Grit Removal

All wastewater from domestic sources and those from many industrial sources contain solid particles that fall into the classification of grit. Grit is primarily of an inorganic composition that is virtually nonputrescible, and frequently of a hardness that is abrasive to metals. Grit does not perform any useful function in the treatment process. The main objective of grit removal is to separate by sedimentation all materials that may be detrimental to the treatment process or process equipment.

There are three principal types of grit removal systems:

Gravity Channel

Gravity Channels are sized to produce a certain optimum maximum flow velocity through the channel. Up to this velocity the majority of grits will fall out of solution and be collected in a bottom dump pit in the channel. An old but effective system in smaller facilities.

Aerated Grit Channels

These channels are long, narrow, relatively deep and aerated with coarse bubble diffusers. Velocity through the channel combined with the rolling motion produced by the aeration, ensures entrained grit being separated from the liquid flow.

Aerated channels are usually used in larger sewage works and may be equipped with a mechanised grit removal device and a conveyor system to a bagging bin.

Vortex Grit Traps

Vortex grit traps remove the grit from sewage inflow in a mechanised vortex flow container. These devices have become the most commonly used method in Australia.

After collection in a channel or vortex trap, grit is further cleaned of putrescible matter in a washer / classifier. The putrescible matter is returned to the treatment process. The washed grit is then removed to a dedicated land fill area for burial.