Post on 21-Dec-2015
transcript
Sedimentation
Sludge Zone
Inle
t Zon
e
Out
let Z
one
Vo = Q/As
vH
t
H Q Q
Aod
VQ
VH s
The overflow rateThe overflow rate
H
Sedimentation
All particles with a settling velocity greater than or equal to the overflow rate will be 100% removed.
Particles with a lesser settling velocity will be removed to a fractional extent. Those that happen to enter the settling zone near the bottom will be completely removed and those that enter near the top will not.
Typical design overflow rates for Typical design overflow rates for settling tanks are: 500-1000 gpd/ftsettling tanks are: 500-1000 gpd/ft22
Fraction Removed = vQAs
Sedimentation
All particles with a settling velocity greater than or equal to the overflow rate will be 100% removed.
Particles with a lesser settling velocity will be removed to a fractional extent. Those that happen to enter the settling zone near the bottom will be completely removed and those that enter near the top will not.
Typical design overflow rates for Typical design overflow rates for settling tanks are: 500-1000 gpd/ftsettling tanks are: 500-1000 gpd/ft22
Sedimentation Tank Configurations
• Rectangular Clarifiers– most common
• Circular clarifiers– Center feed– Peripheral feed
• Flocculator-Clarifiers
Sedimentation Tank Design
• Side water depth: about 12 ft.
• settling velocities: 2-6 ft/hr
• retention time: 4-8 hr
• overflow rates: 500-1000 gpd/ft2 or 0.3-0.7 gpm/ft2
• linear velocities: less than 0.5 ft/min
Sedimentation Tank Design
• Side water depth: about 12 ft.
• settling velocities: 2-6 ft/hr
• retention time: 4-8 hr
• overflow rates: 500-1000 gpd/ft2 or 0.3-0.7 gpm/ft2
• linear velocities: less than 0.5 ft/min
Sedimentation Tank Configurations
• Rectangular Clarifiers– most common
• Circular clarifiers– Center feed– Peripheral feed
• Flocculator-Clarifiers
Filtration
• A “polishing” solid/liquid separation step
• Intended to remove particles
• Other impacts– biodegradation– organics adsorption (especially to GAC)– Mn and Fe adsorption
Types of Filtration
• Granular media filters– slow sand filters– rapid sand filters– high-rate granular media filters
• Membrane filters– microfiltration, ultrafiltration, nanofiltration
• Cake filtration– diatomaceous earth
Filtration: Mechanisms• Interception
– lines of flow strike media
• sedimentation
• diffusion
• straining– too large to fit between spaces
• flocculation– promoted by increased turbulence
Filter Design
Type Filtr. Rate(m/hr)
Media Size(mm)
Bed Depth(m)
Slow Sand 0.04-0.4 0.25-0.35 1.0
RapidSand
5-10 0.45-1.0 0.5-1.0
High-rate 10-35 0.8-2.0 1.2-2.5
Diatom.Earth
2.5-7.5 0.01-0.05
4.9 m/hr = 2 gpm/ft4.9 m/hr = 2 gpm/ft22From Tobiason, 1995