Iowa City Nutrient Reduction Study

IAWEA 2016 Annual Conference

Jay Brady, P.E.

June 8, 2016

Presentation Overview

• Plant Background

• Process Configurations

• Study Drivers

• Flows and Loadings

• Performance – Nitrogen

• Performance – Phosphorus

• Potential NPDES Permit Limits

• Supplemental Technologies

• Observations

IC South WWTP The culmination of a 40 year vision of

migrating wastewater treatment out of the city

Chuck Meyer, P.E. Chief Civil Engineer Stanley Consultants

Chuck Schmadeke, P.E. Public Works Director City of Iowa City

NORTH WWTP

SOUTH WWTP

Iowa River

South Plant ~ 15 years of conception, planning, and study work Constructed 1990 5 mgd Capacity BOD Removal, Surface Aerators Serves SE Iowa City

NORTH WWTP

SOUTH WWTP

Iowa River

Napolean Park Lift Station

Connector Infrastructure Constructed in 1996-1999 84/96 inch trunk sewers Napolean Park Lift Station

South Plant – 2003

7

2003 MLE Process – Nitrification & Denitrification

North Plant – 2008 Flood

NORTH WWTP

SOUTH WWTP

Iowa River

Napolean Park Lift Station

South Plant Expanded in 2012-14 to 24 mgd and Significant Organic Load Capacity Nutrient Reduction – MLE/A2O Processes $46 million Investment N. Plant Closed and Decommissioned 2015

Design Flows and Loads

S. Plant N & S Plants 2025

Flow (mgd) 10/25/60 18.6, 33.1, 45 24, 43/30, 62

BOD5 (lb/d) 16,554 21,643 32,658

TSS (lb/d) 17,000 22,075 34,385

TKN (lb/d) 2,940 4,665 6,311

Plant Process Configurations - MLE

The BAR Process

13

Bioaugmentation

R = Reaeration or Regeneration

Plant Process Configurations – A2O

Study Drivers

• Iowa Nutrient Reduction Policy (INRP)

• NPDES Permit Requirements:

– Plant Optimization Study

– Evaluation of Possible Upgrade Requirements

– 66% TN Reduction, 75% TP Reduction or

10/1 mg/L effluent values

• Focus: Operational

Adjustments/Optimization for Nutrients

Flows and Loads

0

5

10

15

20

25

30

35

40

45

ADW ADF AWW MWW

Flow, mgd

Flows and Loads

Average Max Month Max Day 0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000CBOD5, lbd

Flows and Loads

Average Max Month Max Day 0

10,000

20,000

30,000

40,000

50,000

60,000

70,000TSS, lbd

Flows and Loads

Average Max Month Max Day 0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000TKN, lbd

Flows and Loads

Average Max Month Max Day 0

200

400

600

800

1,000

1,200

1,400TP, lbd

Flows and Loads

Flows and Loads

Optimization Trial

• North Plant shutdown February 7, 2014

• MLE Mode February – December 23, 2014

• A2O Mode December 23, 2014 – March 31, 2016

MLE Operational Performance - TN

MLE Operational Performance - TP

A2O Operational Performance - TN

A2O Operational Performance - TP

Estimated Nutrient Mass Limits

• Assumes log distribution of data

• 99th percentile TNe, TPe

• Compute mass limits based on Design AWW

Parameter Allowable Average Mass Loading, lb/d

At Max Month design flow, mg/L

At Design ADF, mg/L

TN 2,148 10.6 17.8

TP 319 1.6 2.6

Must operate Nutrient Reduction Systems

Supplementary Technologies

• Increased Internal Mixed Liquor Recycle (IMLR)

• Primary Sludge Fermenter

• Ferric Chloride Addition

Supplementary Technologies - IMLR

• 2012 design re-used some original piping for the

the IMLR resulting in IMLR capacity of 25 mgd or

~2:1 ratio to influent Q for average flows at the

2025 design flow. A IMLR of 3 or 4:1 is ideal for

optimal TN reduction.

• Additional piping and changes to the IMLR

pumping would be required to optimize the

IMLR:Qo Ratio

Supplementary Technologies - Fermenter

• Volatile Fatty Acids (VFAs) aka soluble

biodegradable chemical oxygen demand are

necessary at the right ratios for both TN and TP

reduction.

• Primary clarifier fermenter is one way of producing

and providing a more consistent source of VFAs

for BNR.

• Need for a fermenter would be due to changing

influent wastewater conditions

Supplementary Technologies – FeCl3

• Option to improve MLE TP reduction by addition at

aeration basin discharge or to BFP operation.

• Also could be needed for A2O if wastewater

conditions change

Supplementary Technologies – Costs

Technology 20-Yr PW Cost

IMLR Increase $2,500,000

Fermenter $5,000,000

Ferric System $3,000,000

Observations

BNR Favorable Influent Characteristics

• Higher influent cBOD5 loadings provide more

organic carbon increasing C:TKN and C:TP ratios.

• AWW/MWW flows of 13/19 mgd were significantly

lower than the historical AWW/MWW flows of

18/29 mgd

• Minimum monthly influent temperature of 15oC is 3

degrees warmer than the basis of design favoring

nitrification kinetics and BNR performance.

• Future conditions could reduce the performance of

the nutrient removal systems.

Observations

A2O Mode

• Achieved TN Reduction of 74%

• Achieved TP Reduction of 82%

• Inconsistent Enhanced Biological Phosphorus

Removal (EBPR) aka ‘Bio-P’ observed and as

predicted by planning/design modeling

• Anaerobic selector PO4-P release suggests some

EBPR activity but not substantial

• A2O mode appears capable to meeting reduction

requirements under current wastewater conditions

Observations

MLE Mode

• Achieved TN Reduction of 75%

• Achieved TP Reduction of 72% (slightly below

target)

• Additional MLE operational trialing recommended

with increased IMLR and addition of ferric chloride

to belt filter press sludge feed

Observations

Investment in additional nutrient reduction

technologies is not warranted at this time.

Future investment may be necessary if BNR

performance declines due to changing wastewater

conditions or increased loadings

Acknowledgements

WWTP Staff – Dave Elias (retired), Tim Wilkey, Roger Overton, Al Figueroa, Steve Flake, Laboratory Staff Don Esping and Lloyd Winchell, BC Process Team

Discussion