The activated sludge process is an
Aerobic suspended system
Understanding Activated Sludge Process Classification
The activated sludge process is a widely used biological wastewater treatment method. To classify it correctly, we need to understand two main aspects: the type of environment regarding oxygen (aerobic or anaerobic) and how the microorganisms are kept in the reactor (attached growth or suspended growth).
Aerobic Nature of Activated Sludge
The term "activated sludge" refers to biomass rich in microorganisms that are actively feeding on the organic matter in the wastewater. This process requires oxygen for the microorganisms to break down organic pollutants effectively. Air or pure oxygen is typically supplied to the aeration tank where the activated sludge is mixed with wastewater. Processes that require oxygen are called aerobic processes.
Suspended Growth in Activated Sludge Systems
In the activated sludge process, the microorganisms form biological flocs (clumps of microbes). These flocs are kept mixed and suspended within the liquid in the aeration tank. Unlike systems where microorganisms grow on a fixed surface (like rocks or plastic media in trickling filters or rotating biological contactors), the biomass in activated sludge is free-floating and mixed throughout the volume of the reactor. Systems where microorganisms are mixed and suspended in the liquid are called suspended growth systems.
Combining these two characteristics, the activated sludge process is an aerobic suspended growth system.
Comparing Options for Activated Sludge
Let's look at why the other options are not correct for the activated sludge process:
- Aerobic attached growth system: This describes processes like trickling filters or rotating biological contactors, where microbes grow as a film on a fixed medium, and the process is aerobic. Activated sludge does not use fixed media for growth; the biomass is suspended.
- Anaerobic attached growth system: This describes processes like anaerobic filters, where anaerobic microbes grow on a fixed medium. Activated sludge is aerobic, not anaerobic, and uses suspended growth, not attached growth.
- Anaerobic suspended growth system: This describes processes like anaerobic lagoons or upflow anaerobic sludge blanket (UASB) reactors, where anaerobic microbes are suspended or form granules in the liquid. Activated sludge is aerobic, not anaerobic.
Therefore, the activated sludge process fits the description of an aerobic suspended system.
| Characteristic | Aerobic Processes | Anaerobic Processes |
|---|---|---|
| Oxygen Presence | Required (Free oxygen) | Not required (Oxygen is toxic) |
| Example (Suspended Growth) | Activated Sludge | Anaerobic Lagoon, UASB |
| Example (Attached Growth) | Trickling Filter, RBC | Anaerobic Filter |
Revision Table: Activated Sludge Process
| Feature | Description |
|---|---|
| Process Type | Biological Wastewater Treatment |
| Oxygen Requirement | Aerobic (requires oxygen) |
| Biomass State | Suspended Growth (microbes mixed in liquid) |
| Microorganisms | Bacteria and other microbes forming flocs |
| Main Function | Removal of soluble and colloidal organic pollutants |
Additional Information on Activated Sludge
The activated sludge process typically involves several key components:
- Aeration Tank: Where wastewater is mixed with activated sludge and aerated to provide oxygen for microbial activity.
- Secondary Clarifier: A settling tank where the mixed liquor (mixture from the aeration tank) is sent. Here, the activated sludge flocs settle out by gravity, separating from the treated wastewater (effluent).
- Sludge Return System: A portion of the settled activated sludge (return activated sludge or RAS) is pumped back to the aeration tank to maintain a sufficient concentration of active microorganisms.
- Waste Sludge (WAS): The excess activated sludge is removed from the system as waste sludge for further treatment and disposal.
The efficiency of the process depends on factors like dissolved oxygen levels, mixing intensity, hydraulic retention time (HRT), and sludge retention time (SRT).
Important Questions from Sewage Treatment
Consider the following statements in respect of anaerobic sludge digester:
1. It is less expensive compared to several other methods available.
2. Processing of separable solids impacts the environment to a minimum.
3. Quantity of separated solids requiring disposal is minimal
4. Digested sludge is very readily dewatered able.
Which of the above statements are correct?Chlorine is sometimes used in sewage treatment:
Consider the following statements regarding contact stabilization process:
1. Primary settling tank is not required in some cases.
2. BOD removal occurs in two stages.
3. Aeration volume requirements are approximately 50% of those of a conventional – or tapered – aeration plant.
4. Returned sludge is aerated for 30 min to 90 min in sludge aeration tank.
Which of the above statements are correct?- A trickling filter is designed to remove ______
If the moisture content of sludge is reduced sludge is reduced from 98% to 96%, the volume of sludge will have decreased by ______.
