Grit Washing

Description and Working Principles

The unit can perform both grit classifying and grit washing.

The mixture water, grit and organic enters by a vortex type inlet imposing to the particles a rotating velocity. While entering the settling tank that velocity must deflect.

Due to the volume of the tank the velocity is reducing: the combination of the velocity reduction and deflection allows the sedimentation of the grit while the lighter particles will float.

The settled grit forms a “grit-bed” on the bottom which is washed from a countercurrent flow of water.

The washed grit reaches the feeding pit of the lifting screw conveyor while the organics go out with the water or through a suitable flange.

A low speed rotating shaft with proper arms improve the separation of organic from the grit.

While is lifted up the grit is dewatered before reaches the outlet.

In case of high organic load, air can be injected in the sedimentation tank.


Performance and Technical Features


  • Throughput up to 100 m3/h 
  • Efficiency: 90 % separation of sand with grain size as small as 200 micron (at nominal flow) 
  • Organic in the Grit: <= 3%.


  • Hopper: Made from stainless steel and designed: to improve the grit settling and to avoid material blockages 
  • Shaftless screw made of high tensile carbon steel or stainless steel 
  • Lifting screw tube: Made from stainless steel, lined inside with stainless steel bars. The design of the unit allows for easy liner replacement


  • Discharge chute 
  • Bagging unit at the grit discharge 
  • The unit can be manufactured from stainless steel on request
  • Air blower


  • Municipal waste water treatment plants for separation, washing and de-watering grit coming from the grit removal processes 
  • Industrial plants in which sand or grit has to be separated, washed and de-watered

Advantages and Innovative Features 

  • One only unit to classify and wash the grit 
  • Washed grit can be landfill or recycled 
  • Shaftless spiral 
  • Absence of bearings 
  • Low speed 
  • Low installation cost