Nitrification and BNR Strategies during Cold Outline Nitrification/denitrification refresher Treatment technologies available for nitrification and BNR/ENR What is the problem?

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  • 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 EFF+QWAS WAS

    Need to maintain minimum MCRT for healthy nitrifying population

    MCRTmin =1

    If actual MCRT > minimum MCRT then complete nitrification can occur

    MCRT is temperature dependent:

    10-14C MCRTmin of 12-16 days

    16-20C MCRTmin of 6-10 days

    Reference: Metcalf and Eddys 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)

    Minimize sludge blankets in clarifier

    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 (C) 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 10C, 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 10C, 1600 MLVSS, With 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

  • Effluent NitrogenWinter 10C, 2400 MLVSS, With 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

  • 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 cla

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