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{float:right|border=2px solid black|width=300px}
!sedtanks.jpg|width=300px!
h5. Figure 1: Sedimentation Tanks at the Cuatro Communidades plant
{float}
h2. |
Introduction
...
and
...
Objectives
...
The
...
Cuatro
...
Communidades
...
plant
...
has
...
two
...
sedimentation
...
tanks
...
designed
...
for
...
an
...
upflow
...
velocity
...
of
...
70
...
m/day.
...
The
...
tanks
...
are
...
shallower
...
than
...
those
...
of
...
previously
...
constructed
...
Aguaclara
...
plants.
...
Like
...
the
...
other
...
plants,
...
the
...
tanks
...
use
...
lamella
...
to
...
increase
...
their
...
efficiency.
...
The
...
sedimentation
...
tanks
...
were
...
designed
...
to
...
accommodate
...
a
...
floc
...
blanket.
...
A
...
floc
...
blanket
...
is
...
suspension
...
of
...
flocs
...
that
...
are
...
too
...
large
...
to
...
rise
...
to
...
the
...
top
...
of
...
the
...
tank
...
and
...
two
...
small
...
to
...
settle
...
out.
...
A
...
floc
...
blanket
...
should
...
act
...
as
...
a
...
filter
...
trapping
...
flocs
...
as
...
they
...
rise
...
to
...
the
...
top
...
of
...
the
...
sedimentation
...
tanks.
...
In
...
the
...
laboratory,
...
...
...
have
...
been
...
show
...
to
...
greatly
...
increase
...
effluent
...
water
...
quality
...
in
...
a
...
flocculation-sedimentation
...
system.
...
The
...
sedimentation
...
tanks
...
in
...
the
...
Cuatro
...
Communidades
...
plants
...
are
...
a
...
much
...
larger
...
less
...
controlled
...
system
...
and
...
it
...
was
...
unclear
...
whether
...
it
...
is
...
possible
...
to
...
form
...
and
...
maintain
...
a
...
floc
...
blanket
...
in
...
the
...
plant.
...
No
...
previous
...
observations
...
of
...
the
...
tanks
...
showed
...
conclusive
...
evidence
...
of
...
a
...
floc
...
blanket.
...
The
...
Cuatro
...
Communidades
...
plant
...
was
...
designed
...
with
...
a
...
plant
...
flow
...
rate
...
of
...
380
...
liters
...
per
...
minute
...
but
...
the
...
available
...
head
...
in
...
the
...
conduction
...
line
...
set
...
a
...
plant
...
flow
...
rate
...
of
...
only
...
190
...
-270
...
liters
...
per
...
minute.
...
At
...
these
...
flow
...
rates
...
no
...
effects
...
of
...
a
...
floc
...
blanket
...
were
...
observed
...
and
...
the
...
upflow
...
velocity
...
may
...
not
...
have
...
been
...
great
...
enough
...
to
...
keep
...
flocs
...
in
...
suspension.
...
One
...
tank
...
was
...
shut
...
off
...
to
...
increase
...
the
...
upflow
...
velocity
...
through
...
the
...
sedimentation
...
tanks
...
and
...
to
...
attempt
...
to
...
form
...
a
...
floc
...
blanket.
Methods
It should be kept in mind that during these tests, the main purpose of the plant was to provide potable water for the communities. These tests were a lower priority and this created several initial challenges to shutting off one sedimentation tank. When all the flow passed through one tank, the head loss through the original effluent launders was high enough to flood the plant. New effluent launders were created to run one tank. They were designed with a head loss of four centimeters using the equation:
| Latex |
|---|
h2. Methods It should be kept in mind that during these tests, the main purpose of the plant was to provide potable water for the communities. These tests were a lower priority and this created several initial challenges to shutting off one sedimentation tank. When all the flow passed through one tank, the head loss through the original effluent launders was high enough to flood the plant. New effluent launders were created to run one tank. They were designed with a head loss of four centimeters using the equation: {latex} \large \[ h = \left( {\frac{Q} {{K A}}} \right)^2 \frac{1} {{2g}} \] {latex} |
where:
...
- Q
...
- is
...
- the
...
- plant
...
- flow
...
- rate
...
- A
...
- is
...
- the
...
- total
...
- area
...
- of
...
- the
...
- effluent
...
- launder
...
- orifices
...
- K
...
- is
...
- a
...
- minor
...
- loss
...
- coefficient
...
- h
...
- is
...
- the
...
- head
...
- loss
...
To
...
increase
...
the
...
area
...
and
...
decrease
...
the
...
head
...
loss
...
the
...
effluent
...
launder
...
holes
...
were
...
increased
...
from
...
5/16
...
in
...
to
...
7/16
...
in.
...
Another
...
problem
...
was
...
that
...
in
...
the
...
first
...
three
...
attempts
...
to
...
run
...
one
...
tank
...
the
...
effluent
...
turbidity
...
increased
...
from
...
below
...
10
...
NTU
...
to
...
above
...
20
...
NTU.
...
At
...
this
...
point
...
it
...
was
...
unacceptable
...
to
...
send
...
the
...
effluent
...
to
...
the
...
distribution
...
line
...
and
...
the
...
water
...
was
...
sent
...
to
...
waste.
...
This
...
procedure
...
could
...
only
...
be
...
maintained
...
for
...
2-3
...
hours
...
during
...
the
...
day
...
without
...
draining
...
the
...
water
...
storage
...
tank
...
for
...
the
...
communities.
...
No
...
improvement
...
in
...
effluent
...
quality
...
was
...
observed
...
in
...
these
...
trials.
...
The
...
plant
...
was
...
recently
...
cleaned
...
before
...
the
...
second
...
and
...
third
...
of
...
the
...
three
...
trials.
...
During
...
these
...
initial
...
trials
...
the
...
incoming
...
turbidity
...
was
...
above
...
100
...
NTU.
...
In
...
order
...
to
...
shut
...
off
...
the
...
plant
...
for
...
a
...
longer
...
period
...
of
...
time,
...
the
...
fourth
...
trial
...
was
...
run
...
at
...
night
...
when
...
the
...
communities
...
were
...
not
...
consuming
...
water.
...
The
...
sedimentation
...
tank
...
was
...
cleaned
...
at
...
9
...
pm
...
before
...
the
...
plant
...
was
...
started.
...
The
...
plant
...
was
...
successfully
...
running
...
by
...
12:00
...
pm
...
with
...
an
...
influent
...
turbidity
...
of
...
40
...
NTU
...
and
...
effluent
...
turbidity
...
of
...
4
...
NTU.
...
It
...
should
...
be
...
noted
...
that
...
the
...
three
...
hours
...
in
...
between
...
were
...
spent
...
cleaning
...
the
...
sedimentation
...
tank
...
and
...
filling
...
the
...
plant.
...
After
...
thirty
...
six
...
hours,
...
the
...
lamella
...
were
...
removed
...
from
...
the
...
tank
...
to
...
see
...
if
...
there
...
was
...
floc
...
blanket
...
beneath
...
them.
...
After
...
the
...
lamella
...
were
...
replaced,
...
the
...
plant
...
continued
...
to
...
run
...
with
...
only
...
one
...
sedimentation
...
tank
...
for
...
the
...
next
...
four
...
days.
...
The
...
incoming
...
turbidity
...
was
...
consistently
...
between
...
20
...
and
...
40
...
NTU.
...
Results
...
and
...
Discussion
...
As
...
was
...
mentioned,
...
in
...
the
...
first
...
three
...
attempts,
...
the
...
effluent
...
turbidity
...
spiked
...
initially.
...
The
...
trials
...
could
...
not
...
be
...
run
...
for
...
longer
...
than
...
three
...
hours
...
without
...
disrupting
...
the
...
communities
...
water
...
supply.
...
In
...
the
...
third
...
of
...
these
...
initial
...
trials,
...
it
...
was
...
hard
...
to
...
visually
...
distinguish
...
between
...
the
...
water
...
at
...
the
...
end
...
of
...
the
...
flocculator
...
and
...
the
...
end
...
of
...
the
...
sedimentation
...
tank
...
closest
...
to
...
the
...
flocculator
...
after
...
an
...
hour.
...
The
...
turbidity
...
measured
...
at
...
the
...
end
...
of
...
the
...
flocculator
...
was
...
119.1
...
NTU
...
and
...
in
...
the
...
back
...
of
...
the
...
sedimentation
...
tank
...
the
...
turbidity
...
was
...
102.4
...
NTU
...
indicating
...
that
...
flocs
...
were
...
directly
...
rising
...
as
...
they
...
entered
...
the
...
back
...
of
...
the
...
sedimentation
...
tanks.
...
However,
...
close
...
to
...
the
...
effluent
...
channel
...
the
...
turbidity
...
measured
...
in
...
the
...
sedimentation
...
tank
...
was
...
27.12
...
NTU
...
indicating
...
that
...
most
...
of
...
the
...
flocs
...
were
...
rising
...
in
...
the
...
back
...
of
...
the
...
tank.
...
This
...
third
...
test
...
was
...
only
...
one
...
and
...
a
...
half
...
hours
...
and
...
the
...
effluent
...
quality
...
from
...
the
...
sedimentation
...
tank
...
was
...
consistently
...
decreasing.
...
It
...
is
...
unclear
...
whether
...
this
...
upflow
...
velocity
...
was
...
too
...
high
...
for
...
the
...
tanks
...
or
...
if,
...
given
...
more
...
time,
...
a
...
floc
...
blanket
...
would
...
have
...
formed.
...
In
...
the
...
fourth
...
test,
...
there
...
was
...
no
...
spike
...
in
...
effluent
...
as
...
had
...
been
...
expected
...
from
...
the
...
first
...
three
...
trials.
...
The
...
plant
...
was
...
run
...
for
...
thirty
...
six
...
hours
...
with
...
no
...
significant
...
changes
...
in
...
effluent
...
quality
...
(figure
...
2).
...
No
...
evidence
...
of
...
a
...
floc
...
blanket
...
was
...
seen
...
in
...
the
...
plant
...
sludge
...
judge.
| Wiki Markup |
|---|
{float:border=2px solid black|width=600px} !sedgraph.gif|width=600px! h5. Figure 2 {float} |
Although
...
the
...
plant
...
was
...
not
...
monitored
...
for
...
the
...
second
...
night,
...
it
...
did
...
not
...
rain,
...
no
...
changes
...
in
...
the
...
plant
...
conditions
...
were
...
observed
...
in
...
the
...
morning
...
and
...
the
...
influent
...
conditions
...
were
...
constant
...
before
...
and
...
after
...
the
...
test.
...
It
...
is
...
reasonable
...
to
...
assume
...
that
...
the
...
influent
...
and
...
effluent
...
did
...
not
...
significantly
...
change
...
in
...
the
...
night.
...
Finally
...
to
...
determine
...
if
...
there
...
was
...
a
...
floc
...
blanket,
...
water
...
was
...
siphoned
...
from
...
different
...
heights
...
in
...
the
...
sedimentation
...
tank.
...
The
...
turbidity
...
was
...
consistently
...
below
...
12
...
NTU
...
below
...
the
...
lamella.
...
However
...
the
...
exact
...
height
...
of
...
the
...
hose
...
was
...
never
...
determined
...
because
...
the
...
hose
...
was
...
slightly
...
buoyant
...
and
...
could
...
not
...
be
...
seen
...
below
...
the
...
lamella.
...
If
...
the
...
test
...
if
...
repeated,
...
the
...
hose
...
should
...
be
...
weighted
...
down
...
or
...
attached
...
to
...
a
...
rigid
...
pole
...
to
...
measure
...
the
...
turbidity
...
at
...
an
...
exact
...
depth.
| Wiki Markup |
|---|
\\ {float:left|border=2px solid black|width=300px} !halflamella.jpg|width=300px! h5. Figure 3: half the lamella were removed from the sedimentation tank {float} |
After
...
thirty
...
six
...
hours,
...
the
...
lamella
...
were
...
removed
...
from
...
the
...
tanks
...
(figure
...
3).
...
Other
...
than
...
the
...
initial
...
disturbance
...
of
...
removing
...
the
...
lamella
...
from
...
the
...
tank
...
the
...
water
...
was
...
fairly
...
clear.
...
It
...
was
...
possible
...
to
...
see
...
to
...
the
...
top
...
of
...
the
...
plates
...
resting
...
in
...
the
...
bottom
...
of
...
the
...
sedimentation
...
tanks.
...
Flocs
...
that
...
had
...
settled
...
in
...
the
...
channel
...
entering
...
the
...
sedimentation
...
tanks
...
were
...
swept
...
into
...
the
...
tank
...
in
...
an
...
attempt
...
to
...
see
...
where
...
they
...
were
...
going.
...
It
...
was
...
not
...
possible
...
to
...
see
...
what
...
happened
...
to
...
these
...
flocs.
...
However,
...
in
...
general
...
it
...
seemed
...
as
...
though
...
more
...
flocs
...
were
...
rising
...
in
...
the
...
middle
...
of
...
the
...
sedimentation
...
tanks
...
than
...
the
...
sides.
...
When
...
the
...
lamella
...
were
...
replaced
...
and
...
one
...
tank
...
was
...
shut
...
off
...
for
...
the
...
following
...
four
...
days,
...
there
...
was
...
no
...
measured
...
improvement
...
in
...
effluent
...
quality.
...
During
...
this
...
period
...
of
...
time
...
the
...
plant
...
influent
...
was
...
consistently
...
below
...
40
...
NTU
...
and
...
the
...
flocculator
...
was
...
working
...
well.
...
These
...
results
...
indicate
...
that
...
flocs
...
were
...
not
...
reaching
...
the
...
sedimentation
...
tanks
...
but
...
settling
...
out
...
in
...
the
...
flocculator,
...
and
...
the
...
channel
...
in
...
between
...
the
...
flocculator
...
and
...
the
...
sedimentation
...
tanks
...
during
...
the
...
thirty
...
six
...
hour
...
test.
...
Figure
...
4
...
shows
...
the
...
sludge
...
build
...
up
...
underneath
...
the
...
plates
...
in
...
the
...
sedimentation
...
tanks
...
after
...
a
...
month
...
without
...
cleaning.
...
Flocs
...
were
...
clearly
...
reaching
...
the
...
sedimentation
...
tanks
...
when
...
the
...
incoming
...
turbidity
...
was
...
higher
...
in
...
the
...
first
...
few
...
trials.
...
It
...
was
...
unclear
...
whether
...
or
...
not
...
a
...
floc
...
blanket
...
could
...
have
...
formed
...
at
...
high
...
incoming
...
turbidities.
...
One
...
tank
...
should
...
be
...
shut
...
off
...
at
...
night
...
when
...
higher
...
turbidities
...
are
...
coming
...
to
...
the
...
plant
...
to
...
see
...
if
...
a
...
floc
...
blanket
...
can
...
formed
...
in
...
a
...
system
...
as
...
complex
...
as
...
the
...
Cuatro
...
Communidades
...
sedimentation
...
tanks
...
given
...
more
...
time.
| Wiki Markup |
|---|
{float:border=2px solid black|width=300px} !sludge.jpg|width=300px! h5. figure 4: sludge settled below the plates in the bottom of the sed tank {float} |
However,
...
if
...
a
...
floc
...
blanket
...
can
...
be
...
formed
...
at
...
this
...
plant
...
given
...
ideal
...
conditions,
...
it
...
may
...
unreasonable
...
to
...
expect
...
that
...
one
...
can
...
be
...
maintained
...
at
...
this
...
plant.
...
The
...
amount
...
of
...
flocs
...
reaching
...
the
...
sedimentation
...
tanks
...
would
...
need
...
to
...
be
...
increased
...
to
...
ensure
...
that
...
the
...
floc
...
blanket
...
could
...
be
...
sustained
...
at
...
low
...
incoming
...
turbidities.
...
Also
...
the
...
plant
...
often
...
needs
...
to
...
be
...
shut
...
off
...
for
...
cleaning
...
or
...
minor
...
malfunctions,
...
at
...
this
...
point
...
the
...
floc
...
blanket
...
would
...
collapse.
...
If
...
the
...
effluent
...
turbidity
...
must
...
initially
...
spike
...
before
...
improving,
...
the
...
first
...
three
...
attempts
...
to
...
run
...
one
...
tank
...
show
...
that
...
it
...
takes
...
longer
...
for
...
the
...
floc
...
blanket
...
to
...
form
...
than
...
the
...
residence
...
time
...
of
...
the
...
communities'
...
water
...
storage
...
tank
...
and
...
their
...
water
...
demand
...
allows.
...