5. Sludge treatment, reuse and disposal. Sludge is produced from the treatment of wastewater in on-site (e.g. septic tank) and off-site (e.g. activated sludge) systems. This is inherently so because a primary aim of wastewater treatment is removing solids from the wastewater.
Definition of central. 1  1 : containing or constituting a center. 2  2 : of primary importance : essential, principal the central character of the novel. 3  3a : situated at, in, or near the center the central part of the stateb : easily accessible from outlying districts a central location for the new theater.
fictional character, fictitious character, character(noun) an imaginary person represented in a work of fiction (play or film or story) she is the main character in the novel. quality, character, lineament(noun) a characteristic property that defines the apparent individual nature of something.