Abstract: A rotating drum screen method for separating solids from thin stillage obtained from ethanol fermentation, the thin stillage comprising one or more of solids and suspended solids. Thin stillage is chemically treated with an anionic polymer to form stable particles of one or more of solids and suspended solids. Introducing the treated thin stillage into a rotating drum screen system. The drum screen includes a filter screen that retains at least a portion of the solids within a hollow portion of the drum screen and which produces a liquid effluent that is discharged from an outer surface of the drum screen. The retained solids are removable from the drum screen via a solid discharge end. A head box is disposed within the hollow portion of the drum screen and has a plurality of fluid flow channel dividers dividing and directing an influent stream outwardly against the drum screen.