A grit removal unit for a wastewater system, comprising: a round grit removal chamber defined by a bottom surface and a substantially annular vertical wall extending up from said bottom surface; a substantially horizontal annular ring extending inwardly from the chamber substantially annular vertical wall to an inner edge having a radius R i, said ring being spaced above said chamber bottom surface; an influent channel through an opening in said chamber substantially annular vertical wall beneath said ring, said influent channel having one influent outer side wall substantially tangential to said chamber substantially annular vertical wall at said influent channel opening in said chamber substantially annular vertical wall, and an influent inner side wall having a substantially flat portion parallel to said one influent outer side wall and a curved portion extending between the chamber bottom surface and the ring, said influent inner side wall curved portion having said radius R i and extending through an arc of at least about 90 degrees, said influent channel having its outlet at an end of the influent inner side wall curved portion; and an effluent channel through an opening in said chamber substantially annular vertical wall above said ring, said effluent channel having one effluent outer side wall substantially tangential to said chamber substantially annular vertical wall at said effluent channel opening in said chamber substantially annular vertical wall, and an effluent inner side wall having a substantially flat portion parallel to said one effluent outer side wall and a curved portion extending upwardly from said ring, said effluent inner side wall curved portion having said radius R i and extending through an arc of at least about 90 degrees, said effluent channel having its inlet at an end of the effluent inner side wall curved portion. a round grit removal chamber defined by a bottom surface and a substantially annular vertical wall extending up from said bottom surface; a substantially horizontal annular ring extending inwardly from the chamber substantially annular vertical wall to an inner edge having a radius R i, said ring being spaced above said chamber bottom surface; an influent channel through an opening in said chamber substantially annular vertical wall beneath said ring, said influent channel having one influent outer side wall substantially tangential to said chamber substantially annular vertical wall at said influent channel opening in said chamber substantially annular vertical wall, and an influent inner side wall having a substantially flat portion parallel to said one influent outer side wall and a curved portion extending between the chamber bottom surface and the ring, said influent inner side wall curved portion having said radius R i and extending through an arc of at least about 90 degrees, said influent channel having its outlet at an end of the influent inner side wall curved portion; and an effluent channel through an opening in said chamber substantially annular vertical wall above said ring, said effluent channel having one effluent outer side wall substantially tangential to said chamber substantially annular vertical wall at said effluent channel opening in said chamber substantially annular vertical wall, and an effluent inner side wall having a substantially flat portion parallel to said one effluent outer side wall and a curved portion extending upwardly from said ring, said effluent inner side wall curved portion having said radius R i and extending through an arc of at least about 90 degrees, said effluent channel having its inlet at an end of the effluent inner side wall curved portion.