Settling and Floatation Part 1

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Settling and Floatation – Part 1

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and Flotation Settling, Gravity division is a physical water and wastewater treatment forms in which suspended and gliding solids are expelled from water by the constrain of gravity. Suspended and gliding solids are either heavier than water or lighter than water and as needs be there are two gravity division procedures, sedimentation and buoyancy. Some fine strong particles with densities heavier than water get appended with air bubbles and are likewise evacuated by buoyancy. Settling or sedimentation is a unit operation in which solids are drawn toward a wellspring of fascination.

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Settling and Floatation In gravitational settling, solids are drawn toward gravity; in diffusive settling, solids are drawn toward the sides of violent winds as an aftereffect of the radial field; and in electric-field settling, as in electrostatic precipitators, solids are attracted to charge plates. Buoyancy is a unit operation in which solids are made to buoy to the surface by virtue of their sticking to moment rises of gasses (air) that ascents to the surface. Because of the solids holding fast to the rising air pockets, they are isolated out from the water. This part examines these three sorts of unit operations as connected to the physical treatment of water and wastewater.

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Settling or Sedimentation Settling has been characterized as a unit operation in which solids are drawn toward a wellspring of fascination. The specific kind of settling that will be talked about in this area is gravitational settling. It ought to be noticed that settling is not quite the same as sedimentation, albeit a few creators consider settling the same as sedimentation. Entirely, sedimentation alludes to the condition whereby the solids are as of now at the base and during the time spent sedimenting. Settling is not yet sedimenting, but rather the particles are tumbling down the water segment in light of gravity. Obviously, when the solids achieve the base, they start sedimenting. In the physical treatment of water and wastewater, settling is regularly completed in settling or sedimentation bowls. We will utilize these two terms conversely.

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Settling Tanks, Basins, or Clarifiers Generally, two sorts of sedimentation bowls (now and then called additionally tanks, or clarifiers) are utilized: rectangular and round. Rectangular settling, bowls or clarifiers, as they are likewise called, are bowls that are rectangular in arrangements and cross segments. In plan, the length may fluctuate from two to four times the width. The length may likewise fluctuate from ten to 20 times the profundity. The profundity of the bowl may shift from 2 to 6 M. The influent is presented toward one side and permitted to course through the length of the clarifier toward the flip side.

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Settling or Sedimentation or settling is a procedure in which water is gathered in bowls and given legitimate confinement time amid which suspended solids exhibit in water is permitted to settle. Sedimentation is a procedure with ease and low vitality prerequisites, be that as it may, appropriate bowl outline is vital for legitimate operation and better productivity. In determining a water and wastewater sedimentation tank measure, the real components to be considered are: - tank cross sectional zone, - tank profundity, - and kind of cleaning system utilized.

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Settling or Sedimentation In indicating a plan reason for water and wastewater sedimentation tanks; three conditions are ordinarily considered: - strong taking care of limit (ton/day), - flood rate (gpm/ft2), and detainment time. Extra plan information required to find out mechanical development, particular gravity of solids, size dispersion of solids, sub-current development, working temperature, and topographical area. Run of the mill measurements of sedimentation tanks are given in Table 1 cry.

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Table 1 Typical Dimensions of Sedimentation Tanks ______________________________________________________ Description Dimensions Range Typical ______________________________________________________ Rectangular Depth, m 3‑5 3.5 Length, m 15‑90 25‑40 Width, m 3‑24 6‑10 Circular Diameter, m 4‑60 12‑45 Depth, m 3‑5 4.5 Bottom Slope, mm/m 60‑160 80 ______________________________________________________

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Shapes and Sizes of sedimentation Tanks Water and wastewater sedimentation tanks are for the most part barrel shaped or rectangular fit as a fiddle (See Figures roar). The proportion between width to length in rectangular sedimentation tanks is running between 1:4 to 1:6 (see Table in slide #5).

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Classification of Suspended Particles تصنيف الحبيبات العالقة بالماء Suspended particles in water and wastewater have been sorted into three general classes: 1 ‑ Discrete particles الحبيبات المنفردة : Particles that won't promptly flocculate, free, settling rate is autonomous of fixation, and stream rate is basic (see Figure bellow‑class 1). Cases of discrete particles are sand, rock washing, and sediment. 2 ‑ Flocculent particles الحبيبات المتلبدة : Particles with generally low fixation, conceivable aggloromation, and their settling is exceedingly influenced by detainment time and stream rate(see Figure bellow‑class 2). 3 ‑ Hindered particles الحبيبات عالية التركيز أوالمضغوطة : Particles with high suspended fixations (as in ooze thickening), their settling is influenced by blending and the length of confinement time (see Figure bellow‑class 3).

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Types of Particle Settling Type I settling , single or discrete molecule, applies to particles that settle with consistent speed - particles will be expelled if v > v s If particles flocculate amid settling, speed for the most part increments – Type II settling As molecule fixation increments with profundity, zone settling happens At base of tank pressure settling happens

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Types Of Sedimentation أنواع الترسيب Types of sedimentation are managed by sorts of solids to be expelled from water, hence, for the three sorts of particles in fluid suspensions , three separate systems and hypothesis of assessing settling speeds and evacuation rates better comprehension of the procedure let us first characterize the diverse settling properties of.

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Types of Particle Settling Type I settling applies to particles that settle with consistent speed - particles will be evacuated if v > v s If particles flocculate amid settling, speed for the most part increments – Type II settling As molecule focus increments with profundity, zone settling happens At base of tank pressure settling happens

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a. Discrete Particles Settling ترسيب الحبيبات المنفردة For discrete particles in watery suspensions and which have thickness more prominent than water, it will quicken descending under the compel of gravity until the resistance of the fluid equivalents the compelling weight of the molecule. As indicated by its weight, shape, and particular weight or thickness, discrete molecule is influenced by the gravity, drag, and lightness drive (see Figure cry). Settling speed for a discrete molecule is roughly consistent and its size rely on upon shape, size, and thickness of the article, and thickness and consistency of the fluid. The constrain adjust on the molecule; FG = FD + FB

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Sedimentation: Particle Terminal Fall Velocity where ν s = settling speed ρ s = thickness of molecule (kg/m 3 ) ρ = thickness of liquid (kg/m 3 ) g = gravitational steady (m/s 2) d = molecule distance across (m) μ = dynamic consistency (Pa·s)

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Particle Terminal Fall Velocity (proceeded with) Force adjust (zero increasing speed) We haven't yet expected a shape circle Assume a _______

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Drag Coefficient: Equations General Equation Laminar stream R < 1 Transitional stream 1 < R < 10 4 Fully turbulent stream R > 10 4

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Sedimentation of Small Particles? How would we be able to expand the sedimentation rate of little particles? Increment d (stick particles together) Increase g (axis) Increase thickness contrast (broke down air buoyancy) Decrease consistency (increment temperature)

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Graphical Solution to Settling Velocity

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Overflow Rate, Q ovr = Q/A Q Area A

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Solids Loading Rate, SLR = (Q*C)/A Q * C Area A

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v l v s h v l v s l

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v l v s h v l v s l Rectangular clarifiers In even tank some rate of particles with v s < v o will be expelled P = 100 (v s/v o ) = rate of particles evacuated with a settling speed of v s in a rectangular sedimentation bowl composed with a flood rate of v o

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Removal Efficiency

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Example (1)

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Settling zone