The document discusses grit in wastewater treatment, describing it as heavy mineral material found in raw sewage. It outlines the purpose and operation of grit chambers used in primary treatment, including types such as horizontal flow and aerated grit chambers. Additionally, it covers the characteristics of clean grit and methods for disposal.

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ASHWANI KUMAR
1NT12CV064

2. GRIT
 Grit is the heavy mineral material found in raw
sewage, and it may contain sand, gravel, silt, cinders,
broken glass, small fragments of metal and other small
inorganic solids.
 Subsiding velocities or specific gravity substantially
greater than those of organic putrescible solids in
water.
 Ex-eggshells, bone chips, sand, gravel, silt etc..
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3. GRIT CHAMBER
 Grit chamber is the second unit operation used in
primary treatment of wastewater and it is intended to
remove suspended inorganic particles such as sandy
and gritty matter from the wastewater
 limited to municipal wastewater
 Grit chambers are provided to protect moving
mechanical equipment from abrasion and abnormal
wear; avoid deposition in pipelines, channel, and
conduits; and to reduce frequency of digester cleaning
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4. TYPES OF GRIT CHAMBERS
 Horizontal Flow Grit Chamber
 Aerated Grit Chamber
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5. HORIZONTAL FLOW GRIT CHAMBER
 Velocity maintained is 0.3 m/s
 Permit the heavier grit to settle but carry organic
particles
 To maintain a constant velocity of flow, a control
section is placed at the end of the channel.
 A control section varies with the c/s area of the flow in
the section in direct proportion to the flow.
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Fig: Horizontal Flow Grit Chamber

7. DESIGN OF GRIT CHAMBERS
 Settling velocity
 Overflow rate
 Detention period
 Bottom scour
 Velocity control devices
 Number of units
 Dimensions of each unit
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8. AERATED GRIT CHAMBER
 It consists of a standard spiral flow aeration tank
provided with air diffusion tubes placed on one side of
the tank.
 Grit particles tend to settle down to the bottom of the
tank at rates dependant upon the particle size and the
bottom velocity of roll of the spiral flow, which
depends on the rate of air diffusion through diffuser
tubes and shape of aeration tank.
 The lighter organic particles are carried with roll of the
spiral motion
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Fig:Aerated grit chamber

10. DISPOSAL OF GRIT
 Clean grit is characterized by the lack of odour
 It is included when detention time is more or flow
through velocity is less
 Disposed by dumping or burying or by sanitary landfill
 Unwashed grit acts a soil conditioner and will give
good yeild
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