Answer to Question #231855 in Civil and Environmental Engineering for Ali

Question #231855

Calculate the size of a rectangular sedimentation tanks to treat a flow of 12,000 m3/d. Adopt an overflow rate of 20 m3/m2-d and detention time of 4 hours. Use two units in parallel. What will be the minimum weir length required if the weir overflow rate is not to exceed 300 m3/m-d? Also check the horizontal velocity.

Expert's answer

"Discharge : 12,000 m^3\/day\\\\\nOverflow Rate OFR = 20 m\/day\\\\\nDepth = 3 m\\\\\nSurface \\space area \\space of \\space rectangular \\space tank \\space Surface \\space area =\\frac{Q}{OFR} = \\frac{12000}{ 20} m^2\\\\\nArea = 600 \\\\\nLet \\space us \\space assume, length \\space to \\space width \\space Ratio \\space be 4:1\\\\\n4x \\times1x = 600\\\\\nx^2 = \\frac{600}{4}\\\\\nx^2 = 150 m \\\\\nX = 3. 162 m \\\\\n4x = 12.649 m \\\\\nLet \\space us \\space adope\\space the \\space dimension \\space of ( 13 \\times 4 ) m^2 \\\\\nDetention \\space time, td = \\frac{D}{vs} = \\frac{3}{20} day \\\\\ntd = \\frac{3}{20}*24 \\\\\ntd = 3.6 hrs \\\\\nwear \\space overflow \\space rate \\space or \\space weir \\space Loading \\space Rate\\\\\nWFR : \\frac{Flow \\space Rate}{ Length} \\\\\n= \\frac{12000}{ 13} m^3 s^{-1} d^{-1}\\\\\n= 312. 5 m^3\/ mday"

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