An Innovative Approach to Retrofitting for Nitrogen Removal...Nitrate Recycle Rate Anoxic Volume...

An Innovative Approach to Retrofitting for Nitrogen Removal OWEA 2017 TECHNICAL CONFERENCE & EXPO

June 29, 2017

Innovation

From Wikipedia:

“The application of better solutions that meet new requirements.”

2

Today’s Topics

Nitrogen Removal from Wastewater

• Principles

• Case Studies

- A: Stabilizing Nitrification in HPO system

- B: Creating an Anoxic zone

- C: Denitrifying STEP ww

All case studies presented include an

(online) process monitoring component

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Why Nitrogen Removal?

Required by Discharge Permit

Improve Water Quality (avoid future limit)

Increase Revenue (water quality trading)

Stabilize Process

Save Energy

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Energy Intensity Benchmarking

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Joint WEF/WERF Webcast: Net‐Zero Energy Solutions for Water Resource Recovery Facilities

Wednesday, October 29th, 2014

1,412

1,934 1,853

1,955

973

1,249 1,118

1,202

0

500

1,000

1,500

2,000

2,500

BasicSecondary

Nitrification BNR ENR

kW

h / M

G

Typical

Best Practice

The Microbiological Nitrogen Cycle

AOB NOB

OHO NO2-

The Microbiological Nitrogen Cycle

AOB NOB

OHO NO2-

3 Requirements for Biological N Removal

Stable nitrification to generate nitrate (NH3 NO3)

Anoxic (low DO, low/negative ORP) conditions

Carbon (BOD) for a source of energy

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Case Study A – HPO Activated Sludge

Short retention time – conditions change fast

Caustic added to effluent to meet pH requirements

Summer limit: 1.9 mg NH3-N / L

Winter limit: 5.0 mg NH3-N / L

(30-day average)

Problems maintaining adequate nitrification, especially in Spring

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Nitrification

Aeration to provide DO > 1.0

Solids Retention Time > 8 days (depends on temperature)

pH – 6.5 to 8.5 (peak rate is around 7.5)

Usually relatively easy to achieve provided DO, SRT, and pH

conditions are maintained within acceptable ranges

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Measuring Nitrification

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Good

Better

Best

Case Study A – Innovations

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Relocated caustic dosing point to upstream from aeration tanks.

Redirected 2nd stage solids to 1st stage.

Installed monitoring system for ammonium, nitrate, and pH.

6

0

12

7

10

0 0

5

10

15

Ammonia Exceedances

CAU

arrives Online process monitoring installed

Case Study B – Extended Aeration Activated Sludge

2 x 1-pass aerated tanks (212 kgal. ea.) –

1 in service for daily flow of 260 kgpd

EQ, Sand filters, chlorine disinfection,

post aeration, aerobic sludge storage

tanks

New discharge limits: 10 mg TIN / L

Fully aerobic (oxic)

Stable nitrification but not designed for

denitrification – no anoxic zones or nitrate

recirculation

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Clarifier

Typical Denitrification Flow Sheet

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Anoxic Oxic

RAS

WW

NO3-N

NO3-N NO3-N

NH3 NO3 NO3 N2

3-4 Q NO3-N

Nitrate recycle

Clarifier

Typical Denitrification Flow Sheet

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Anoxic Oxic

RAS

WW

NO3-N

NO3-N NO3-N

NH3 NO3 NO3 N2

3-4 Q NO3-N

Nitrate recycle

Case Study B – Innovations

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Convert EQ tank to anoxic zone?

Convert 1 of 2 aerated tanks to anoxic zone?

Build anoxic zone into existing online aeration tank?

Case Study B – Innovations

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Convert EQ tank to anoxic zone?

Convert 1 of 2 aerated tanks to anoxic zone?

Build anoxic zone into existing online aeration tank?

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

0123456789

101112

pH

NO

3-N

(m

g N

/L)

NO3-N pH

Case Study B – Nitrate Recirculation?

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No nitrate recirculation

Instead: Intermittent aeration of oxic zone for increased denitrification Lead blower “off” 3 x / day

2 blowers operated continuously for nitrification of peak morning load

Case Study B - Process Monitoring System

Anoxic Oxic

A N A N O H O H

Case Study C: STEP system

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WWTP on new housing development / early in build-out

Nitrate recycle system but no external carbon

Nitrates in effluent exceed limits / nitrification stable

Troubleshooting Denitrification

Oxic /

effluent Anoxic Condition Remedy

Low NO3 Low NO3 DN not limited None as long as

nitrification is stable

High NO3 Low NO3 Nitrate limited Increase nitrate recycle

High NO3 High NO3 Carbon limited Increase carbon dosing

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Case Study C

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Oxic

NO 3

Anoxic

NO 3

Nitrate

Recycle

Rate

Anoxic

Volume Carbon

Initial 16.4 15.6 100% 1 x N/A

Stop nitrate recycle pump 10.6 5.1 0% 1 x N/A

Resume nitrate recycle /

add anoxic volume 7.0 3.9? 15 / 75 2x N/A

New nitrate method 14.1 7.3

Add mixer to 2 nd anoxic zone 22.2 10.8

Case Study C: Optical Nitrate Probe

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8

9

10

11

12

13

14

15

16

2:3

3 P

M

10

:33

PM

6:3

3 A

M

2:3

3 P

M

10

:33

PM

6:3

3 A

M

2:3

3 P

M

10

:33

PM

2:1

1 P

M

10

:11

PM

6:1

1 A

M

2:1

1 P

M

10

:11

PM

6:1

1 A

M

3:4

0 P

M

Eff

luen

t N

O3-N

(m

g/L

)

Case Study C – Simple Carbon Dosing System

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Peristaltic pump – off the shelf

Gycerin – safe alternative to methanol

Case Study C

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Oxic

NO 3

Anoxic

NO 3

Nitrate

Recycle

Rate

Anoxic

Volume Carbon

Initial 16.4 15.6 100% 1 x N/A

Stop nitrate recycle pump 10.6 5.1 0% 1 x N/A

Resume nitrate recycle /

add anoxic volume 7.0 3.9? 15 / 75 2x N/A

New nitrate method 14.1 7.3

Add mixer to 2 nd anoxic zone 22.2 10.8

Add carbon dosing system 10.1 0.7

Case Study C – Effluent Monthly Total Inorganic Nitrogen (TIN)

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Summary

Innovation to provide N removal requires an understanding of the biology to cultivate and enrich critical populations.

Innovation includes modifications to existing equipment, developing new ways to operate, or creating new systems from off-the-shelf materials and equipment.

Online process monitoring is valuable for understanding what is limiting treatment performance and quickly evaluating viability of solutions.

Case Study A: HPO system – modified chemical dosing point and implemented new solids recirculation to stabilize nitrification.

Case Study B: Extended Aeration – constructed new zone, operational modification to aeration to create anoxic conditions.

Case Study C: STEP system influent – optimized nitrate recirculation, added carbon dosing system to stabilize denitrification.

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Acknowledgments

Jon van Dommelen, Ohio EPA Compliance Assistance Unit

Delaware County RSD Wastewater Facility Operations Department

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Questions?

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