75050 m ySCt ee nne SolutionDesign of primary settling tank

Solution

Design of primary settling tank: assume surface settling rate = 40 m3 /m2 d

Discharge = 5000 × 6 = 30000 × 10^3

Therfore the surface area of tank = 30000 × 10^3/40 × 10³ = 750m2

Assume width = 10m

Theoritical length = 750/10 = 75 m

Hence provide 2 tanks in parallel

Total length of each tank = 75/2 +2 (inlet)+2 (outlet)

= 41.5m

Provide detention time of 1.5 h

Liquid depth required = 75 * 1.5 / 41.5 = 2.71m

Provide total depth = 2.71 + 0.5 (freeboard) + 0.25 (space for sludge) = 3.46m