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　　EMSELEnvironmental Management Systems Engineering Lab.

　　BIOMATHDepartment of Applied Mathematics, Biometrics and Process Control

　　Optimizing Biological Nutrient Removal Processes (EMSEL)

　　(2007 3 9 )EMSEL, Kyung Hee Univ.(ckyoo@khu.ac.kr or ChangKyoo.Yoo@biomath.ugent.be)

　　Presentation Review of Theory – Nitrification – Denitrification – Phosphorus Removal Optimization for nutrient removal – Nitrification Optimization – Denitrification Optimization Systematic optimization protocol for N and P removal – Case study 1 : SBR, Belgium – Case study 2 : Haaren, carrousel, Netherlands Problems and Troubleshooting (?)ChangKyoo Yoo - 2

　　References1.Jeanette A. Brown, P.E., DEE, (Executive Director SWPCA, CSWEA)- Optimizing Biological Nitrogen Removal Processes, USA 2.Dean Pond, Black Veatch (WWTP Operators School)Biological Wastewater Treatment Operators School, USA 3.Kim J.K, University of Wisconsin Madison, Biological Nutrient Removal Theories and Design, USA 4.Tao Jiang, BIOMATH , Belgium, UNESCO-IHE, Calibrating a Side-stream Membrane Bioreactor using ASM1, Belgium 5. Henze, DTU, Activated Sludge Model 1,2,2d,3, Denmark 6.Peter A. Vanrolleghem, Laval Univ., Optimal but robust N and P removal in SBRs, Canada

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　　Advanced Treatment Systems

　　What are the effects of N and P in receiving waters?

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　　What are the effects of N and P in receiving waters? Increases aquatic growth (algae) Increases DO depletion Causes NH4 toxicity Causes pH changes

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　　Nitrogen Removal Purpose– Reduce effluent N (ammonia and nitrates) – Biological or chemical – Reduce nutrient load on stream – Reduce algae growth – Reduce oxygen depletion

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　　Why is it necessary to treat the forms of nitrogen? Improve receiving stream quality Increase chlorination efficiency Minimize pH changes in plant Increase suitability for reuse Prevent NH4 toxicity Protect groundwater from nitrate contamination

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　　What are the forms of nitrogen found in wastewater? TKN = 40% Organic + 60% Free Ammonia Typical concentrations: Ammonia-N = 10-50 mg/L Organic N = 10 – 35 mg/L No nitrites or nitrates Forms of nitrogen: Organic N TKN Ammonia Total Nitrite N Nitrate

　　ChangKyoo Yoo - 8

　　Why is it sometimes necessary to remove P from municipal WWTPs? Reduce phosphorus, which is a key limiting nutrient in the environment Improve receiving water quality by:– Reducing aquatic plant growth and DO depletion – Preventing aquatic organism kill

　　Reduce taste and odor problems in downstream drinking water supplies

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　　Advanced Treatment SystemsIdentify and explain the objectives of the following advanced treatment systems:– Further removal of organics – Further removal of suspended

　　solids – Nutrient removal (N and P) – Removal of dissolved solids

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　　Advanced Treatment Systems

　　How is N removed or altered by conventional secondary (biological) treatment?

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　　Nitrification

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　　Nitrification Oxidation of ammonia nitrogen to nitrite nitrogen by nitrosamonas group:– NH4+ + O2 2H+ + NO2-

　　Oxidation of nitrite nitrogen by nitrobacter group:– NO2- + O2 NO3-

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　　Nitrification NH4+ Nitrosomonas NO2 NO2- Nitrobacter NO3 Notes:– – – – Aerobic process Control by SRT (4 + days) Uses oxygen 1 mg of NH4+ uses 4.6 mg O2 Depletes alkalinity 1 mg NH4+ consumes 7.14 mg alkalinity – Low oxygen and temperature = difficult to operateChangKyoo Yoo - 14

　　Un-aerated Bioreactor (Anoxic Zone)

　　Primary EffluentAnoxic

　　Nitrate RecycleAerobic

　　RAS WAS

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　　Characteristics of an Un-aerated Bioreactor Anoxic Microorganisms– Facultative heterotrophic-use carbon for the formation of new biomass – Use nitrate/nitrite instead of oxygen – Oxygen is preferred

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　　Nitrifier Minimum Aerobic SRT Varies with Temperature.9 8 7 6 5 4 3 2 1 0 10

　　Minimum SRT (Days)

　　Nitrification

　　No Nitrification

　　15

　　20 Temp (Deg Cent)

　　25

　　30

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　　Effective Nitrification

　　Achieved by: Effective nitrification – Adequate Aerobic SRT Temperature – Sufficient Oxygen Transfer Capacity Maintain a DO of 2 mg/l at peak loadings – pH 6.5, preferably 7 Accomplished by sufficient alkalinity (Effluent concentration at least 50 mg/l – No inhibitory materials

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　　Nitrification Optimization Summary Test nitrification rate occasionally Select appropriate SRT Keep DO at 2 mg/l Keep pH about neutral (optimal 7.5 to 8.5) Provide sufficient alkalinity

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　　Denitrification

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　　Denitrification

　　Using methanol as carbon source: 6 NO3- + 5 CH3OH N2 + 5 CO2 + 7 H2O + 6 OH Using an endogenous carbon source: C5H7NO2 + 4.6 NO32.8 N2 + 5 CO2 + 1.2 H2O + 4.6 OH-

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　　Denitrification NO3- denitrifiers (facultative bacteria) N2 gas + CO2 gas Notes:– Anoxic process – Control by volume and oxic MLSS recycle to anoxic zone – N used as O2 source = 1 mg NO3- yields 2.85 mg O2 equivalent – Adds alkalinity 1 mg NO3- restores 3.57 mg alkalinity – High BOD and NO3- load and low temperature = difficult to operate

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　　Denitrification with Supplemental CarbonMethanol or other carbon source

　　Primary Effluent

　　Nitrate Recycle

　　RAS WAS

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　　Denitrification is Controlled by Mixed Liquor Recirculation.

　　90 80 70 60 50 40 30 20 10 0 0 100 200

　　Denitrification (%)

　　% Denit = R/(R+Q) * 100

　　300

　　400

　　500

　　Mixed Liquor Recirculation (%)

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　　Effective Denitrification

　　Size based on anoxic SRT– Typically 1 to 2 day

　　s depending on temperature

　　Effective Denitrification – Sufficient Anoxic Volume (Anoxic SRT) – Sufficient Carbon – Sufficient mixed liquor recirculation

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　　External Carbon Methanol Stoichiometry– 2.5 (NO3-N) + 1.5 (NO2-N) + 0.87 (DO) – Or, approximately 3 mg CH3OH/mg NO3-N – Requires 1 to 3 day SRT in secondary anoxic zone depending on temperature

　　Other carbon sources technically feasible but generally more expensive.

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　　Denitrification Optimization Summary Minimize DO in anoxic zone ( 0.2 mg/l) Have 2Q to 4 Q recycle capabilities Provide sufficient carbon (readily biodegradable COD) Maximize use of secondary anoxic zones

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　　Phosphorus

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　　Phosphorus Removal Purpose– – – – – Reduce effluent P Biological or chemical method Reduce nutrient load on stream Reduce algae growth Reduce oxygen depletion

　　Application / Mechanism– Biological – Chemical

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　　Phosphorus Removing MechanismPO 43-

　　Facultative bacteria Acetate plus Substrate fermentation products Anaerobic

　　Energy

　　Acinetobacter spp. (Phosphorus Poly-P removing PHB bacteria, slow grower)

　　Aerobic

　　EnergyBOD + O2

　　PHB Poly-P

　　PO 4

　　3-

　　+CO2 + H2O

　　New biomass

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　　Continued …

　　Phosphorus Removal Biological

　　Q

　　Anaerobic Zone

　　Aerobic Zone

　　Final Clarifier

　　Effl

　　P Release

　　P Luxury Uptake

　　RAS

　　WAS

　　P RemovalChangKyoo Yoo - 31

　　Continued …

　　Phosphorus Removal ChemicalPrimary Clarifier Aerobic Zone Final Clarifier Effl

　　Q

　　Chemical Coagulant

　　Chemical Coagulant

　　RAS

　　WAS P Removal

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　　Effective Phosphorus Removal Size based on SRT– Typically 7 to 10 days depending on temperature

　　Effective Denitrification – Sufficient Anaerobic Volume (Anaerobic SRT) – Sufficient influent carbon – Competition between denitrification and phosphorous removal bacteria Sensitive to influent carbon Unstable processChangKyoo Yoo - 33

　　/

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　　Guidelines for Biological Nutrient Removal (BNR) Process SelectionNitrogen Removal Four

　　Stage Bardenpho Process Modified Ludzack-Ettinger (MLE) Process

　　Phosphorus Removal Only A/O

　　Process

　　Nitrogen and Phosphorus Removal Five

　　Stage Bardenpho (Phoredox) Process University of Cape Town (UCT) Process Modified UCT Process Virginia Initiate Process (VIP)ChangKyoo Yoo - 35

　　Schematic Process Configuration for Optional OperationsMixed liquor recycle, rMixed liquor recycle, a Secondary clarifier Anaerobic Influent Effluent Sludge recycle, s Anoxic Aerobic

　　Phoredox process UCT process Modified UCT processChangKyoo Yoo - 36

　　Process Selection Based on TKN/COD ratio (Initial Screening)Nitrogen Removal TKN/COD

　　0.09: Bardenpho process TKN/COD 0.10: MLE process

　　Nitrogen and/or Phosphorus Removal TKN/COD

　　0.07 ~ 0.08: A/O,

　　A2/O, Phoredox process (modified Bardenpho) TKN/COD 0.12 ~ 0.14: UCT process TKN/COD 0.11: Modified UCT process

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　　Systematic optimization protocol for N and P removal

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　　Introduction WWTP are complex systems Complex models can help in:– – – – Understanding the processes Plant design Plant optimisation Plant control

　　In practice– Which model to choose? – How to calibrate the model? – How to optimize the processneed for calibration and optimization protocolChangKyoo Yoo - 39

　　Why Model-based Optimization ?Solving Problems for wwtp systemsSystem under study Optimized System

　　Experimenting Reality

　　Virtual RealityModel of the System

　　Simulate

　　Solution for the System

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　　The systematic optimisation protocol

　　Systematize and standardize the model-based optimisation using mechanistic models (ASM2d for N- P- removal) Objective oriented iterative protocol A grid of scenarios (full-factorial design) built on the basis of the degrees of freedom and the constraints of the SBR system Selection and calibration of a suitable model to describe the biological processes Simulation and evaluation of a multitude of scenarios Selection of the best scenario Implementation final evaluation

　　1. Objective(s) 2. Framework of the optimization 3. Model selection and calibration

　　4. Scenario analysis5. Evaluation of the results of scenarios 6. Implementation of the best scenario 7. Measurement campaign No Target reached? YesEND

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　　Plant Information

　　Necessary information for model calibration

　　Mass balance, Operating parameters (SRT, HRT, control)

　　Aeration Hydraulics

　　Model based w.w. characterizationFlowrates COD fractionation (SS, SF, XS, XI, SI)

　　Biomass characterizationKinetic, stoichiometric parameters Active biomass fractions

　　N, P fractions, TSSChangKyoo Yoo - 42

　　Biomass composition

　　Biomath calibration protocolStage II – Plant survey/data analysis Design data– Plant layout/configuration, volumes, pumps, aerators,...

　　Operational data– Flow rates, sludge recycle/waste, control strategies,...

　　Measured data– Influent/effluent characterisation (COD,TKN,PO4,NO3,...) – On-line measurements (DO,T,pH,...) – TSS (RAS and effluent), sludge age/production,...

　　Mass balances– Flow rate, sludge (including N P) – Important for data quality check (e.g. sludge age)ChangKyoo Yoo - 43

　　Case study (I) - SBR Developing a robust biological system– Detect the major sources of process disturbances as soon as possible – Useful to keep the sludge as stable as possible – Volume (80 L), SRT (10 d) and HRT (12 h), 6 hour cycle mode – Six on-line measurements (DO, ORP, pH, conductivity, temperature, weight)InfluentAnaerobi c + filling Aerobic Anoxic Aerobic Settling Draw

　　Concentratio n

　　Effluent

　　60ChangKyoo Yoo - 44

　　150

　　60

　　30

　　45

　　15

　　Cycle time (min)

　　Introduction

　　Both N P removal successfully demonstrated at lab-scale and full-scale SBR installations. SBR offers more flexibility in operation (compared to continuous systems) –a key aspect in process optimisation. A myriad of operating strategies to optimise nutrient removal performance in SBRs. Usually developed at lab- or pilot-scale only comparison of a few operating scenarios Increasingly, mathematical models (e.g. ASM1 for N-removal and ASM2d for N- P- removal) are used to search for the optimal operating scenario

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　　50

　　100

　　150 200 250 Time (min)

　　300

　　350

　　50

　　100

　　150 200 250 Time (min)

　　300

　　350

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　　Scenario analysis

　　Construction of grids of scenariosChoose a range and interval for the degrees of freedoms: SO-sp: [0.2, 0.4, 0.6, 0.8, 1,2] Vstep-feed: [0, 5, 10] TANB: [60, 70, 80] TAER: [130, 140, 150] Intermittent aeration frequency:[1, 2, 4, 8]

　　Full-factorial design of degrees of freedoms: total 648 scenarios Each scenario simulated for 30 days (3 X SRT)

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　　Scenario analysis

　　Formulation of grids of scenarios:

　　Configuration of intermittent aeration frequencies step-feed of influent ( )

　　reference

　　TANB Fill/anaerobic Aerobic react Anoxic react Settle Draw TAER TANX

　　TAER2

　　IAF1TS TD

　　TC

　　TANB Fill/anaerobic Aerobic react Anoxic react Settle Draw TAER/2 TANX/2 TAER/2 TANX/2

　　IAF2TAER2 TS TD TC

　　Scenario analysis

　　TANB Fill/anaerobic Aerobic react Anoxic react Settle Draw TANB Fill/anaerobic Aerobic react Anoxic react Settle Draw

　　IAF4TAER2 TS TD TC

　　IAF8TAER2 TS TD TC

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　　Evaluation of the scenarios

　　Effluent quality

　　Effluent quality of 648 scenarios were analysed, general conclusions: Increasing TANB improves P-removal but decreases Nremoval Increasing TAER slightly improves the nitrification but negative effect on denitrification. The SO-sp is the most critical/dictates the overall behaviour of the system. The step-feed has a positive effect on the denitrification. Increasing the intermittent aeration frequency (IAF) increases N P removal

　　ChangKyoo Yoo - 49