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h2. |
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Abstract {cloak:id=Abstract} |
Enter
...
text
...
here
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Introduction {cloak:id=Introduction} |
Coagulation
...
is
...
the
...
process
...
of
...
chemically
...
destabilizing
...
solutions
...
whereby
...
electrolytes
...
are
...
added
...
into
...
solution
...
so
...
as
...
to
...
reduce
...
the
...
charge
...
on
...
the
...
colloidal
...
particles,
...
thus
...
facilitating
...
their
...
close
...
approach
...
and
...
aggregation.
...
In
...
water
...
treatment
...
processes,
...
the
...
primary
...
electrolyte
...
introduced
...
into
...
solution
...
as
...
the
...
primary
...
coagulant
...
is
...
aluminum
...
sulfate
...
(Al2(SO4)3),
...
also
...
known
...
as
...
Alum.
...
Flocculation
...
is
...
the
...
subsequent
...
process
...
whereby
...
particles
...
collide
...
and
...
form
...
large
...
aggregates,
...
or
...
flocs.
...
Flocculation
...
involves
...
producing
...
collisions
...
between
...
suspended
...
particles
...
that
...
are
...
strong
...
enough
...
to
...
overcome
...
the
...
repulsive
...
potential
...
barrier
...
between
...
particles,
...
but
...
that
...
will
...
not
...
simultaneously
...
break
...
up
...
the
...
flocs
...
already
...
in
...
suspension.
...
Improving
...
the
...
effectiveness
...
of
...
coagulation
...
and
...
flocculation
...
will
...
greatly
...
enhance
...
the
...
efficiency
...
of
...
small
...
scale
...
water
...
treatment
...
systems,
...
which
...
will
...
drive
...
down
...
costs
...
and
...
make
...
the
...
technology
...
more
...
feasible
...
and
...
attractive
...
to
...
communities.
...
One
...
of
...
the
...
important
...
contributors
...
to
...
the
...
formation
...
of
...
flocs
...
is
...
the
...
chemical
...
coagulant
...
aluminum
...
sulfate
...
(Alum).
...
When
...
dissolved
...
in
...
water,
...
alum
...
dissociates
...
and
...
the
...
multivalent
...
aluminum
...
ions
...
(Al3+)
...
form
...
various
...
species
...
that
...
have
...
an
...
average
...
positive
...
charge.
...
Since
...
most
...
suspended
...
colloidal
...
matter
...
in
...
surface
...
waters
...
have
...
an
...
overall
...
negatively
...
charged
...
surface,
...
the
...
dissolved
...
Al
...
species
...
will
...
adsorb
...
onto
...
the
...
surfaces
...
of
...
these
...
particles
...
and
...
reduce
...
its
...
net
...
surface
...
charge,
...
thus
...
lowering
...
the
...
barrier
...
for
...
floc
...
formation.
...
The
...
appropriate
...
amount
...
of
...
alum
...
required
...
to
...
facilitate
...
total
...
particle
...
removal
...
via
...
the
...
sedimentation
...
of
...
flocs
...
is
...
dictated
...
by
...
a
...
couple
...
key
...
parameters:
...
The
...
concentration
...
of
...
clay
...
particles
...
and
...
other
...
natural
...
organic
...
matter
...
(specifically
...
the
...
chemical
...
properties
...
of
...
these
...
contaminants
...
and
...
their
...
reactivity
...
with
...
the
...
dissolved
...
Al
...
species)
...
will
...
effect
...
how
...
much
...
alum
...
is
...
needed.
...
The
...
alkalinity
...
of
...
the
...
water
...
will
...
also
...
effect
...
how
...
well
...
the
...
coagulant
...
will
...
perform.
...
In
...
the
...
current
...
laboratory
...
flocculator
...
experimental
...
setup,
...
there
...
are
...
several
...
parameters
...
that
...
control
...
the
...
flocculator
...
process.
...
Our
...
main
...
objective
...
in
...
conducting
...
research
...
with
...
the
...
lab
...
flocculator
...
is
...
to
...
be
...
able
...
to
...
isolate
...
each
...
of
...
the
...
parameters
...
in
...
order
...
to
...
understand
...
their
...
specific
...
roles
...
in
...
the
...
flocculation
...
process
...
and
...
to
...
optimize
...
overall
...
flocculator
...
efficiency.
...
While
...
the
...
need
...
to
...
fully
...
understand
...
the
...
mechanism
...
by
...
which
...
alum
...
coagulates
...
particles
...
was
...
not
...
immediately
...
pressing,
...
it
...
was
...
important
...
for
...
our
...
research
...
to
...
determine
...
the
...
most
...
effective
...
alum
...
dose
...
for
...
various
...
levels
...
of
...
turbidity
...
in
...
order
...
to
...
temporarily
...
remove
...
alum
...
dosing
...
as
...
a
...
variable
...
in
...
our
...
later
...
experiments.
...
In
...
order
...
to
...
isolate
...
and
...
temporarily
...
remove
...
alum
...
as
...
a
...
variable,
...
a
...
relationship
...
between
...
alum
...
dose
...
and
...
influent
...
turbidity
...
must
...
be
...
determined.
...
For
...
a
...
given
...
influent
...
turbidity,
...
there
...
is,
...
theoretically,
...
an
...
optimal
...
amount
...
of
...
alum
...
that
...
should
...
be
...
added
...
to
...
the
...
influent
...
in
...
order
...
to
...
form
...
the
...
greatest
...
amount
...
of
...
flocs
...
and
...
thus
...
producing
...
the
...
lowest
...
effluent
...
turbidity.
...
This
...
optimal
...
alum
...
dose
...
should,
...
therefore,
...
change
...
with
...
different
...
influent
...
turbidities.
...
The
...
objective
...
of
...
our
...
first
...
experiment
...
was
...
to
...
determine
...
the
...
optimal
...
alum
...
dose
...
for
...
various
...
influent
...
turbidities.
...
While
...
finding
...
this
...
relationship
...
is
...
integral
...
to
...
our
...
later
...
experiments,
...
the
...
empirical
...
values
...
would
...
not
...
necessarily
...
apply
...
to
...
vertical
...
flocculators
...
used
...
in
...
water
...
treatment
...
plants
...
designed
...
for
...
Honduras.
...
First,
...
differences
...
in
...
flocculator
...
design,
...
and
...
thus
...
intensity
...
and
...
quality
...
of
...
mixing,
...
could
...
greatly
...
affect
...
the
...
appropriate
...
alum
...
dose
...
for
...
various
...
turbidities.
...
Moreover,
...
the
...
levels
...
of
...
contaminants
...
in
...
the
...
waters
...
in
...
Honduras
...
will
...
have
...
very
...
different
...
dissolved
...
matter
...
in
...
it
...
that
...
will
...
react
...
to
...
alum
...
much
...
differently
...
than
...
in
...
our
...
experiments.
...
However,
...
the
...
purpose
...
of
...
our
...
investigating
...
optimal
...
alum
...
dose
...
is
...
not
...
to
...
give
...
operators
...
in
...
Honduras
...
a
...
alum
...
dosing
...
guide,
...
but
...
to
...
develop
...
a
...
control
...
method
...
in
...
our
...
experiments
...
that
...
will
...
render
...
alum
...
dosing
...
a
...
temporary
...
non-variable.
...
Future
...
experiments
...
may
...
need
...
to
...
be
...
performed
...
to
...
determine
...
whether
...
the
...
effects
...
of
...
alum
...
can
...
vary
...
with
...
different
...
mixing
...
intensities
...
or
...
other
...
variables.
...
After
...
determining
...
the
...
optimal
...
alum
...
dose
...
for
...
different
...
influent
...
turbidities,
...
we
...
proceed
...
to
...
run
...
experiments
...
with
...
other
...
variables,
...
such
...
as
...
velocity
...
gradient
...
(G)
...
and
...
Gtheta,
...
an
...
indicator
...
of
...
the
...
cumulative
...
extent
...
of
...
mixing
...
experienced
...
after
...
one
...
pass
...
through
...
a
...
reactor.
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{toggle-cloak:id=Methods} |
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Methods {cloak:id=Methods} |
The
...
...
...
was
...
used
...
in
...
this
...
experiment.
...
In
...
order
...
to
...
isolate
...
alum
...
dose
...
as
...
the
...
only
...
variable
...
in
...
our
...
experiment,
...
we
...
must
...
maintain
...
mixing
...
at
...
a
...
constant.
...
If
...
we
...
maintain
...
both
...
flow
...
rate
...
and
...
flocculator
...
length
...
(hence
...
residence
...
time)
...
constant,
...
we
...
can
...
keep
...
mixing
...
constant.
...
The
...
length
...
of
...
the
...
tube
...
was
...
inherited
...
from
...
the
...
summer
...
team,
...
as
...
our
...
team
...
did
...
not
...
replace
...
the
...
tube
...
that
...
had
...
already
...
been
...
attached
...
to
...
the
...
set
...
up.
...
The
...
calculation
...
for
...
the
...
length
...
of
...
the
...
tube
...
was
...
done
...
by
...
measuring
...
the
...
outer
...
diameter
...
of
...
the
...
cylinder
...
around
...
which
...
the
...
tube
...
was
...
wrapped
...
(plus
...
adjustments
...
for
...
the
...
thickness
...
of
...
the
...
tube
...
itself)
...
and
...
multiplying
...
that
...
by
...
¿
...
to
...
give
...
the
...
circumference
...
and
...
then
...
multiplying
...
the
...
circumference
...
by
...
the
...
number
...
of
...
times
...
the
...
tube
...
wrapped
...
completely
...
around
...
the
...
cylinder.
...
The
...
affective
...
diameter
...
was
...
42
...
cm
...
and
...
the
...
tube
...
wrapped
...
around
...
the
...
cylinder
...
approximately
...
15.5
...
times,
...
giving
...
a
...
total
...
length
...
of
...
approximately
...
20.45
...
meters.
...
Given
...
that
...
the
...
flocculator
...
length
...
is
...
fixed,
...
we
...
must
...
select
...
and
...
hold
...
constant
...
a
...
flow
...
rate
...
that
...
is
...
will
...
cause
...
adequate
...
amount
...
of
...
mixing
...
but
...
that
...
will
...
not
...
break
...
up
...
flocs.
...
From
...
observations
...
of
...
past
...
experiments
...
and
...
reports
...
done
...
by
...
past
...
lab
...
floc
...
teams,
...
a
...
Gbar
...
(average
...
velocity
...
gradient)
...
of
...
roughly
...
40
...
sec-1
...
was
...
selected
...
as
...
the
...
Gbar
...
that
...
will
...
be
...
used
...
in
...
every
...
run
...
of
...
this
...
particular
...
alum
...
dose
...
experiment.
...
The
...
equations
...
relating
...
Gbar
...
to
...
the
...
flow
...
rate
...
Q
...
for
...
laminar
...
pipe
...
flow
...
are
...
as
...
displayed
...
below.
...
Note
...
that
...
the
...
transition
...
between
...
laminar
...
flow
...
to
...
turbulent
...
flow
...
in
...
long
...
smooth
...
pipes
...
occurs
...
at
...
a
...
Reynolds
...
number
...
of
...
roughly
...
Re
...
=
...
2300.
...
This
...
translates
...
to
...
a
...
flow
...
rate
...
of
...
roughly
...
9.69
...
mL/sec
...
through
...
the
...
0.42m
...
diameter
...
pipes
...
used
...
in
...
this
...
experimental
...
setup.
...
Since
...
the
...
pumps
...
are
...
unable
...
to
...
pump
...
fluid
...
through
...
the
...
pipes
...
at
...
those
...
speeds,
...
it
...
is
...
valid
...
to
...
assume
...
that
...
the
...
flow
...
in
...
the
...
pipes
...
will
...
be
...
laminar
...
for
...
our
...
experiments.
...
The
...
flow
...
rate
...
at
...
which
...
all
...
our
...
experiments
...
will
...
be
...
run
...
is
...
Q
...
=
...
1.33
...
mL/sec
...
which
...
produces
...
a
...
Gbar
...
=
...
42
...
sec-1.
...
The
...
alum
...
stock
...
had
...
not
...
been
...
used
...
up
...
at
...
the
...
start
...
of
...
our
...
experiments,
...
but
...
we
...
noticed
...
that
...
contaminants
...
in
...
the
...
form
...
of
...
dust
...
and
...
lint
...
had
...
fallen
...
and
...
aggregated
...
at
...
the
...
bottom
...
of
...
the
...
alum
...
stock
...
tank.
...
These
...
aggregated
...
contaminants
...
had
...
the
...
potential
...
to
...
clog
...
up
...
the
...
very
...
narrow
...
feed
...
tubes
...
that
...
led
...
out
...
of
...
the
...
alum
...
stock
...
container.
...
Furthermore,
...
while
...
fine
...
tuning
...
the
...
Process
...
Controller
...
methods,
...
we
...
noticed
...
that
...
that
...
the
...
current
...
concentration
...
of
...
5000
...
mg/L,
...
a
...
dose
...
of
...
5
...
mg/L
...
could
...
not
...
be
...
produced
...
by
...
the
...
peristaltic
...
pump.
...
While
...
Process
...
Controller
...
read
...
a
...
value
...
of
...
5
...
mg/L
...
for
...
the
...
alum
...
dose,
...
the
...
pump
...
was
...
not
...
spinning
...
and
...
thus
...
not
...
pumping
...
the
...
amount
...
indicated
...
by
...
Process
...
Controller.
...
The
...
solution
...
to
...
this
...
problem
...
was
...
to
...
dilute
...
the
...
alum
...
to
...
a
...
lower
...
concentration
...
(1500
...
mg/L
...
in
...
our
...
case)
...
so
...
that
...
a
...
higher
...
alum
...
flow
...
rate
...
would
...
be
...
required
...
to
...
obtain
...
a
...
particular
...
influent
...
concentration
...
than
...
when
...
it
...
was
...
at
...
5000
...
mg/L.
...
To
...
determine
...
the
...
optimal
...
alum
...
dose
...
needed
...
for
...
an
...
influent
...
water
...
turbidity
...
of
...
100
...
NTU,
...
we
...
set
...
up
...
a
...
special
...
program
...
in
...
Process
...
Controller.
...
We
...
varied
...
the
...
alum
...
dose
...
added
...
to
...
the
...
influent
...
stream
...
from
...
0
...
mg/L
...
to
...
45
...
mg/L
...
in
...
increments
...
of
...
5
...
mg/L
...
for
...
an
...
influent
...
turbidity
...
of
...
50,
...
75,
...
100,
...
and
...
150
...
NTU.
...
This
...
range
...
in
...
alum
...
doses
...
was
...
selected
...
based
...
on
...
previous
...
observations
...
that
...
40
...
mg/L
...
of
...
alum
...
produced
...
best
...
results
...
at
...
a
...
turbidity
...
on
...
the
...
order
...
of
...
100
...
NTU.
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{toggle-cloak:id=Results} |
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Results {cloak:id=Results} |
After
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running
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a
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set
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of
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alum
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incremented
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experiments
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on
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influent
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turbidities
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of
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50,
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75,
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100,
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150
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NTU,
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we
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extracted
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the
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data
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for
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analysis.
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Normally,
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a
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Mathcad
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program
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developed
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by
...
the
...
previous
...
teams
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would
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have
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been
...
utilized
...
to
...
gather,
...
parse,
...
and
...
extract
...
relevant
...
data
...
recorded
...
through
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out
...
the
...
experimental
...
runs;
...
however,
...
our
...
team
...
had
...
not
...
been
...
introduced
...
to
...
the
...
software
...
at
...
the
...
time
...
of
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this
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report's
...
submission
...
and
...
had
...
to
...
parse
...
and
...
analyze
...
the
...
data
...
with
...
Microsoft
...
Excel.
Figure 1: Settling curves for various alum doses at an influent turbidity of 50 NTU.
Figure 2: Settling curves for various alum doses at an influent turbidity of 75 NTU.
Figure 3: Settling curves for various alum doses at an influent turbidity of 100 NTU.
Figure 4: Settling curves for various alum doses at an influent turbidity of 150 NTU.
Figures 1-4 display the time series plots of turbidity during the settle state in which flocculated particles are allowed to settle in a quiescent environment inside the modified glass cylinder of the effluent turbidimeter. The effectiveness of alum is measured by the size of flocs after flocculation. Since we do not have the equipment needed to observe and measure the sizes of flocs formed after each experiment, we can only observe the rate at which flocs settle under quiescent conditions and the final settled turbidity. Since the experiments were run under identical conditions, the mechanisms creating the flocs are identical from run to run; therefore, the composition of the flocs (their shape and density) should be relatively uniform. This fact allows us to directly relate the settling rate of the flocs to the size of the flocs, while neglecting factors such as electrostatic interactions and porosity (which would affect drag coefficients and densities.) Final turbidity is a measure of whether of how much suspended particles were not affected by the alum---a high final turbidity would indicate that an inadequate amount of alum was introduced compared to the amount of contaminants in solution. Therefore,the optimal alum dose should be indicated by the curve with the quickest settling rate and final turbidity.
The 100 NTU figure (Figure 3) is missing curves for the experiments run at 0 mg/L and 5 mg/L because the data obtained for those two runs were interrupted by the interference of the 7kPa pressure sensor going in and out of voltage range. The data was omitted from the figure because of those errors. The 100 NTU experiments were the first experiments to be run, so the error was fixed and eliminated. The subsequent experiments at 100 NTU are correct as well as the runs for 50, 75, 150 NTU.
For the 50 NTU experiments (Figure 1) a general trend can be seen that indicates final turbidity decreases as alum dose increase. There is an unexpected anomaly in the relationship between the 0 mg/L curve and the 5 mg/L curve. Contrary to expectations, it appears that the quality of the final water was worse off after adding 5 mg/L of alum as opposed to having no alum present. The cause of this discrepancy is unclear, but it appeared to be an isolated occurrence as the experiments run with 75 (Figure 2) and 150 NTU (Figure 4) were consistent with expectations. Another general observation deduced from comparing each of the figures is that the settling rate of flocs increases dramatically between the alum dose of 5 mg/L and 10 mg/L. This trend occurred across all turbidities (this observation is less obvious in the 100 NTU run, but the data does not necessarily oppose this observation) and is a phenomena that may be of significance in understanding alum effectiveness. A second observation deduced from comparing each of the figures is that the marginal effectiveness (measured in both final turbidity and initial rate of settle) of increasing alum dose decreases significantly after about 25-30 mg/L of alum. It is expected that a point will be reached at which additional alum addition will not significantly reduce turbidity, and it is in the proximity of this alum dose that we suspect the optimal alum dose will be. More experiments should be run to obtain better data resolution at the alum doses between 25-55 mg/L. The largest alum dose used in these experiments was 45 mg/L, and while the curves show that the marginal benefit gained by adding more alum in the 40-45 mg/L range is minimal, extending the alum dose range will give more definitive evidence that we have indeed reached a critical value in alum dose.
The lowest turbidity reading reached in each of the four turbidity experiments were in the 10 NTU range. Additionally, it appears that for the higher alum doses, the curve flattened out at approximately the same elapsed time in each of the four influent turbidity experiments. This indicates that at higher influent turbidities (higher particle concentrations), particle aggregation becomes easier and therefore effluent flocs are generally bigger and settle out faster.
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{toggle-cloak:id=Discussion} |
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Discussion {cloak:id=Discussion} |
The
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experiments
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proved
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that
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the
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addition
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of
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alum
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into
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turbid
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waters
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prior
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to
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flocculation
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improves
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particle
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aggregation,
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leading
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to
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higher
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settling
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velocities
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and
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cleaner
...
effluent
...
water.
...
The
...
experiments
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do
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not
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show
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conclusive
...
evidence
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of
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where
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the
...
optimal
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alum
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dose
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is
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for
...
the
...
different
...
levels
...
of
...
turbidity.
...
The
...
fact
...
that
...
the
...
curves
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are
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so
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similar
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in
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all
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four
...
figures
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suggests
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that
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the
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optimal
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alum
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doses
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changes
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only
...
slightly
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for
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this
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range
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of
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turbidity
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values.
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More
...
experiments
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should
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be
...
done
...
to
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refine
...
the
...
data
...
resolution
...
of
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the
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25-55
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mg/L
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alum
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dose
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range
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for
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each
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of
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the
...
4
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turbidities.
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