Grit Classifier

Johnson Screens^® Grit Classifiers offer a solution to removing, washing and dewatering grit and sand, in addition to protecting downstream mechanical equipment and improving the performance and reliability of drainage systems.

The Grit Classifiers consists of a shaftless spiral screw conveyor and conical hopper. Effluent flows into the hopper, where the grit and sand settles out. Settled grit is conveyed, washed and dewatered within the screw conveyor, then disposed of into a container.

Effluent contaminated with grit and organic matter discharges into the top of the hopper close to the periphery, where a coerced, slow rotational movement is produced and aided by the central stirrer. This rotational movement, together with sufficient retention for variations of particle settling velocities, induce the grit and sand to spiral and settle by gravity to attain greater than 95 percent removal of 200 µm to 250 µm size grit particles.

Maintained flow velocities prevent any suspended organic matter from settling with the mineral. Furthermore, wash water enters from the screw classifier into the bottom of the hopper and, aided by the central stirrer, the grit and sand particles abrade against each other, scouring any attached organic matter from their surface. This scouring process is further enhanced by air agitation. Eventually, the grit is conveyed by the screw classifier, washed, dewatered and discharged into a container. Removal of organic matter greater than 97 percent is attainable.

Suspended organic matter discharges from the classifier hopper at intermittent frequencies and can either be returned to the flow and onward to the secondary treatment, or back to the works inlet. The option of continuous bagging systems are available to receive the grit and abate odor. The grit can then be sealed without personal contact.
 
For more information on the Grit Classifier, please contact us.