Step screens are installed in wastewater treatment plants, after separation of large waste solids , to protect another equipment from damage or to avoid interruption of further treatment processes.
Step screens are intended for fine treatment and collect waste of fine and medium sizes from industrial and domestic wastewater, which then removed and discharged to the transporter or the waste bin.
The screens are intended for use in wastewater with a pH of 6.5-8.5.
Screens of different dimensions are made of stainless steel AISI 304 (or AISI 316, on demand). Dimensions of the step screens are selected depending on required flow rate, wastewater solids and dimensions of the channels as well as wastes’ treatment/transport methods
Step screens consist of two sets of plate blocks (movable and fixed) that are made of stainless steel and mounted into the screens’ frames. Movable and fixed plates are placed one between another, while space between them is ensured by special inserts made of stainless steel. The solids are moved periodically to the top edge of the frame via the plane parallel circular motion of the movable plate block. Transporting part of the plate block (not submerged) can be made of plastic material.
The spacing between plates in standard realization varies from 3 to 6 mm.
The grid is installed onto a special prop, which is adjusted to the floor on both sides of the channel. The screen is therefore fastened to the cross beam and it is possible to lift the screen over the channel for its maintenance. When the screen is being installed in limited space conditions, e.g. in short channel when there is no possibility to lift the screen mounted on axis, special telescopic prop is used.
A pneumatic sand removal device is installed on the screen bottom. The purpose of this is to remove the obstacles which can disrupt the plate block movement.
Due to the step screen operation principle, the contamination layer (which is formed on the working surface), creates an additional filtering effect. It allows to extract contaminants much smaller than screen’s spacing. The screen's operation periodicity depends on the equipment automation scheme
Screen automation can be done according to different parameters:
Alarm systems of the normal operation indication, the emergency stops, the wastewater maximum level in the channel and others are provided. It is possible to transfer equipment status data to a higher level automated process control system depending on the client’s requirements. The screen is supplied with a safety device to avoid damage to the screen’s parts. The safety device stops the screen operation when large waste hits on the filtering mesh, or when any other object blocks free plate movement. Light and sound alarms turn on simultaneously when the safety device is active.
The screens, together with a conveyor, compacting press and slide gates, are included in a high-performance complex for mechanical wastewater treatment. Equipping the control system with programmable modules makes it possible to integrate complex sub systems into one system with a common control center and remote dispatching.
Technical characteristics of standard equipment*
|Channel width, mm||500...2300|
|Channel depth, mm||600...3500|
|Openings, mm||3; 5; 6|
|Inclination angle, degree||50|
|Height of waste disgharge, mm||Depending on the project|
|Electric drive (380 V, 50 Hz), power, kW||0,75; 1,5|
|Protection level of electric drive||IP 55|
* It is possible to produce the screens in different dimensions on demand