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Operation of Activated Sludge Nitrification

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Operation of Activated Sludge Nitrification 6/24/2020 1 Operation of Activated Sludge Nitrification Paul Dombrowski, Woodard & Curran, Inc. Spencer Snowling, Hydromantis, Inc. 2 1 6/24/2020 How to Participate Today • Audio Modes • Listen using Mic & Speakers • Or, select “Use Telephone” and dial the conference (please remember long distance phone charges apply). • Submit your questions using the Questions pane. • A recording will be available for replay shortly after this webcast. 3 Paul Dombrowski, PE, BCEE, F.WEF, Grade 6 Operator (MA) Chief Technologist Woodard & Curran, Inc. 4 2 6/24/2020 Spencer Snowling, Ph.D, P.Eng V.P., Product Development Hydromantis Environmental Software Solutions, Inc. 5 Webinar Agenda • Introductions • Activated Sludge Overview • Simulator Description and Overview • Nitrification Theory and Examples • Simulator Examples • Hydromantis Project • Questions 6 3 6/24/2020 Activated Sludge Overview 7 Activated Sludge Operation • The Activated Sludge Process is a SYSTEM . Aeration Tank . Secondary Clarifier . RAS & WAS Pumps . Aeration Equipment • Secondary Treatment (BOD, TSS) . Aeration Tanks - Convert soluble, colloidal and remaining suspended BOD into biomass that can be removed by settling . Secondary Clarifiers – Flocculate, settle and compact solids to provide effluent low in TSS . KEY – Create a biomass that flocculates well and settles rapidly 8 4 6/24/2020 Key Activated Sludge Relationships Solids Retention Time (days) “Average time any particle remains in Reactor Tanks” SRT = lbs MLSS in Reactor Tanks lbs/d WAS (Xw) + lbs/d Effluent TSS (Xe) What parts of this can an operator control? 9 Key Activated Sludge Relationships Aerobic Solids Retention Time (days) “Average time any particle remains in Aeration Tanks” Aerobic SRT = lbs MLSS in Aeration Tank lbs/d WAS (Xw) + lbs/d Effluent TSS (Xe) What parts of this can an operator control? 10 5 6/24/2020 Secondary Clarifier Impacts on BNR Two Key Concepts: • Effluent TSS contains nutrients • Secondary clarifiers define allowable reactor MLSS . High Aerobic SRT required for nitrification . As SRT increases for a given reactor volume, MLSS concentration must increase . As a result, allowable MLSS can limit SRT 11 Process Simulators 12 6 6/24/2020 Simulator Overview • Model = Series of equations that defines a process or plant . Model based on mass balances and biological conversions of organics (COD), nitrogen, phosphorus and solids • Simulator = Program that uses a process model to experiment with a plant configuration • OpTool Overlay = Plant-specific layout that provides graphical interface for plant operational testing and training 13 GPS-X Process Simulator 14 7 6/24/2020 Process Simulator Layout 15 Nitrogen in the Environment 16 8 6/24/2020 Forms of Nitrogen Total Soluble Nitrogen Soluble Kjeldahl Nitrogen Organic Inorganic Nitrogen Nitrogen Particulate Organic - N Soluble Organic - N Ammonia - N Nitrite - N Nitrate - N Total Kjeldahl Nitrogen NOX -N Total Nitrogen 17 Why Remove Nitrogen? • Toxicity: Ammonia • Oxygen Demand: Ammonia • Groundwater Contamination: Nitrate • Eutrophication: Total Nitrogen . Long Island Sound . Narragansett Bay . Chesapeake Bay . San Francisco Bay 18 9 6/24/2020 Environmental Conditions • Aerobic . Free dissolved oxygen present • Anoxic . No free dissolved oxygen . Nitrite and/or nitrate present • Anaerobic . No free dissolved oxygen . No nitrite or nitrate 19 Biological Nitrogen Removal • Assimilation . Incorporation of nitrogen into cell mass, typically 5% of BOD removed (7-10% of VSS formed) • Ammonification . Conversion of organic nitrogen into ammonia • Nitrification . Oxidation of ammonia to nitrite then nitrate • Denitrification . Reduction of nitrate to nitrogen gas 20 10 6/24/2020 Nitrification 21 Nitrification Basics + - + NH4 -N + 2 O2 NO3 -N + 2 H + H2O + Bacteria Autotrophic Bacteria – Ammonia and Nitrite Oxidizing Bacteria (AOB and NOB) + . Energy from Oxidation of NH4 -N - . Carbon from HCO3 (BiCarbonate) . Aerobic Organisms – DO Sensitive (Require 4.6 lb/lb NH4-N) . Low Growth Rate – Temperature Sensitive . Produces Acid – Consumes Alkalinity (7.2 lb/lb NH4-N) . pH Sensitive – Acclimation . Sensitive to Toxics NITRIFICATION DOES NOT RESULT IN A NET REMOVAL OF NITROGEN FROM WASTEWATER! NITRIFICATION MUST PRECEDE DENITRIFICATION! 22 11 6/24/2020 Nitrification Basics Basic Process Description : Aerobic Conditions in Mixed Liquor (Aerobic Zone) AOB NOB NH4-N NO2-N NO3-N New New O2 + HCO3 O + HCO Cells 2 3 Cells 23 DO Impact on Nitrification 100% 90% 80% 70% 60% 50% 40% Nitrification (%of Rate max) 30% 20% 10% 0% 012345678910 DO Concentration (mg/L) 24 12 6/24/2020 Temperature Impacts on Nitrification 1.40 1.20 1.00 0.80 0.60 0.40 Maximum Nitrifier Specific Growth Rate (mg/mg-d) Rate Growth Specific Nitrifier Maximum 0.20 0.00 0 5 10 15 20 25 30 Wastewater Temperature (deg C) 25 Activated Sludge Nitrification • System Microbiology . Can occur concurrent or following BOD removal . Heterotrophs grow faster than Nitrifiers, so must reduce overall system growth rate . Depends on Aerobic SRT • Single Sludge Nitrification . Continuous Flow Systems . Sequencing Batch Reactors (SBR) . Membrane Bioreactors (MBR) • Separate Sludge Nitrification 26 13 6/24/2020 Separate Sludge Nitrification Influent Secondary Nitrified Effluent Effluent Aeration Aeration Tank Secondary Tank Secondary (fully Clarifier (fully Clarifier aerobic) aerobic) RAS RAS Pump Pump BOD Removal Nitrification Stage Stage 27 Single Sludge Nitrification Effluent Influent Aeration Secondary Tank Clarifier RAS Pump Waste Sludge BOD Removal, Nitrification 28 14 6/24/2020 Min. Aerobic SRT for Nitrification 22 Assumptions: 20 DO = 2 mg/L Eff NH3-N = 1 mg/L 18 Kn = 1 mg/L pH > 7.2 Source: 16 1993 EPA Nitrogen Control Manual 14 12 10 Min. Aerobic SRT = y = 18.507e-0.098x Aerobic SRT (days) SRT Aerobic 8 6 4 2 0 4 6 8 1012141618202224 Wastewater Temperature (deg C) 29 Steady State Nitrification – Temp. 30 28 Assumptions: DO = 2 mg/L 26 Eff NH3-N = 1 mg/L Kn = 1 mg/L 24 22 20 18 16 14 12 10 Effluent Ammonia-NEffluent (mg/L) 8 6 4 2 0 012345678 Aerobic SRT (days) Aerobic SRT (days) @ 10C Aerobic SRT (days) @ 20C 30 15 6/24/2020 Process Simulator – ASRT Example 31 32 16 6/24/2020 33 Steady State Nitrification – D.O. 35 Effluent Ammonia @ DO=3 mg/L Effluent Ammonia @ DO=2 mg/L 30 Effluent Ammonia @ DO=1 mg/L Effluent Ammonia @ DO=0.5 mg/L 25 Assumptions: Influent BOD = 220 mg/L Influent TKN = 40 mg/L T = 15 deg C 20 Kn = 1 mg/L 15 Effluent Ammonia-N (mg/L) Ammonia-N Effluent 10 5 0 0123456789101112 Aerobic SRT (days) 34 17 6/24/2020 Process Simulator – DO Example 35 Aerobic SRT for Nitrification 22 Assumptions: 20 DO = 2 mg/L Eff NH3-N = 1 mg/L 18 Kn = 1 mg/L pH > 7.2 Source: 16 1993 EPA Nitrogen Control Manual 14 12 Operating Aerobic SRT @ PDF = 2.0 10 Aerobic SRT (days) Aerobic 8 6 Minimum Aerobic SRT 4 for Nitrification 2 0 4 6 8 10 12 14 16 18 20 22 24 Wastewater Temperature (deg C) 36 18 6/24/2020 Nitrification Performance – 4 Years 15.0 50 12.5 45 10.0 40 7.5 35 Aerobic Aerobic SRT (days) 5.0 30 2.5 25 0.0 20 Jul-00 Jan-01 Jul-01 Jan-02 Jul-02 Jan-03 Jul-03 Jan-04 -2.5 15 -5.0 10 -7.5 5 -10.0 0 Conc. (mg/L) Ammonia Effluent Calculated 7-Day Moving Avg. Min. Aerobic SRT (days) Actual Aerobic SRT (days) Calculated 7-Day Moving Avg Aerobic SRT Goal (days) Eff NH3-N (mg/L) 37 Nitrification Performance – 2002 15.0 50 12.5 45 10.0 40 . 7.5 35 Aerobic SRTAerobic (days) 5.0 30 2.5 25 0.0 20 Sep-01 Nov-01 Dec-01 Feb-02 Apr-02 May-02 Jul-02 Sep-02 Oct-02 Dec-02 -2.5 15 Period when Actual Aerobic SRT less than SRT Goal but more than Minimum -5.0 10 -7.5 5 . -10.0 0 (mg/L) Conc. Ammonia Effluent Calculated 7-Day Moving Avg. Min. Aerobic SRT (days) Actual Aerobic SRT (days) Calculated 7-Day Moving Avg Aerobic SRT Goal (days) Eff NH3-N (mg/L) 38 19 6/24/2020 Nitrification Performance – 2003 15.0 50 12.5 45 10.0 40 . 7.5 35 Aerobic SRT (days) SRT Aerobic 5.0 30 2.5 25 0.0 20 Dec-02 Jan-03 Mar-03 May-03 Jun-03 Aug-03 Oct-03 Nov-03 -2.5 15 Nitrification Re-acclimation Period -5.0 10 -7.5 5 Period when Actual Aerobic SRT less . than SRT Goal but more than Minimum -10.0 0 (mg/L) Conc. Ammonia Effluent Calculated 7-Day Moving Avg. Min. Aerobic SRT (days) Actual Aerobic SRT (days) Calculated 7-Day Moving Avg Aerobic SRT Goal (days) Eff NH3-N (mg/L) 39 Nitrite “Lock” • Nitrite-N is an intermediate product of nitrification • Causes: . Low aerobic SRT . Low pH . NOB toxicity • Impacts: . Chlorine demand (5 mg Cl per mg NO2-N) . Disinfection performance problems . Effluent toxicity • Solutions 40 20 6/24/2020 Alkalinity Check • Should maintain at least 50-75 mg/L Alkalinity in Effluent • Effluent Alkalinity = Alkinf –Alknit + Alkdenit • Alkalinity also consumed through Chemical P Removal • Chemicals typically used to add Alkalinity: . Sodium Hydroxide (NaOH) – aka Caustic Soda . Sodium Carbonate (Na2CO3) – aka Soda Ash . Sodium Bicarbonate (NaHCO3) – aka Baking Soda . Magnesium Hydroxide (Mg(OH)2) – aka Milk of Magnesia . Potassium Hydroxide (KOH) – aka Caustic Potash or Lye . Quicklime (CaO) 41 Evaluating and Improving Nitrification Increase Aerobic SRT BIOMASS OXYGEN Increase DO Concentration . Increase MLSS Concentration . Increase Aeration Volume . Add Fixed Film Media UNDERSTAND Reduce Organic ALKALINITY/pH THE LIMITING SLUDGE FACTORS PRODUCTION Loading to Reactors Add Alkalinity . Improve PC . Improve denitrification Performance . Chemical addition . Chemical Addition 42 21 6/24/2020 Nitrification Case Study 43 Nitrification Case Study • North Davis Sewer District, Syracuse, Utah • 80 sq.
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