ABSTRACT
The minor residuals of wastewater treatment include scum, grit, and screenings. Grit is invariably landfilled, and there is virtually no reuse of this material. Screenings are usually landfilled and occasionally ground and released to the digester, a management practice that is falling out of favor since screenings digest very poorly. Scum floats on the surface of the wastewater and could be considered to be the aggregate bathtub ring of the wastewater collection area. Scum contains flotables, which include most of the plastics that reach the wastewater treatment plant. Plastics articles in the influent flow include plastic tampon applicators, condoms, and adhesive bandages. Plastic tampon applicators are most commonly associated with scum, although they reach the beaches through a number of pathways. During primary treatment, scum is collected from the surface of the sedimentation tanks or skimming tanks.
