GRIT CHAMBER...

PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHIOFF: UNIVERSITY ROAD, KARACHI-75280.

GRIT CHAMBER...


Grit chambers are basin to remove the inorganic particles to prevent

damage to the pumps, and to prevent their accumulation in

sludge digesters.


Types of Grit Chambers Mechanically cleaned Manually cleaned In mechanically cleaned grit chamber, scraper

blades collect the grit settled on the floor of the grit chamber.

The grit so collected is elevated to the ground level by several mechanisms such as bucket elevators, jet pump and air lift.

Manually cleaned grit chambers should be cleaned at least once a week.

The simplest method of cleaning is by means of shovel.


Aerated Grit Chamber An aerated grit chamber consists of a

standard spiral flow aeration tank provided with air diffusion tubes placed on one side of the tank.

The grit particles tend to settle down to the bottom of the tank.

Settling rates dependant upon the particle size and the bottom velocity of roll of the spiral flow.


Design criteria Recommended for horizontal flow and aerated grit

chamber. Flow= maximum Detention time= 30-90 s (usually 60 s) Flow through velocity, vh= 0.2-0.4 m/s (usually 0.3 m/s) Settling velocity= 0.016-0.021 m/s for 0.2 mm dia particle = 0.01-0.015 m/s for 0.15 mm dia particles Liquid depth= 1-1.5 m Length= 3-25 m Quantity of grits= 0.022-0.075 m3/1000 m3 of flow


Determination of settling velocityTransition law: The design of grit chamber is based on

removal of grit particles with minimum size of 0.15 mm and therefore Stoke's law is not applicable to determine the settling velocity of grit particles for design purposes.

v2 = 4g(ρs-ρw)d 3 CDρw


Where:g= acceleration due to gravity (assume 9.81

m/s2)ρw= density of water (1000 Kg/m3)ρs= density of solid particles (normally of specific gravity

2.65=2.65*1000=2650 Kg/m3)d= dia of particlesCD= coefficient of drag force depends on flow

condition


NIAZ AHMEDSOCES

PCSIR LAB COMPLEXCELL NO.

03333259613

THANK YOU!!!

GRIT CHAMBER...

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