Q1: In a grit chamber of a sewage treatment plant,

ANS:D - all the above.

1. Flow velocity 0.15 m to 0.3 m/sec is kept: Grit chambers are designed to allow the settling of heavy particles, such as sand, gravel, and other debris, from wastewater. To facilitate the settling process, an appropriate flow velocity range is maintained within the grit chamber. Typically, flow velocities between 0.15 m/s to 0.3 m/s are maintained to ensure that the heavier particles settle effectively without being carried away by the flow.
2. Depth of 0.9 m to 1.20 m is kept: The depth of the grit chamber is an important parameter in ensuring effective grit removal. By maintaining a certain depth range, typically between 0.9 m to 1.20 m, there is sufficient hydraulic retention time for sedimentation to occur. The depth allows for the settling of grit particles while allowing the lighter organic matter to remain in suspension and be carried further downstream.
3. One minute of detention period is kept: The detention time, or hydraulic retention time, refers to the average length of time that wastewater remains in the grit chamber. A detention period of one minute is commonly used in grit chambers to provide sufficient time for settling to occur. During this time, the flow velocity is controlled to allow particles to settle out of the wastewater before it continues through the treatment process.

Therefore, all of the statements provided are accurate in describing the operational parameters typically maintained in a grit chamber of a sewage treatment plant. These parameters are essential for ensuring effective grit removal and overall treatment efficiency within the plant.