Comminutors or Shredders are the patented devices, which break the larger sewage solids to about 6 mm in size when the sewage is screened through them. Such a device consists of a revolving slotted drum, through which the sewage is screened (Fig.) Cutters mounted on the drum, shear the collected screenings against a comb until they are small enough to pass through 5 mm to 10 mm ‘wide slots of the drum. These are usually arranged in through 5 mm to 10 mm wide slots of the drum. These are usually arranged in pairs to facilitate repairs and maintenance. Comminutors are of recent origin and eliminate the problem of disposal of screening, by reducing the solids to a size which can be processed elsewhere in the plant. They should always be preceded by grit chambers to prevent their excessive wear.