Activated Sludge MOP OM-9, 2nd Edition

1.      1.  Introduction

·          References

2.      2. Process and Equipment Description

·          Introduction

·          Description of Unit Processes

                                 I.      Basic System Components

                               II.      Microbiology and Biochemistry

·          Basic Process Goals

                                 I.      Carbonaceous Biochemical Oxygen Demand Removal

                               II.      Nitrification

                              III.      Nitrogen Removal—Denitrification

                           IV.      Biological Phosphorous Removal

·          Process Variations

                                 I.      Loading Rates

                               II.      Reactor Configuration

1.      Ideal Complete Mix

2.      Ideal Plug-Flow

3.      Reactors-in-Series

4.      Sequencing Batch Reactors

5.      Oxidation Ditch

                              III.      Feed and Aeration Patterns

1.      Conventional

2.      Contact Stabilization and Sludge Reaeration

3.      Stop Feed

4.      Tapered Aeration

5.      Selectors

·          Other Modifications

                                 I.      High-Purity Oxygen

                               II.      Coupled Systems

                              III.      Combined Systems

·          Biological Nutrient Removal Processes

                                 I.      Single-Sludge Processes

1.      Single-Sludge Ammonia Oxidation

2.      Single-Sludge Nitrogen Removal                 

3.      Single-Sludge Phosphorus Removal

4.      Single-Sludge Nitrogen and Phosphorus Removal

                               II.      Multiple-Sludge Systems   

1.      Multiple-Sludge Nitrification

2.      Multiple-Sludge Nitrogen Removal

·          Factors Affecting Process Efficiency

·          Description of Facilities and Equipment Used

                                 I.      Biological Reactors

                               II.      Aeration Systems

1.      Diffused Aeration

                              III.      Air Delivery

2.      Mechanical Aeration

3.      Mixing

                           IV.      Clarification

                             V.      Return and Waste Activated Sludge Systems 

                           VI.      Recirculation Pumping

·          References

3.      3. Process Control

·          Introduction

·          Primary Components for Controlling Activated Sludge Systems

                           I.      Introduction

                         II.      Controlling Activated-Sludge Inventories

1.      Food-to-Microorganism Ratio

2.      Mean Cell Residence Time

3.      Sludge Age, Solids Retention Time, and Mean Cell Residence Time

4.      Constant Mixed Liquor Suspended Solids

5.      Selecting a Control Strategy

6.      Temperature Effects

                              III.      Aeration and Dissolved Oxygen Control

                           IV.      Secondary Clarifier and Solids Separation Process Control

1.      Control Parameters

2.      Solids Blanket

3.      Return Activated-Sludge Control

4.      Sludge Settleability and Foaming

a.      Filamentous Organisms

b.      Foam Control

5.      Membrane Processes for Solids Separation

                             V.      Process Control for Carbonaceous Biochemical Oxygen Demand Removal

                           VI.      Changing Process Configurations  

1.      Conventional

a.      Complete Mix

b.      Selectors

c.      Plug Flow

d.      Step Feed/Contact Stabilization

2.      Other Configurations and Modifications

a.      Combining Fixed-Growth Systems

b.      Addition of Powdered Activated Carbon

c.      Chemical Addition

·          Process Control for Nitrification

                                 I.      Two-Stage or Two-Sludge Nitrification

·          Process Control for Denitrification    

·          Process Control for Phosphorus Removal  

·          Process Control for Sequencing Batch Reactors

·          Tracking Process Performance

                           I.      Introduction

                         II.      Performance Parameters

1.      Special Considerations

                        III.      Data Quality

                     IV.      Control Charts

1.      Using the Control Chart to Determine Process Problems

                       V.      Computerized Spreadsheets and Databases

·          Activated Sludge Models

·          Automated Process Control

                           I.      Loop Controllers

                         II.      Programmable Logic Controllers

                        III.      Distributed Control System

·          References

4.      4..Energy Management

·          Introduction

·          Energy Costs

·          Energy Use in Wastewater Treatment Plants

·          Energy Saving Opportunities

                           I.      Process Considerations

1.      General

2.      Number of Reactors

3.      Reactor Design

4.      Nitrification

5.      Denitrification

6.      Dissolved Oxygen Levels

7.      Optimizing Mean Cell Residence Time

8.      Volumetric Power Input

                         II.      Equipment Operations

1.      Aeration System Components

a.      Mechanical Aerators

b.      Diffused Aeration System

·          Alpha

·          Tank Depth

·          Bubble Size

·          Airflow Rate

·          Diffuser Density

·          Fouling

2.      Pumping Equipment

a.      Intermediate or Primary Effluent Pumps

b.      Return Activated-Sludge Pumps

c.      Waste Activated-Sludge Pumps

d.      Internal Recycle Pumps            

3.      Clarifiers

4.      Equipment Start-Up Procedures

·          Automatic Sensors and Controls

                           I.      General

                         II.      Dissolved Oxygen Control

                        III.      Pump Control

                     IV.      Other Sensors and Controls

·          Equipment Maintenance

·          Energy Management Plan

·          Case Studies

                           I.      Plant A

1.     Energy Consumption

2.     Conservation Program

                         II.      Plant B

1.     Energy Consumption

2.     Conservation Program

2.     Plant C

                        III.      Conservation Program

·          References

5.      5..Troubleshooting

·          Introduction

·          Keys to Troubleshooting

·          Troubleshooting Tests

                           I.      Mixed Liquor Settleability Test

                         II.      Sludge Volume Index

                        III.      Microscopic Examination

                     IV.      Mixed Liquor Respiration Rate

·          Operational Problems and Possible Solutions

                           I.      Introduction

                         II.      Biological Reactors

1.      Diffused Air and Mechanical Aeration Systems

a.      Diffused Air Systems

b.      Mechanical Aeration Systems

·          Inadequate Mixing and Aeration

·          Hydraulic Surging and Flooding

·          Impeller Fouling

2.      Biological Reactor Foaming

a.      Stiff White Foam

b.      Excessive Brown Foams

c.      Very Dark or Black Foam

                        III.      Secondary Clarifiers

1.      Solids Washout

a.      Equipment Malfunction

b.      Hydraulic Overload

c.      Solids Overload

d.      Temperature Currents

2.      Bulking Sludge

a.      Filamentous Microorganisms Present           

b.      Filamentous Foaming

c.      Filamentous Bulking

d.      Filamentous Microorganisms Not Present

3.      Clumping/Rising Sludge

4.      Cloudy Secondary Effluent

a.      Protozoa Present But Inactive 

b.      Protozoa Present and Active

c.      Few or No Protozoa

5.      Ashing

6.      Pinpoint Floc

7.      Straggler Floc

8.      Floating Sludge Due to Deep Tank Aeration

·          Biological Nutrient Removal Systems

                           I.      Introduction

                         II.      Biological Phosphorus Removal Processes

                        III.      Nitrification Systems

                     IV.      Biological Nitrogen Removal

·          Design Audit

·          Troubleshooting Guides

·          References

·          Suggested Readings

6.      6. Aerobic Digestion

·          Description of Process

·          Operational Parameters

                           I.      Waste Sludge Characteristics

                         II.      Oxygen Requirements

                        III.      pH      

                     IV.      Temperature

                       V.      Mixing

                     VI.      Solids Retention Time

·          Description of Facilities

                           I.      Types of reactors

                         II.      Air and Oxygen Supply Equipment

·          Process Control

                           I.      Batch Operation

                         II.      Continuous Operation

1.      Continuous-Feed Digesters

                        III.      Solid–Liquid Separation

·          Process Performance

                           I.      Solids Reduction

                         II.      Pathogen Reduction

                        III.      Reactor Loading

·          Troubleshooting

                           I.      Clogging of Air Diffusers

                         II.      Low Dissolved Oxygen Concentrations

                        III.      Nuisance Odors

                     IV.      Excessive Foaming

                       V.      Solids Deposition

                     VI.      Low pH

                    VII.      Freezing

·          Data Collection and Laboratory Control

                           I.      Maintenance Management Program

                         II.      Maintenance Tasks

1.      Aeration and Oxygen Supply

2.      Mixing and Pumping Equipment

3.      Instrumentation and Control

                        III.      Records

·          References

·          Appendix A:             Nutrient Balance Determination and Correction Strategies

·          Appendix B:             pH Adjustment Using Caustic Soda (pH too low)

·          Appendix C:             pH Adjustment Using Lime (pH too high)

·          Appendix D:            Control of Filamentous Organisms Using Chlorine

·          Appendix E:             Settling Aid Determination for Improved Mixed Liquor Suspended Solids

·          Appendix F:             Testing Equipment for Monitoring and Process Control

                           I.      Control Versus Monitoring

                         II.      Process Control Loop

                        III.      Equipment Alternatives

                     IV.      Ammonia

1.      Ammonia Electrodes

                       V.      Turbidity

1.      Secchi Disk

2.      Turbidimeters and Nephelometers

·          Appendix G:            Alkalinity Adjustment

·          Appendix H:             Activated-Sludge System Safety

·          Appendix I:            Preventive Maintenance Schedule (Typical)

·          List of Tables

2.1             Typical process loading ranges for the activated-sludge process.

4.1             Average total energy consumption.

4.2             Effect of nitrification on oxygen requirements.

4.3             Volumetric power requirements.

4.4             Plant A—Secondary treatment power components.

4.5             Results of identified energy conservation measures for Plant B.

5.1             Filament types as indicators of conditions causing activated-sludge bulking.

5.2             Concentrations of inorganic pollutants affecting activated-sludge treatment processes.

5.3             Troubleshooting guide for biological phosphorus removal.

5.4             Troubleshooting guide for nitrification and denitrification processes.

5.5             Troubleshooting guide for dual nutrient removal processes.

5.6             Troubleshooting guide for aeration system problems in biological reactors.

5.7             Troubleshooting guide for foaming problems.

5.8             Troubleshooting guide for solids washout/billowing solids.

5.9             Troubleshooting guide for bulking sludge.

5.10         Troubleshooting guide for sludge clumping.

5.11         Troubleshooting guide for cloudy secondary effluent.

5.12         Troubleshooting guide for ashing and pinpoint/straggler floc.

6.1            Chracteristics of supernatant from aerobic digestion systems.

6.2            Troubleshooting guide for aerobic digestion

·          List of Figures

2.1             Schematic diagram of a typical activated-sludge process.

2.2             Plug flow activated-sludge process with folded biological reactor.

2.3a            Typical sequencing batch reactor operation for one cycle.

2.3b            ICEAS™ system operation.

2.4            Oxidation ditch.

2.5             Contact stabilization activated-sludge process.

2.6             Step-feed activated-sludge process.

2.7             Typical selector configurations.

2.8             Closed-tank, high purity oxygen system schematic.

2.9             Schematic flowsheet for combined processes.

2.10         Carbonaceous/nitrification activated-sludge process.

2.11         Modified Ludzack–Ettinger process for nitrogen removal.

2.12         Wurhmann process for nitrogen removal.

2.13         Four-stage Bardenpho™ process for nitrogen removal.

2.14         A/O™ process.

2.15         PhoStrip™ process.

2.16         A²/O™ process for phosphorus removal.

2.17         Modified Bardenpho™ process for phosphorus and nitrogen removal.

2.18a            University of Cape Town and VIP processes for phosphorus and nitrogen removal.

2.18b            Modified University of Cape Town process for phosphorus and nitrogen removal.

2.19            Two-stage, carbonaceous-nitrification system.

3.1             Control chart sample.

4.1             Typical energy consumption of various wastewater treatment processes.

4.2             Activated-sludge system energy requirements.

4.3             Denitrification credit as a function of denitrification efficiency.

4.4             Power requirements as a function of mixed liquor DO.

4.5             Volumetric power requirements.

4.6             Comparative energy consumption for various diffusers.

4.7             Typical power consumption for a variable airflow system.

4.8             Typical power consumption for a variable liquid flow system.

4.9             Influent plumbing—Original drawdown.

4.10         Influent plumbing—Modified drawdown.

4.11         Annual electrical consumption.

4.12         Annual electrical cost.

4.13         Annual average billed demand.

4.14         Schematic of Plant C.

4.15         Comparison of conventional and selector modes of operation at Plant C.

5.1             Index to troubleshooting guides based on settleability test results.

5.2             Filamentous bacteria.

5.3             Stalked ciliates.

5.4             Rotifers.

5.5             Biological reactor surface turbulence.

5.6             Foaming problems.

5.7             Nocardia.

5.8             Dark foam in influent well of secondary clarifier.

5.9             Solids washout in clarifier.

5.10         Sludge bulking in clarifier.

5.11         Clumping in clarifier.

5.12         Ashing in clarifier.

6.1            Influence of solids retention time and liquid temperatures on the oxygen uptake rates in aerobic digestion.

6.2            Effect of solids retention time on reduction of biodegradable solids by aerobic digestion.

6.3            Relative solids destruction of several sludges by aerobic digestion.

6.4            Volatile solids reduction as a function of digester liquid temperature and digester solids retention time.