Johnson Screens® Grit Tank is designed to separate grit from organics and raw sewage water.
The screened wastewater enters the grit tank at the bottom of the chamber where a tangential rotational movement is generated due to the curved chamber. As the grit tank is designed to handle variations in flow, a specially designed agitator rotates and maintains a constant rotational velocity inside the tank.
Due to the constant radial rotation the solids are very quickly collected within the centre of the grit chamber from where they then pass into the bottom of the grit collection tank. The grit-free wastewater then exits and flows onto the next treatment step.
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.
Johnson Screens® Grit Washer is a cost effective solution for washing and dewatering of grit, it also protects downstream mechanical equipment and improves the performance and reliability of drainage systems.
The Grit Washer consists of a shaft-less spiral screw conveyor and conical hopper. Effluent flows into the hopper where the grit settles out. The settled grit is conveyed, washed and dewatered within the screw conveyor, then disposed into a container.
Sand washing and classifier
Brickhouse offer the sand washing & classifier system from Werkstoff + Function, a German company that specializes in inlet works equipment for water and wastewater treatment plants.
The W+F sand washing classifier is designed to meet Germany’s stringent organics separation targets. The sand washing classifier is a compact design in stainless steel fabrication with inbuilt sand bed monitoring capability and controlled by standalone PLC.
Traditional grit classifiers only dewater the grit and end up retaining most of the organics. This results in odours, flies nuisance and the requirement for disposing of the grit at landfills.
Regulations in Europe have moved to stringent sand washing standards. In Germany, these standards demand organics concentrations reduced down to either 3% or 5% dependent on the particular installation. The high standards open up cost effective options for disposal of the washed grit.
With increasing disposal costs from screenings and organics contaminated grit it is highly recommended that a cost-benefit analysis be undertaken for all new or renovated grit removal system installations. Payback periods for grit washing equipment of three years or less are not uncommon.
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