Nutrient Removal Optimization at OECCAlyssa Mayer, PEHazen and Sawyer

Presentation Overview

Project BackgroundBNR Design ConsiderationsProcess Model DevelopmentPreliminary Alternatives Evaluation ResultsConclusions and Next Steps

Olentangy Environmental Control Center (OECC)

North Plant (1.5 mgd) and South Plant (4.5 mgd)

Facility Plan is focused on:• Energy efficiency• BNR optimization• Leveraging existing infrastructure

Effluent Nutrient Limits MonthlyNH3-N (Winter), mg/L 1.28NH3-N (Summer), mg/L 0.78Total NOx-N, mg/L 4.58Total Phosphorus, mg/L 1.0

Process Modeling Task

Develop Process Model to:• Evaluate existing

biological treatment configuration

• Perform alternatives analysis for future improvements to meet nitrogen and phosphorus limits

3

Meeting with plant staff and evaluation of historical data Detailed Sampling

wastewater characterization

ModelingBioWin Model Calibration

Alternatives Analysis

4

2

1

Biological Nutrient Removal

Enhanced Biological Phosphorus Removal

6

Operational Considerations for EBPRAnaerobic

Zone Sizing

Carbon:TP

Limited DO, NO3 Return

DO Control

Effluent Solids Concentration

Anaerobic Zone

INFLUENT

RAS

Low DO

High DO or NO3-N

Size of Anaerobic Zone Effectively Reduced

Available Carbon for PAOs Reduced by OHOs

P-rich biomass

Low P effluent

Recycle Loading

Biological Nitrogen Removal

Aerobic Anoxic

Nitrification Denitrification

Operational Considerations for Nitrogen Removal

NRCY

Anoxic Zone

DO Control

Aerobic SRT

NitrificationDenitrification

Temp/pH/AlkalinityCarbon:TN

Anoxic Conditions

Recycle Rate

Existing Aeration Tank Configuration

Aerated Operation70 minutes

Unaerated Operation50 minutes

Ferric

Process Model Development

Historical Data Evaluation and Sampling Plan Development

Low Influent BOD and TSS measuredSludge production reflects more typical strength wastewaterConsistently meet effluent nutrient requirements with intermittent aeration operation and chemical additionAdditional sampling planned to verify influent, solids, BNR performance Sampling

Locations

Special Sampling Observations

• Influent CBODs for sampling week higher than historical average (~typical domestic)

• Influent sampler may underestimate solids (as compared with grab)

• Consistent sludge production at multiple points of measurement

• Very good biological phosphorus removal performance

0

5

10

15

20

25

StepFeed

13A 13B 14A 14B 15B MLSS Sec Eff

Nutrient Profile

NH3-N NO3 NO2 PO4-P

012345678

13 Z1 13 Z2 13 Z3 14 Z1 14 Z2 14 Z3 15 Z1 15 Z2 15 Z3

DO Profile

Aerobic Anoxic

Process Model Development

Influent Loading and

Characteristics

Intermittent Aeration

Operation

Ferric Addition

Aerobic Digester

Aeration and Decanting

Dewatering Schedule and

Capture

Good Match on Solids Production and Effluent Quality

Parameters units Measured Modeled % Difference Pass 3 MLSS mg/L 2,190 2,010 -8%WAS Load ppd 5,400 5,320 -1%Hauled sludge ppd 6,730 7,330 9%

Parameters units Measured Modeled % Difference Secondary Effluent TKN mg/L 2.0 1.96 -2%Secondary Effluent NH3 mg/L 0.6 0.58 -2%Secondary Effluent NOx-N mg/L 4.86 5.45 12%Secondary Effluent TP mg/L 0.12 0.14 --Secondary Effluent PO4-P mg/L 0.02 0.01 --

Modeled a Period of Time Outside Sampling Week

• Adjustment to the measured Influent CBOD, TSS necessary to match solids production and effluent quality.

• Historical data and modeling suggest variable EBPR performance over time

June – November 2017

Parameters units Jun - Nov 2017Measured Modeled

Sludge ProductionPass 3 MLSS mg/L 2,640 2,210WAS Load ppd 6,360 5,610Hauled sludge ppd 3,470 3,640EffluentFinal Effluent TSS mg/L 1.1 1.0Final Effluent cBOD mg/L 1.1 1.32Final Effluent TKN mg/L 1.1 1.52Final Effluent NH3 mg/L 0.13 0.38Final Effluent NOx-N mg/L 3.6 4.64Final Effluent TP mg/L 0.46 0.51

Nutrient RemovalAlternatives Analysis

OECC Influent Design Criteria

Parameter Historical (2014-2017)

Projected

Annual Average Max Month “Build-out” Annual Average

Flow, mgd 3.3 6.0 7.7 12.0

Concentrations

Parameter Historical(2014-2017) Sample Week Low Strength High Strength

TSS, mg/L 119 167 112 209

cBOD, mg/L 69 187 125 234

TKN, mg/L - 34 23 43

NH3-N, mg/L 18 24 16 30

TP, mg/L 5.1 4.7 3.2 5.9

Preliminary Biological Process AlternativesTypical Nutrient Removal Performance

Configuration TN Removal Bio-P Removal

A/O(Anaerobic/Oxic) ○ ○ ○ ○ ○ ● ● ● ● ○MLE(Anoxic/Oxic) ● ● ● ○ ○ ○ ○ ○ ○ ○A2O(Anaerobic/Anoxic/Oxic) ● ● ● ○ ○ ● ● ● ○ ○4-Stage(Anoxic/Oxic/Anoxic/Oxic) ● ● ● ● ● ● ○ ○ ○ ○5-Stage(Anaerobic + 4-Stage) ● ● ● ● ○ ● ● ● ● ●

● Good Performance○ Poor Performance

Biological Process Alternatives

4-Stage

5-Stage

“One OECC” Concept

Operate North and South Trains in Series as one process• Use North Volume for

Anaerobic (if 5 stage) and Anoxic

• Use South Volume for Aerobic, 2nd Anoxic and Reaeration

Future AA Alternatives Evaluation Results

ParameterMonthly Limits Low Strength Wastewater High Strength Wastewater

4-Stage 5-Stage 4-Stage 5-Stage

Final Effluent QualityFinal Effluent NH4-N, mg/L 0.78 / 1.28 0.08 0.08 0.08 0.07Final Effluent NOx-N, mg/L 4.58 1.7 2.9 3.1 4.2Final Effluent TP, mg/L 1.0 0.7 0.7 0.7 0.7Required Chemical AdditionFerric Addition, gpd -- 375 200 775 200Methanol Addition, gpd -- 0 0 0 80Solids ProductionTotal Sludge, ppd -- 4,300 3,900 8,700 7,600

Preliminary Conclusions and Next Steps

DCRSD can leverage existing infrastructure at OECC to meet future nutrient limits at future design flows and loads using a 4 or 5 stage BNR process Chemical coagulant will likely be required to meet TP limits, regardless of chosen process, some supplemental carbon may also be necessaryNext Steps:LCA including supplemental carbon, chemical coagulant, sludge disposal costs

Thank you!

Alyssa Mayer, PE513-469-5135amayer@hazenandsawyer.com

Acknowledgements:OECC Operations StaffDCRSD Engineering StaffHazen Sampling Team