design a circular and reactangular sedimentation tank
1) average flow=20 MLD
2) Surface loading=100m³/m²/d of tank area.
Effluent weir loading= 360 m³/ d/ m length of weir
Answers
Step-by-step explanation:
Assume an overflow rate of 40 m3/d.m2 and a water temperature of 12 °C. Provide the following in your summary of the design: Qdesign; Number of tanks; Width of each tank; Length of each tank; Side water depth; Depth of sludge zone; L:D; vf; Reynolds number; Froude Number; Number of Launders; Launder Length; Wier Loading; Type of sludge collector.
Answer:
Settling
Solid liquid separation process in which a suspension is separated into two phases –
Clarified supernatant leaving the top of the sedimentation tank (overflow).
Concentrated sludge leaving the bottom of the sedimentation tank (underflow).
Purpose of Settling
To remove coarse dispersed phase.
To remove coagulated and flocculated impurities.
To remove precipitated impurities after chemical treatment.
To settle the sludge (biomass) after activated sludge process / tricking filters.
Principle of Settling
Suspended solids present in water having specific gravity greater than that of water tend to settle down by gravity as soon as the turbulence is retarded by offering storage.
Basin in which the flow is retarded is called settling tank.
Theoretical average time for which the water is detained in the settling tank is called the detention period.
Design Details
Detention period: for plain sedimentation: 3 to 4 h, and for coagulated sedimentation: 2 to 2.5 h.
Velocity of flow: Not greater than 30 cm/min (horizontal flow).
Tank dimensions: L:B = 3 to 5:1. Generally L= 30 m (common) maximum 100 m. Breadth= 6 m to 10 m. Circular: Diameter not greater than 60 m. generally 20 to 40 m.
Depth 2.5 to 5.0 m (3 m).
Surface Overflow Rate: For plain sedimentation 12000 to 18000 L/d/m2 tank area; for thoroughly flocculated water 24000 to 30000 L/d/m2 tank area.
Slopes: Rectangular 1% towards inlet and circular 8%.