Test: Aerated Grit Chambers - Civil Engineering (CE) MCQ

The design of a horizontal flow type is such that as wastewater flows through in horizontal direction at a certain velocity (0.3m/s) particles will start to settle at the channel before reaching the outlet point.

A grit chamber is usually installed before primary sedimentation tanks and it is sensible to say that it should be placed well before wastewater pumps. There are basically three different types of grit chambers.

Manually cleaned grit chambers should be cleaned at least once a week. The simplest method of cleaning is by means of shovel. The grit washing mechanisms are also of several designs most of which are agitation devices using either water or air to produce washing action.

Grit chamber is needed to protect major mechanical equipment from wear and tear including and remove the inorganic particles to prevent damage to the pumps and to prevent their accumulation in sludge digesters.

The specific gravity of heavier particles is 2.65. Grit chambers are nothing but like sedimentation tanks, designed to separate the intended heavier inorganic materials (specific gravity about 2.65) and to pass forward the lighter organic materials.

Sedimentation tanks and grit chambers are similar, designed to separate the intended heavier inorganic materials (specific gravity about 2.65) and to pass forward the lighter organic materials.

The horizontal velocity considered while designing a grit chamber is 0.25-0.4m/sec. In most cases, it is considered as 0.3 m/sec. The setting velocity for the removal of 21mm material is 1-1.3m/ sec.

The settling velocity of discrete particles can be determined using an appropriate equation depending upon Reynolds number. Stoke’s law holds good for Reynolds number, Re below 1.