Abstract: The present invention relates to an up-flow rake bar screen having a multiplicity of bars which are parallel to one another and which are spaced from one another across the screen. At least a portion of each bar is curved so that, when that portion is viewed from a position at which, when the screen is in use, fluid has not yet passed through the screen, that portion of the bar appears convex.

Abstract: The invention relates to the treatment of liquid waste such as sewage. The invention provides a method of screening of liquid waste to remove solid material therefrom, comprising passing the liquid waste in a downward stream through a suspended sack filter, and agitating the sack filter and the liquid stream by discharging a stream of bubbles upwardly through the liquid from below the sack filter. The invention also provides an inlet screen, comprising an upright hollow column (1), having an opening at the top across which a sack filter (6) is positioned, the sack filter extending downwardly into the column, and an air diffuser (8) at the lower end of the column, and an outlet (5, 23, 34) from the column, whereby in use liquid waste flows into the top of the column, through the sack filter to the outlet, the sack filter and liquid waste being agitated by discharge of air from the air diffuser.