Aerated Grit Chamber

Aerated grit chambers are widely used for selective removal of grit. The spiral roll of the aerated grit chamber liquid drives the grit into a hopper located under the air diffuser assembly (see Figure 7.15.2). The shearing force of the air bubbles strips the inert grit of much of the organic material that adheres to its surface.

Aerated grit chamber performance is a function of roll velocity and detention time. Adjusting the air feed rate controls the roll velocity. Nominal air flow values are 0.15 to 0.45 m3/min of air per meter of tank length (m3/min • m). The liquid detention time is usually about 3 min at the maximum flow. Length-to-width ratios range from 2:5 to 5:1 with depths of 2 to 5 m.

The grit that accumulates in the chamber varies depending on the type of sewer system (combined type or separate type) and the efficiency of the chamber. For combined systems, 90 m3 of grit per million cubic meters of sewage (30 m3/106 m3) is not uncommon; in separate systems, the amount is something less than 30m3/106m3. Deposited grit is normally recovered by air lift or screw conveyor. The grit is buried in a sanitary landfill.

Aerated grit chambers are extensively used at medium-and large-size treatment plants. They offer the following advantages over velocity-controlled grit channels:

An aerated chamber can also be used for chemical addition, mixing, and flocculation before primary treatment. Wastewater is freshened by air, reducing odors and removing additional BOD5. Minimal head loss occurs through the chamber. Grease removal can be achieved if skimming is provided. By controlling the air supply, the chambers can remove grit of low-putrescible organic content. By controlling the air supply, the chambers can remove grit of any specified size. However, due to the variable specific gravity and the size and shape of the particles, some limitations on removal may exist.

Helical Liquid Flow Pattern

Helical Liquid Flow Pattern

Effluent

Grit Related Civil Engineering

Influent nlet

Trajectory of Grit Particles

Hopper

FIG. 7.15.2 Aerated grit chamber. (Reprinted, with permission, from Metcalf & Eddy, Inc. and G. Tchobanoglous. 1979, Wastewater engineering: Treatment, disposal, reuse (New York: McGraw-Hill).

Trajectory of Grit Particles

Hopper

FIG. 7.15.1 Mechanical grit removal facility. A. Plan view; B. Longitudinal section.

FIG. 7.15.2 Aerated grit chamber. (Reprinted, with permission, from Metcalf & Eddy, Inc. and G. Tchobanoglous. 1979, Wastewater engineering: Treatment, disposal, reuse (New York: McGraw-Hill).

Influent nlet

Effluent

Grit Chamber Top View Drawing

SECTIONAL ELEVATION THROUGH GRIT WASHING COMPARTMENT FIG. 7.15.3 Detritus tank and grit washer.

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Responses

  • Magnus Ollila
    How air bubbles take the grit along with it in aerated grit chamber?
    2 years ago
  • maia
    What is helical flow aerated gritchannel?
    2 years ago
  • s
    What are grit chamber in wastewater treatment plant?
    2 years ago
  • carl burrows
    What is aerated grit channel?
    2 years ago

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