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# المحاضرة 4-12

الكلية كلية الهندسة     القسم  الهندسة البيئية     المرحلة 4
أستاذ المادة محمد عبد مسلم عبد الله الطفيلي       04/07/2018 08:57:08

Determine the interface subsidence velocity ? v?_ .The subsidence velocity is determined by computing the slope of the tangent drawn from the initial portion of the interface settling curve. The computed velocity represents the unhindered settling rate of the sludge.

v= ((H_o-H_2))/t_2 = ((0.75 m-0.3 m))/(29.5 min) ((60 min)/h)=0.92 m/h

Determine the clarification rate. Because the clarification rate is proportional to the liquid volume above the critical sludge zone, it may be computed as follows:

Q=3800 m^3/d ((0.75 m-0.188 m)/(0.75 m))=2847 m^3/h

Determine the area required for clarification. The required area is obtained by dividing the clarification rate by the settling velocity.

A=Q/v= ((2847 m^3/h)/((24 h/d)(0.92 m/h)))=129 m^2

The controlling area is the thickening area (165 m2) because it exceeds the area required for clarification (129 m2).

Solids,kg/d= (3800 m^3/d)(3000 g/m^3 )/(?10?^3 g/kg)=11400 kg/d

Solid loading = (11400 kg/d)/(165 m^2 )=69.1 kg/m^2.d
Hydraulic loading rate = (3800 m^3/d)/(165 m^2 )=23 m^3/m^2.d

Compression Settling ( Type 4 Settling )
When the concentration of particles is high enough to bring the particles into physical contact with each other, compression settling will occur. Consolidation of sediment at the bottom of the clarifier is extremely slow. The rate of settlement decreases with time due to increased resistance to flow of the fluid.
The volume required for the sludge in the compression region can also be determined by settling test. The rate of consolidation has been found to be proportional to the difference in the depth at time t and the depth to which the sludge will settle after a long period of time. The long-term consolidation can be modeled as a first-order decay function, as given by :

H_t- H_?=(H_2- H_? ) e^(-i (t-t_2))
Where :
H_t = sludge height at time t, m
H_? = sludge depth after long settling period, on the order of 24 h, m
H_2 = sludge height at time t2, m
i = constant for a given suspension

Stirring serves to compact solids in the compression region by breaking up the floc and permitting water to escape. Rakes are often used on sedimentation equipment to manipulate the solids and thus produce better compaction.

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .