Hint: The first aim in water treatment is that the elimination of any pathogenic microorganisms present. When water has little or no movement suspended solids sink to the underside under the force of gravity and form a sediment.
Complete step-by-step answer:
Sedimentation is that the process of allowing particles in suspension in water to settle out of the suspension under the effect of gravity. The particles that settle out from the suspension become sediment, and in water treatment is thought as sludge. When a thick layer of sediment continues to settle, this can be referred to as consolidation.
In water treatment sedimentation could be accustomed to reduce the concentration of particles in suspension before the applying of coagulation, to scale back the number of coagulating chemicals needed, or after coagulation and, possibly, flocculation. When sedimentation is applied after coagulation, its purpose is typically to cut back the concentration of solids in suspension in order that the following filtration can function most effectively.
Sedimentation is one in all several methods for application before filtration: other options include dissolved air flotation and a few methods of filtration. Generically, such solids-liquid separation processes are sometimes brought up as clarification processes.
Methods for sedimentation include horizontal flow, radial flow, inclined plate, ballasted floc and floc blanket sedimentation.
When particle concentration increases beyond about 1% then adjacent particles progressively affect, i.e. Hinder, the behaviour of every other. If particle concentration increases from 8% v/v, the suspension is within a fully hindered regime. The properties of the suspension are now a function of the volumetric concentration of the particles within the suspension.
For particle concentrations greater than about 18% v/v, the upper interface between the water and suspension should be distinct. For concentrations but about 18%, the interface is diffuse, increasingly so with smaller concentrations.
When particle concentration is about 26% v/v adjacent particles become in permanent contact with one another specified the suspension enters the thickening regime. Hindered settling in water treatment exploits suspensions with concentrations between about 12 and 22% v/v. A suspension during this range is named a floc blanket, which is truly a fluidised bed.
Therefore, the correct option is A, true.
Note: Sedimentation reduces water turbidity, but it's not consistently effective in reducing microbial contamination. However, turbidity reductions often improve microbial reductions by physical and chemical disinfection processes, like solar treatment and chlorination, respectively. Sedimentation or gravity settling of highly turbid water is suggested as a pretreatment for systems. Furthermore, sedimentation of particles improves the aesthetic qualities of the water and thereby increases its acceptance by consumers. Pretreatment of turbid household water by sedimentation is usually recommended because it requires a minimum of materials or skill.