...
alum
...
dosing
...
Alum
...
Dose
...
Alum
...
dosing
...
has
...
been
...
an
...
important
...
variable
...
throughout
...
flocculation
...
history.
...
It
...
is
...
considered
...
an
...
art
...
form
...
and
...
is
...
generally
...
picked
...
up
...
through
...
practice
...
and
...
experience.
...
At
...
the
...
Cornell
...
Water
...
treatment
...
plant
...
the
...
operators
...
rely
...
on
...
past
...
data
...
and
...
a
...
streaming
...
current
...
director
...
to
...
establish
...
their
...
alum
...
dosing.
...
They
...
also
...
rely
...
on
...
some
...
rules
...
of
...
thumb
...
that
...
are
...
affected
...
by
...
the
...
temperature
...
and
...
the
...
turbidity
...
of
...
the
...
water.
...
It
...
appears
...
that
...
the
...
higher
...
the
...
temperature
...
the
...
less
...
alum
...
is
...
needed.
...
This
...
data
...
is
...
displayed
...
in
...
Table
...
1.
...
Table
...
1.
...
Rule
...
of
...
thumb
...
data
...
used
...
by
...
Cornell
...
University's
...
Water
...
Treatment
...
Plant
...
Operators.
...
|
...
|
...
|
...
|
...
Temperature
...
>
...
10°C
...
|
...
|
...
Temperature
...
<
...
10°C
...
|
...
|
...
|
...
|
...
NTU
...
|
...
|
...
Alum
...
dose
...
(mg/L)
...
|
...
|
...
Alum
...
dose
...
(mg/L)
...
|
...
|
...
|
...
1
...
|
...
17
...
|
...
10
...
|
...
|
...
10
...
|
...
27
...
|
...
20
...
|
...
|
...
50
...
|
...
43
...
|
...
34
...
|
...
|
...
100
...
|
...
60
...
|
...
46
...
|
...
|
...
200
...
|
...
77
...
|
...
60
...
|
...
In
...
an
...
attempt
...
to
...
automate
...
and
...
decrease
...
the
...
mystery
...
behind
...
alum
...
dosing
...
the
...
log
...
relationship
...
equation
...
(Y
...
=
...
A
...
+
...
B*log(NTU))
...
was
...
used
...
to
...
test
...
its
...
impact
...
on
...
flocculation
...
in
...
the
...
pilot
...
plant
...
flocculator.
...
After
...
the
...
value
...
of
...
A
...
was
...
lowered
...
and
...
the
...
tube
...
settlers
...
stopped
...
clogging
...
there
...
appeared
...
to
...
be
...
good
...
floc
...
formation
...
and
...
clean
...
water
...
being
...
produced
...
in
...
the
...
flocculator.
...
While
...
the
...
third
...
section
...
appeared
...
to
...
break
...
floc
...
ups
...
the
...
alum
...
dosing
...
was
...
sufficient
...
so
...
that
...
by
...
the
...
end
...
of
...
the
...
second
...
section
...
the
...
turbidity
...
was
...
usually
...
around
...
1
...
NTU
...
and
...
was
...
almost
...
always
...
below
...
2
...
NTU
...
(see
...
Figure
...
12
...
and
...
Figure
...
18).
...
The
...
raw
...
water
...
turbidity
...
coming
...
into
...
the
...
flocculator
...
stayed
...
between
...
2
...
and
...
6
...
NTU
...
during
...
most
...
tests
...
that
...
were
...
run.
...
While
...
the
...
turbidity
...
is
...
low
...
equation
...
18
...
allows
...
good
...
floc
...
formation
...
and
...
for
...
clean
...
water
...
to
...
be
...
produced
...
by
...
AguaClara
...
technology.
...
Alum
...
dosing
...
was
...
also
...
investigated
...
by
...
watching
...
floc
...
formation
...
in
...
the
...
flocculator
...
at
...
different
...
alum
...
doses.
...
This
...
was
...
done
...
in
...
an
...
attempt
...
to
...
note
...
if
...
it
...
was
...
possible
...
to
...
visually
...
discern
...
when
...
the
...
alum
...
dose
...
needed
...
to
...
be
...
changed.
...
Doses
...
of
...
0,
...
5,
...
20,
...
and
...
50
...
mg/L
...
were
...
noted.
...
Upon
...
observing
...
0
...
alum
...
dose,
...
it
...
was
...
very
...
clear
...
that
...
there
...
wasn't
...
any
...
improvement
...
through
...
the
...
tank.
...
In
...
fact
...
the
...
whole
...
way
...
through
...
the
...
flocculator
...
it
...
looked
...
as
...
though
...
there
...
were
...
tiny
...
particles
...
floating
...
along
...
with
...
big
...
particles
...
and
...
this
...
never
...
changed.
...
When
...
observing
...
5
...
mg/L
...
the
...
difference
...
was
...
hard
...
to
...
discern.
...
It
...
appeared
...
that
...
there
...
was
...
improvement
...
through
...
the
...
tank.
...
The
...
last
...
two
...
sections
...
didn't
...
appear
...
to
...
have
...
as
...
many
...
small
...
particles
...
in
...
between
...
some
...
of
...
the
...
larger
...
particles
...
were
...
but
...
the
...
flocs
...
that
...
were
...
seen
...
appeared
...
to
...
be
...
smaller
...
than
...
those
...
observed
...
when
...
using
...
equation
...
18.
...
When
...
I
...
raised
...
the
...
alum
...
dose
...
to
...
20
...
at
...
first
...
there
...
appeared
...
to
...
be
...
a
...
rush
...
of
...
floc
...
at
...
the
...
beginning
...
that
...
moved
...
up
...
the
...
first
...
section
...
of
...
the
...
tank.
...
It
...
is
...
not
...
clear
...
if
...
this
...
was
...
due
...
to
...
the
...
introduction
...
of
...
the
...
higher
...
alum
...
dose
...
or
...
not.
...
After
...
the
...
initial
...
rush
...
of
...
flocs
...
the
...
water
...
entering
...
the
...
tank
...
didn't
...
seem
...
as
...
dirty
...
as
...
the
...
raw
...
water
...
entering
...
the
...
tank
...
without
...
any
...
alum.
...
The
...
floc
...
formation
...
appears
...
earlier
...
in
...
the
...
tank,
...
after
...
about
...
a
...
third
...
of
...
the
...
first
...
section.
...
They
...
are
...
still
...
small
...
at
...
this
...
point
...
but
...
the
...
improvement
...
over
...
the
...
end
...
of
...
the
...
first
...
section
...
and
...
the
...
middle
...
of
...
the
...
second
...
section
...
is
...
rapid.
...
Most
...
of
...
the
...
particles
...
are
...
in
...
floc
...
and
...
there
...
are
...
not
...
as
...
many
...
particles
...
in
...
between
...
flocs.
...
When
...
I
...
finally
...
increased
...
the
...
dose
...
to
...
50
...
mg/L
...
the
...
water
...
in
...
the
...
first
...
section
...
appeared
...
to
...
have
...
the
...
same
...
small
...
particles
...
in
...
between
...
larger
...
particles
...
as
...
the
...
raw
...
water
...
when
...
there
...
was
...
no
...
alum
...
added..
...
Through
...
the
...
tank
...
it
...
appeared
...
that
...
there
...
lots
...
of
...
medium
...
to
...
small
...
sized
...
flocs,
...
almost
...
as
...
though
...
there
...
were
...
more
...
medium
...
sized
...
flocs
...
and
...
not
...
any
...
large
...
flocs.
...
It
...
does
...
not
...
look
...
like
...
the
...
flocs
...
are
...
large.
...
They
...
are
...
small
...
and
...
never
...
get
...
bigger
...
throughout
...
the
...
tank.
...
There
...
are
...
a
...
few
...
rare
...
flocs
...
that
...
could
...
be
...
considered
...
large.
...
This
...
is
...
contrary
...
to
...
what
...
I
...
had
...
expected
...
to
...
see,
...
I
...
thought
...
I
...
would
...
see
...
the
...
same
...
type
...
of
...
floc
...
as
...
when
...
the
...
tube
...
settlers
...
were
...
clogging.
...
It
...
appeared
...
almost
...
as
...
though
...
by
...
overdoing
...
it
...
negated
...
the
...
effect
...
of
...
the
...
alum,
...
by
...
creating
...
the
...
reverse
...
charge
...
on
...
the
...
particles
...
which
...
again
...
had
...
a
...
repelling
...
affect.
...
Alum Dose
For the majority of testing, alum dose was set by equation 18. After the change of A from 15 to 10 was made this approach was effective for the low turbidities that the flocculator experienced this summer. Hopefully in the future the raw water turbidity will change enabling testing of higher turbidities. Through use of equation 18, observing the floc tank and conversations with the operators at the water treatment plant it has become apparent that there is still a lot of research that needs to be done regarding alum dose. Observing the floc tank was helpful in being able to identify different kinds of floc and what different alum doses looked like in the water entering the water treatment plant. The water treatment plant has now switched to a different coagulant but if they had to go back to alum they said they would use past experience and alum doses as well as jar tests to set their doses. This suggests that for each water treatment plant an equation, formula or at least a rule of thumb could be developed off of past water treatment for future dosing. If this formula would be translatable to other water treatment plants and different water types is uncertain. The run increment alum dose test should help to shed light on alum dosing as it allows the alum dose to be changed while at a relatively constant raw water turbidity. Hopefully the data from this test will show either an optimum dose or a small range of optimal doses for specific settled water turbidity.
Design Suggestions (for future plants)
If a serpentine flow is again used, future designs should include a way to make the dividers a more central part of the design, and a material that does not deform easily but holds its structure and can be sealed to the tank should be chosen. If this is not a possibility then re-enforcement to the dividers should be added to ensure that deformation does not cause problems with baffle skipping. This way the width of the sections can be easily controlled as well as locations where leaks could be problematic could be observed during installation. The problem with making the divider and the tank not one central piece is that it is difficult to make the two pieces fit together and make them water tight.
Another suggestion that would make maintenance of the tank easier would be to include an outlet that could be opened and closed nearer to the bottom of the tank than the outlet pipe currently is. The current design leaves water at a height of a few inches above the bottom that needs to be pumped out before the tank is fully drained. Even then with the design of the dividers the bottom of the tank can never be fully drained because the bottom piece of the divider covers most of the bottom of the tank. This is problematic if repairs to the caulk or Kwik Foam need to be made, as they seal best on dry surfaces.
When dealing inside the tank the current configuration of the modules is sturdy and provides a structure that allows the baffles to move as a whole maintaining baffle spacing. This is an advantage as it ensures that they are evenly spaced and that the value of G is constant throughout each module. One of the problems encountered this summer was that in the pilot plant configuration the inlet and outlet are both pipes that were added that decreased the space in the first and last section of the flocculator. If this design is to be replicated the space that the inlet and outlet occupy should be taken into account when designing the number of baffles. This is due to the fact that the connector pipes that are used to keep the baffles from drifting to the end could become caught on the exit pipe and cause the baffles to be pushed against the inlet. When lowering the modules into the tank they need to be lowered very carefully and each portion of the section needs to be lowered at the same time, necessitating at least two people, usually three. If the modules were bent the connector pipes would pop out of the caps and it would be hard to replace them. The connectors are important because of the forces that they carry.
Optimal Alum Dose Testing
Because the pilot plant takes water directly from the stream, environmental conditions change all the time and affect the incoming turbidity to the plant as well as the chemical composition of the particles causing turbidity. It is therefore necessary to determine the best alum dose for each day of testing to ensure the formation of good flocs. This requirement was implemented in the following way:
The Process Controller was used under the "Increment Alum" setting, which starts the Alum Dose at 0 mg/L, and increments at 5 mg/L until it reaches a maximum of 40 mg/L. Each of the alum doses ran for a 30-minute period, or for about 3 times the residence time of the tank. After the completion of the test, data processing was performed to select the data from the last 10 minutes of each individual alum increment. The first 20 minutes of data were rejected because the residence time in the flocculator was 10 minutes, and the residence time in the tube settler was also about 10 minutes. Therefore, in order to get readings from the final turbidimeter that were representative of the alum dose that we were testing, we discarded the first 20 minutes of data at each alum dose. The outgoing turbidity (from turbidimeter 4) was then analyzed for each increment, and the alum dose achieving the lowest turbidity was selected for the second part of the experiment.