unit operation
DESCRIPTION
Unit operationTRANSCRIPT
![Page 1: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/1.jpg)
UNIT OPERATION
EXPERT LECTUREON
Delivered BY:
DR. N. J. MISTRY, PROFESSORCivil Engineering Department
Sardar Vallabhbhai National Institute of Technology, Surat - 7
![Page 2: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/2.jpg)
UNIT OPERATIONSScreeningMixingFlocculationSedimentationFloatationElutriationVacuum FiltrationHeat Transfer and Drying
PRELIMINARY TREATMENT SYSTEM
Approach ChannelScreen ChamberGrit ChamberSkimming Tank )Oil and Grease Traps)
PRIMARY TREATMENT SYSTEM
Above +PSTReduces 60 – 70 % of Settleable Suspended Solids and30 – 32 % of Organic Suspended Solids
![Page 3: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/3.jpg)
BAR SCREEN
Clarifier
![Page 4: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/4.jpg)
Plot for Computation of Volume of an Equalization Basin
EQUALIZATION TANK
![Page 5: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/5.jpg)
SCREEN CHAMBER
Screen Type Size of Clear Opening
Coarse Screen More than 50 mm
Medium Screen 25 – 50 mm
Fine Screen 10 – 25 mm
DESIGN CONSIDERATIONS
Where
hL = head loss (m)
β = bar shape factor
W = width of bar facing the flow
b = clear spacing between the bars
hV = velocity head of flow approaching the rack (m)
= inclination of the bars
Head loss is also computed by the expression
hL = 0.0729 (v2 – v2h)
Where hL = head loss (m)
v = velocity of flow through screens, m/s
vh = velocity of flow before screens, m/s (approach velocity)
sinθv
h4/3
bW
βL
h
![Page 6: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/6.jpg)
GRIT CHAMBER
Design Criteria
Flow maximum
Peaking factor 2.5 – 3.0
Detention time, t 30 – 90 s (usually 60 s)
Flow through velocity, vh 0.2 – 0.4 m/s (usually 0.3 m/s)
Settling velocity, vs 0.016 – n0.021 m/s for particles of 0.2 mm diameter
0.01 – 0.015 m/s for particles of 0.15 mm diameter
and specific gravity of 2.65
Liquid depth, D 1 – 1.5 m
Length, L 3 – 25 m
Quantity of grits 0.022 - 0.075 m3/1000 m3 of flow
Overflow rate 1200 – 1700 m3/m2-d (at Qpeak) (1200 – 1700)
![Page 7: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/7.jpg)
GRIT CHAMBER
![Page 8: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/8.jpg)
DETERMINING SETTLING VELOCITY
Where
g = acceleration due to gravity (usually assumed as 9.81 m/s2
Pw = density of water (usually assumed as 1000 kg/m3
Ps = density of solid particles
(normally of specific gravity 2.65 = 2.65 x 1000 = 2650 kg/m3
d = diameter of particles (usually assumed as 0.2 mm = 0.2 x 10-3 m
CD = coefficient of drag force depends on flow conditions
(or Reynolds number, Re)
g3C
)d4(V
wD
wss
ρ
ρρ
![Page 9: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/9.jpg)
SKIMMING TANK (OIL AND GREASE TRAP)
Detention time 3 – 30 min.
Surface area 250 m2/m3 flow
PST as a Load Reducing Unit for Secondary Treatment System
![Page 10: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/10.jpg)
SKIMMING TANK
![Page 11: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/11.jpg)
PRIMARY SEDIMENTATION TANK
Dimensions
Rectangular Tank: Range Typical
Length (m) 15 – 100 30
Width (m) 3 – 30 10
Depth (m) 2.5 – 5 4
Circular Tank:
Diameter (m) 3 – 60 30
Depth (m) 3 – 5 4
Bottom slope, mm/mm 0.02 – 0.05 0.03
![Page 12: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/12.jpg)
DETENTION TIME (Hydraulic Retention Time, HRT)
V = Q x t
(days)Q
Vt
24(hours)Q
Vt
Where
t = detention time in days
V = volume of basin in m3
Q = flow of wastewater in m3/d
Schematic Diagram for Concept of Short-circuit of Flow
![Page 13: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/13.jpg)
FLOW THROUGH VELOCITY OR HORIZONTAL VELOCITY, Vh
t
l
taken time
travelled distance Vvelocity, throughFlow
h
The volume of the tank, V = L x B x D
The cross-sectional area of the tank, AX= B x D
time(liquid) tank of volume
tV
Q Rate,Flow The
th
VL
tL
hV
hVQ
xorA
xAQ
hV
hV
XAQ
D)BLV( tL
DBQ
![Page 14: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/14.jpg)
SURFACE LOADING RATE (SLR) OR OVERFLOW RATE (OFR)
)
)/2
3
(m area surface
(mflow SLR
d
= settling velocity (m/d)
Therefore, numerically SLR = Vs
WEIR LOADING RATE (WLR)
d/mm(m) length weirtotal
/d)(m rateflow RateOverflow Weir 3
3
Depth of Tank D = Vs x t (Vs = SLR)
Total depth D = net depth + free board + sludge zone depth
= D + 0.3 + D1
= D+0.3+10% of D
![Page 15: Unit operation](https://reader033.vdocuments.us/reader033/viewer/2022061515/553b106d550346f92f8b4634/html5/thumbnails/15.jpg)
75
THANK YOU FOR YOUR
ATTENTION