Step Screens

Step screens installed downstream of bar screens are used in lieu of primary treatment at some treatment plants. This configuration increases downstream liquid and sludge processing by removing the fine solids at the headworks. In particular, the use of step screens for fine screening has been noted for decrease the amount of sludge produced.

The screen is composed of two thin vertical stainless steel plates that are shaped like steps, one of the plates is stationary, while the other rotates. The stationary and rotating stainless steel step plates alternate across the width of the channel opening forming the step screen face.

The rotating plate rotates in an upright motion. As it gyrates through this motion, debris is collected on the face of the screen which is lifted to the subsequent steps with every rotating motion.

Thus, transferring the solids to the discharge point where they are washed and brushed into a compactor or storage hopper. The continuous motion of rotating steps provides self cleaning for the screening surface, eliminating the need for addition cleaning devices such as brushes and spray bars.

Space opening for step screen plates typically range between 3 to 6 mm or (0.12 to 0.24 in [metric system chart]), in some cases openings may be as small as 1 mm or (0.04in). Because the openings are so small, solids collect on the face of the screen creating a screening carpet that further enhances the solids capture of the step screen.