The screw press is a mechanical device that can press continuous fat-containing materials under very high pressure to squeeze out the oil, and then continuously discharge the pressed cake. Considerable efforts were made in the late 18th century to develop a continuously operating press because the intermittent operating hydraulic presses of that era were too labor intensive.
In 1900, Valerius D. Anderson invented a feasible continuous screw press. As early as 1876 he began working on the design of a continuous press and experimented with a series of screw conveyor-like devices. This unit has perforated walls and a baffle-type gate at the discharge end. However, each time the gate is closed, the product simply rotates with the axis. His major invention was to equip the spiral blade with a break in the middle (today's continuous screw oil press also operates on this principle). In 1990, he obtained a patent for his first combined press. It divided the spiral blade of the standard fine feeder into several segments and mounted them on a central shaft. There were no spiral blades in some places between the segments. The shaft was placed Enter the inside of the cylindrical shell. There are many holes in the shell to allow the grease to flow out. A spring-loaded conical throttle gate backpressures the material. The material rotates with the spiral but stops when it reaches the area where there is no spiral. This causes the shaft to push the material against the throttle gate device and generate sufficient pressure.
What is mentioned above is the earliest screw press developed. I wonder if the screw press you are talking about used in sewage treatment plants is used for oil extraction.