Journal of Environmental Protection, 2011, 2, 1370-1374
doi:10.4236/jep.2011.210159 Published Online December 2011 (http://www.SciRP.org/journal/jep)
Copyright © 2011 SciRes. JEP
Preparation and Study of a Composite Flocculant
for Papermaking Wastewater Treatment
Defang Zeng1,2, Dan Hu1,2, Jie Cheng1,2
1School of Resource and Environmental Engineering, Wuhan University of Technology, Wuhan, China; 2Hubei Key Laboratory of
Mineral Resource Processing and Environment, Wuhan, China.
E-mail: 516777198@qq.com
Received September 16th, 2011; revised October 23rd, 2011; accepted November 25th, 2011.
ABSTRACT
A high flocculation performance composite flocculant was prepared with sodium alginate, polyaluminium ferric chlo-
ride and cationic polyacrylamide. And the composite flocculant was used in papermaking wastewater treatment. Results
indicated that it achieve the best flocculation performance when the raw material mass ratio was 2:1:1, the dosage of
the composite flocculant was 20 mg/L, and the removal efficiency of COD and turbidity with this composite flocculant
reached 89.6% and 99.2%, respectively.
Keywords: Sodium Alginate, Polyaluminium Ferric Chloride, Cationic Polyacrylamide, Flocculation
1. Introduction
Papermaking wastewater contains lignin, cellulose, di-
fficult degradation substances and many tiny colloidal
materials [1-3]. And flocculation is widely used to pa-
permaking wastewater pretreatment or advanced treat-
ment [4]. Flocculants are the materials, which are used in
fast solid-liquid separations. They act on a molecular
level on the surfaces of the particles to reduce repulsive
forces and increase attractive forces [5].
Sodium alginate flocculant is widely used in medicine,
food, printing, dyeing, papermaking and other industries
as its gelling ability, stabilizing properties, and high vis-
cosity in aqueous solutions [6-8]. Sodium alginate is a
polysaccharide carbohydrate which is a linear polymer
consisting of (1-4)-poly-β-D-mannuronic acid and (1-4)-
α-L-guluronic acid [9-11]. Sodium alginate can be ex-
tracted from the kelp seaweeds and other algae [12]. So-
dium alginate is a flocculation reinforcing agent in pa-
permaking wastewater treatment and it is acted as a
framework material in flocculation. It will accelerate the
forming of flocculation particles and shorten the time of
flocculation.
As an inorganic polymer flocculant, polyaluminium fer-
ric chloride is widely used in industrial wastewater be-
cause of the bigger flocs, more rapid settling and wide sub-
ject range of pH compared with aluminum sulfate and
polyaluminium chloride [13]. And cationic polyacryla-
mide as a flocculant aid, it could reduce the dosage of
flocculants, increase the flocculation rate and improve
the stability of flocs in wastewater treatment [14]. Agui-
lar et al. used polyacrylamide as flocculant aid to im-
prove the process of coagulation-flocculation [15].
On the basis of the advantages of sodium alginate,
polyaluminium ferric chloride and cationic polyacryla-
mide, we tried to prepare a composite flocculant consist-
ing of sodium alginate, polyaluminium ferric chloride
and cationic polyacrylamide to treat papermaking waste-
water. The main objective of this study was to evaluate
the flocculation performance of the composite flocculant.
2. Materials and Methods
2.1. Materials
Sodium alginate (SA) was procured from Chemical Re-
agent Factory (Shanghai, China). Polyaluminium ferric
chloride (PAFC) was purchased from Chemical Co., LTD
(Shenyang, China). Cationic Polyacrylamide (CPAM) was
obtained from Silver Rings Chemical Co., LTD (Guang-
zhou, China). All chemicals were of analytical grade.
2.2. Preparation of the Composite Flocculant
SA, PAFC and CPAM were added to the distilled water
until dissolution to make a stock solution, respectively.
The stock solution of SA, PAFC and CPAM was mixed
using a magnetic stirrer (Model 78-1, Jintan splendor
equipment manufacture Co., LTD, Jiangsu, China), ad-
justing pH, stirring and settling for some period of time
Preparation and Study of a Composite Flocculant for Papermaking Wastewater Treatment1371
to prepare the composite flocculant.
2.3. Flocculation Experiment
Wastewater samples from the wastewater before air flo-
tation phase with 1208mg/L of COD, 415NTU of turbid-
ity value, 7.1 of pH and 30˚C of water temperature was
supplied by a Paper Mill located at Hubei province in
China.
In each experiment, once the composite flocculant was
added, the wastewater was stirred at a certain velocity for
a few minutes on a six-port combined mixer (Model S2-1,
Scientific Apparatus Company, Shengzhen, China), kept
the wastewater settling for a while, the upper fluid was
used to measure COD and turbidity in the treated water
samples.
COD was measured with a COD digestion device (Mo-
del 5B-1C, Lian Hua Environmental Protection Science
and Technology Co., LTD, Lanzhou, China). Turbidity
was measured with a turbidity meter (Model XZ- 1B, Lei
Gu Apparatus Co., LTD., Shanghai, China). All experi-
ments were conducted at least in triplicate.
3. Results and Discussion
3.1. The Preparation Conditions of the
Composite Fl occul a nt
The orthogonal experimental was conducted to confirm
the optimum conditions of the composite flocculant. And
the mass ratio of the raw material, pH and reaction time
were chosen as the factors. Table 1 was the orthogonal
layout of the composite flocculant. Table 2 was the re-
sults of the orthogonal experimental. k1, k2, k3 were the
mean removal efficiencies of COD each factor under
three levels. And kІ, kП, kШ were the mean removal effi-
ciencies of turbidity each factor under three levels. As
shown in Table 2, the optimum formula was A2B3C2 on
removing COD and turbidity. On removing COD, the
influence of the materials’ mass ratio was much more than
pH and reaction time, and the influence of reaction time
was more than pH. On removing turbidity, the materials’
mass ratio was the most influence, the next was reaction
time and the last was pH. When SA:PAFC:CPAM was
2:1:1, the best flocculation performance was achieved.
3.2. Effect of Dosage of the Composite Flocculant
To determine the effect on COD and turbidity removal
Table 1. Orthogonal layout of the composite flocculant.
Factors A(SA:PAFC:CPAM) B(pH) C(Reaction time/h)
Level 1 1:1:1 5.5 1
Level 2 2:1:1 6.5 1.5
Level 3 2:2:1 7.5 2
Table 2. Orthogonal layout of the composite flocculant and
its analysis.
FactorsA B C
Removal rate
of COD (%)
Removal rate of
turbidity (%)
1 1 1 1 75.6 86.2
2 2 2 2 80.5 91.8
3 3 3 3 71.2 83.7
4 1 2 3 74.8 83.9
5 2 3 1 79.4 91.0
6 3 1 2 70.7 85.4
7 1 3 2 73.9 85.9
8 2 1 3 74.4 85.1
9 3 2 1 64.3 80.0
k1 74.76773.56773.100
k2 78.10073.20075.033
k3 72.10074.83373.467
R 6.0001.5331.933
kІ 85.33385.56785.733
kП 89.30085.23387.700
kШ 83.03386.86784.233
R 6.2671.6343.467
using composite flocculant, a series of tests were con-
ducted to determine the optimal dosage of composite flo-
cculant. Six kinds dosage of the composite flocculant
were prepared. And the optimal one was determined. The
results indicated that the optimal dosage was sample 4, as
shown in Table 3. And the optimal dosage of the com-
posite flocculant was 20 mg/L. The efficiency in the re-
moval of COD and turbidity were enhanced with the in-
creased dosage of composite flocculant. And the removal
efficiencies of COD and turbidity reached the highest
level when treated by sample 4 flocculant formula. How-
ever, with the continuously increased dosage of composite
flocculant, the effect on reducing the concentrations of COD
and turbidity was gradually decreasing. It was because that
the particles would be encompassed by excess dosage of
composite flocculant, losing the chance to combine with
other particles and reaching another stable situation. It
made the particles difficult to aggregation and reduced
the flocculation efficiency. So, the optimal dosage was
Table 3. Effect of dos ag e on flocculation effect.
Sample Dosage of the composite
flocculant (mg/L)
Removal rate of
COD (%)
Removal rate of
turbidity (%)
1 5 75.6 88.6
2 10 79.1 91.5
3 15 81.9 93.3
4 20 83.5 95.8
5 25 76.7 95.1
6 30 76.2 93.7
Copyright © 2011 SciRes. JEP
Preparation and Study of a Composite Flocculant for Papermaking Wastewater Treatment 1372
sample 4 composite flocculant, and the optimal removal
efficiency of COD and turbidity were 83.5% and 95.8%,
respectively.
3.3. Effect of pH Value
A series of tests were conducted to study the flocculation
effectiveness of composite flocculant under different pH
(3.08, 5.18, 7.18, 8.10, 9.08, 10.10). Wastewater sample
was treated under the six different pH values. The experi-
mental results in Ta ble 4 showed that the highest removal
rate of COD and turbidity at pH 7 - 8. The explanation for
this as follows: Colloidal substances were usually nega-
tively charged in papermaking wastewater, while CPAM
contained acylamino and it had great cationic degree and
strong positive electricity, so that it had a good charge neu-
tralization ability and it could adsorb particles for com-
pressing double-charge-layer to made particles destabilize.
Besides, the methyl of acylamino was hydrophobic. It
would reach toward the surrounding in wastewater sample;
increased the interfacial tension of solid-liquid, the repul-
sive force and the contact angle of water; thus improved
the effect of flocculation. But it would reduce the treat-
ment effect when pH value was too high. The alkaline en-
vironment was prone to cause rapid hydrolysis of alumi-
num ions in flocculation and the charge neutralization abi-
lity would be reduced [16].
3.4. Effect of Stirring Speed
A series of tests were conducted to study the flocculation
effectiveness of composite flocculant under different stir-
ring speed. The experimental results in Table 5 showed
that the removal efficiency of COD and turbidity reached
Table 4. Influe nce of pH on flocculation effect.
pH Removal rate of COD (%) Removal rate of turbidity (%)
3.08 76.4 81.2
5.18 79.6 92.4
7.18 83.7 94.9
8.10 85.8 97.0
9.08 81.7 94.7
10.10 74.4 81.3
Tabl e 5 . Inf l u e nc e of r a pi d s ti r ring sp ee d on f l oc c ul a ti o n ef f e-
ct.
Rapid stirring
speed (r/min)
Removal rate
of COD (%)
Removal rate
of turbidity (%)
140 78.2 90.1
160 81.4 92.6
180 84.2 95.4
200 87.1 97.3
220 83.8 94.4
240 81.6 91.8
87.1% and 97.3%, respectively, at the rapid stirring speed
of 200 r/min. And Table 6 showed that the removal effi-
ciency of COD and turbidity reached 87.8% and 97.5%,
respectively, at the slow stirring speed of 40r/min. It could
be attributed to the effect of mixture and reaction stages of
the flocculation process [17]. At the mixture stage, rapid
stirring speed was required to make the composite floccu-
lant diffuse into the wastewater rapidly and evenly. It cre-
ated good conditions for the hydrolytic polymerization and
made colloid destabilization and aggregation. At the reac-
tion stage, slow stirring speed was required to make floc-
culation particles into large flocs with good settalbility.
But the stirring speed should not be too fast as it would
break down the flocs and affected the effect of flocculation.
So, the stirring speed played an important role in floccula-
tion.
3.5. Effect of Stirring Time
A series of tests were conducted to study the flocculation
effectiveness of composite flocculant under various stir-
ring time. The experimental results in Table 7 showed that
the removal efficiency of COD and turbidity reached
88.4% and 98.2%, respectively, at the rapid stirring time of
2.5 min. And Table 8 showed that the removal efficiency
of COD and turbidity reached 89.1% and 98.9%, respec-
tively, at the slow stirring time of 9 min. The explanation
for this was two-folded: At the mixture stage, it only
needed few minutes to make the composite flocculant dif-
fuse into wastewater and got good flocculation effect. At
the reaction stage, it needed a little longer to make the
Table 6. Influence of slow stirring speed on flocculation
effect.
Slow stirring
speed (r/min)
Removal rate
of COD (%)
Removal rate
of turbidity (%)
20 79.0 91.3
30 83.4 95.4
40 87.8 97.5
50 84.3 96.2
60 82.5 93.8
70 80.2 92.5
Table 7. Influence of rapid stirring time on flocculation
effect.
Rapid stirring
time (min)
Removal rate
of COD (%)
Removal rate
of turbidity (%)
0.5 79.1 91.7
1.0 80.9 93.0
1.5 83.6 95.2
2.0 86.4 96.3
2.5 88.4 98.2
3.0 85.8 96.6
Copyright © 2011 SciRes. JEP
Preparation and Study of a Composite Flocculant for Papermaking Wastewater Treatment1373
Table 8. Influence of slow stirring time on flocculation effe-
ct.
Slow stirring
time (min)
Removal rate
of COD (%)
Removal rate
of turbidity (%)
6 82.5 92.9
7 84.6 95.6
8 86.3 97.0
9 89.1 98.9
10 87.8 97.2
11 83.4 94.3
flocculation particles into big one and it would sediment
rapidly so as to improved flocculation effect. The second
reason was the effect of sodium alginate. As a polymeric
flocculant, sodium alginate mixed in wastewater only need
few minutes and it would make sense rapidly.
3.6. Effect of Settling Time
Settling time had a direct influence on the effect of floccu-
lation. A series of tests were conducted to study the floc-
culation effectiveness of composite flocculant under vari-
ous settling time (10, 15, 20, 25, 30, 35 min). The removal
rate of COD and turbidity reached 89.6% and 99.2%, re-
spectively, at the settling time of 30 min as shown in Table
9. Sediment stage followed after the flocculation process.
The removal rate of COD and turbidity would very low if
the settling time was too short. Some of small flocs and
suspended matter would not reach the bottom of the beakers
so as to the low removal efficiency of COD and turbidity.
The removal rate of COD and turbidity would increase
with the increasing of settling time. But it would stay the
same when the settling time reached the optimal one.
3.7. The Mechanism of Flocculation
Sodium alginate was an anionic polyelectrolyte and it
was a high polymer material with carboxyl groups. It had
the structure of three-dimensional. Sodium alginate was a
flocculation reinforcing agent in papermaking wastewa-
ter treatment and it was acted as a framework material in
flocculation.
Polyaluminium ferric chloride was an inorganic ma-
cromolecule flocculant. It combined the advantages of alu-
minum salt and ferric salt flocculant. Polyaluminium fe-
rric chloride made the colloid destabilization and aggrega-
tion [18]. Its own positive charge would neutralize ne-
gative charge of the colloid to make the colloid into flocs
and sediment so as to remove pollutants.
Cationic polyacrylamide was an organic macromolecule
flocculant. Its polymer long chain which was adsorbing on
the surface of the particles would adsorb the other particles.
That was, cationic polyacrylamide linked many particles
together and made them into flocs [19,20]. Besides, its
positive charge would neutralize negative charge of the co-
Table 9. Influence of settling time on flocculation effect.
Settling time
(min)
Removal rate
of COD (%)
Removal rate
of turbidity (%)
10 85.9 94.8
15 86.4 96.3
20 87.0 97.2
25 88.1 98.3
30 89.6 99.2
35 89.6 99.2
lloid to make the colloid into flocs and sediment so as to
remove pollutants.
With the adding of sodium alginate in wastewater, it
was good at adsorbing the colloid at the synergistic effect
of materials which closed to carboxyl groups. And the
positive charge of polyaluminium ferric chloride and ca-
tionic polyacrylamide neutralized negative charge of so-
dium alginate to avoid decreasing the removal rate of
COD and turbidity. Besides, positive charge’s mutual su-
perposition of polyaluminium ferric chloride and cationic
polyacrylamide could improve the ability of charge neu-
trality.
With the force of sodium alginate, polyaluminium
ferric chloride and cationic polyacrylamide, the compos-
ite flocculant made a good flocculation performance on
removing COD and turbidity in papermaking wastewater.
4. Conclusions
A composite flocculant was prepared for treating paper-
making wastewater and its effect of the flocculation was
studied. And the conclusions as follows:
The composite flocculant consisting of sodium algi-
nate, polyaluminium ferric chloride and cationic pol-
yacrylamide and the optimal dosage of the composite
flocculant was 20 mg/L;
The optimal treatment conditions were that pH value
was adjusted to 7 - 8; rapid stirring speed and slow
stirring speed were 200 r/min and 40 r/min, respec-
tively; rapid stirring time and slow stirring time were
2.5 min and 9 min, respectively; and settling time
was 30 min.
The highest removal rate of COD and turbidity with
the composite flocculant reached 89.6% and 99.2%,
respectively.
5. Acknowledgements
This project was supported through ministry of science
and technology in China of small medium enterprise tech-
nology innovation foundation and department of science
and technology in Hubei province, China of science and
technology research foundation, which we thank together
in this.
Copyright © 2011 SciRes. JEP
Preparation and Study of a Composite Flocculant for Papermaking Wastewater Treatment
Copyright © 2011 SciRes. JEP
1374
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