STOP CHASING THE SOLIDS REDUCED DESIGN FLOWS FOR THE NEW WAS THICKENING FACILITY AT

ASHBRIDGES BAY TREATMENT PLANT

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S. Liver*, S. Atlin**, P. Coleman*, and R. McKinley**

* Black & Veatch**City of Toronto

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1. Project Overview 2. Why Consider Reduced Design Flows3. Operational Approach4. Analytical Approach5. Findings

AGENDA

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ERV

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• Driver: Stop co-thickening in PCs as part of City‘s overall Wet

Weather Flow Strategy and abandon aged DAF thickening

• Objective: Construct WAS Thickening Facility with sufficient

capacity so that all future WAS flows can be thickened through a single process.

PROJECT OVERVIEW

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WAS Pumps and WAS Piping •Automate WAS pumps•Replace 12 PLCs with GE RX31 PLCs

Incineration Facility Conversion to TWAS•Demolish Incineration and Waste Heat Recovery Facility•Construct new facility on existing pile foundations• Integrate TWAS facility with adjacent buildings•Design basis: 26 MLD•Preselect centrifuges, relocate 2 centrifuges from HTP•New workshop, administration space, storage areas

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DAF Building •Convert to Storage Building•Remove equipment, piping, pumps•New main floor to cover DAF tanks•Perform work after TWAS Facility is

commissioned

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ASHBRIDGES BAY TREATMENT PLANT

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DRIVERS

• 37 MLD future peak• 6,500 mg/L • Based on historical data

ORIGINAL DESIGN CRITERIA

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DES

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FLO

WS

• Quantities measured didn’t match CAS theory• Contribution of solids from Humber and North

Toronto confounded data• Historical dataset affected by biosolids “outlets”• Requirement to Nitrify• “Phantom RAS”

DRIVERS FOR CONSIDERING REDUCED DESIGN FLOWS

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EDU

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DES

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WS

MASS BALANCE - SIMPLIFIED

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Influent: 818 MLDSecondary ClarifierBOD RemovalPrimary Clarifier

Thickening

Co-Thickening

WAS Flow Rate

North Toronto

Humber

Sewer Shed

Splitter Box“Phantom RAS”

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1. Improved flexibility in biosolids contracts

2. Weekly process control meetings

3. Use of a Business Intelligence Tool

OPERATIONAL APPROACH

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1. Statistical Analysis2. Mass Balance

ANALYTICAL APPROACH

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1. Statistical Data Review of 2012 and “New Operating Regime” August-December 2013

2. Factors affecting WAS volume3. Development of Mass Balance4. Reconciling 2011 Engineering Study Report

proposed design point

STATISTICAL ANALYSIS

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• findings

DATA REVIEW - THE BOX AND WHISKER PLOT

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Maximum

Half of the values are within this box

Minimum

MedianHalf of the values are above and below this value

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DATA REVIEW - TOTAL WAS FLOW RATE

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2007-2009 Feb 2012 to Dec 2012 Aug 2013 to Dec 2013

WAS

Flow

Rat

e (M

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2011 Engineering Study Report Data

2012 Data

New Operating Regime Data

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DATA REVIEW – CO-SETTLING FLOW

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2007-2009 Feb 2012 to Dec 2012 Aug 2013 to Dec 2013

Co-S

ettlin

g Fl

ow (M

LD)

2011 Engineering Study Report Data

2012 Data

New Operating Regime Data

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DATA REVIEW – DAF FLOW

140

5

10

15

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25

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2007-2009 Feb 2012 to Dec 2012 Aug 2013 to Dec 2013

WAS

Flow

to D

AF (M

LD)

2011 Engineering Study Report Data

2012 Data New Operating Regime Data

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DATA REVIEW – WAS THICKNESS

150.00

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0.90

1.00

Feb 2012 to Dec 2012 Aug 2013 to Dec 2013

WAS

Con

cent

ratio

n (%

w/w

)

2012 Data

New Operating Regime Data

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DATA REVIEW – FLOW VS. CONCENTRATION

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3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

WAS

Flo

w R

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(MLD

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WAS Concentration (mg/L)

Y axis: Flow in MLD

X Axis: Concentration in mg/L

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HISTORICAL DATA

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3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

WAS

Flo

w R

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(MLD

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WAS Concentration (mg/L)

Yr 2012 25th-75th %ile

Yr 2013 - Aug-Dec25th-75th %ile

What is difference?Nitrifiying (longer SRT)

Better Control of WAS ConcentrationLess Co-Settling

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• Thickening‐ Co-Thickening‐ DAF or Centrifuge

• Solids Load from Humber & NTP• Impact of Nitrification• Evaluation at current flows• Evaluation at plant-rated flow (818 MLD)

MASS BALANCE USED TO EVALUATE:

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MASS BALANCE

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MASS BALANCE: 2012 – 2013 PRODUCTION

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3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

WAS

Flo

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(MLD

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WAS Concentration (mg/L)

Yr 2012 25th-75th %ile

Yr 2013 - Aug-Dec25th-75th %ile

Average 2012 -2013 Sludge Production~ 88,070 kg/d

52% of WAS to Co-Settling

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FACTORS AFFECTING VOLUME – CO-SETTLING

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3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

WAS

Flo

w R

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(MLD

)

WAS Concentration (mg/L)

Yr 2012 25th-75th %ile

Yr 2013 - Aug-Dec25th-75th %ile

Impact of No Co-Settling88,070 kg/d -> 68,156 kg/d

23% less WAS as mass

The New NormalNo need to co-settle when new facility is built

52% Co-Settling

0% Co-Settling

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FACTORS AFFECTING WAS VOLUME - SRT

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3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

WAS

Flo

w R

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(MLD

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WAS Concentration (mg/L)

Yr 2012 25th-75th %ile

Yr 2013 - Aug-Dec25th-75th %ile

SRT 6 days -> 3 days = 10% more WAS massSRT 6 days -> 9 days = 5% less WAS mass

3 day SRT

9 day SRT

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FACTORS AFFECTING WAS VOLUME - HUMBER

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3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

WAS

Flo

w R

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(MLD

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WAS Concentration (mg/L)

Yr 2012 25th-75th %ile

Yr 2013 - Aug-Dec25th-75th %ile

Why can't you use textbook numbers?28% of the WAS Mass is due to the Humber TP

With HTP

Without HTP

FIN

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NEW DESIGN ENVELOPE

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3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

WAS

Flo

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(MLD

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WAS Concentration (mg/L)

Yr 2012 25th-75th %ile

Yr 2013 - Aug-Dec25th-75th %ile

576 MLD

1.3 X 818 MLD

26 MLD X 5,000 mg/L = 130,000 kg/d

818 MLD

2011 Engineering Study

FIN

DIN

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• 26 MLD WAS‐ 818 MLD (ABTP rated capacity)‐ Humber at rated capacity‐ No co-thickening‐ 6 day SRT (SRT impact is less than 10%)‐ Peaking Factor 30% on mass basis‐ 5,000 mg/L WAS concentration (minimum at peak flow)

DESIGN POINT - RECOMMENDATION

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FIN

DIN

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• Recommend Reducing Design Flow from 37 MLD to 26 MLD- Peaking Factor 30% on mass basis - 5,000 mg/L WAS Concentration

• 5 Duty – 2 Standby “40-inch bowl” centrifuges

• Key Reasons:- Installing centrifuges eliminated co-settling and

“recycle of solids”- Improved solids control vs. 2007-2009 operation

IMPLICATIONS

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THANK YOU !

QUESTIONS ?