

The hydraulic detention time in the aeration basin is decreased by increasing the RAS flow rate.

the basic activated sludge process
The Basic Activated Sludge Process

Effluent

Influent

Mixed liquor

Secondary clarifier

Aeration basin

WAS

RAS

this is how the myth got started25
This Is How The Myth Got Started
  • HRT = VAB/(Q + QRAS)
  • But this is not correct. Why?
the basic activated sludge process28
The Basic Activated Sludge Process

Effluent

Influent

Mixed liquor

Secondary clarifier

Aeration basin

WAS

RAS

tanks are full no influent effluent was
Tanks Are Full; No Influent, Effluent, WAS

Mixed liquor

Secondary clarifier

Aeration basin

RAS

truth 2
Truth 2

As Glen Daigger stated Sunday: “Bugs only know SRT; they do not know HRT”.

The hydraulic detention time in the aeration basin is not affected by the RAS flow rate.

slide31

Myth 3

The MLSS concentration can be controlled by the RAS flow rate.

slide35

d)

40

2

30

20

Solids Flux (lb/ft

10

0

Over Loaded To Under Loaded, MLSS Goes Up

0

5

10

15

Solids Concentration (g/L)

slide36

Truth 3

The MLSS concentration can be controlled by the RAS flow rate, but you don’t want to because it’s limited and it requires blankets in the clarifiers (see Truth 1).

myth 4
Myth 4

Process control means keeping the MLSS concentration or the F:M ratio or the SRT constant.

slide39

Settles well

Compacts well

Flocculates well

In Essence Our Jobs Are Very Simple

As David Jenkins almost said on Sunday, we want a sludge that:

slide40

You Cannot Control What You Do Not Measure

Process control should be based on maintaining stable, optimal sludge quality.

truth 4
Truth 4

Process control means maintaining stable, optimal sludge quality (that meets permit).

myth 5
Myth 5

The MLSS concentration, the F:M ratio, and the SRT can be controlled simultaneously .

equation for mlss concentration
Equation For MLSS Concentration

XML = {XINF-ISS + [Yg( )]}

So – S

SRT

HRT

1 + bSRT

truth 5
Truth 5

Fix the SRT to achieve permit compliance and let the MLSS and F:M “drift” to wherever they want to.

slide46

Thank you!

  • Myth 1
  • Myth 2
  • Myth 3
  • Myth 4
  • Myth 5