Preparation and Study of a Composite Flocculant for Papermaking Wastewater Treatment

doi:10.4236/jep.2011.210159

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Journal of Environmental Protection, 2011, 2, 1370-1374

doi:10.4236/jep.2011.210159 Published Online December 2011 (http://www.SciRP.org/journal/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: [email protected]

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

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

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.

Preparation and Study of a Composite Flocculant for Papermaking Wastewater Treatment

1374

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