Aquaculture Engineering

Mechanical filters - Rotary screens

Unit 12 - Management of ponds

Filtration

Classification according to form of materials

Mechanical filters

Rotary screens
Rotary screens are used where screen plugging is a problem, where labour for screen cleaning is expensive or where it is not feasible to shut down while the screen is cleaned. Rotary screens, as the name indicates are rotating screens constructed such that the screens operates only partially submerged in the water that is to be filtered. The submerged section filters water passing though it continuous rotation causes a section of screen to alternately filter and be above the water surface,where it passes in front of a back washing system. Thus backwashing is continuous and automatic enabling the screen to operate continuously with low head loss and a low labour requirement. Rotary screens do produce significant quantities of backwash water containing a high concentration of solids.

There are two types of rotary screen

• Axial flow rotary screens
• Radial flow rotary screens

Fluid passes through an axial flow screen parallel to the axis of rotation of the screen. In a radial flow screen flow travels radially toward or away from the axis of rotation.