GRIT CHAMBER...
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The document discusses grit chambers, which are basins used to remove inorganic particles from wastewater to prevent damage to pumps and accumulation in sludge digesters. It describes two types - mechanically cleaned chambers, which use scraper blades and elevators to remove settled grit, and manually cleaned chambers, which are cleaned with shovels weekly. Design criteria for grit chambers include a detention time of 30-90 seconds, maximum flow, and settling velocities of 0.016-0.021 m/s for 0.2mm particles and 0.01-0.015 m/s for 0.15mm particles. Transition laws are provided to determine settling velocities for grit particle design.
GRIT CHAMBER...
- 2. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280. GRIT CHAMBER...
- 3. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280. Grit chambers are basin to remove the inorganic particles to prevent damage to the pumps, and to prevent their accumulation in sludge digesters.
- 4. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280. 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.
- 5. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280. 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.
- 6. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280. 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
- 7. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280. Determination of settling velocity Transition 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(s-w)d 3 CDw
- 8. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280. Where: g= acceleration due to gravity (assume 9.81 m/s2) w= density of water (1000 Kg/m3) s= density of solid particles (normally of specific gravity 2.65=2.65*1000=2650 Kg/m3) d= dia of particles CD= coefficient of drag force depends on flow condition
- 9. PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI OFF: UNIVERSITY ROAD, KARACHI-75280.