wastewater engineering - notes for design of activated sludge processes

Wastewater Engineering ‐ Notes for Design of Activated Sludge Processes

Alfonso José García Laguna

Wastewater Engineering

Notes for Design of Activated Sludge Processes


February 2016


Alfonso José García Laguna Page 1 of 126

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



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



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



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



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



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.



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



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



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



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.



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.



2. Process Selection

2.1. Nitrogen Removal Processes

Metcalf & Eddy – Description and Selection of Nitrogen Removal Processes



Process Selection



Processes Description – Nitrogen Removal Processes



Advantages and Limitations of Nitrogen Removal Processes



CEDEX – Description and Selection on Nitrogen Removal Processes



2.2. Biological Phosphorus Removal Processes (BPR) (Bio‐P)

Metcalf & Eddy – Biological Phosphorus Removal Processes (BRP)



Process Description and Selection



CEDEX – Description and Selection on Biological Phosphorus Removal Processes (BRPs)



3. Typical Design Parameters

3.1. Nitrogen Removal Processes – Typical Design Parameters

Metcalf & Eddy



CEDEX



3.2. Biological Phosphorus Removal Processes (BPRs) – Typical Design Parameters

Metcalf & Eddy – Observed Influent BOD/P and COD/P Ratios for Different BPR Processes



CEDEX – Design Considerations and Parameters



4. Process Design

4.1. BOD/COD Removal and Nitrification



4.1.1. Metcalf and Eddy Method

Equations and Variables



Kinetic Coefficients



Design Steps



Example



4.1.2. ATV‐131 Method

Symbols and Abbreviations



Plants without Nitrification

Step 1 – Calculation of the Sludge Age



Step 2 – Calculation of the Sludge Production



Step 3 – Calculation of Biological Reactor Volume



Step 4 – Calculation of Required Recirculation and Cycle Time



Step 4 – Calculation of Oxygen Requirements



Step 5 – Calculation of Alkalinity



4.2. BOD/COD Removal and Nitrification‐Denitrification – Anoxic/Aerobic Reactor Design




Anoxic/Aerobic Reactor Design Considerations



Anoxic Tank Design using the Specific Denitrification Rate (SDNR)



Kinetic Coefficients



Design Steps



Example



4.2.2. ATV‐131 Method



Plants with Nitrification and Nitrification‐Denitrification

Step 1 – Calculation of the Sludge Age



Plants with Nitrification



Plants with Nitrification – Denitrification



Step 2 – Calculation of the Proportion of Reactor Volume for Denitrification



Step 3 – Calculation of the Sludge Production



Step 4 – Calculation of Biological Reactor Volume



Step 5 – Calculation of Required Recirculation and Cycle Time



Step 6 – Calculation of Oxygen Requirements



Step 7 – Calculation of Alkalinity



4.2.3. CEDEX Method



4.3. Phosphorus Biological Removal (BPR) (Bio‐P)


Process Design Considerations



Wastewater Characteristics



Anaerobic Contact Time

Solids Retention Time (SRT)



Waste Sludge Processing



Chemical Addition Capability



Process Control

Effect of Dissolved Oxygen and Nitrate in Recycle Flows

Effect of Recycle Streams with Released Phosphorus



Effluent Suspended Solids

Solids Separation Facilities



Methods to Improve Phosphorus‐Removal Efficiency in BPR Systems



Biological Phosphorus‐Removal Process Performance



Example



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