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Sludge Screening, the Aspirin for

headaches or a Business Case for

Better Biosolids Management

Biosolids, Odor and Corrosion Conference August 2015

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2

Industry took advantage of biosolids

management cost drop

0

5

10

15

20

25

30

35

40

45

50

1988 1990 1992 1994 1996 1998 2000 2002 2004

$ p

er w

et t

on

Year

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3

Advantages led to ignoring problems

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4

Problems led to Bans

2001 2004 1999

Restricted Use Reasonable

Limited

Actual Ban Practical Ban

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CHARLOTTE

COLLIER

DE SOTO

HIGHLANDS

LEE

SARASOTA

HARDEE MANATEE

BROWARD

DADE

GLADES

HENDRY

MARTIN

MONROE

OKEECHOBEE

PALM

BEACH

ST. LUCIE Status of

Biosolids Bans

in Florida

Practical Ban, Class AA Exempt

Ordinance Regulates Land Application

Developing/Revising Ordinance

No Significant Available Sites

Ban on Class B

Practical Ban

No Ordinance Enacted

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?

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“The other side” uses fear

All we have is Science and Nature

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8

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9

Typical Solids Handling Process

Primary Clarifier

Solids Tank

Thickening

Digestion Dewatering Hauling

Beneficial Use

Headworks Aeration

Basins Secondary Clarifier

Filters,

Disinfection,

Discharge

Sludge and

Scum

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Why Screen Sludge?

Thickening

Digestion Dewatering Hauling

Beneficial Use

• Minimize inorganic volume downstream

• Decrease maintenance

• Decrease digester maintenance

• More efficient hauling

• Higher quality biosolids

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Screen type depends on sludge

• Dilute Sludge

– Primary, scum, waste activated

sludge

– Inconsistent content

– Intermittent flow

– Target plastic, rags, large

inorganic debris

Thickening

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Dilute Sludge Screens

• Fine Screens (≥ 3mm openings)

• Slotted, not perforated

• Gravity flow (open channel)

• Screening and handling separate steps

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Screen type depends on sludge

• Thickened

– Higher solids concentration

– More consistent content

– Constant flow

– Target hair, fibers, small

inorganic matter

Thickening

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Thickened Sludge Screens

• Perforated openings (< 3 mm openings)

• Pressurized (14-18 psi)

• Constant flow (200 – 500 gpm, <4%)

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Dallas Central WWTP – Case Study

• 150 – 350 mgd

• 2 primary plants

• Trickling Filters

• Primary sludge, WAS,

scum pumped to

Southside WWTP

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Solids Process Flow Diagram

Headworks Primary

Clarifiers Trickling

Filters

Secondary

Clarifiers

Aeration

Basins

Final

Clarifiers

Solids

Holding Tank

To Solids

Processing

(Southside

WWTP)

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Accumulation of Inorganics Causes O&M

Challenges

To Solids

Processing

(Southside

WWTP)

Solids

Holding Tank

Primary

Solids

•Severe impeller wear

•Frequent clogging

•Mixing system clogging

•Mixing pump wear

•> 3 feet of floatables 9

feet of inorganics

WAS

•Equipment maintenance

•Inorganic build-up in digesters

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Alternatives Evaluation Resulted in

Selection of 3 mm Step Screens

Selection Criteria

Number Required

Performance

Flexibility

Operator Attention

Maintenance Attention

Capital Cost

2 6

$1.8 M $5.9 M

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Elevated Structure

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Passive Overflow Weir

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Mat to capture snails

Large Differential

Head

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Cubic Feet per Million Gallons

Source: WEF MOP 8, Fig. 9.7

3 mm screens were selected to build a snail removal mat

Screen Openings, Inches

0

2

4

6

8

10

12

0 1 2 30.5 1.5 2.5

46%

54%

3 mm

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The Step Screens Work

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The Step Screens Work

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The Step Screens Work

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The Screens Capture Snails Without the

Mat

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Cubic Feet per Million Gallons

Source: WEF MOP 8, Fig. 9.7

Screen size is critical factor in facility

Screen Openings, Inches

0

2

4

6

8

10

12

0 1 2 30.5 1.5 2.5

46%

54%

3 mm

6 cy (162 cf per day), average flow of 2.8 MGD

55

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Sludge Screening, the Aspirin for

headaches or a Business Case for

Better Biosolids Management

Biosolids, Odor and Corrosion Conference August 2015