Evaluation of Energy and Nutrient Reduction through Process Modeling:

How much can your Utility save?

Leon Downing, Ph.D.Freese and Nichols, Inc.

TACWA MeetingJuly 31, 2009

Outline

• “Introduction” to process modeling• Modeling process• Example applications• Successful implementation

Introduction

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• “Models are simplified versions of reality” Melcer et al, 2003

• You only get out what you put in . . .

Introduction• A dynamic model that considers multiple aspects of a

WWTP concurrently• Several software programs available

– GPSX– BioWin

Process Modeling Process

• Data gathering• Influent characterization• Calibration• Verification• Analysis

Data Gathering• Basin dimensions and volumes• Process flow diagram

– Including sidestreams• Influent

– Flow rates, BOD, ammonia, phosphorus, alkalinity

• Performance– Effluent values– MLSS, wasting rates, recycle rates, effluent solids,

sludge blankets

Influent Characterization

• All BOD is not created equally– Particulate– Dissolved– Colloidal– Readily degradable– Etc, etc

• Characterization is ideal to accurately assess what you have to treat

• Critical when evaluating nutrient removal

Influent Characterization

• Parameter fitting

Influent Values Measured Historic “fitted”

tCOD 367 - 354

fCOD 169 - 151

ffCOD 136 - 133

cBOD5 - 116 107

VSS - 61 62

TSS - 94 95

Influent CharacterizationCOD Influent Fractions Value

Fbs - Readily biodegradable [gCOD/g tCOD] 0.284

Fac - Acetate [gCOD/g rbCOD] 0.121

Fxsp - Non-colloidal slowly degradable [gCOD/g slowly degr. COD] 0.700

Fus - Unbiodegradable soluble [gCOD/g tCOD] 0.092

Fup - Unbiodegradable particulate [gCOD/g tCOD] 0.450

Fna - Ammonia [gNH3-N/gTKN] 0.723

Fnox - Particulate organic nitrogen [gN/g Organic N] 0.250

Fnus - Soluble unbiodegradable TKN [gN/gTKN] 0.020

FupN - N:COD ratio for unbiodegradable part. COD [gN/gCOD] 0.035

Fpo4 - Phosphate [gPO4-P/gTP] 0.750

FupP - P:COD ratio for influent unbiodegradable part. COD [gP/gCOD] 0.011

Particulate substrate COD:VSS ratio 3.26

Particulate inert COD:VSS ratio 3.26

Calibration• Measure kinetic parameters of nitrifying bacteria in bench-

scale experiments• Match model to field sampling data

• Samples along length of basin, not just effluent

Verification

• Test the calibrated model under different conditions• Verify that the model matches historic performance

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0.2

0.4

0.6

0.8

1

1.2

Ammon

ium (m

gN/L)

Historic DataModeled Data

Analysis

• Model is calibrated and verified for existing conditions– A fully functional, simplified version of reality

• So what now?– Operational analysis– Capacity analysis– Improvement analysis

Nutrient Removal• Phosphorus removal• Nitrogen removal• Impact of internal mixed liquor recycle

(IMLR)/nitrified recycle ratio (NRCY)• Chemical vs. biological

• How much volume do we need?• How much can we remove?• How much chemical would we need?

Nutrient Removal

Nutrient Removal

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0% 5% 10% 15% 20% 25%

Efflu

ent P

 (mgP/L)

% Anoxic/Anaerobic of Total Volume

Nutrient Removal

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0 10 20 30 40 50 60 70 80NRCY (MGD per basin)

Tota

l Pho

spho

rus (

mg/

L)189 MGD265 MGD

Probable Permit Limit

Possible Permit Limit

Nutrient Removal

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0 10 20 30 40 50 60 70 80NRCY (MGD per basin)

Tota

l Nitr

ogen

(mgN

/L)

189 MGD265 MGD

Probable Permit Limit

Possible Permit Limit

Nutrient Removal

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NRCY [-]

NH

3-N

(mgN

/L)

23 C18 C

Nutrient Removal

• Estimate chemical requirements– Per mg/l of P removed– Example is a 6 MGD plant with 8 mgP/L in

influent

Phosphorus Removed Ferric Chloride Required Solids ProductionChemcially Gallons 55 gallon drums 270 gallon totes Pounds Cubic yards

mg/L per day per week per week per day per week7 620 78.9 16.1 1,671 1,3116 530 67.5 13.7 1,432 1,1235 440 56.0 11.4 1,193 9364 350 44.5 9.1 955 7493 270 34.4 7.0 716 5622 180 22.9 4.7 477 3741 90 11.5 2.3 239 187

Energy Savings – Anoxic Zones

• Substitute nitrate for oxygen in anoxic zones• Impact of anoxic volume• Impact of internal mixed liquor recycle

(IMLR)/nitrified recycle ratio (NRCY)

Energy Savings – Anoxic Zones

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0% 5% 10% 15% 20% 25%

Airflo

w Req

uired (scfm)

% Anoxic/Anaerobic of Total Volume

Energy Savings – Anoxic Zones

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0 10 20 30 40 50 60 70 80NRCY (MGD per basin)

Aer

atio

n Sa

ving

s (s

cfm

)

144 MGD189 MGD265 MGD

Energy Savings – DO Control

• Over-aeration can be a large money sink• Accurately prediction of cost savings• Dynamic simulations can be run

– Specific aeration parameters entered– Minimum aeration for mixing specified

Energy Savings – DO Control

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1 2 3

Basin Zone

ExistingDO Control

Airflo

w(scfm)

How do I carry out a successful modeling project?

• What questions do you need to answer?

• What level of sophistication does your model need?

• Determine how big of a box you need to draw

Questions?