Q1: In case of Imhoff tanks,

ANS:E - All the above.

1. The shape is rectangular: Imhoff tanks have a unique design that consists of two chambers, one above the other. The upper chamber is a settling compartment, while the lower chamber is a digestion compartment. While the overall structure resembles a rectangular tank, the internal configuration involves distinct partitions that separate the settling and digestion chambers.
2. Detention period is 2 hours: The detention period refers to the amount of time sewage remains in the tank for settling and digestion processes. In the case of Imhoff tanks, the detention period is typically longer than 2 hours. This extended detention allows for adequate settling of solids in the upper chamber and subsequent digestion of settled sludge in the lower chamber.
3. The velocity of flow is restricted to 0.30 m/minute: Imhoff tanks operate at low flow velocities to facilitate effective settling of suspended solids. The flow velocity within the tank is intentionally restricted to promote sedimentation of solids and separation of liquid from sludge. The specified velocity restriction ensures that turbulence is minimized, allowing solids to settle efficiently.
4. Surface loading is limited to 30,000 litres/m² of plan area per day: Surface loading refers to the rate at which sewage is applied to the surface area of the tank. Imhoff tanks are designed to handle a specific surface loading to prevent overloading and ensure optimal performance. The specified limit of 30,000 litres per square meter of plan area per day helps maintain proper hydraulic and treatment capacities within the tank.