All
wastewater from a domestic source, and those from many industrial sources
contain solid particles that fall into the classification of grit. Grit
is primarily of an organic composition that is virtually nonputrescible,
and frequently of a hardness that is abrasive to metals. The main objective
of grit removal is to separate by sedimentation all materials that may
be detrimental to the treatment process.
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.
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 such as the Pista or Jetta types 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.
