Operation of Activated Sludge Nitrification Paul Dombrowski, Woodard - PDF document

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 (X w ) + lbs/d Effluent TSS (X e ) 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 (X w ) + lbs/d Effluent TSS (X e ) 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 NO X - 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 - -N + 2 H + + H 2 O + Bacteria NH 4 + -N + 2 O 2 NO 3 Autotrophic Bacteria – Ammonia and Nitrite Oxidizing Bacteria (AOB and NOB) Energy from Oxidation of NH 4 + -N  - (BiCarbonate) Carbon from HCO 3  Aerobic Organisms – DO Sensitive (Require 4.6 lb/lb NH 4 -N)  Low Growth Rate – Temperature Sensitive  Produces Acid – Consumes Alkalinity (7.2 lb/lb NH 4 -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 NH 4 -N NO 2 -N NO 3 -N New New O 2 + HCO 3 O 2 + HCO 3 Cells Cells 23 DO Impact on Nitrification 100% 90% 80% 70% Nitrification Rate (% of max) 60% 50% 40% 30% 20% 10% 0% 0 1 2 3 4 5 6 7 8 9 10 DO Concentration (mg/L) 24 12

6/24/2020 Temperature Impacts on Nitrification 1.40 1.20 Maximum Nitrifier Specific Growth Rate (mg/mg-d) 1.00 0.80 0.60 0.40 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 Secondary Influent Nitrified Effluent Effluent Aeration Aeration Secondary Tank Secondary Tank Clarifier (fully Clarifier (fully aerobic) aerobic) RAS RAS Pump Pump BOD Removal Nitrification Stage Stage 27 Single Sludge Nitrification Effluent Secondary Influent Aeration Clarifier Tank RAS Pump Waste Sludge BOD Removal, Nitrification 28 14

6/24/2020 Min. Aerobic SRT for Nitrification 22 Assumptions: DO = 2 mg/L 20 Eff NH 3 -N = 1 mg/L Kn = 1 mg/L 18 pH > 7.2 Source: 16 1993 EPA Nitrogen Control Manual 14 Aerobic SRT (days) 12 10 Min. Aerobic SRT = y = 18.507e -0.098x 8 6 4 2 0 4 6 8 10 12 14 16 18 20 22 24 Wastewater Temperature (deg C) 29 Steady State Nitrification – Temp. 30 Assumptions: 28 DO = 2 mg/L Eff NH 3 -N = 1 mg/L 26 Kn = 1 mg/L 24 22 Effluent Ammonia-N (mg/L) 20 18 16 14 12 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 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 Assumptions: 25 Influent BOD = 220 mg/L Influent TKN = 40 mg/L Effluent Ammonia-N (mg/L) T = 15 deg C 20 Kn = 1 mg/L 15 10 5 0 0 1 2 3 4 5 6 7 8 9 10 11 12 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 NH 3 -N = 1 mg/L Kn = 1 mg/L 18 pH > 7.2 Source: 16 1993 EPA Nitrogen Control Manual 14 Aerobic SRT (days) 12 Operating Aerobic SRT @ PDF = 2.0 10 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 Aerobic SRT (days) 10.0 40 7.5 35 5.0 30 2.5 25 Effluent Ammonia Conc. (mg/L) 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 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 Aerobic SRT (days) 10.0 40 7.5 35 5.0 30 2.5 25 0.0 20 Effluent Ammonia Conc. (mg/L) 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 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 Aerobic SRT (days) 12.5 45 10.0 40 7.5 35 5.0 30 2.5 25 0.0 20 Effluent Ammonia Conc. (mg/L) 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 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