Attached Growth Processes in Secondary Wastewater Treatment

Secondary wastewater treatment is an essential process in removing organic and inorganic pollutants from wastewater after primary treatment. There are various methods used for secondary treatment, including both suspended growth and attached growth processes. Attached growth processes involve the growth of microorganisms on a medium or support surface, allowing them to form a biofilm that treats the wastewater.

The following secondary wastewater treatment methods are examples of attached growth processes:

1. Trickling Filter:
- In a trickling filter, wastewater is distributed over a bed of rocks, gravel, or plastic media.
- The media provides a large surface area for the growth of microorganisms, which form a biofilm on the media surface.
- As wastewater trickles over the biofilm, the microorganisms break down organic matter, converting it into carbon dioxide and water.
- The treated wastewater then passes through the filter bed and is collected for further treatment or discharge.

2. Bio Tower:
- A bio tower is a vertical structure filled with a packing material, such as plastic or wooden media.
- Wastewater is sprayed onto the top of the tower, allowing it to flow down through the media.
- Microorganisms attach to the media and form a biofilm, which degrades organic contaminants in the wastewater.
- The biofilm also provides a large surface area for the transfer of oxygen from the air to the microorganisms, promoting aerobic treatment.

3. Rotating Biological Contactor (RBC):
- In an RBC, a series of circular discs or cylinders are partially submerged in the wastewater.
- As the discs rotate, microorganisms grow on their surface, forming a biofilm.
- As the biofilm comes into contact with the wastewater, it metabolizes organic matter and nutrients.
- The rotation of the discs provides aeration to the biofilm, ensuring an oxygen-rich environment for the microorganisms.

Conclusion:
In summary, the trickling filter, bio tower, and rotating biological contactor are all examples of attached growth processes used in secondary wastewater treatment. These processes involve the growth of microorganisms on a medium or support surface, forming a biofilm that treats the wastewater by breaking down organic matter and promoting aerobic treatment.

Activated sludge process is an example of suspended growth process.