The SpiraSnail® is specifically designed to provide dedicated dewatering for the output from high-performance Hydro International grit separation / washing units such as the Grit King.®  The SpiraSnail® provides effective, affordable grit dewatering that is ideal for smaller plants with peak flows of up to 10 MGD.

Unlike conventional washing and dewatering screws that attempt to wash and dewater grit in the same process, the SpiraSnail® is only used for dewatering. Combining washing and dewatering in the same process results in turbulence that churns up fine grit and allows it to be released back into the plant. By focusing just on dewatering, SpiraSnail® screw speeds can be slower, allowing retention of fine grit while outputting a clean dry product with low organics and water content. 

Its unique clarifier design, low loading rates, and slow screw speeds mean that the SpiraSnail® provides high capture efficiency while minimizing re-suspension of captured materials, and its low number of wear parts, easy access for maintenance and washwater-free operation keeps operating and maintenance costs to a minimum. 


  • Grit dewatering at smaller wastewater treatment plants
  • Treatment plant retrofits

Only SpiraSnail® 

  • Is optimized for use with the Grit King® grit removal system to provide high performance fine grit removal for smaller plants

You can watch a brief video demonstrating the SpiraSnail®  here. Download the SpiraSnail® brochure here

Designed for

Coarse particles
Fine particles


Get efficient grit dewatering optimized for smaller plants

Having been designed specifically to address flows of up to 10 MGD peak, the SpiraSnail® is optimized for use at smaller plants - meaning that it is able to provide efficient, economical dewatering while maintaining the standards of performance that wastewater treatment plant operators demand. 

Get operator-friendly dewatering

The SpiraSnail® is designed with the operator in mind. Its minimal number of wear parts and easy access for maintenance reduce maintenance time. Maximized internal clearances prevent clogging, and a unique clarifier design allows the auger trough to be rotated away from the clarifier, allowing maintenance even while the unit remains full of water. 

Prevent odor

The SpiraSnail® is a fully enclosed system with easy access when you want it open and secure closures to minimize odor issues. 

Minimize maintenance costs

The SpiraSnail®'s shafted screw design prevents the need for difficult to replace liners or steel wear bars, and the 4-bolt external bearing can be accessed from outside the trough, saving both time and money when it comes to inspection and maintenance. 

NEW! SpiraSnail® Compact 

For plants with very tight space limitations, Hydro International also offers the SpiraSnail® Compact. The system utilizes the same shafted screw design as the original SpiraSnail® but has a smaller footprint and is also shorter than the standard SpiraSnail® system. By limiting design influent flows to ≤ 125 gpm (7.9 L/s) the SpiraSnail® Compact can achieve 95%  capture of all grit 106 micron and larger.

SpiraSnail Compact
SpiraSnail Compact System 
How it works

How it works

  1. Flow from the grit washing system is introduced tangentially into the SpiraSnail® clarifier to begin the  dewatering process. This tangential entry forces the grit to the outside of the clarifier cone.

  2. From the outside of the clarifier cone grit settles into the SpiraSnail® conveyor trough.

  3. The slowly rotating shafted screw conveys the captured grit and dewaters it as it moves towards the discharge chute and into the grit receptacle ready for landfilling.

  4. Clarified water passes over the perimeter weir before being sent back to the plant for further treatment.

Unlike conventional screw classifier systems, the SpiraSnail® is only used for dewatering and not grit washing. This reduces the speed at which the screw needs to rotate, thereby minimizing the turbulence that would otherwise release captured fine grit particles.


Technical information

Technical information


  • 95% removal of grit 106 micron and larger
  • 75% removal of grit 75-106 micron
  • >60% total solids in output grit at design flow
  • <20% volatile solids in output grit at design flow

Conveying capacity 

  • 0.75 yd3 / hour 

Design Notes 

  • Variable frequency drive in the control panel provides flexibility, allowing screw speed adjustment to match changing local operating conditions
  • Optional explosion proof motor allows the system to operate in classified environments
  • Standard 304 stainless steel construction (316 SS optional) 
  • Standard odor cover 
  • Optional NEMA 7/4X controls


Case Studies

Case Studies