United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
&EPA
Research and Development
EPA-600/S2-82-012 August 1982
Project Summary
The Effect of Total Water
Reuse and Alum Control on
First Pass Retention
Michael D. Strutz
The escalating cost of raw materials,
coupled with more stringent effluent
limitations, have led papermakers to
consider wet end chemistry optimiza-
tion as a solution to these problems.
They have also become aware of the
possible benefits to be derived from
increased Whitewater reuse. While
certain construction paper and paper-
board manufacturers have used total
water reuse to solve their problems,
other categories of paper manufactur-
ing have not been so successful.
Product quality deterioration, caused
by poor wet end control and the
resulting build up of dissolved inorganic
and organic contaminants, have ham-
pered achieving complete water reuse.
A previous study at Miami University,
dealing with fine paper complete
water reuse, cited the control of first
pass retention as the key to a success-
ful total water reuse strategy.
By using pulp-derived dissolved
organic material as a variable, the
current study makes use of a dynamic
retention/drainage jar to show the
negative effects of these compounds
on retention. The negative effects can
be overcome by controlling the alum
concentration to satisfy the cationic
demand which this material exhibits.
Excessively high alum concentrations,
however, are shown in the study to de-
crease retention in a system where a
high molecular weight cationic poly-
mer was used. Controlling alum con-
centrations will reduce the negative
effects of dissolved organics in closed
systems and achieve maximum effi-
ciency from costly polymer retention
aids.
Interferences to the alum titration
technique for measuring alum in
Whitewater samples were investigat-
ed. Iron and pulp-derived organic
material were found to interfere
slightly with the method, causing
higher results than the actual alum
concentration in the sample. However,
the method was found to be suitable
for control purposes.
Various levels of pulp-derived or-
ganic material tended to hold zeta
potential at zero over a wide range of
alum concentrations. This phenome-
non occurred at organic concentrations
above approximately 200 ppm. This
factor should be taken into considera-
tion when using zeta potential as a wet
end optimization parameter.
A retention control strategy for total
water reuse is proposed. It is based on
the measurement and manipulation of
alum concentrations in the stock
chest, in low shear systems where no
polymer is used — to control the
electrokinetic balance for proper
coagulation, and in high shear systems
where polymers are used — to eliminate
the negative effects due to alum/poly-
mer interactions.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Cincinnati. OH,
to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
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Introduction
The pulp and paper industry is facing
the implementation of stricter effluent
limitations proposed by the U.S. Environ-
mental Protection Agency. By 1984, the
industry may be required to reduce its
effluent discharge of Biochemical
Oxygen Demand and Total Suspended
Solids from current levels. In meeting
the previous Best Practicable Treatment
Technology regulations, industry en-
vironmentalists recognized the cost-
effectiveness of in-process recycle/
reuse techniques for reducing effluent
loadings. In fact, many mills in several
subcategories of the industry have
implemented total water reuse strategies
for the complete elimination of their
discharge. It is the purpose of this
research to investigate the possibility of
total water reuse in the non-integrated
fine paper su beat ego ry, specifically in
the manufacture of a high opacity offset
grade.
Miami University investigated a
totally closed Whitewater system during
the production of an offset grade in
19771. The buildup of dissolved and
suspended solids in the Whitewater
system was monitored over a 96-hour
period. Paper samples were collected at
regular intervals during the trial and
various quality analyses were performed.
The study concluded that problems
would arise in the areas of sizing,
brightness reversion, and first pass
retention. The authors recommended
that these problems could be controlled
by optimizing wet end chemistry,
thereby controlling first pass retention.
By computer simulation, they observed
that this strategy would, in turn,
eliminate the sizing and brightness
reversion problems. The key is control-
ling retention.
In the study of retention, it has been
observed that small amounts of dissolved
organic material can decrease the
effectiveness of cationic retention aids.
These dissolved materials can be lignin,
hemicellulose, fatty and resin acids, or
lignosulfonic acids. Their presence in
the papermaking system causes a
higher cationic demand, thereby in-
creasing the amount of cationic retention
aid required to reach optimum floccula-
tion. According to classical electrokinetic
theory, the buildup of dissolved inor-
ganic materials in closed Whitewater
systems would decrease the amount of
cationic retention aid required to reach
optimum flocculation. This was shown
to be true by Unbehend2 using mono-
valent and divalent cations, such as
sodium chloride and magnesium chloride.
Dissolved organic and inorganic
materials in the system can be consid-
ered controlled or uncontrolled variables
from a process control standpoint.
Those materials coming into the system
from the raw water or raw materials are
generally considered not controllable. A
process control variable such as alum,
however, may become uncontrolled in a
closed system. That is, if the concentra-
tion of alum in the system is not closely
watched, a situation may develop where
retention is adversely affected. Avery3
demonstrated this by decreasing the
alum concentration in a system using
cationic starch. Retention on the
machine was significantly improved.
This same phenomenon has also been
shown to occur with synthetic organic
retention aids. Excessive amounts of
these retention aids in the system will
also cause stock dispersion and poorer
retention4.
It becomes increasingly clear from the
previous discussion that the control of
retention will become more complicated
in a total closed system. In the 1977
machine trial at Miami University,
dissolved organic and inorganic solids,
as well as alum, continued to build up
during the run. Based on this information,
the objectives of the current study are:
to determine how the alum demand
changes under wet end conditions
found in a totally closed system; to
determine if the higher concentrations
of dissolved organic and inorganic
solids will interfere with the alum
titration measurement technique; and
to investigate alum control as a tech-
nique to improve retention in a totally
closed system.
Phase I - Bench Scale
Retention Analyses
A series of experiments was performed
to observe the effects of dissolved
organics, dissolved inorganics, alum, and
shear on the retention of fines in a vaned
Dynamic Retention/Drainage Jar5. A
76 micron, 14.5% open area electro
deposited nickel screen was used in the
jar. The furnish used is shown in Table
1. A 33 factorial design was used at the
low shear level, 300 revolutions per
minute (r.p.m.), and two 23 factorial
experiments were performed at the
medium and high shear levels (600 and
900 r.p.m.). All experiments were
performed at room temperature and pH
4.50 ± 0.02 units. The pH was adjusted
using HCI or NaOH. The levels for the
independent variables are shown ir
Table 2. Dissolved inorganics were
treated cumulatively as the total o
various levels of calcium, magnesium,
manganese, and iron derived frorr
observations during a previous totall\
closed machine run. The individual
levels for the dissolved inorganics are
shown in Table 3. The dissolved organics
used in the study were obtained by
beating bleached kraft fiber, filtering ofl
the solids, and concentrating the
dissolved organic material in the filtrate
using reverse osmosis. The levels of
dissolved organics used correspond
approximately to levels of volatile
dissolved solids measured during a
previous closed machine run on this
paper grade.
Effect of Organics
Figure 1 shows the data plotted at the
low dissolved inorganic level and the
negative effect of increasing concentra-
tions of dissolved organics on retention.
At 1 % alum, 300 r.p.m., and 1100 ppm
organics, the decrease in retention was
approximately 24%. The effect at 600
r.p.m. was about 6% and at 900 r.p.m.
there was no significant decrease in
retention (95% confidence limits for all
the data was ± 3.4%) The fines retention
at 600 r.p.m. was 35%, whereas at 900
r.p.m. it was about 25%.
Effect of Inorganics
Figure 2 shows two distinctly different
effects from increasing levels of dis-
solved inorganics. At the low dissolved
organic level, an increase in the level of
dissolved inorganics causes a decrease
in retention, while at the medium and
high levels, adding the dissolved inor-
ganics causes an increase in retention.
Although the zeta potential results do
not correlate perfectly with the results
obtained, a general relationship can be
observed. That is, depending on the
initial zeta potential of the system, the
addition of dissolved organic or inorganic
compounds may cause either an increase
or decrease in retention. Adding dis-
solved inorganics to a system exhibiting
a positive zeta potential will cause a
decrease in retention, whereas adding
them to a system exhibiting a negative
zeta potential will cause an increase in
retention. This would agree with clas-
sical electrokinetic theory which states
that maximum coagulation occurs at
zero zeta potential.
Effect of Alum
Figure 1 illustrates how the alum
demand of the system changes according
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Table 1. Experimental Furnish
Component
%
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90
80
70
* 60
50
.o
|
30
20
10
O
+26
Legend
® 0 ppm organics
& 550 ppm organics
(3 1100 ppm organics
Note: All data @ 300 R.P.M., pH 4.5. 1% alum
Zeta potential, in millivolts, adjacent to data point
Low Medium
Dissolved organics, relative concentration
High
Figure 2. Effects of organic and inorganic concentrations on retention.
90
80
70
60
.
I50
I
40
30
20
10
-10
0
-20
-10m Note: Alldata @ 30°. R-P-M., pH4.5, 1100ppm
organics, low inorganic cocentration
Zeta potential, in millivolts, adjacent
to data point
Legend
® Fines retention
• Ash retention
10 15 20
Alum concentration, %
25
30
Figure 3. Effects of alum concentration and Zeta potential on ash and fines retention.
4
of fines and ash decreases. \l i
apparent from a papermaking point o
view that the retention of fines and asl
takes precedence and alum should bi
controlled on that basis.
Effect of Dissolved Organics or
Zeta Potential
In the previous experiments, many o
the data points, particularly the pointsa
the intermediate and high dissolve!
organic levels, exhibited zero zeti
potential. Separate experiments wen
conducted to determine if this pheno
menon was characteristic of a systerr
containing quantities of dissolvee
organic material. Various quantities o
this material were added to a typica
furnish, the fiber was filtered off, anc
the zeta potential of the fines determined
Figure 4 shows the results of this
experiment which was conducted with
distilled water. Figure 5 shows the
results of the same experiment conduct
ed with tap water.
In both cases, tap water and distillec
water, similar curves were obtainec
using alum and no organic material. The
charge on the particles changed frorr
negative to positive at approximately 2%
alum. The curve peaked at about +15
mV zeta potential then steadily decreaseo
with further increases in alum concen-
tration. This phenomenon has been
previously illustrated in the literature6
and has been attributed to formation ol
aluminum hydroxide and the increasing
sulfate ion buildup.
Figure 4 also illustrates that the
increase in the dissolved organic
material in the sample has the effect of
suppressing the zeta potential and
increasing the alum demand, i.e., the
amount of alum required to reach zero
zeta potential. The suppression of the
zeta potential can also be seen in Figure
5. This phenomenon seems to be
characteristic of the organic material and
not of aluminum hydroxide formation
and sulfate ion buildup. There seems to
be a point around 200 ppm of organics
where the charge on the particles will
not reverse, i.e., will not become
positive. It is theorized that a neutrally
charged organic polymer is being
formed and is coating the particle
surface. This effect, coupled with
neutrally charged aluminum hydroxide
formation and sulfate ion buildup, is
creating a stable, neutrally charged
structure resistant to charge reversal. It
is acting in a similar manner in which
starch forms a protective colloid.
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+20
+ /0
3-20
*
j
-30
-40
-50
Legend
© 0 pp/n organics
A //O ppm organics
(3 220 ppm organics
Note; All data @ pH 4.5, in distilled water.
10 15 20
Alum concentration, %
25
30
Figure 4. Effects of organic and alum concentration on Zeta potential in
distilled water.
+50
+40
Note: All data @ pH 4.5 in tap water.
-30
Legend
Alum, Oppm organics
Aluminum chloride, 0 ppm organics
Alum. 220 ppm organics
Aluminum chloride. 220 ppm organics
o
0
5
21.4
Alum concentration* %
42.8 64.2 85.6
Aluminum Concentration, ppm
25
107.0
30
128.4
Figure 5. Effects of organic and alum concentration on Zeta potential in tap water.
These results make one question the
usefulness of zeta potential even in this
purely ionic system. It would be benefi-
cial at low alum levels, i.e., below the
isoelectric point, but would lose signifi-
cance as a control tool at higher levels.
Effect of Polymer
Two experiments were conducted to
test the hypothesis that the decrease in
retention observed during the 1977
closed machine run at Miami University
was caused by the effect of high alum
concentrations on the effectiveness of
the cationic polymer retention aid which
was used. These two experiments were
conducted with a high molecular weight
cationic acrylamide copolymer (Hercules,
Inc. Reten 210). The furnish contained
30% ash in the form of filler clay;
otherwise, it was the same as the
experimental furnish previously used.
Two shear levels, 300 and 600 rpm's,
were investigated.
Figure 6 shows the results at the low
shear level, 300 rpm. The retention
curve for the "no polymer" situation
shows a characteristic trend with
retention increasing sharply and reach-
ing a peak at 86%, with additional alum
not resulting in any further increases.
Retention levels off at approximately
85%. For the situation where polymer is
used at 0.05% on fiber, the results are
much different. Retention is best at 0%
alum and continually decreases at
higher alum concentrations, from a
maximum fines retention at 98% atO%
alum, to a low of 65% at 20% alum.
Retention with the polymer is consis-
tently worse than without the polymer at
alum concentrations above about 5% on
fiber. Alum evidently has a negative
effect on the bridging retention mecha-
nism of the polymer.
Figure 7 shows the experimental
results at the higher shear level,
600 rpm. The same decreasing trend in
retention with the polymer is evident
with the magnitude of the effect being
much greater. Retention decreased
from a maximum of 85% at 0% alum, to
a minimum of about 15% at 30% alum.
With no polymer, retention peaked at
30% at 4% alum, and showed a gradual
decreasing trend with increasing alum
concentrations.
Phase II • Alum Titration
Method Interference Analysis
The series of experiments conducted
during Phase I illustrated the fact that
the alum demand of the system changes
according to the chemistry of the wet
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700
90
80
70
c
£
60
50
40
30
20
With high molecular weight cationic polymer
A Dynamic retention/drainage jar, polymer @ 0.05%
• Dynamic retention/drainage jar, no polymer
A Pilot paper machine, polymer @ 0.05%
10
Alum, % on fiber
20
Figure 6. Retention vs. alum with and without cationic polymer (low shear/.
end, at least at the low shear levels. It
was hypothesized that any compound in
the system besides alum might present
the possibility of interfering with the
flouride titration either by reacting with
the fluoride (a positive interference), or
by reacting with the alum and making it
inaccessible to the fluoride (a negative
interference). The objective of this
phase was to determine whether or not
the concentrations of dissolved inorganic
and organic compounds expected to be
found in totally closed systems would
interfere with the titration.
A series of simple comparison experi-
ments were conducted holding the alum
concentration constant at a low level
(100 ppm) and the suspected interfering
compounds at high levels. The interfer-
ences investigated were organics, iron,
calcium, magnesium and manganese.
Each experiment was replicated five
times.
Table 4 shows the average difference
associated with each variable. In the
case of the organic concentrate and
iron, a positive interference of 19 ppm
and 5 ppm was observed. If both were
present, an interference of 24 ppm as
alum may result from their presence in
the sample. Therefore, if this sample
had been taken from the headbox of
machine operating of 0.5% consistency,
the titration would have predicted
approximately one half of a percent
more alum than was actually present.
The interference due to iron was due to
the greater affinity to fluoride, having a
higher charge density than the other
inorganic ions evaluated. The organic
concentrate used for the study also
contained a substantial quantity of
metal ions, especially calcium, which
could possibly explain the positive
interference which it exhibited.
From a process control point of view,
the titration is sufficiently accurate to
enable monitoring and control of alum,
based on the parameters used in this
study. The papermaker should be aware
of possible interferences in their
particular system and screen any
additives for possible interference to
allow proper interpretation of results
from the titration.
Summary and Conclusion
In developing a wet end optimization
strategy for total water reuse, a paper-
maker should consider how a particular
retention control strategy will ultimately
affect paper quality and machine
runability. Porwal7 has shown the
contribution of alum to scale problems
on machine wires. Other researchers
have shown how excessive alum
concentrations can adversely affect the
action rf synthetic organic retention
aids. This study has demonstrated how
excessive alum concentrations alone
will adversely affect retention. Work is
continuing at Miami University on how
excessive alum concentrations will
affect paper quality.
From a retention point of view, the
following conclusions can be drawn
from this study:
1. In a totally closed system, some
means of controlling the alum
concentration will be necessary.
This will involve measuring the
concentration of alum prior to its
point of addition, and making
adj ustments to the addition rate to
maintain the proper quantity of
alum in the system. The optimum
alum level will vary with system
conditions.
2. In a totally closed system, the
buildup of dissolved organic and
inorganic compounds may or may
not adversely affect retention
depending on the relative concen-
tration of each. The negative
effects of increasing organic
concentrations can be overcome
by properly adjusting the alum
level, or they may be overcome if
-------
80
70
60
50
c
o
30
20
10
600 RPM
4.50 pH
10 20
Alum, % on fiber
30
Figure 7. Retention vs. alum 1ith and without cationic polymer (medium shear).
Table4. Alum Titration Interferences
Substance (ppm) Average Difference
Volume Titrant (mis) Alum Equivalent (ppm)
Organic concentrate (1 WO)
Iron (14)
Calcium (130)
Magnesium (40)
Manganese (5)
+0.138
+0.034
0
0
O
+ 19
+ 5
0
0
0
parameter and may cause a false
interpretation of where theoptimum
alum concentration occurs.
4. At high shear levels, polymer
retention aids will be required to
achieve satisfactory retention.
Computer simulation of the data
collected during the 1977 machine
trial at Miami University predicted
25% ash retention as being satis-
factory. Ash retention levels at
medium and high shear levels
during the current study were
below 25%. Alum levels in polymer
systems should be closely watched,
especially where cationic polymers
are being used, to achieve maximum
retention benefits, based on the
data collected during this study.
5. For control purposes, the alum
titration, using a fluoride selective-
ion electrode, is sufficiently accu-
rate based on the variables consid-
ered during this study. The paper-
maker should be aware of possible
interferences in their particular
system and screen any additives
for possible interference to allow
proper interpretation of results
from the titration.
Material and Methods
One experiment tested the filtration
concentration and chemical analysis of
ten kilograms of bleached kraft pulp.
The results are shown in Table 5. The
data shows that carbohydrates repre-
sent approximately 23% by weight of
the identified organic material. Xylans
account for over 80% of this fraction.
Uronic acids are the next largest
fraction at 2.78% followed by acid
insoluble lignm and acid soluble lignin
at approximately 2% each. Of the
inorganic material identified, calcium
represents the largest fraction at 6.3%
by weight followed by sodium at 3%.
These two elements represent almost
85% of the identified inorganic material
in the sample. About 40% of the organic
material and 19% of the inorganic
material remains unidentified. Addition-
al analytical work is being performed to
account for this material.
other inorganics build up in the
system in appropriate amounts.
The particular organic/inorganic
balance in the system should be
recognized prior to alum addition.
Zeta potential may be measured
for this purpose if organic concen-
trations are not excessively high.
3. When using zeta potential as
retention optimization parameter,
the papermaker should be careful
not to equate a zero reading with
optimum conditions in the wet
end. The level of dissolved pulp-
derived material has a significant
effect on the measurement of that
References
1. Heller, P., Scott, W.E., and Springer,
Under Conditions of Complete Water
Reuse" TAPPI 62(12):79-84 (1979)
2. Unbehend, J.E., "Mechanisms of
Soft and Hard Floe Formation in
Dynamic Retention Measurement"
TAPPI 59(10):74-77 (1976)
. S. GOVERNMENT PRINTING OFFICE: 1982/659 -095/540
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3. Avery, L.P., "Evaluation of Retention
Aids - The Quantitative Alum Analysis
of a Papermaking Furnish and the
Effect of Alum on Retention" TAPPI
62(2):43-46(1979)
4. Beck., U., et al., "Theoretical and
Practical Contributions to the Elucida-
ation of Retention Problems" Woc-
henblatt Fur Papierfabrikation 105
(11/12):391-398 (June 1977)
5. Britt, K.W., "The Fines Fraction of
Paper Stock" TAPPI CA Report No.
57:89-97(1975)
6. Lindstrom, T., and Soremark, C.
"Electrokinetic Aspects of Internal
Rosin-Sizing" Svensk Papperstidning
Nr. 1:22-28(1977)
7. Porwal, S.K., Springer A., and
Proctor, A., "Scale Deposits on the
Fourdrinier Wire of a Fine-Paper
Machine" TAPPI 63(6):67-69
(1980)
TableS. Organic Concentrate Analysis
Compound
Weight (%)
Acid Insoluble (Klason) Lignin
Acid Soluble Lignin
Total Carbohydrate
Araban
Xylan
Mannan
Galactan
Glucan
Uronic Acid
Oleic Acid
Linoleic Acid
Tetrachloroguaiacol
Chloride
Sulfate
Aluminum
Calcium .
Iron
Magnesium
Manganese
Sodium
Ash I550°C)
Unidentified
2.085
1.950
22.750
1.150
18.400
0.650
1.000
1.550
2.780
0.003
0.001
0.033
0.192
0.020
0.301
6.300
0.394
0.288
0.03 J
3.030
30.100
59.842
Michael D. Strutz is with Miami University. Oxford, OH 45056.
Paul de Percin is the EPA Project Officer (see below).
The complete report, entitled "The Effect of Total Water Reuse and A lum Control
on First Pass Retention," (Order No. PB 82-231 309; Cost: $10.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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