wastewater engineering - notes for design of activated sludge processes
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Wastewater Engineering ‐ Notes for Design of Activated Sludge Processes
Alfonso José García Laguna
Wastewater Engineering
Notes for Design of Activated Sludge Processes
Alfonso José García Laguna
February 2016
Wastewater Engineering ‐ Notes for Design of Activated Sludge Processes
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Index
1. Biology, Kinetics and Stoichiometry ................................................................................................ 4
1.1. Nitrification ............................................................................................................................. 4
Steps of Nitrification ........................................................................................................................... 5
Type of Bacteria – Nitrosomonas and Nitrobacter ............................................................................. 5
Nitrification ‐ Kinetics .......................................................................................................................... 5
Nitrification ‐ Stoichiometry ............................................................................................................... 5
1.2. Denitrification ......................................................................................................................... 7
Steps of Denitrification ....................................................................................................................... 7
Type of Bacteria – Heterotroph Facultative Microorganisms under Anoxic Conditions .................... 7
Denitrification – Kinetics ..................................................................................................................... 8
1.3. Phosphorus Biological Removal (Bio‐P) .................................................................................. 9
Type of Bacteria – Acinetobacter, Slow Growth and Simple Substrates as VFAs (Volatile Fatty acids) ............................................................................................................................................................ 9
Steps of Phosphorus Biological Removal (Bio‐P) .............................................................................. 10
Ratio BOD/PT and COD/PT for a Proper Bio‐P .................................................................................. 11
2. Process Selection .......................................................................................................................... 12
2.1. Nitrogen Removal Processes ................................................................................................ 12
Metcalf & Eddy – Description and Selection of Nitrogen Removal Processes ................................. 12
Process Selection .............................................................................................................................. 13
CEDEX – Description and Selection on Nitrogen Removal Processes ............................................... 23
2.2. Biological Phosphorus Removal Processes (BPR) (Bio‐P) ...................................................... 28
Metcalf & Eddy – Biological Phosphorus Removal Processes (BRP) ................................................. 28
Process Description and Selection .................................................................................................... 29
CEDEX – Description and Selection on Biological Phosphorus Removal Processes (BRPs) .............. 32
3. Typical Design Parameters ............................................................................................................ 39
3.1. Nitrogen Removal Processes – Typical Design Parameters .................................................. 39
Metcalf & Eddy .................................................................................................................................. 39
CEDEX ................................................................................................................................................ 40
3.2. Biological Phosphorus Removal Processes (BPRs) – Typical Design Parameters .................. 41
Metcalf & Eddy – Observed Influent BOD/P and COD/P Ratios for Different BPR Processes .......... 41
CEDEX – Design Considerations and Parameters .............................................................................. 42
4. Process Design .............................................................................................................................. 50
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4.1. BOD/COD Removal and Nitrification .................................................................................... 50
4.1.1. Metcalf and Eddy Method ............................................................................................ 51
Equations and Variables .................................................................................................................... 51
Kinetic Coefficients ........................................................................................................................... 52
Design Steps ...................................................................................................................................... 53
Example ............................................................................................................................................. 54
4.1.2. ATV‐131 Method ........................................................................................................... 67
Symbols and Abbreviations ............................................................................................................... 67
Plants without Nitrification ............................................................................................................... 72
Step 1 – Calculation of the Sludge Age ............................................................................................. 72
Step 2 – Calculation of the Sludge Production.................................................................................. 73
Step 3 – Calculation of Biological Reactor Volume ........................................................................... 75
Step 4 – Calculation of Required Recirculation and Cycle Time ....................................................... 76
Step 4 – Calculation of Oxygen Requirements .................................................................................. 77
Step 5 – Calculation of Alkalinity ...................................................................................................... 80
4.2. BOD/COD Removal and Nitrification‐Denitrification – Anoxic/Aerobic Reactor Design ...... 82
4.2.1. Metcalf and Eddy Method ............................................................................................ 82
Anoxic/Aerobic Reactor Design Considerations ............................................................................... 83
Anoxic Tank Design using the Specific Denitrification Rate (SDNR) ................................................. 84
Kinetic Coefficients ........................................................................................................................... 86
Design Steps ...................................................................................................................................... 88
Example ............................................................................................................................................. 90
4.2.2. ATV‐131 Method ........................................................................................................... 94
Plants with Nitrification and Nitrification‐Denitrification ................................................................. 95
Step 1 – Calculation of the Sludge Age ............................................................................................. 95
Plants with Nitrification .................................................................................................................... 96
Plants with Nitrification – Denitrification ......................................................................................... 97
Step 2 – Calculation of the Proportion of Reactor Volume for Denitrification ................................. 98
Step 3 – Calculation of the Sludge Production................................................................................ 101
Step 4 – Calculation of Biological Reactor Volume ......................................................................... 103
Step 5 – Calculation of Required Recirculation and Cycle Time ..................................................... 104
Step 6 – Calculation of Oxygen Requirements ................................................................................ 105
Step 7 – Calculation of Alkalinity .................................................................................................... 108
4.2.3. CEDEX Method ............................................................................................................ 110
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4.3. Phosphorus Biological Removal (BPR) (Bio‐P) .................................................................... 111
4.3.1. Metcalf and Eddy Method .......................................................................................... 111
Process Design Considerations ....................................................................................................... 111
Wastewater Characteristics ............................................................................................................ 112
Anaerobic Contact Time .................................................................................................................. 114
Solids Retention Time (SRT) ............................................................................................................ 114
Waste Sludge Processing ................................................................................................................ 115
Chemical Addition Capability .......................................................................................................... 116
Process Control ............................................................................................................................... 117
Effect of Dissolved Oxygen and Nitrate in Recycle Flows ............................................................... 117
Effect of Recycle Streams with Released Phosphorus .................................................................... 117
Effluent Suspended Solids ............................................................................................................... 118
Solids Separation Facilities .............................................................................................................. 118
Methods to Improve Phosphorus‐Removal Efficiency in BPR Systems .......................................... 119
Biological Phosphorus‐Removal Process Performance .................................................................. 120
Example ........................................................................................................................................... 122
5. Bibliography ................................................................................................................................ 125
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1. Biology, Kinetics and Stoichiometry
Autotroph Microorganisms: Organisms that are able to make energy‐containing organic molecules from inorganic raw material by using basic energy sources such as sunlight or chemical reactions.
Heterotroph Microorganisms: Organisms that make use of food that comes from other organisms in the form of fats, carbohydrates and proteins.
1.1. Nitrification
Nitrification is the Biological Aerobic Process by which the Ammonia Nitrogen (N‐NH4+) is transformed in Nitrates (N‐NO3‐).
Organic Biodegradable Nitrogen is Hydrolyzed by Heterotroph bacteria called Nitrosomonas and Nitrobacter producing Ammonia Nitrogen (NH4+).
Fig.1. Nitrification Stoichiometry
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Steps of Nitrification
1. Organic Biodegradable Nitrogen is hydrolyzed by Heterotrophs Bacteria, giving as a result Ammonia Nitrogen.
2. Ammonia Nitrogen (N‐NH4+) is converted in Nitrates (NO3‐) by bacteria called Nitrosomonas and Nitrobacter.
Type of Bacteria – Nitrosomonas and Nitrobacter
Nitrosomonas and Nitrobacter, called globally “Nitrifying Microorganism”, are Chemoautotroph:
Source of Energy: Inorganic Red‐Ox Reactions Source of Cell Carbon (Biomass Carbon): Inorganic Carbon Acceptor of Electrons: Oxygen
Nitrification ‐ Kinetics
The velocity of reaction of the first reaction, the formation of Nitrites (NO2‐) starting from Ammonia (NH4+) is significantly lower than the velocity of formation of Nitrates (NO3‐) starting from Nitrites (NO2‐).
So the kinetic of the Global Reaction is controlled by the First Reaction and the Limiting Substrate is the Ammonia Nitrogen (N‐NH4+).
Nitrification ‐ Stoichiometry
Fig.1. Nitrification Stoichiometry
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1. Oxidation of 1 g of Ammonia Nitrogen (N‐NH4+) generates 1 g of Nitrogen as Nitrates (N‐NO3‐) and consumes 4.57 g of Oxygen (O2).
2. Oxidation of 14 g of Ammonia Nitrogen (NH4+) generates 2 ions Hydrogen (H+) (acidity) that consumes 2 equivalents of Alkalinity (Bicarbonate) (HCO3‐) from the wastewater. As 1 equivalent of Alkalinity are 50 g/L as CaCO3 we have the following: Oxidation of 1 mg of Ammonia Nitrogen (N‐NH4+) consumes 7.14 mg CaCO3/L of Alkalinity.
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1.2. Denitrification
Denitrification is the Biological Anoxic Process by which the Nitrate Nitrogen (NO3‐) is transformed in Nitrogen Gas (N2) released to the atmosphere.
Steps of Denitrification
1. Ammonia Nitrogen (NH4+) is transformed in Nitrogen Gas (N2) released to the atmosphere.
Type of Bacteria – Heterotroph Facultative Microorganisms under Anoxic Conditions
“Denitrifying Bacteria” are Heterotroph Facultative under Anoxic Conditions:
Source of Energy: Carbonaceous Organic Matter Source of Cell Carbon (Biomass Carbon): Carbonaceous Organic Matter Acceptor of Electrons: Nitrates
Fig.2. Denitrification Stoichiometry
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Denitrification – Kinetics
1. Removal/Consumption of 1 g of Nitrate (NO3‐) as Nitrogen consumes 2.86 g of Oxygen (O2).
2. Removal/Consumption of 14 g of Nitrate Nitrogen (N‐NO3) generates 1 equivalents of Alkalinity (OH‐). As 1 equivalent of Alkalinity are 50 g/L as CaCO3 we have the following: Removal/Consumption of 1 g of N‐NO3 generates 3.57 g CaCO3 of Alkalinity.
Fig.2. Denitrification Stoichiometry
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1.3. Phosphorus Biological Removal (Bio‐P)
Heterotroph Bacteria called PAOs (Phosphorus Accumulation Organisms) have the following characteristics:
1. PAOs release P in Anaerobic Conditions.
2. PAOs accumulate P in Aerobic Conditions.
Type of Bacteria – Acinetobacter, Slow Growth and Simple Substrates as VFAs (Volatile Fatty acids)
PAOs are Heterotroph Bacteria under Anoxic and Oxic Conditions:
Source of Energy: VFA (Volatile Fatty Acids) Source of Cell Carbon (Biomass Carbon): VFA (Volatile Fatty Acids) Acceptor of Electrons: Nitrate (Anoxic Conditions) Oxygen (Oxic Conditions)
PAOs and Non‐PAOs
PAOs o Nitrifying PAOs (NPAOs): They respire Oxygen (O2). o Denitrifying PAOs (DPAOs): They respire Nitrate (N‐NO3)
Non‐PAOs
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o Glycogen‐Accumulating Organisms (GAOs): Carry out the COD Removal because they are able to recycle carbon in similar fashion as PAOs and aerobically accumulate glycogen instead of polyphosphate.
Steps of Phosphorus Biological Removal (Bio‐P)
1. Step 1 ‐ Anaerobic Conditions – Uptake of VFAs and Release of Poly‐P
1. PAOs mainly take up carbon sources such as Volatile Fatty Acids (VFAs) and store them intracellularly as Polyhydroxybutyrate (PHB) and Polyhydroxyalkanoates (PHAs).
2. In the PAOs, the excision of Polyphosphate (Poly‐P) and release of Phosphate (PO4,3‐) from the cell supply the required energy for the bio‐transformations.
3. Moreover, the glycolysis of internally stored glycogen also can provide reducing
power for PHA formation.
4. However, the metabolic pathways of both the PAOs and GAOs are still unclear to some extent, so is the indirect role that GAOs play in P‐removal.
2. Step 2 – Aerobic/Oxic Conditions ‐ Uptake of Poly‐P and Oxidation of Stored PHAs
1. PAOs takes Phosphate (PO4,3‐) and store it as intracellular Poly‐P.
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2. Polyhydroxyalkanoates (PHAs) are oxidized.
The amount of Phosphate excreted during the Anaerobic phase is less than the amount taken up during the Aerobic or Denitrifying phase.
Net phosphorus is taken up into the organisms, and Phosphorus can be removed readily from the wastewater by wasting Phosphorus‐Rich Sludge.
Ratio BOD/PT and COD/PT for a Proper Bio‐P
Total P (TP) concentration in the Effluent is a function of the Ratio BOD/TP or COD/TP.
TP (Effluent) = f(BOD/TP) = f(COD/TP)
For a DBO/PT < 20 or COD/PT < 40 the Efficiency of the Bio‐P is low, and need the Chemical Precipitation with FeCl3.
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2. Process Selection
2.1. Nitrogen Removal Processes
Metcalf & Eddy – Description and Selection of Nitrogen Removal Processes
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Process Selection
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Processes Description – Nitrogen Removal Processes
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Advantages and Limitations of Nitrogen Removal Processes
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CEDEX – Description and Selection on Nitrogen Removal Processes
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2.2. Biological Phosphorus Removal Processes (BPR) (Bio‐P)
Metcalf & Eddy – Biological Phosphorus Removal Processes (BRP)
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Process Description and Selection
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CEDEX – Description and Selection on Biological Phosphorus Removal Processes (BRPs)
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3. Typical Design Parameters
3.1. Nitrogen Removal Processes – Typical Design Parameters
Metcalf & Eddy
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CEDEX
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3.2. Biological Phosphorus Removal Processes (BPRs) – Typical Design Parameters
Metcalf & Eddy – Observed Influent BOD/P and COD/P Ratios for Different BPR Processes
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CEDEX – Design Considerations and Parameters
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4. Process Design
4.1. BOD/COD Removal and Nitrification
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4.1.1. Metcalf and Eddy Method
Equations and Variables
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Kinetic Coefficients
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Design Steps
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Example
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4.1.2. ATV‐131 Method
Symbols and Abbreviations
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Plants without Nitrification
Step 1 – Calculation of the Sludge Age
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Step 2 – Calculation of the Sludge Production
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Step 3 – Calculation of Biological Reactor Volume
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Step 4 – Calculation of Required Recirculation and Cycle Time
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Step 4 – Calculation of Oxygen Requirements
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Step 5 – Calculation of Alkalinity
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4.2. BOD/COD Removal and Nitrification‐Denitrification – Anoxic/Aerobic Reactor Design
4.2.1. Metcalf and Eddy Method
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Anoxic/Aerobic Reactor Design Considerations
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Anoxic Tank Design using the Specific Denitrification Rate (SDNR)
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Kinetic Coefficients
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Design Steps
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Example
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4.2.2. ATV‐131 Method
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Plants with Nitrification and Nitrification‐Denitrification
Step 1 – Calculation of the Sludge Age
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Plants with Nitrification
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Plants with Nitrification – Denitrification
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Step 2 – Calculation of the Proportion of Reactor Volume for Denitrification
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Step 3 – Calculation of the Sludge Production
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Step 4 – Calculation of Biological Reactor Volume
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Step 5 – Calculation of Required Recirculation and Cycle Time
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Step 6 – Calculation of Oxygen Requirements
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Step 7 – Calculation of Alkalinity
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4.2.3. CEDEX Method
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4.3. Phosphorus Biological Removal (BPR) (Bio‐P)
4.3.1. Metcalf and Eddy Method
Process Design Considerations
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Wastewater Characteristics
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Anaerobic Contact Time
Solids Retention Time (SRT)
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Waste Sludge Processing
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Chemical Addition Capability
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Process Control
Effect of Dissolved Oxygen and Nitrate in Recycle Flows
Effect of Recycle Streams with Released Phosphorus
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Effluent Suspended Solids
Solids Separation Facilities
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Methods to Improve Phosphorus‐Removal Efficiency in BPR Systems
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Biological Phosphorus‐Removal Process Performance
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Example
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5. Bibliography
1. Wastewater Engineering Treatment and Reuse (4th Edition) ‐ Metcalf & Eddy
2. Handbook Biological Wastewater Treatment ‐ Design of Activated Sludge Systems (2nd Edition) ‐ Adrianus van Haandel and Jeroen van der Lubbe
3. STANDARD ATV‐DVWK‐A 131E ‐ (May 2000) ‐ Dimensioning of Single‐Stage Activated Sludge Plants ‐ German Association for Water, Wastewater and Waste
4. XXV Course about Wastewater Treatment and O&M of WWTPs – (November 2007) ‐ CEDEX – Spain Government – Ministry of Environment and Ministry of Infrastructures
5. ONDEO DEGREMONT – Water Treatment Handbook