The correct answer is: C. More and less.
Detention time is the length of time that water remains in a sedimentation tank. Overflow rate is the rate at which water flows over the top of a sedimentation tank.
In plain sedimentation, the detention time is typically longer than in sedimentation with coagulation. This is because the particles in plain sedimentation are not destabilized, so they take longer to settle out of the water.
The overflow rate is typically lower in plain sedimentation than in sedimentation with coagulation. This is because the particles in plain sedimentation are not destabilized, so they do not settle out of the water as quickly.
Coagulation is a process that destabilizes particles in water, making them easier to settle out. This is done by adding a chemical called a coagulant, which causes the particles to form larger flocs. These flocs are then able to settle out of the water more quickly.
As a result of coagulation, the detention time required for sedimentation is reduced. This is because the flocs settle out of the water more quickly, so they do not need to remain in the sedimentation tank for as long.
The overflow rate is also increased in sedimentation with coagulation. This is because the flocs are larger and settle out of the water more quickly, so they do not need to be removed from the sedimentation tank as quickly.