Aeration Tank
Aeration tank is the correct option where aerobic bacteria breaks down organic waste present in sewage.
- Function:
In the aeration tank, sewage is mixed with oxygen to create an aerobic environment. This environment is conducive to the growth of aerobic bacteria, which break down organic waste through the process of oxidation.
- Process:
The aerobic bacteria in the aeration tank utilize the organic matter in the sewage as a food source. As they break down the organic waste, they also reproduce, increasing their population and further accelerating the breakdown process.
- Importance:
This aerobic breakdown of organic waste is crucial in sewage treatment as it helps to reduce the level of pollutants in the sewage, making it safer to discharge into the environment.
- Result:
By the time the sewage leaves the aeration tank, a significant portion of the organic waste would have been broken down by the aerobic bacteria, resulting in a cleaner effluent that can move on to further treatment processes.
In conclusion, the aeration tank plays a vital role in sewage treatment by providing the ideal conditions for aerobic bacteria to break down organic waste present in the sewage.

The correct answer is A: aeration tank.
The aeration tank is where aerobic bacteria breaks down organic waste present in sewage. Here is a detailed explanation:
Definition:
- An aeration tank is a component of a sewage treatment plant where the process of biological oxidation of organic matter takes place.
- It is also known as an activated sludge tank.
Function:
- The aeration tank provides an environment that promotes the growth of aerobic bacteria.
- These bacteria utilize oxygen to break down the organic waste present in sewage through the process of aerobic digestion.
Process:
- Sewage is initially collected in the primary settling tanks, where solid particles settle to the bottom and form sludge.
- The liquid portion, known as sewage effluent, is then transferred to the aeration tank.
- In the aeration tank, air or oxygen is continuously supplied to create a favorable environment for aerobic bacteria.
- The aerobic bacteria digest the organic waste, including organic compounds and nutrients, present in the sewage effluent.
- This digestion process results in the conversion of organic matter into carbon dioxide, water, and bacterial biomass.
- The bacterial biomass formed is known as activated sludge.
Advantages of Aeration Tank:
- The aeration tank facilitates the removal of organic matter, nutrients, and pathogens from sewage, leading to improved water quality.
- It helps in reducing the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the sewage effluent.
- The process of aerobic digestion in the aeration tank is efficient in breaking down complex organic compounds.
- It provides a controlled environment for the growth of beneficial bacteria, preventing the release of harmful substances into the environment.
In conclusion, the aeration tank is where aerobic bacteria breaks down organic waste present in sewage.