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Optimizing a Pure Oxygen Wastewater Treatment Plant

Randal W. Samstag, PE, BCEE Principal Technologist

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Outline

• HPO Basics • HPO Upgrade Case Studies

– West Point WWTP Pilot Plant – Bellingham Post Point WWTP

• Conclusions

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The High Purity Oxygen (HPO) Process

• Invented by Union Carbide Corp. in early 1970s • “High Purity Oxygen”

– Cryogenic Plant (95 – 99%) – Pressure Swing Adsorption (88 – 93%) – Vacuum Swing Adsorption (88 – 93%)

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HPO Upgrade Case Studies

• West Point WWTP HPO Pilot Plant • Bellingham Post Point WWTP

– HPO Modifications Project – Nitrogen Removal Upgrades

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West Point WWTP

Pilot Plant

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Wef2003Samstag.ppt

West Point HPO Test Facility

• 4-stage HPO pilot facility (Lotepro) – 20-30 gpm – SRT: 1-2 days

• Mar - Dec 1988

• 3 modes evaluated: – Plug Flow – Contact/Reaeration – Anaerobic Selector w/ Plug Flow

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HPO Test Facility Schematic

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Settleability Data from HPO Test Facility

0 100 200 300 400 500 600 700 800 900

SVI,

mL/

g

Min Ave Max

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Wef2003Samstag.ppt

The Culprits

• Microscopic evaluation found filaments

– Thiothrix II

– Type 021N

• Sulfur oxidizing aerobes

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Influence of SRT and Temp on PAO

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10

12

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10 15 20 25 30

Temperature (Degrees C)

Was

hout

Aer

obic

SR

T (D

ays)

Nitrifier Washout Nocardia Washout PAO Washout

EBPR

EBPR and Nitrification

No EBPR

Mammais and Jenkins, 2001

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PAO Have Higher Floc Density

• PAO form Neisser-positive cell clumps

• Compact flocs settle faster than highly filamentous sludges

• Bio P organisms have a higher density than typical zoogleal or filamentous organisms

Schuler and Jang, 2007

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Bellingham Post

Point WWTP

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The Bellingham Post Point WWTP

• 20 mgd capacity HPO activated sludge plant

• 10 ton/day pressure swing absorption HPO system

• Three HPO basin stages

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Settleability History

• Average SVI of 170 mL/g from 1999 to 2004 • Filament caused settleability problems

– Type 1701 (Low DO) – Type 1863 (Low SRT)

• Periodically high VFA feed from influent sewer and from solids dewatering operation 3-4 days per week leading to slime bulking

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Idea for Improvement – Anaerobic Selector

• Provide zone for uptake of VFA • Encourage growth of phosphorus accumulating

organisms (PAO) • Increasing population distribution of PAO increases floc

density • PAO have a compact morphology and higher density than

other typical activated sludge bacteria (Schuler and Jenkins)

• Experience at three other HPO plants (SE Essex SD, Hyperion, SE San Francisco)

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The HPO Modifications Project

• Improve settleability by converting first stage to anaerobic selector

• Replace aerators to improve oxygen transfer • Add variable speed drives to mixers to improve

control and save power • Selectors added capacity for interim operation until

major capacity upgrade could be completed

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SVI History Before and After Conversion to Anaerobic Selector

Comparison of SVI and MCRT

0

50

100

150

200

250

300

350

07/17/05 12/14/05 05/13/06 10/10/06 03/09/07 08/06/07 01/03/08 06/01/08

SVI (

mL/

g)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

MC

RT

(Day

s)

SVI 7/Avg ml/g MCRT 7/Avg Days

Aerobic

Anaerobic

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The Original Aerators

• Conventional conically shaped low speed aerators with bottom impellors

• Estimated standard aerator efficiency (SAE) - 3.2 pounds of oxygen per hour per horsepower

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New Aerators

• m2t Technologies • Flat-bladed surface

aerators without bottom impellers

• Initial estimate of SAE (second stage conditions) – 4.0 pph/hp

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Low Speed Testing for First Stage Aerators

• Tested to deliver 0.5 ft per second velocity at the bottom of the test tank at low speed in first stage (anaerobic / aerobic)

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High Speed Testing

• Test-tank tested at approximately 3.9 pph/hp under high speed conditions simulated for second stage

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Simulation of Variable Speed Control

• Simulations by Michael Stenstrom of UCLA indicated up to 35% savings in power with VSD control

• Savings only occur when aerators are under-loaded 2

4

6

8

10

12

14

16

0 5 10 15 20 25

DO1DO2DO 3

Dis

solv

ed O

xyge

n C

once

ntr

atio

ns

(mg

/L)

Time (hours)

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Summary Comparison Performance

Description Aerobic (2006) Anaerobic (2007) Difference (%)

O2 (tpd) 7.2 6.7 -6.8%

O2 (lb/mgal) 1,291 1,212 -6.5%

O2 (lb/lb BOD) 1.21 1.15 -5.7%

SVI (mL/g) 155.71 126.77 -22.8%

Estimated Mixer Power (hp)

222.2 125 -77.9%

Estimated Oxygen Power (hp)

215.2 201.6 -6.8%

Estimated Total Power (hp)

437.5 326.6 -34.0%

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Project Budget

• Total cost - $670,000 • Puget Sound Energy grant - $330,000 • City of Bellingham cost - $340,000

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Comparison of Operating Modes Actual Bellingham Operation

HPO Operation - 2006 • 100% Aerobic • 2.2 Days Aerobic SRT • 157 mL/g SVI • 2,400 mg/L MLSS

Anaerobic Selector Operation - 2007

• 67% Aerobic • 1.6 Days Aerobic SRT • 126 mL/g SVI • 2,900 mg/L MLSS

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Comparison of Operating Modes Actual Bellingham Capacity

HPO Operation - 2006 Anaerobic Selector

Operation - 2007

20 MGD Capacity 22 MGD Capacity

10 Percent Increase

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What About BNR Conversions?

• Concerns about HPO – CO2 accumulation -> low pH -> suppresses

nitrification – As SRT increases HPO becomes less and less

economical compared to fine bubble – Examples:

• LOTT (Olympia, Washington) • Denver Metro • Indianapolis • Bellingham • All abandoned HPO for BNR

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Oxygen Supply Cost as function of SRT

$0

$100

$200

$300

$400

$500

$600

$700

$800

1.5 2.5 8.0

Uni

t Cos

t of O

xyge

n ($

/ton)

SRT (Days)

HPO: New VPSA HPO Plant AAS: New Diffused Aeration System

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HPO Conclusions

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30 Wef2003Samstag.ppt

Conclusions from the HPO Test Facility

• Anaerobic selectors at the HPO test facility failed because low SRT, low temperature prevented formation of an environment supportive of EBPR. PAO were washed out.

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Conclusions from the Post Point Project

• Anaerobic selector provided a way to control settleability by encouraging PAO and taking up excess VFA

• Improved oxygen transfer efficiency of new aerators saved power

• Variable speed control of DO provided power savings and improved process control

• The upgrade provided a 10 Percent capacity increase for interim operation

• For BNR upgrade, fine bubble was more economical

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Thank you!

Questions?

Randal Samstag

rsamstag@carollo.com

206-684-6532 (office)

206-851-0094 (mobile)

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Generalized Conclusions about HPO The Initial Claims Experience

• Less O2 consumption • O2 consumption depends more on SRT than on DO

• Better settling sludge • Little evidence of better settleability at a given SRT

• Can operate at a higher MLSS • If settling is not better, no justification for higher MLSS

• Smaller tank volume required • If settling is not better, no justification for smaller tanks

• More power efficient than conventional aeration

• Power efficiency depends on SRT

• Can be used for nitrification • High CO2 decreases pH and inhibits nitrification

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MLSS Showed Indications Phosphorus Accumulating Organisms

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Recent SVI and SRT Data from West Point WWTP

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0

50

100

150

200

250

300

350

400

450

12/4/05 12/4/06 12/4/07 12/3/08 12/3/09 12/3/10

SRT

(Day

s)

SVI (

mL/

g)

West Point SVI and SRT Data

SVI SRT (day) Linear (SVI) 30 per. Mov. Avg. (SVI) 30 per. Mov. Avg. (SRT (day)) Linear (SRT (day))

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Summary Comparison Operation

Description Aerobic (2006)

Anaerobic (2007)

Difference (%)

Flow (mgd) 12.2 12.1 -0.8%

BOD (ppd) 12,852 12,994 1.1%

MLSS (mg/L) 1,763 2,057 14.3%

Total SRT(days) 2.2 2.4 6.5%

Aerobic SRT (days) 2.2 1.6 -40.3%

DO (mg/L) 13.3 7.4 -78.8%

Temp (Deg C) 17.57 17.24 -1.9%

O2 Purity (%) 88% 89% 1.4%

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Comparison of Operating Modes Typical Operating Assumptions

Classical HPO Operation • 100% Aerobic • 1.5 Days Aerobic SRT • 200 mL/g SVI • 1,700 mg/L MLSS

Anaerobic Selector Operation

• 85% Aerobic • 2.5 Days Aerobic SRT • 120 mL/g SVI • 2,200 mg/L MLSS

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Comparison of Operating Modes Capacity Impact

Classical HPO Operation Anaerobic Selector

Operation

13 MGD Capacity 17 MGD Capacity

30 Percent Increase