Question

You are hired to design a rectangular sedimentation tank (length to width ratio = 3:1 and detention time ~ 2 h) for a new water treatment plant (flow rate: 0.04 m3/s; temperature: 20 ℃). Suspended particles can be removed when the overflow rate is higher than the settling velocities of particles. You have finished characterizing the influent particles (assuming all of them are spherical) and obtained the following results:

Particle diameter (m)	Particle density (kg/m3)	Percentile
50	1.4 x 103	90
60	1.5 x 103	80

Assume Type I sedimentation. For practical construction purpose, each dimension (W, L or H) will be rounded to an accuracy of 0.1 m.

1. What will be the dimensions (W x L x H, in m) of the sedimentation tank for removing 80% of suspended solids?

2. What will be the dimensions (W x L x H, in m) of the sedimentation tank for removing 90% of suspended solids?

Answer 1

efficiency of so flow rate S rate & zoom b.om my detention time to of fook 2 ha a 2x3600 s 7200 s volume VE Q. A . 0.04*7200 288 m 3 width } =) 11-36 surface over flow rate length Vo 0.04 BUL 38 382 To have lie Vsettling X 100 Voverflow 86 5) Vsetling - 0.8 Voverflow =) Us=o.gv. Since pesticle diameter can not be som or 60m (as question) . so, I am taking site as and Gomm so xios of oo x 103 m stated i the 50 mm we have settling velocity Vs = 418 (6-1) drediometer in (m) Tas temperature in (oc) 3T 4 70 d² es specific granty. be for deo.imm Iw

... Vs S, 418 3x204 To 100 ( - ) (som69 ) :) ( ***100) . 418 Ir nxio? * *103 130 0.5434 mm mm/s S Since, 0.8 svo Vs= --) Vo: 0.68 mm/ also, Vos 9 BU o.on =) 33²- 382 0.04 0.68x103 B- π 4.43 m ) B~ 4.5m L: 38 = 13.5 m height = volume 288 BXL ~ 4.75m 13.sxh.s of The dimensions of the tank removing the huspended solide are ( W xlxH) foo 804. fie 4.5x13.5x4.75).

To have an efficiency of goy. re Vsetning Voverflow 0.9 =) Va 0.9 VO Since, V = 418 (n-1).do ( 914 ) V = 401 1.5 mm --) (convoys 8 mays Vo = Imm/s 3x20 + 70 0.98 Since, Vos ♡ 0.04 BL 0.04 382) Irix103 382 = B = 3.5m since, L=3B » Lilo.sm .: depth volume BL 10.5x3.5 7.8 m To achieve a removal of goy dimensions of the tank (wx 4x4)m he (7.5*10.5*7-8 ) ore (