Depending on the type of grit trap, they separate the grit either by gravity (grit channels, lamellae separators) or centrifugal force (circular and vortex grit traps). Scraper blades or screw conveyors are often used to clear a grit channel. Solids removal in the further course of the process is effected by pump, grit classifier or integrated grit classifying screw. HUBER grit traps are available in many different designs.
For reasons of operating reliability of wastewater treatment plants it is necessary to separate grit, gravel and other mineral materials transported with the wastewater (an average of 60 l from 1000 m³ of wastewater according to DWA Work Sheet M369) from the digestable organic material.
Good grit separation prevents operational problems, such as grit sedimentation in aeration tanks and digestors, reduces wear of subsequent equipment, such as pumps or stirrers, and avoids clogging of sludge hoppers and sludge lines.
While as much as possible of the mineral matter should be removed, as much organic matter as possible should remain in the wastewater. Testing of the grit capture rate is usually done with a grit particle size of 0.2 mm.
The most common grit separating systems in use are grit channels, circular grit traps and vortex grit traps. Grit is either separated by gravity sedimentation (grit channels) or centrifugal force (circular and vortex grit traps).
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