Fundamental Concepts: Fundamental Concepts: Sedimentation Sedimentation

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Fundamental Concepts:
Fundamental Concepts:
Sedimentation
Sedimentation
Ann Kenimer
Ann Kenimer
Texas A & M University
Texas A & M University
University Curriculum Development for
University Curriculum Development for
Decentralized Wastewater
Decentralized Wastewater
Management
Management
NDWRCDP Disclaimer
NDWRCDP Disclaimer
This work was supported by the National Decentralized Water
This work was supported by the National Decentralized Water
Resources Capacity Development Project (NDWRCDP) with
Resources Capacity Development Project (NDWRCDP) with
funding provided by the U.S. Environmental Protection Agency
funding provided by the U.S. Environmental Protection Agency
through a Cooperative Agreement (EPA No. CR827881
through a Cooperative Agreement (EPA No. CR827881
-
-
01
01
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0)
0)
with Washington University in St. Louis. These materials have
with Washington University in St. Louis. These materials have
not been reviewed by the U.S. Environmental Protection
not been reviewed by the U.S. Environmental Protection
Agency. These materials have been reviewed by
Agency. These materials have been reviewed by
representatives of the NDWRCDP. The contents
representatives of the NDWRCDP. The contents
of these materials do not necessarily reflect the views and
of these materials do not necessarily reflect the views and
policies of the NDWRCDP, Washington University, or the U.S.
policies of the NDWRCDP, Washington University, or the U.S.
Environmental Protection Agency, nor does the mention of trade
Environmental Protection Agency, nor does the mention of trade
names or commercial products constitute their endorsement or
names or commercial products constitute their endorsement or
recommendation for use.
recommendation for use.
CIDWT/University Disclaimer
CIDWT/University Disclaimer
These materials are the collective effort of individuals from
These materials are the collective effort of individuals from
academic, regulatory, and private sectors of the
academic, regulatory, and private sectors of the
onsite/decentralized wastewater industry. These materials have
onsite/decentralized wastewater industry. These materials have
been peer
been peer
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-
reviewed and represent the current state of
reviewed and represent the current state of
knowledge/science in this field. They were developed through a
knowledge/science in this field. They were developed through a
series of writing and review meetings with the goal of formulati
series of writing and review meetings with the goal of formulati
ng
ng
a consensus on the materials presented. These materials do not
a consensus on the materials presented. These materials do not
necessarily reflect the views and policies of University of
necessarily reflect the views and policies of University of
Arkansas, and/or the Consortium of Institutes for Decentralized
Arkansas, and/or the Consortium of Institutes for Decentralized
Wastewater Treatment (CIDWT). The mention of trade names or
Wastewater Treatment (CIDWT). The mention of trade names or
commercial products does not constitute an endorsement or
commercial products does not constitute an endorsement or
recommendation for use from these individuals or entities, nor
recommendation for use from these individuals or entities, nor
does it constitute criticism for similar ones not mentioned.
does it constitute criticism for similar ones not mentioned.
Citation
Citation
Kenimer, Ann L., J.
Kenimer, Ann L., J.
Villeneuve
Villeneuve
and S.
and S.
Shelden
Shelden
.
.
2005. Fundamental Concepts: Sedimentation
2005. Fundamental Concepts: Sedimentation
-
-
Power Point Presentation.
Power Point Presentation.
in
in
(M.A. Gross and
(M.A. Gross and
N.E. Deal, eds.) University Curriculum
N.E. Deal, eds.) University Curriculum
Development for Decentralized Wastewater
Development for Decentralized Wastewater
Management. National Decentralized Water
Management. National Decentralized Water
Resources Capacity Development Project.
Resources Capacity Development Project.
University of Arkansas, Fayetteville, AR.
University of Arkansas, Fayetteville, AR.
Sedimentation
Sedimentation


Sedimentation
Sedimentation
is the gravitational
is the gravitational
accumulation of solids at the bottom of a
accumulation of solids at the bottom of a
fluid (air or water)
fluid (air or water)
Types of Settling
Types of Settling
Four types of sedimentation:
Four types of sedimentation:


Discrete settling
Discrete settling


Flocculant settling
Flocculant settling


Hindered settling
Hindered settling


Compression
Compression
Examples of Settling Types
Examples of Settling Types
Discrete
Discrete
Flocculant
Flocculant
Hindered
Hindered
Types of Sedimentation
Types of Sedimentation


In
In
discrete settling
discrete settling
individual particles
individual particles
settle independently
settle independently


It occurs when there
It occurs when there
is a relatively low
is a relatively low
solids concentration
solids concentration
Types of Sedimentation
Types of Sedimentation


In
In
flocculant
flocculant
settling
settling
, individual
, individual
particles stick
particles stick
together into
together into
clumps called flocs
clumps called flocs


This occurs when
This occurs when
there is a greater
there is a greater
solids concentration
solids concentration
and chemical or
and chemical or
biological reactions
biological reactions
alter particle
alter particle
surfaces to enhance
surfaces to enhance
attachment
attachment
Types of Sedimentation
Types of Sedimentation


In
In
hindered settling
hindered settling
,
,
particle
particle
concentration is
concentration is
great enough to
great enough to
inhibit water
inhibit water
movement
movement


Water must move in
Water must move in
spaces between
spaces between
particles
particles
Types of Sedimentation
Types of Sedimentation


Compression
Compression
settling
settling
occurs
occurs
when particles
when particles
settle by
settle by
compressing the
compressing the
mass below
mass below
Sedimentation Rate
Sedimentation Rate


Stoke’s Law
Stoke’s Law


Used for spherical particles
Used for spherical particles


Assumes no fluid mixing, so usually will not
Assumes no fluid mixing, so usually will not
work for gasses
work for gasses
µ
ρ

ρ
=
18
)
(
w
p
g
d
v
2
p
Sedimentation Rate
Sedimentation Rate
v
dg
p
2
=

()
ρρ
µ
pw
18


v
v
p
p
= particle settling velocity (
= particle settling velocity (
m
m
/
/
s
s
or
or
ft
ft
/
/
s
s
)
)


ρ
ρp
p
= particle density (
= particle density (
kg
kg
/
/
m
m
3
3
or
or
lb
lb
/
/ft
ft
3
3
)
)


ρ
ρw
w
= fluid density (
= fluid density (kg
kg
/
/
m
m
3
3
)
)


d = particle diameter (m or ft)
d = particle diameter (m or ft)


g = gravitational acceleration (9.81
g = gravitational acceleration (9.81
m
m
/
/
s
s2
2
or 32.2
or 32.2
ft
ft
/
/s
s
2
2
)
)


µ
µ
= dynamic viscosity (Ns/m
= dynamic viscosity (Ns/m
2
2
or lbs/ft
or lbs/ft
2
2
)
)
Applications
Applications


Stoke’s Law can be used to determine the
Stoke’s Law can be used to determine the
surface area of a settling tank
surface area of a settling tank


Set the critical velocity equal to the settling
Set the critical velocity equal to the settling
velocity of the smallest particle
velocity of the smallest particle


The overflow rate is equal to the flow rate into
The overflow rate is equal to the flow rate into
the tank divided by the surface area
the tank divided by the surface area


Setting the overflow rate equal to the critical
Setting the overflow rate equal to the critical
settling velocity allows time to capture
settling velocity allows time to capture
smallest particles of interest
smallest particles of interest
Applications
Applications
OFR
v
Q
A
c
==


OFR = over flow rate (
OFR = over flow rate (m
m
/
/
s
s
or
or ft
ft
/
/
s
s
)
)


v
v
c
c
= critical settling velocity (
= critical settling velocity (
m
m
/
/
s
s
or
or
ft
ft
/
/s
s
)
)


Q = the flow rate into the basin (
Q = the flow rate into the basin (
m3
m3
/
/
s
s
or cfs)
or cfs)


A = the surface area of the basin (m
A = the surface area of the basin (m
2
2
or ft
or ft2
2
)
)