From a structural point of view, the screen is a perforated metal plate or a metal grid, according to the nature of floating debris is removed and sizing of the screen perforation size. According to its aperture size can be divided into coarse filter machine and microfiltration; different forms according to the installation, the screen can be divided into fixed, rotary and electric rotary three.
(1) Fixed Screen: Fixed mesh pattern of attempts to prevent the wedge-shaped grid, the size of 0.25 ~ 1.5mm, according to the characteristics of the water quality of wastewater treatment, the gridlines on the screen and then covered with 16 ~ 100 mesh stainless steel mesh or nylon mesh.
(2) Rotary screen: rotary hydraulic rotary screen and the screen has two kinds trommel drum. Hydraulic rotary screen circular table-shaped, with a certain velocity sewage into the small end, impact and gravity of water makes the rotating sieve, the water is filtered in the flow process from small to big-endian end of the impurities from the large end down scum trough.
(3) Electric rotary: Electric rotary is usually installed in the pressure pipe, sieve diameter of 5μm ~ 5mm. Small perforations, retention of suspended matter much, will increase the number of cleanings.