Download pdf - Nitrification and BNR Strategies during Cold · PDF filePresentation Outline Nitrification/denitrification refresher Treatment technologies available for nitrification and BNR/ENR

Presentation Outline

Nitrification/denitrification refresher

Treatment technologies available for nitrification and BNR/ENR

What is the problem?

BNR/ENR VPDES permitting

Causes of reduced BNR performance during winter

Cold wet weather strategies

Case Studies – Kearney, NE; Christiansburg, Abingdon

Advances in process control

Nutrient Removal - Nitrification

Nitrifying bacteria (AOB and NOB) use alkalinity for cell growth (autotrophic); do not remove BOD; and utilize CO2 from air

Temperature sensitive

Require excess DO

Consumes 7.1 mg/L of Alkalinity per mg/L of NH3-N

Nutrient Removal - Denitrification

Denitrifying bacteria remove BOD but use NO3 instead of O2

Denitrification requires anoxic conditions….. NO3 but no O2

Recover 3.6 mg/L of Alkalinity per mg/L of NO3-N

Nitrification Factors - Mean Cell Residence Time (MCRT)

MCRTactual = MLVSS × Volume of Aeration Tank

QEFF× 𝑋EFF+QWAS× 𝑋WAS

Need to maintain minimum MCRT for healthy nitrifying population

MCRTmin =1

µ𝑚𝑎𝑥𝑁 −𝑏𝑁

If actual MCRT > minimum MCRT then complete nitrification can occur

MCRT is temperature dependent:

10-14˚C MCRTmin of 12-16 days

16-20˚C MCRTmin of 6-10 days

Reference: Metcalf and Eddy’s Wastewater Engineering: Treatment, Disposal, and Reuse 5th edition, 2014.

Nitrification Factors - Temperature

Optimum temperature for nitrification is 77 to 95oF

Growth rate decreases by 50% at 64oF

Growth rate decreases by 75% at 46 to 50oF

No activity at 39oF

MinimumMCRT

DesignMCRT

Ammonia(mg/L)

MCRT (days)

Treatment Technologies

Trickling Filters and RBCs (BOD and NH3) Activated Sludge (BOD, NH3, and BNR)• MLE• e-MLE• Bardenpho

Vendor Activated Sludge (BOD, NH3, and BNR) – No Primaries• Sequencing Batch Reactor• Oxidation Ditch• Aeromod Sequox™• D-ditch• Counter Current Aeration (Schreiber)

Modified Activated Sludge (BOD, NH3, and BNR)• Moving Bed Biofilm Reactor• Integrated Fixed Film• Membrane Bioreactor

Hybrids (BOD, NH3, and BNR)• Biological Aerated Filters• Filters (nitrifying and denitrifying)

What is the Problem?

Nitrification and BNR are significantly impacted by cold wastewater temperatures

Cold Wet Weather Events (CWWE) The problem is compounded in the

northeast and mid-Atlantic during winter months because• 40+ inches of annual precipitation• Wet weather events produce peak day

flows that are 5-10 Q• These flows are likely due to inflow of

snow melt, cold rain inflow, and/or river inflow

• In Virginia, we have seen influent WW temperatures as low as 39oF

VPDES Permitting

Nutrient limits (TN & TP) in Virginia are based upon annual concentration and loading (saving grace)

NH3 or TKN limits are weekly maximum and monthly average

When in doubt: maintain aeration and maintain solids inventory (avoid washout)

After the CWWE, return basins to established SOP and BNR will quickly return

VPDES Permitting

Primary Causes of Reduced BNRPerformance During CWWE

Solids inventory management

Reduced influent BOD

Reduced hydraulic retention time

Elevated influent dissolved oxygen

Lack of side stream nutrient management

TN and TP effluent concentrations are low due to dilution

Cold Wet Weather Strategies

Focus collection system on identification and correction of inflow sources

Make sure that all tanks, clarifiers, and filters are in service

If you have equalization, plan for it to be empty in advance of CWWE

Equalize nutrient-laden sidestreams

Provide more biomass in winter; minimize wasting if you can

Minimize sludge blankets in clarifier

Increase aerobic HRT – anoxic/aerobic swing zones – go aerobic

Be prepared to add metal salt for P removal

Enhanced process control - consider installing ion specific electrode to monitor nitrogen

In Virginia, BNR during CWWE is not as important; maintain biomass and nitrification - TN removal will recover quickly after CWWE

City of Kearney TF/SC WWTP

Activated Sludge

Headworks

Primary Clarifiers

Secondary ClarifiersDisinfection

Dewatering

Trickling Filters

City of Kearney WWTP

City of Kearney BioWin Data

Influent:• Average Daily Flow – 3.5 MGD

• Current Design Flow = 4.8 MGD

• Future Design Flow = 5.8 MGD

• Total cBOD = 220 mg/L

• TSS = 237 mg/L

• Ammonia = 24.7 mg/L

Nebraska Winter:• Routine air temperatures less than 0oF

• Trickling Filter WW temperature greater than 11oF

City of Kearney BioWin Data

Steady State BioWin Model ResultsSeason Summer Winter Summer Winter

Flow (mgd) 4.8 4.8 5.9 5.9

Total cBOD (mg/L) 2.32 2.89 2.90 4.74

TSS (mg/L) 5.70 6.31 6.27 7.58

Ammonia (mg/L) 0.19 1.10 0.27 4.21

Total Nitrogen (mg/L) 13.93 14.83 12.05 16.73

Current Performance:

• Average Daily Flow – 3.5 MGD

• Winter NH3 Performance less than 1 mg/L-N

• Future NH3 Limit – 1.2 mg/L at 5.9 MGD

Town of Christiansburg WWTP

Activated SludgeInfluent EQ

Headworks

Primary Clarifiers

Secondary Clarifiers

Anaerobic Digestion

Disinfection

Effluent PS

Dewatering

History and Design

Expansion to 4 MGD completed in 2000• For future growth• Due to CWWE NH3 Violations

Rerated WWTP to 6 MGD in 2008 ADF – 2.5 MGD; PDF – 10+ MGD Plug Flow Activated Sludge – configured for 5-stage process in future High influent Nitrogen:• TKN of 40 mg/L • NH3 of 30 mg/L

Converted to MLE over 2014 and 2015• Primarily to recover alkalinity and avoid the use of lime• Anoxic selector to enhance floc-forming bacteria and improved settling

TN has averaged:• 10 mg/L in summer • 11 mg/L in winter

Town of Christiansburg WWTP

Strategies at Christiansburg

Make sure that all tanks, clarifiers, and filters are in service

Equalization (2.6 MG)

Equalize nutrient-laden sidestreams (not planned)


Maintain aeration in aerobic zones

Town of Christiansburg BioWin Data

Influent:

• Flow = 2.5 MGD

• Total cBOD = 204 mg/L

• TSS = 255 mg/L

• Ammonia = 30 mg/L-N

BioWin Simulation Example of GBT slug loading

• Anaerobically digested sludge campaign thickened 1 to 2 times per week.

• Can double the NH3 in one day

Town of Christiansburg BioWin Data

Steady State BioWin Model ResultsSeason Summer Winter Winter Winter

Temperature (⁰C) 20.0 10.0 10.0 10.0

Filtrate Storage No No* Yes* Yes

MLVSS (mg/L) 1,600 1,600 1,600 2,400

Recycle Rate (%) 400% 400% 400% 400%

Flow (mgd) 2.5 2.5 2.5 2.5

Total cBOD (mg/L) 1.75 2.45 2.45 1.73

TSS (mg/L) 7.52 7.17 7.17 7.17

Ammonia (mg/L) 0.34 4.97* 4.97* 2.30

Total Nitrogen (mg/L) 11.2 13.2 13.2 12.2

* Steady State BioWin Modeling Based Average Conditions. See Time Series Charts For Plant Reaction To Campaign Thickening.

Town of Christiansburg BioWin PFD

Screened Influent

1-Anoxic

Effluent

Sludge

Recycle Pump

RAS Pump

WAS Pump

Primary Clarifier

2-Aerobic 3A-Aerobic 4-Aerobic3B-Aerobic 5-Anoxic

Secondary Clarifier

Anaerobic DigesterGravity Belt Thickener

PS Pump

Effluent NitrogenWinter 10⁰C, 1600 MLVSS, No Filtrate Storage

12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM12 AM

CO

NC

(m

gN

/L)

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0

Effluent Total N Effluent Ammonia N Effluent Nitrite + Nitrate

Christiansburg BioWin PFDWith Filtrate Storage

Screened Influent

1-Anoxic

Effluent

Sludge

Recycle Pump

RAS Pump

WAS Pump

Primary Clarifier

2-Aerobic 3A-Aerobic 4-Aerobic3B-Aerobic 5-Anoxic

Secondary Clarifier

Anaerobic DigesterGravity Belt Thickener

PS Pump

Filtrate Storage

Effluent NitrogenWinter 10⁰C, 1600 MLVSS, With Filtrate Storage


CO

NC

(m

gN

/L)

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0


Effluent NitrogenWinter 10⁰C, 2400 MLVSS, With Filtrate Storage


CO

NC

(m

gN

/L)

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0


Town of Abingdon WCWRF

Activated Sludge Influent EQ

Headworks

Primary Clarifiers

Secondary Clarifiers

Anaerobic Digestion

Disinfection

Dewatering

Town of Abingdon WCWRFHistory and Design

Expansion from 2.75 MGD to 4.95 MGD in 2007• For future growth

• Wet weather treatment

• Ammonia limit due to discharge to Wolf Creek

• Provide treatment above and beyond VPDES requirements

Existing CMAS converted to MLE• Anoxic selector to enhance settling

• TN removal without expanding tank volume

Cloth media filtration

Converted secondary clarifier to sidestream storage

Town of Abingdon WWTP

Town of Abingdon BioWin PFD

Screened Influent

1-Anoxic Effluent

Sludge

Recycle Pump

RAS Pump

WAS Pump

Primary Clarifier2-Aerobic 3-Aerobic Secondary Clarifier

Anaerobic DigesterCentrifugeCentrate Storage

PS Pump

4-Aerobic

Thickener

NH4 Correction

Strategies at Town of Abingdon’s WCWRF

Equalization (1.6 MG) Equalize nutrient-laden

sidestreams (conversion of abandon secondary clarifier)


Maintain aeration in aerobic zones

Cloth media filter provides limited protection from washout

Case Study Improved Process and Control

• CHA SBR Pilot Study for high TKN waste stream

• AERATE and MIX controlled by ion selective sensor NH4+/NO3-

• Continuous DO and ORPmonitoring

Case Study Improved Process and Control

ANOXIC MIX

AERATE

Aeration Basin Control Ammonia Based Aeration Control (ABAC)

DO

PLCVFD

NH4

1. Ammonia feedback control2. Cascade DO Control

• NH4 ≤ 1.5 mg/L then DO = 0.5 mg/L• NH4 ≥ 1.5 mg/L then DO = 2.0 mg/L

Anoxic Oxic

Nitrate → Nitrogen NH4→ Nitrite → Nitrate

In Conclusion

Focus on maintaining nitrification

Focus on maintaining solids inventory

Prepare for the next CWWE by:

• Utilizing all tanks

• Managing high nutrient return sidestreams

• Empty equalization storage

After the CWWE:

• Provide environmental conditions for BNR, and it will recover quickly

Acknowledgements

Ryan Hendrix – Town of Christiansburg

Sarita Moore – Town of Abingdon

Charles Bott, PhD, PE – HRSD

Stephanie Klaus, PE - HRSD

Questions and Comments