Plain sedimentation
Plain sedimentation is the operation in which impurities are separated by the gravitational settling of particles. It is a commonly used process in water and wastewater treatment plants to remove suspended solids and other impurities from the liquid.

Process
The process of plain sedimentation involves allowing the water to stand undisturbed in a sedimentation tank or basin. During this time, the heavier particles in the water settle down to the bottom of the tank due to gravity, forming a sediment layer. The clear water above the sediment layer is then removed for further treatment or use.

Gravity settling
Gravity settling is the principle on which plain sedimentation operates. It relies on the difference in density between the suspended particles and the water. Heavier particles such as sand, silt, and clay settle faster, while lighter particles and organic matter may take longer to settle. The settling process is influenced by factors such as particle size, shape, and concentration, as well as the temperature and velocity of the water.

Advantages
Plain sedimentation has several advantages in water and wastewater treatment:

1. Simple operation: The process is relatively simple and requires minimal equipment and maintenance.
2. Cost-effective: It is a cost-effective method for removing suspended solids and reducing turbidity in water.
3. Efficient removal: Plain sedimentation can remove a significant amount of suspended solids, including larger particles and coarser sediments.
4. Compatibility: It can be combined with other treatment processes, such as coagulation and filtration, for enhanced removal efficiency.

Limitations
Despite its advantages, plain sedimentation also has some limitations:

1. Slow process: Sedimentation can be a slow process, especially for fine particles, and may require a sufficient detention time in the sedimentation tank.
2. Inefficient for smaller particles: It may not effectively remove smaller particles or colloidal matter, which may require additional treatment processes.
3. Settled sludge handling: The accumulation of settled sludge at the bottom of the tank requires proper management and disposal to prevent odor, contamination, and operational issues.

In conclusion, plain sedimentation is an important operation in water and wastewater treatment plants for the removal of impurities through the gravitational settling of particles. It is a cost-effective and efficient method for reducing turbidity and removing larger suspended solids. However, it may not be suitable for the removal of smaller particles and may require additional treatment processes for complete purification.