Comminuters may be located in open channels for straight-through flow or at the end of a channel with a bottom discharge. Solids from comminuters and grinders can cause problems in downstream processes if deposits of plastic or other inorganic matter are allowed to accumulate in aeration and digestion tanks. A comminuter consists of a slotted drum that slowly rotates on a vertical axis. Grinders, or macerators, consist of two sets of shaft-mounted, counter-rotating, and intermeshing cutters that trap solids and chop, rather than shred, them into smaller particles. Grit and other solids can result in severe wear on grinders, and routine inspection of the cutter teeth and bearings is required. As an alternative to screening systems that remove solids from influent steams, some wastewater treatment plants use either comminuters or grinders to reduce solids into particles ranging in size from 1/4″ to 3/4″ without removing them from the flow.