4 Different Ways to Remember Sewage Treatment Plant – 1st
Raw Sewage Inlet
Introduction of untreated sewage into the treatment plant.
Large Debris and Grit Removal
Removal of large debris and trapping of grit. Formation of primary sludge.
Difference: Primary sludge comprises settleable solids, grit, and other large materials.
BOD: High
Sequential Filtration
Further removal of suspended solids and finer particles. Clarification of water. Formation of secondary sludge.
BOD: Moderate
Sedimentation Tank
Settling of suspended solids. Clarification of water. Formation of tertiary sludge.
Difference: Secondary sludge is formed from the sedimentation of remaining suspended solids.
BOD: Moderate
Dissolved Oxygen: Low
Aeration Tanks
Biological degradation of organic matter. Mechanical aeration for aerobic microbial growth. Formation and maintenance of activated sludge. Reduction of Biochemical Oxygen Demand (BOD). Formation of flocs.
Flocs Contain: Aggregates of fungi and bacteria, aiding in settling and removal from the treated water.
Inoculum Role: Introduction of a small portion of activated sludge back into the aeration tank to seed and accelerate microbial growth.
BOD: Low
Dissolved Oxygen: High
Settlement Tanks
Settling of activated sludge. Separation of treated effluent from residual sludge. Clarification of water.
BOD: Low
Dissolved Oxygen: High
Anaerobic Digester
Anaerobic digestion of sludge. Production of biogas. Stabilization of sludge. Formation of digested sludge.
Biogas Production: Microbial digestion produces methane-rich biogas, a source of renewable energy.
Components of Biogas: Methane, Carbon Dioxide, Hydrogen Sulfide
BOD: Low
4 Different Ways to Remember Sewage Treatment Plant – 2nd
| Raw Sewage Inlet | |
|---|---|
| Introduction of untreated sewage into the treatment plant |
| Large Debris and Grit Removal (Primary/Physical Treatment) | |
|---|---|
| Removal of large debris | |
| Trapping of grit | |
| Initial physical separation | |
| Formation of primary sludge | |
| Difference: Primary sludge comprises settleable solids, grit, and other large materials. | |
| BOD: High |
| Sequential Filtration (Primary/Physical Treatment) | |
|---|---|
| Further removal of suspended solids and finer particles | |
| Filtration with decreasing pore sizes | |
| Clarification of water | |
| Formation of secondary sludge | |
| BOD: Moderate |
| Sedimentation Tank (Primary/Physical Treatment) | |
|---|---|
| Settling of suspended solids | |
| Clarification of water | |
| Formation of tertiary sludge | |
| Difference: Secondary sludge is formed from the sedimentation of remaining suspended solids. | |
| BOD: Moderate | |
| Dissolved Oxygen: Low |
| Aeration Tanks (Secondary/Biological Treatment) | |
|---|---|
| Biological degradation of organic matter | |
| Mechanical aeration for aerobic microbial growth | |
| Formation and maintenance of activated sludge | |
| Reduction of Biochemical Oxygen Demand (BOD) | |
| Formation of flocs | |
| Flocs Contain: Aggregates of fungi and bacteria, aiding in settling and removal from the treated water. | |
| Inoculum Role: Introduction of a small portion of activated sludge back into the aeration tank to seed and accelerate microbial growth. | |
| BOD: Low | |
| Dissolved Oxygen: High |
| Settlement Tanks (Secondary/Biological Treatment) | |
|---|---|
| Settling of activated sludge | |
| Separation of treated effluent from residual sludge | |
| Clarification of water | |
| BOD: Low | |
| Dissolved Oxygen: High |
| Anaerobic Digester (Secondary/Biological Treatment) | |
|---|---|
| Anaerobic digestion of sludge | |
| Production of biogas | |
| Stabilization of sludge | |
| Formation of digested sludge | |
| Biogas Production: Microbial digestion produces methane-rich biogas, a source of renewable energy. | |
| Components of Biogas: Methane, Carbon Dioxide, Hydrogen Sulfide | |
| BOD: Low |
4 Different Ways to Remember Sewage Treatment Plant – 4th
+------------------------------------+
| Raw Sewage Inlet |
| |
| - Introduction of untreated |
| sewage into the treatment |
| plant |
+-------------------+----------------+
|
v
+------------------------------------+
| Large Debris and Grit Removal |
| (Primary/Physical Treatment) |
| |
| - Removal of large debris |
| - Trapping of grit |
| - Initial physical separation |
| - Formation of primary sludge |
| |
| Difference: |
| Primary sludge comprises |
| settleable solids, grit, and |
| other large materials. |
| |
| BOD: High |
+-------------------+----------------+
|
v
+------------------------------------+
| Sequential Filtration |
| (Primary/Physical Treatment) |
| |
| - Further removal of suspended |
| solids and finer particles |
| - Filtration with decreasing |
| pore sizes |
| - Clarification of water |
| - Formation of secondary sludge |
| |
| BOD: Moderate |
+-------------------+----------------+
|
v
+------------------------------------+
| Sedimentation Tank |
| (Primary/Physical Treatment) |
| |
| - Settling of suspended solids |
| - Clarification of water |
| - Formation of tertiary sludge |
| |
| Difference: |
| Secondary sludge is formed |
| from the sedimentation of |
| remaining suspended solids. |
| |
| BOD: Moderate |
| Dissolved Oxygen: Low |
+-------------------+----------------+
|
v
+------------------------------------+
| Aeration Tanks |
| (Secondary/Biological Treatment)|
| |
| - Biological degradation of |
| organic matter |
| - Mechanical aeration for |
| aerobic microbial growth |
| - Formation and maintenance of |
| activated sludge |
| - Reduction of Biochemical |
| Oxygen Demand (BOD) |
| - Formation of flocs |
| |
| Flocs Contain: |
| - Aggregates of fungi and |
| bacteria, aiding in settling |
| and removal from the treated |
| water. |
| |
| Inoculum Role: |
| Introduction of a small portion |
| of activated sludge back into |
| the aeration tank to seed and |
| accelerate microbial growth. |
| |
| BOD: Low |
| Dissolved Oxygen: High |
+-------------------+----------------+
|
v
+------------------------------------+
| Settlement Tanks |
| (Secondary/Biological Treatment) |
| |
| - Settling of activated sludge |
| - Separation of treated effluent |
| from residual sludge |
| - Clarification of water |
| |
| BOD: Low |
| Dissolved Oxygen: High |
+-------------------+----------------+
|
v
+------------------------------------+
| Anaerobic Digester |
| (Secondary/Biological Treatment)|
| |
| - Anaerobic digestion of sludge |
| - Production of biogas |
| - Stabilization of sludge |
| - Formation of digested sludge |
| |
| Biogas Production: |
| Microbial digestion produces |
| methane-rich biogas, a source |
| of renewable energy. |
| |
| Components of Biogas: |
| - Methane |
| - Carbon Dioxide |
| - Hydrogen Sulfide |
| |
| BOD: Low |
+------------------------------------+
Updated One
+------------------------------------+
| Raw Sewage Inlet |
| |
| - Introduction of untreated |
| sewage into the treatment |
| plant |
+-------------------+----------------+
|
v
+------------------------------------+
| Large Debris and Grit Removal |
| (Primary/Physical Treatment) |
| |
| - Removal of large debris |
| - Trapping of grit |
| - Initial physical separation |
| - Formation of primary sludge |
| |
| BOD: High |
+-------------------+----------------+
|
v
+------------------------------------+
| Sequential Filtration/Sedimentation |
| (Primary/Physical Treatment) |
| |
| - Further removal of suspended |
| solids and finer particles |
| - Filtration/sedimentation for |
| clarification of water |
| - Formation of secondary sludge |
| |
| BOD: Moderate |
+-------------------+----------------+
|
v
+------------------------------------+
| Activated Sludge Process |
| (Secondary/Biological Treatment) |
| |
| - **Aerobic biological treatment**|
| - Introduction of primary or |
| secondary sludge and raw wastewater|
| - Aeration tanks with mechanical |
| agitation for oxygen supply |
| - Growth and activity of activated|
| sludge microorganisms |
| - Biodegradation of organic matter|
| - Reduction of BOD |
| - Formation of flocs (sludge aggregates) |
| |
| Components of Activated Sludge: |
| - Bacteria |
| - Fungi |
| - Protozoa |
| |
| Inoculum Role: |
| - Introduction of a small portion |
| of existing activated sludge to |
| seed and accelerate microbial |
| growth. |
| |
| Flocs Function: |
| - Capture and remove organic matter|
| from wastewater |
| |
| BOD: Low |
| Dissolved Oxygen: High |
+-------------------+----------------+
|
v
+------------------------------------+
| Settlement Tanks |
| (Secondary/Biological Treatment) |
| |
| - Settling of activated sludge |
| - Separation of treated effluent |
| from residual sludge |
| - Clarification of water |
| |
| BOD: Low |
| Dissolved Oxygen: High |
+-------------------+----------------+
|
v
+------------------------------------+
| Anaerobic Digester (Optional) |
| (Tertiary/Sludge Treatment) |
| |
| - Stabilization and volume reduction |
| of sludge under anaerobic conditions |
| - Biogas (methane) production |
| |
| BOD: Low |
+------------------------------------+
**Key Differences between Sludge Types:**
| Sludge Type | Formation | BOD (Biological Oxygen Demand) | Dissolved Oxygen |
|------------------|--------------------------------------------------------|----------------------------------|------------------|
| Primary Sludge | Settling of large particles in primary treatment | High | Low |
| Secondary Sludge | Settling of remaining suspended solids in secondary treatment | Moderate | Moderate |
| Activated Sludge | Growth and aggregation of microorganisms in aeration tanks | Low | High |
Note:
The diagram now includes a box specifically focusing on the activated sludge process, highlighting its key components and functions.
The composition and characteristics of activated sludge are detailed:
Microbial community: Composed of bacteria, fungi, and protozoa, each playing specific roles in organic matter degradation.
Flocs: Aggregates of activated sludge microorganisms and organic matter, facilitating the capture and removal of pollutants from the wastewater.
Inoculum: A small portion of existing activated sludge introduced to seed and accelerate the growth of the microbial community in new batches.
The differences between primary, secondary, and activated sludge in terms of formation, BOD, and dissolved oxygen levels are summarized in a table for clarity.
The diagram is updated with the optional inclusion of an anaerobic digester for sludge stabilization and biogas production.