Identification of Wastewater Treatment System Configuration and Process Characteristics

Identify Wastewater Treatment Configurations and Process

Introduction

Following are schematics of typical wastewater treatment facility configurations in Canada. Some general items to note with respect to the configurations are:

  • Arrows into the schematic indicate inputs, such as coagulants. These inputs may be zero at your facility. Therefore, if there is an arrow into the schematic at a point where you do not add materials or energy, the schematic may still apply to your plant.
  • Arrows out of the schematic indicate outputs from the process, such as screening materials, biosolids or effluent. These are the points in the process that may result in reportable substances being released or transferred.
  • To keep schematics generic, some have options (shown with a diamond "or") indicated. For example, disinfection is an option at the end of many plant configurations.
  • At the end of each configuration, a summary of emission points from that process is listed. All emission points in the facility and in the collection system must be considered when estimating release amounts.

Identify the configuration that most closely matches the plant on which you are reporting. Once your facility is identified, identify emission points that apply to your facility to continue.

 

1. Direct Discharge or Preliminary Mechanical Plant

See text below for long description.

Summary
This configuration includes no treatment, or simple preliminary treatment. The system entails:

  • screening and release of effluent to a water body (screening may be as simple as the grates on the main outfall), or
  • screening followed by grit removal and release of effluent to a water body.

Features

  • Direct discharge is the release, without treatment, of wastewater to a surface water body.
  • Preliminary treatment is the most basic level of treatment.
  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • With the addition of grit removal, preliminary treatment also removes heavier, settleable particles.
  • Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids, and
  • effluent.

 

2. Primary Mechanical Plant

See text below for long description.

Summary
Primary treatment uses a series of separators to remove solids from the water stream. No controlled biological treatment takes place.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Grit removal removes heavier, settleable particles
  • Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.
  • Primary clarification removes a fraction of the solids and organics from the water stream, producing primary sludge and scum outputs. The sludge may be further treated [note: could include digestion] prior to disposal.
  • Coagulant may or may not be used to increase solids' removal in the primary clarification stage. Typical coagulants used are metal salts -- aluminum sulphate or ferric chloride. If not used, this arrow input on the diagram is zero. Primary treatment facilities using coagulants are sometimes referred to as Enhanced Primary Plants.
  • Primary plants may or may not include disinfection. If there is no disinfection, the effluent from the primary clarifiers is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or an energy input, such as UV radiation. Dechlorination using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids
  • primary sludge
  • scum, and
  • effluent.

 

3a. Secondary Lagoon Aerobic-facultative (also known as Facultative)

See text below for long description.

Summary
Aerobic-facultative lagoons (or facultative lagoons) are configured as single or multiple-cell facilities. Treatment occurs through passive air-water interface transfers and photosynthetic reactions. The lower anaerobic zone of an aerobic-facultative lagoon provides sludge stabilization, volume reduction and storage. Lagoons are classified as secondary treatment facilities, although their performance in terms of contaminant removal efficiency is often well below that of other secondary plants.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Aerobic-facultative lagoons comprise an upper aerobic zone and a lower anaerobic zone. Settleable solids are stored in the lower zone where they are anaerobically reduced to inert solids. Aerobic treatment occurs in the upper zone by means of passive air-water interface transfers and photosynthesis. Mechanical systems to increase oxygen transfer rates are not used in this configuration.
  • Figure 5 depicts a two-cell facility for illustrative purposes. However, this configuration applies for any number of lagoon cells.
  • Lagoons may or may not include disinfection. If there is no disinfection, lagoon effluent is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or an energy input, such as UV radiation. Dechlorination using a reducing agent, such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • lagoon biosolids (when removed periodically), and
  • effluent.

 

3b. Secondary Lagoon Aerated

See text below for long description.

Summary
Aerated lagoons are configured as single- or multiple-cell facilities. The aerated cell is equipped with mechanical systems to actively supply oxygen. The lower anaerobic zone of an aerated aerobic-facultative lagoon provides sludge stabilization, volume reduction and storage. Aerated lagoons are classified as secondary treatment facilities, although their performance in terms of contaminant removal efficiency is often well below that of other secondary plants.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Mechanical aeration systems are typically surface mechanical or diffused air (depicted as the air input arrow in Figure 6.) Off-gassing from mechanically-aerated lagoons is at higher levels than from the passive system (Figure 5).
  • Aerated lagoons can be configured as either a complete-mix cell, followed by an aerobic-facultative lagoon for solids separation, or by a partially-mixed aerated lagoon which allows solids' separation and anaerobic stabilization in the lower, unmixed zone.
  • Figure 6 depicts a complete-mix first stage and aerobic-facultative second stage lagoon for illustrative purposes. However, this configuration applies to any lagoon system equipped with a mechanical aeration system.
  • Lagoons may or may not include disinfection. If there is no disinfection, the lagoon effluent is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or an energy input, such as UV radiation. Dechlorination, using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • lagoon biosolids (when removed periodically), and
  • effluent.

 

4. Secondary Treatment Activated Sludge (Suspended Growth)

See text below for long description.

Summary
Conventional activated sludge plants include biological treatment and primary clarification (for solids' separation). The activated sludge process comprises an aerated biological reactor and a secondary clarifier for solids' separation. Some sludge is returned to the reactor to maintain the aerobic biomass at an optimal concentration for high- treatment efficiency through the metabolic synthesis of organic and inorganic compounds. This configuration also includes activated sludge facilities practising Enhanced Secondary Treatment -- coagulant addition for phosphorus removal and aeration capacity for nitrification demands.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Grit removal removes heavier, settleable particles. Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.
  • Primary clarification removes a fraction of the solids and organics from the water stream, producing primary sludge and scum outputs.
  • Coagulant may or may not be used to increase solids' removal in the primary clarifier. Typical coagulants used are metal salts -- aluminum sulphate or ferric chloride. If not used, this arrow input on the diagram is zero.
  • The secondary aerobic stage comprises a complete-mix reactor with either mechanical or diffused-air aeration systems followed by a secondary clarifier. A portion of the sludge from the clarifier is recycled to maintain an optimal mixed-liquor concentration in the reactor. The reactor and separator phases of an activated sludge plant configured as a sequencing batch reactor, are combined in a single tank.
  • Coagulant for phosphorus removal may or may not be added prior to the secondary aerobic stage. If not, the input arrow in the diagram would be zero.
  • Primary and waste-activated sludge is usually stabilized on site through anaerobic or aerobic digestion and further thickened or dewatered prior to ultimate disposal. (See Biosolids Processing at the end of this section.)
  • Activated Sludge plants may or may not include disinfection. If there is no disinfection, the effluent from the secondary clarifier is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or as an energy input, such as UV radiation. Dechlorination, using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids
  • primary sludge
  • scum
  • waste-activated sludge, and
  • effluent.

 

5. Secondary Treatment Extended Aeration (Suspended Growth)

See text below for long description.

Summary
Typically, extended aeration plants are of smaller capacity than conventional activated sludge plants and do not include primary sedimentation. They are characterized by long hydraulic-retention times, higher mixed-liquor concentration and long sludge ages.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Grit removal removes heavier, settleable particles. Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.
  • The secondary aerobic stage comprises a complete-mix reactor with either mechanical or diffused-air aeration systems followed by a secondary clarifier. A portion of the sludge from the clarifier is recycled to maintain an optimal mixed-liquor concentration in the reactor. The reactor and separator phases of an extended aeration plant configured as a sequencing batch reactor, are combined in a single tank.
  • Coagulant for phosphorus removal may or may not be added prior to the secondary aerobic stage. If not, the input arrow in the diagram would be zero.
  • Waste-activated sludge is usually stabilized on site through aerobic digestion and may be further thickened or dewatered prior to ultimate disposal. (See Biosolids Processing at the end of this section.)
  • Extended aeration plants may or may not include disinfection. If there is no disinfection, the effluent from the secondary clarifier is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or as an energy input, such as UV radiation. Dechlorination, using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids
  • waste-activated sludge, and
  • effluent.

 

6. Secondary Treatment Fixed Film (Trickling Filter, Rotating Biological Contactor)

See text below for long description.

Summary
Fixed film plants rely on the development of biological growth through direct contact with air. They are also referred to as "attached growth" or "supported growth" plants. The most common fixed film configurations are Trickling Filters (TFs) and Rotating Biological Contactors (RBCs). TFs may be configured as a packed tower with forced air or a shallow, naturally-ventilated circular filter bed. RBCs comprise a series of circular, closely-spaced, partially-submerged, parallel plastic plates rotating on a horizontal shaft. With each revolution of the shaft, the biomass is progressively exposed to air and then submerged in the flow. Coagulants for phosphorus removal may be used.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Grit removal removes heavier settleable particles. Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.
  • Primary clarification removes a fraction of the solids and organics from the water stream, producing primary sludge and scum outputs.
  • For TFs, the secondary aerobic stage comprises a system of fixed nozzles or rotating distribution arms to evenly distribute the raw influent over a tower or filter bed of artificial or natural biomass support media (e.g. plastic or stone). TFs often incorporate pumped effluent recycle to keep the biomass wet.
  • An RBC aerobic zone comprises a semi-circular baffled trough in which the plates rotate, bringing the biomass into contact with the raw influent.
  • Biomass continually sloughs off the support media and is separated in the final clarifier.
  • Fixed film processes may be configured for nitrification, requiring the addition of sequential aerobic zones.
  • Fixed film plants typically use less energy than suspended growth plants.
  • Sludge may be stabilized on-site through anaerobic or aerobic digestion and further thickened or dewatered prior to ultimate disposal. (See Biosolids Processing at the end of this section.)
  • Fixed film plants may or may not include disinfection. If there is no disinfection, the effluent from the secondary clarifier is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or as an energy input, such as UV radiation. Dechlorination, using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids
  • primary sludge
  • scum
  • secondary sludge, and
  • effluent.

 

7. Secondary Treatment Biological Nutrient Removal (Suspended Growth)

See text below for long description.

Summary
Biological Nutrient Removal (BNR) implies nitrification, de-nitrification and biological phosphorus removal. BNR plants are essentially activated sludge plants with anaerobic and anoxic zones ahead of the aerobic reactor and an aerated mixed liquor return to the anoxic zone. BNR plants can include any number of sequential anaerobic, anoxic and aerobic zones and the difference in configuration between them and a conventional plant is usually clear. Oxidation ditches can be converted to BNR by careful selection of the pumping rate and positioning of the raw influent feed.

Biological Phosphorus Removal (BPR) plants eliminate the secondary anoxic de-nitrification zone and aerated recycle but maintain the front-end anaerobic zone to promote the growth of a biomass containing a higher proportion of cellular phosphorus. Coagulants are not necessarily used in BPR plants, although coagulants may be used to achieve higher phosphorus removal efficiency.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Grit removal removes heavier settleable particles. Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.
  • Primary clarification removes a fraction of the solids and organics from the water stream, producing primary sludge and scum outputs.
  • The anaerobic and anoxic reactors ahead of aeration are usually mixed. The aerobic stage comprises a complete-mix reactor with either mechanical or diffused air aeration systems followed by a secondary clarifier. Return-activated sludge from the clarifier is combined with the incoming raw feed in the anaerobic reactor. The recycle flow rate to the anoxic zone is typically several times greater than the raw influent flow.
  • BNR facilities produce less sludge than plants using coagulants.
  • Primary and waste activated-sludge is usually stabilized on site through anaerobic or aerobic digestion and further thickened or dewatered prior to ultimate disposal. (See Biosolids Processing at the end of this section.)
  • BNR and BPR plants may or may not include disinfection. If there is no disinfection, the effluent from the secondary clarifier is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or as an energy input, such as UV radiation. Dechlorination, using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids
  • primary sludge
  • scum
  • waste-activated sludge, and
  • effluent.

 

8. Tertiary Treatment Activated Sludge (Suspended Growth) with Filtration

See text below for long description.

Summary
Tertiary plants typically involve the addition of filtration to a conventional activated sludge process for high solids' removal.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Grit removal removes heavier settleable particles. Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.
  • Primary clarification removes a fraction of the solids and organics from the water stream, producing primary sludge and scum outputs.
  • Coagulant may or may not be used to increase solids' removal in the primary clarifier. Typical coagulants used are metal salts -- aluminum sulphate or ferric chloride. If not used, this arrow input on the diagram is zero.
  • The secondary aerobic stage comprises a complete-mix reactor with either mechanical or diffused air aeration systems followed by a secondary clarifier. A portion of the sludge from the clarifier is recycled to maintain an optimal mixed-liquor concentration in the reactor. The reactor and separator phases of an activated sludge plant configured as a sequencing batch reactor, are combined in a single tank.
  • Coagulant for phosphorus removal may or may not be added prior to the secondary aerobic stage. If not, the input arrow in the diagram would be zero.
  • Typically, filters are a granular media that provide higher solids' removal through particle straining and physical-chemical reactions if coagulants are used.
  • Primary and waste-activated sludge is usually stabilized on site through anaerobic or aerobic digestion and further thickened or dewatered prior to ultimate disposal. (See Biosolids Processing at the end of this section.)
  • Tertiary-activated sludge plants may or may not include disinfection, although they are more likely to do so. If there is no disinfection, the effluent from the secondary clarifier is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or as an energy input, such as UV radiation. Dechlorination, using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids
  • primary sludge
  • scum
  • waste-activated sludge, and
  • effluent.

 

9. Tertiary Treatment Biological Nutrient Removal (Suspended Growth) with Filtration

See text below for long description.

Summary
Tertiary Biological Nutrient Removal (BNR) plants typically involve the addition of filtration to a conventional BNR process for high solids' removal.

Features

  • Screening removes larger solids and objects from the water stream. The size of material removed depends on the spacing of the bars.
  • Grit removal removes heavier settleable particles. Air may or may not be used for grit removal. If not, this arrow input on the diagram is zero and the rate of off-gassing will be lower.
  • Primary clarification removes a fraction of the solids and organics from the water stream, producing primary sludge and scum outputs.
  • The anaerobic and anoxic reactors ahead of aeration are usually mixed. The aerobic stage comprises a complete-mix reactor with either mechanical or diffused air aeration systems followed by a secondary clarifier. Return-activated sludge from the clarifier is combined with the incoming raw feed in the anaerobic reactor. The recycle flow rate to the anoxic zone is typically several times greater than the raw influent flow.
  • BNR facilities produce less sludge than plants using coagulants.
  • Typically, the filters are a granular media that provide higher solids' removal through particle straining and physical-chemical reactions if coagulants are used. Primary and waste-activated sludge is usually stabilized on site through anaerobic or aerobic digestion and further thickened or dewatered prior to ultimate disposal. (See Biosolids Processing at the end of this section.)
  • Tertiary BNR plants may or may not include disinfection, although they are more likely to do so. If there is no disinfection, the effluent from the secondary clarifier is released directly. If disinfection is provided, it could be through the input of an oxidant, such as chlorine, or as an energy input, such as UV radiation. Dechlorination, using a reducing agent such as sulphur dioxide, may or may not be practised prior to discharge.

Potential Sources of Reportable NPRI Substance Releases

  • air releases
  • screening solids
  • grit solids
  • primary sludge
  • scum
  • waste-activated sludge, and
  • effluent.

 

10. Biosolids Processing

Biosolids treatment is the stabilization of solids removed from primary and/or secondary sedimentation units. Treatment for biosolids can involve a series of processes. Figure 13 identifies typical biosolids processes, various combinations of which are in use for biosolids treatment at wastewater facilities. Each of these processes may result in air or on-site releases, or may result in transfers off site when biosolids are transported for disposal or land application.

Identify the biosolids treatment components applicable to your facility. These will assist you in identifying releases or transfer routes for your facility.

See text above for long description.

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