What term is used to refer to the deposits of foreign materials at the bottom of water bodies or wastewater lines?

The term "sludge" specifically refers to the deposits of foreign materials that accumulate at the bottom of water bodies or within wastewater lines. These deposits consist of organic and inorganic matter that settle due to gravity during the treatment processes in wastewater treatment plants. Sludge contains solids that are too heavy to remain suspended in the water and is a critical component in the treatment process, as it can be further processed or treated to reduce its volume and harmful potential.

In contrast, effluent refers to the treated water that is discharged from a treatment facility, while filtrate is the liquid that has passed through a filter, leaving solid particles behind. Biosolids are the organic solids generated from the treatment of sewage and can be reused as fertilizer or a soil amendment, but they undergo additional treatment and stabilization compared to sludge.