Lecture 4: Sedimentation
Islamic University of Gaza ‐Environmental Engineering DepartmentWater TreatmentEENV 4331Lecture 4: SedimentationDr. Fahid Rabah1
4. Sedimentation in water Treatment4.1 Definition of Sedimentation:It is the process of removing solid particles heavier than waterby gravity force. Particles that will settle within a reasonable period of timecan be removed using a sedimentation tank (also calledclarifiers). Sedimentation is used in water treatment at the locationsindicated in Figures 1 through 4.2
4. Sedimentation in water Treatment4.2 Applicationsppof sedimentation in water treatment:1.2.3.4.Plain settling ( or pre‐sedimentation) of river surfacewater .In filtration treatment plants treating surface water toremoves flocculated solids. The sedimentation tank comesafter the flocculation tank.In Softening treatment plants treating hard water toremoves flocculated solids. The sedimentation tank comesafterft theth flocculationfll ti tank.t kIn aeration treatment plant removing iron and manganesefrom ground water3
4. Sedimentation in water Treatment4.3 Geometryy of sedimentation tanks: Sedimentation tanks are either rectangular or circulartanks.Figures 5 to 10 show typical sedimentation tanks used inwater treatment.4
DistributionFigure 1: Filtration Treatment Plant (River Water)5
nFlocculationStorageS diSedimentationt tiDistributionFigure 2 : Filtration Treatment Plant6
GroundWaterRapid ionStorageRecarbonationDistributionFigure 3: Softening Treatment Plant Single stage softening7
geDistributionFigure 4 : Aeration Treatment Plant( iron and manganese removal plant)8
Figure 5 : Rectangular sedimentation Tank9
Figure 6 : Rectangular sedimentation Tank10
Figure 7 : Circular sedimentation Tank11
Figure 8 : Circular sedimentation Tank12
Figure 9 : Circular sedimentation TankSolid contact type13
Figure 10 : Circular sedimentation TankSolid contact type14
Figure 11 : Rectangular sedimentation Tanksludge collection system15
Figure 12 : Rectangular sedimentation Tanksludgel d collectionll ti systemt16
Figure 13 : Rectangular sedimentation Tanksludgel d collectionll ti systemt17
Figure 14 : Rectangular sedimentation Tanksludgel d collectionll ti systemt18
4. Sedimentation in water Treatment4.3 Theoretical background on Sedimentation4 3 1 Type of particles :4.3.11) Discrete / individual particle- Size, velocity constant during the settling- DensityDit 2,0002 000 – 2,2002 200 kkg/m/ 32) Flocculent particles- Size, velocity fluctuates during the settling- Particles flocculate and grow bigger in size- Density 1,030 – 1,070 kg/m319
4. Sedimentation in water Treatment4.3.2 Three classes of particles settling :Type 1i)Particles settle discretely at a constant velocityii) Settle as individual particles and do not flocculate.iii) E.g. : Sand, grit materialiv) Occurs during :i)Pre‐sedimentation for sand removalii) Settling of sand during rapid sand filter cleaningv) Concentration : very low20
4. Sedimentation in water TreatmentType 2i)Flocculate during sedimentationii) Size constantly changingiii) Settling velocity is changingiv) Settling velocity increase with depth and extent of flocculation.v) Occurs during :i)Alum or iron coagulationvi) Concentration : low21
4. Sedimentation in water TreatmentType 3 or Zonei)Settle as mass and form a layer – “blanketii) Concentration high (greater than 1000 mg/L)iii) Distinct clear zone and sludge zone are present.iv) Occurs during :i)Lime‐softening sedimentationii) Sludge thickeners in water treatment.22
4. Sedimentation in water Treatment4.4 Sedimentation theory23
4. Sedimentation in water Treatment‐Settling velocity (vs) must be determined to assure good sedimentation tank design.‐Overflow rate (vo) must be set at some value LESS THAN or EQUAL to VsHQHHQvs t V l * W * H As Q Hvs tButSoQv0 Asv0 v sWhereQ flow rate(m3/h)As surfacefarea (m( 2)H depth of water, mW tank width, mL tank length,length mt detention time, hr24
4. Sedimentation in water Treatment4.5 Design of Sedimentation tanks4 5 1 Plain Sedimentation:4.5.1Particles settle separately:4g( s )dVs 3CD Vs settling velocityD particle diameterρ water densityρs pparticle densityyCD drag coefficients25
4. Sedimentation in water Treatment4.5.1 Plain Sedimentation:Drag coefficient is calculated as:Re 1,, Laminaraa Flowo CD 1 Re 104, Transitional Flow Re 104,WhereTurbulent Flow R Reynolds number24RCD243 0 .34RRC D 0.40 Vs D Rµ dynamic viscosity , N.s/m2 26
4. Sedimentation in water Treatment4 5 Design4.5D i off SSedimentationdit ti ttanksk4.5.1 Plain Sedimentation:At laminar flow, settling velocity equation is simplified to Stocks law:g ( s )D2vs 18 Vs settling velocityD particle diameterρ water densityρs pparticle densityyCD drag coefficients27
4. Sedimentation in water TreatmentExample 4.141:Find the settling velocity (vs) for sand particles with a diameter of 0.020mm.ρ 2650 kg/m3, µ 1.002X10‐3 N.s/m2 at 20 0C,β 0.05 , ƒ 0.03. what is vs for particleswith D 0.50 5 mm?Solution:Assume first the flow is laminar and check for Reynolds number:9.80( 2650 1000)(0.02 *10 3 ) 2vs 3.59 X 10 4 m / s 318 *1.002 *10 Vs D 1000 * 3.58 *10 4 * 0.20 *10 3R 0.00715 3 1.002 *10R 1 , so itslaminar flowFor particles with D 0.5mm:9.81( 2650 1000)(0.5 *10 3 ) 2vs 0.22m / s18 *1.002 *10 3 Vs D 1000 * 0.22 * 0.50 *10 3 110R 1.002 *10 3 R 1 , so its transitional flow28
4. Sedimentation in water TreatmentsoCD 243 0 .34 0 .841101104 * 9.81(2650 1000)0.5 *10 3vs 0.11 m / s3*110 *1000Solve again for Re :Solve again fir CD :Solve again for vs :Re 55R 1 , so its transitional flowO.KC D 1.18vs 0.10m / sTake v 0 v s 3 . 59 * 10 4 m / s 31 m / d 31 m 3 / m 2 .d29
4. Sedimentation in water Treatment4.5 Design tanks4 5 1 Plain Sedimentation:4.5.1Example 4.2:Design pre‐sedimentation tanks to be used to remove grit and sand from a riverwater thath isi usedd to produced20000 m3/d drinkingd i ki water .UseU theh overflowfl rate anddhorizontal velocities calculated in example 4.1. Use two tanks.Solution:Take v0 vs 31 m 3 / m 2 .dv0 QQ Asw*l*Flow/tank (Q/2) 20000/2 10000 m3/dhAs 10000/31 322.5 m2 Select Width to length ratio 1:4 AA W* 4W 322.5322 5 m22W 8.98W 8 98 m , L 35.9235 92 (take(t k WW 9 m, L L 36 m)) Assume detention time 3 hrsH t*V0 (3*31 )/24 3.88 m 3.90 m Vh Q/(W*H) 10000/(24*60*9*3.9)10000/(24*60*9*3 9) 0.1980 198 m/min Take weir loading rate 250 m3/m.d:L weir Q/Wload 10000/250 40 m , Use suspended troughs inside the tank.30
Figure 15 :Rectangularsedimentation Tank31
4. Sedimentation in water TreatmentExample 4.3:Repeat example 4.3 using circular tank.Note: the maximum tank diameter is 40 mSolution:Take v0 vs 31 m / m .d32Qv0 As*Flow/tank (Q/2) 20000/2 10000 m3/dAs 10000/31 322.5 m2 As πD2/4 322.5 m2D 20.27 m 20.30 m 40 m Assume detention time 3 hrsH t*V0 (3*31)/24 3.88 m 3.90 mCheck horizontal velocity at the beginning and end of settling zones: Vh Q/(π Din H) 10000/(24*60*3.14*3.9*3.9) 0.145 m/min (End of inlet zone) Vh Q/(π DoutH) 10000/(24*60*3.14*24*3.9) 0.024 m/min (beginning of outlet zone) TakeT k weiri loadingl di ratet 250 m3/m.d:/ dL weir Q/Wload 10000/250 40 m , Use suspended troughs inside the tank.Available Length πD total π(2H D) 3.14*(2*3.9 20.30) 88.23 m 40 m O.KAvailable W load Q/L 10000/88.2310000/88 23 113.34113 34 m3/m2.dd 250 m3/m.d/m d O.KOK32
DtotalH side wall height (tank depth)Din HDout H DDtotal 3H DD diameter calculated fromthe Over flow rateDinDoutD/2O tl t zone HOutletHDtotalDoutD/2Figure 16 :Circularsedimentation TankDimensions definitionDinHinlet zone H33
Figure 17 :Circularsedimentation Tank34
4. Sedimentation in water Treatment4.5 Design of Sedimentation tanks4 5 2 Flocculent Sedimentation ( type 2 and 3):4.5.2The design procedure for sedimentation tanks of type 2 and 3 arethe same as type 1. The difference is mainly in the overflow rate (v0). The following table gives the design criteria of these two types.ProcessSettling typeDetentiontime(h)Surfaceloading rate(m3/m2.d)Weir ening32‐640‐6025035
Lecture 4: Sedimentation Dr. Fahid Rabah 1. 4. Sedimentation in water Treatment 4.1Definition of Sedimentation: It is the process of removing solid particles heavier than water by gravity force. .
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research hoped to discover how current sedimentation rates in North Carolina affect water supply and reservoir management. This paper will review major study findings, including current data availability, sedimentation rates, and monitoring and sedimentation prevention practices. It will then prov
CIVL 1112 Water Treatment - Sedimentation 6/7. Sedimentation Example 3 If the settling velocity of the floc particles is 0.055 cm/s, determine the area of the sedimentation tank. Assume a factor of safety of 1
Equilibrium Sedimentation & Sedimentation Velocity: Random Walks in the presence of forces.
5. 7 Horizontal Flow Sedimentation Tank 51 5. 8 Radial and Vertical Flow Sedimentation Tanks 52 5. 9 Sedimentation Tank — Typical Design 54 5.10 Sedimentation Tank - Simple Inlet & Outlet Arrangements 57 5.11 Tilted Plate Clarifier 59 5.12 Rapid Sand Filter - Main Features 62 5.13 Rapid Filter - Typical Design 63 5.14 Declining Rate Operation 68
sedimentation could be beneficial for system compliance. Effect on Turbidity Sedimentation may remove suspended solids and reduce turbidity by about 50 to 90 percent, depending on the nature of the solids, the level of pretreatment provided, and the design of the clarifiers. Common values are in the 60 to 80 percent range (Hudson, 1981).
Sedimentation tank at the Drøbak wastewater treatment plant . To simulate the sedimentation process, we use such initial conditions as: inlet - velocity inlet, outlet - outflow. Design of the tank was created by GAMBIT software, based on the original geometry of the sedimentation tank. CFD models are used to describe the behavior of
RP-2 ISO 14001:2015 Issued: 8/15/15 DQS Inc. Revised: 5/12/17 Introduction This Environmental Management System Assessment Checklist is a tool for understanding requirements of ISO14001:2015 “Environmental management systems – Requirements with guidance for use”. The Checklist covers Clauses 4-10 requirements with probing questions about how an organization has addressed requirements and .
