Open impeller is the correct type of impeller used for centrifugal pumps dealing with water containing slurry and sewage. The other options mentioned, such as one-side shrouded impeller, two-side shrouded impeller, and double section impeller, are not specifically designed for handling slurry and sewage.

Below are the details explaining why an open impeller is the appropriate choice for this application:

1. Open Impeller:
An open impeller consists of blades mounted on a shaft without any shrouds or coverings. It is characterized by its simplicity, easy maintenance, and ability to handle slurry and sewage effectively. The open design allows solids, such as slurry particles and sewage debris, to pass through without clogging or blocking the impeller.

2. Handling Slurry:
Slurry is a mixture of water and solid particles, which can be abrasive and cause wear and tear on pump components. The open impeller design is less prone to blockages and damage from abrasive particles, as the solids can pass through the impeller freely. This feature helps to maintain the pump's efficiency and prolong its service life when dealing with slurry.

3. Handling Sewage:
Sewage contains various solid materials, including human waste, toilet paper, and other debris. The open impeller design allows the pump to handle sewage without clogging or jamming. The absence of shrouds or coverings prevents the accumulation of solids around the impeller, ensuring smooth operation and reducing the risk of pump failure.

4. Easy Maintenance:
Since the open impeller does not have any shrouds or coverings, it is easier to inspect, clean, and maintain. The absence of complicated parts simplifies the maintenance process, reducing downtime and associated costs.

In summary, an open impeller is the ideal choice for centrifugal pumps dealing with water containing slurry and sewage due to its ability to handle solids without clogging or jamming, resistance to wear from abrasive particles, and ease of maintenance.