Grit Dewatering, Washing System Designed For Smaller Treatment Plants

Grit Dewatering, Washing System Designed For Smaller Treatment Plants
The SpiraSnail screw-type grit dewatering system from Hydro International

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The SpiraSnail screw-type grit dewatering system from Hydro International, designed to work in combination with the GritCup washing system, achieves 95 percent removal of grit 106 microns and larger and 70 to 75 percent removal of 75 to 106 micron particles, helping reduce grit deposition and abrasive wear in downstream processes.

Applications include new wastewater treatment plants, treatment plant retrofits with a peak capacity of 10 mgd, or as a replacement for worn or ineffective grit treatment systems.

“The GritCup and SpiraSnail system has been specifically developed as a joint solution to grit washing and dewatering,” says Adam Neumayer, operations director, Hydro International U.S. Wastewater Division. “Many smaller- and medium-sized treatment plants have struggled with the cost of grit-related maintenance from abrasive wear and deposition of grit.”

Conventional washing and dewatering systems can lose fine grit particles, sending them back to the process, and contain large volumes of organics that increase the weight and volume of material to be disposed. The organics retain water and decompose, creating odors.

“The GritCup and SpiraSnail system produces few volatile solids, so odors are reduced,” he says.

Optimized for intermittent operation to reduce energy usage, the GritCup features large internal clearances and internal volumes, reducing the risk of plugging from solids and wet-weather grit volumes. In the SpiraSnail, grit slurry enters the conically shaped clarifier tangentially and under a baffle, preventing exposure to the clarified effluent exiting over the perimeter weir. Grit follows a predetermined path to the slowly turning screw, reducing the risk of becoming resuspended and discharged.

Grit from the collection device is fed tangentially into the GritCup at a rate of 200 gpm. High-energy vortex separation forces larger particles to the perimeter of the GritCup while smaller grit particles and nonorganic matter remain suspended before settling into the boundary layer at the bottom of the unit and swept to the center for collection. Collected solids are discharged via a tangential underflow pipe.

Solids are dewatered by the rotating (2 rpm) Archimedes screw as it moves toward discharge. Clarified water is returned to the treatment plant. The combined system does not require washwater.

“Both parts of the system have very low maintenance, which is achieved mainly via visual inspection,” Neumayer says.



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