The device used for aeration in the combined aerator is the Diffuser plate and paddles.

Explanation:
The combined aerator is a type of equipment used for the treatment of wastewater. It is designed to provide both aeration and mixing in a single unit. The device used for aeration in the combined aerator is the diffuser plate and paddles.

Function of the Diffuser Plate:
The diffuser plate is a perforated plate that is located at the bottom of the combined aerator. It is responsible for releasing air into the wastewater. The air is distributed evenly across the surface of the diffuser plate through small holes or nozzles. This ensures that the air is dispersed uniformly throughout the wastewater, promoting efficient aeration.

Function of the Paddles:
The paddles in the combined aerator are rotating mechanical components that are attached to a central shaft. The paddles are responsible for mixing the wastewater and creating turbulence. As the paddles rotate, they create a swirling motion in the wastewater, which helps in dispersing the air and promoting the contact between the air and the wastewater.

Working of the Diffuser Plate and Paddles:
When the combined aerator is in operation, air is supplied to the diffuser plate through an air blower. The diffuser plate releases the air bubbles into the wastewater. At the same time, the paddles rotate, creating a swirling motion in the wastewater. This motion helps in distributing the air bubbles throughout the wastewater and promoting the contact between the air and the organic matter present in the wastewater.

Advantages of the Diffuser Plate and Paddles:
1. Efficient Aeration: The diffuser plate ensures that the air is distributed evenly and uniformly across the wastewater, maximizing the contact between the air and the organic matter. This promotes efficient aeration and enhances the degradation of organic pollutants.
2. Effective Mixing: The paddles create turbulence and mixing in the wastewater, ensuring that the air bubbles are dispersed throughout the wastewater. This helps in achieving uniform aeration and enhances the oxygen transfer efficiency.
3. Compact Design: The combined aerator with diffuser plate and paddles is a compact unit that combines aeration and mixing in a single device. This saves space and simplifies the wastewater treatment process.

In conclusion, the diffuser plate and paddles are essential components of the combined aerator for efficient aeration and mixing in the treatment of wastewater.