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 . <EOS>