A screen assembly configured to separate coarse (larger) and fine (small) materials from an effluent flow. The assembly includes a plurality of bars having different heights. The bars are arranged to form larger spaces for separating coarser material from the effluent flow, and arranged to form smaller spaces for separating finer materials from the effluent flow. The effluent flows into the larger spaces first, and subsequently flows out of the smaller spaces. The assembly includes a cleaning device operable to remove the materials from both the large and small spaces.