What type of sludge is the most common residual produced in water plant sedimentation basins?

The most common type of sludge produced in water plant sedimentation basins is alum sludge. This is primarily because alum, or aluminum sulfate, is widely used as a coagulant during the water treatment process. When alum is added to raw water, it causes particles to clump together (a process known as flocculation), making it easier for them to settle out during sedimentation. The resulting settled material is referred to as alum sludge.

This type of sludge contains not only the residual aluminum from the coagulant but also the aggregated particles that have been removed from the water. Since sedimentation basins are designed specifically to allow this settling process to occur, the alum sludge becomes the predominant residual, especially in systems employing alum for coagulation.

Other types of sludge, while they may contribute in certain conditions or systems, are not as predominant in standard water treatment operations focused on sedimentation. Understanding the role of coagulants like alum in the water treatment process is critical when discussing sludge types produced in treatment facilities.