Ch3_3 sedimentation

Ch3_3 sedimentation - Chapter 3-3 Settling (or...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 3-3 Settling (or Sedimentation, clarification) Physical removal of dense/heavy suspended solids from water by exposing the water to relatively quiescent conditions to allow settleable solids to be removed by the action of the force of gravity. The water tank for such as a process is called “settling tank (basin)”, “sedimentation tank (basin)”, or “clairfier”.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Sedimentation Factors affecting particle settling Particle density Particle concentration Dilute suspension Dilute suspension Concentrated suspension Surface flocculent nature Discrete particles Flocculating particles Sedimentation Type III Settling : Zone Settling Type IV Settling : Compression Settling Type I Type II Type II Settling : Flocculating Settling Type II Settling : Flocculating Settling Type I Settling : Discrete Settling Type I Settling : Discrete Settling Length (or time) Height
Background image of page 2
Type-I Settling Theory Settling discrete particles in dilute suspension . Dilute suspension --> particles will not be close enough to interference their velocity field. Discrete particles --> no flocculation (aggregation) of particles. z z Time
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Type I Settling: Discrete Settling Type I settling is characterized by settling of individual particles  without interaction with adjacent particles.The shape, size and  density of the particles remain unchanged during settling.  Examples of Type I Settlings Examples of Type I Settlings  :Settling of sand, grit etc. Application Application  :Design of primary settling tank, grit chamber L H Raw Water  Clarified Water Definition Definition Side view
Background image of page 4
Determination of Settling Velocity: Type I Settling: Why do we need to determine settling velocity? By knowing the settling velocity of the particles, we can estimate the time required for the particles to reach at bottom of the tank thus their removal. Knowing the time, we can calculate the capacity of the settling tank for given % removals of particles. Raw water flows at a rate of 2000 m 3 /min into a settling tank of 3 m high. If 85% of the particles have settling velocity 0.5 m/min. How big settling tank is needed to completely remove of the particles? Example Time Settling Height Tank Velocity Settling =
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Velocity Settling Height Tank Time Settling = min / 5 . 0 3 m m Time Settling = Settling Time = 6 mins = hydraulic retention time Size of the settling tank = ( 2000 m 3 /min ) x (6 min) = 12000 m 3
Background image of page 6
Method 1: Determine the Settling Velocity by the Settling Theory Gravity force: f g = ρ p g V p Buoyant force: f b = w g V p Drag force: f = C A v /2 f g f f b Vt = terminal velocity
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Settling Theory For spherical particles, Therefore, (3-2-1) becomes while d d d A V p p 3 2 ) 2 ( ) 2 ( 3 4 2 3 = = π ) turbulent ( 4 . 0
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 36

Ch3_3 sedimentation - Chapter 3-3 Settling (or...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online