n extended aeration sewage treatment plant (STP) is a biological wastewater treatment system that provides an extended period of aeration to promote the growth of microorganisms that break down organic matter in sewage. This process typically involves maintaining aerobic conditions for an extended duration, which allows for effective treatment of wastewater. It’s commonly used for municipal and industrial wastewater treatment.

The extended aeration sewage treatment plant (STP) works through a biological wastewater treatment process that involves the following steps:

1. Inflow: Wastewater from homes, industries, or other sources is collected and directed into the treatment plant.

2. Screening and Primary Treatment: Large solids and debris are removed from the wastewater through screens and settling tanks.

3. Aeration Tank: The primary wastewater is then introduced into the aeration tank, which is a key component of the extended aeration process. Here, air is continuously pumped into the tank to create aerobic (oxygen-rich) conditions.

4. Microbial Growth: Microorganisms, such as bacteria and fungi, are naturally present in the wastewater or added as part of the treatment process. In the aerated environment of the tank, these microorganisms begin to multiply and feed on the organic pollutants in the wastewater.

5. Biological Treatment: Over an extended period (usually 24-48 hours or longer), the microorganisms break down organic matter and pollutants in the wastewater into simpler, less harmful substances, primarily carbon dioxide and water. This biological treatment phase is what distinguishes extended aeration from other sewage treatment methods.

6. Secondary Clarifier: After the aeration and biological treatment phase, the treated wastewater flows into a secondary clarifier. Here, the microorganisms and any remaining suspended solids settle to the bottom of the tank as sludge.

7. Treated Effluent: The clear, treated effluent at the top of the secondary clarifier is discharged or subjected to further treatment processes if necessary.

8. Sludge Handling: The sludge collected at the bottom of the clarifier can be treated further or dewatered to reduce its volume before disposal.

9. Return of Microorganisms: In many extended aeration systems, some of the microorganisms from the clarifier are returned to the aeration tank to maintain a healthy population.

This process relies on the natural action of microorganisms to break down organic pollutants, making it an environmentally friendly method of sewage treatment. Extended aeration STPs are often chosen for their effectiveness in treating wastewater with minimal chemical use and energy consumption.