Question

1.A rectangular settling basin with a length to widith rato of 3:1 receives a flow of 850000 l/d the basin depth is 4 m and the detention time of water in the tank is 144minutes

(I)what are the surface overflow rate and horizontal velocity if the is distributed uniformly across the cross sectional area of the tank

(II) Calculate the weir loading rate if the leght is 2 times the basin widith

2.Design a set of three rapid sand filters to treat water for the community of 100000 people with a maximum water demand of 270L/capday.pitot plant studies indicate that the filtration rate of the rapid sand filters is 4500 liters/hour /m2.take the length to widith ratio filters to be 1.5:1

Answer 1

Please uprote criven length L B mi- width mols 8640 S = 2.5hrs Flow, 850000 litres g. 838 X10 x 103 day defention time, tea 144 minutes - volume of the beesin the basin , v= o. ta 9.838x103 x 8640 85 m? depth ... surface volume surface = um= area 85 = 21.25 m H since, area - BxL = 3 B 382 21.25 =) B ~ 2.7 m um 8 m surface overflow rate SLR = -3 9.838*10 BxL 21. 25 SLR = 4.63 SLR many mors m²-day w 40 m surface overflow rate SLRs no m/med Horizantal velocity velocity u L 8 - = 3.33 ta 2.4 93 mori : 9. 26x10 mys

) ܗ ܙܢ 11 di- - LE RB B 9.838 x 10 Pro) I ta = .8040s 3 - volume 85 m depth H = 4m .: surface area silos 85 4 - 4.25m? 3.26 m LA B= 21.25 ) BE & La 3.3 m 6.52 m si 6.5 m weir loeding sate - Flow -3 9.838 x 10 length of of weir 6.5 1:5136103 1 m%-s ~ 130. 7 m%m-d weir leading rate WLR | 130. 130.7 m/on.d

al 2 f 1ooooo number bersans = water demand 270 Y capito-day : Tota demand 0 100000 K270 10 27000 m mo/day Q: 0.3125 m3 m?) Total Oo 1125ooo letres/hr Rate of filtration 1 ROF = 4500 liters/hr/m² =) Total area 1125000 R OF - 250 m2 4500 set of three rapid sand filters Area of each filter Areal/ Total 501 - = 83.33 m? 3 length 1.S L I, Lo lo SB and th B LxB = 83.33 83.33 =) 1.SB? - 83.33 ) B: 7.45 m La 11.2m Allume . depth of 3m each filter dimensions of each rapid sand filter (LxBxH) 11.2 x 7.45x3