Bentonite Adsorption & Coagulation Treatment of Recycled Fiber Pulping Wastewater

doi:10.4236/eng.2013.510B064

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Engineering, 2013, 5, 314-320

http://dx.doi.org/10.4236/eng.2013.510B064 Published Online Octob er 2013 (http://www.scirp.org/journal/eng)

Bentonite Adsorption & Coagulation Treatment of

Recycled Fiber Pulping Wastewater

Tingzhi Liu , Kaiyang Zheng, Defa Wang, Shuai Li, Haoyu Wang

School of Material Sci ence& Technol ogy, Tianjin University of Sci ence & Technol ogy,

Tianjin Key Laborato ry of Pulp & Paper, Tianjin, China

Email: [email protected]

Received July 2013

ABSTRACT

A bentonite & PAM particle floc culation system was employed in recycled fiber pulp wastewater treatment in t his pa-

per. The o ptimum cond itions of the adsorption & coagulation treatment was explored and optimized and effects of the

treatment were focused on, especially stickies substances removal. U nd er t he optimal conditions, the removal of MTBE

extract and cationic demand reached 91.26% and 86.93%, and the average particle size in the treated wastewater pollu-

tants is reduced from 40.95 μm to 0.5 μm. I n this treatment the removal of CODcr, turbidity, SS and color were 89.67%,

99.56%, 95.58% and 93.08%, respectively. The results showed that the particle flocculation system was effective for

the treatment of recycled fiber pulp wastewater, especially for controlling the stickies.

Keywords: Recycled Fibe r Pulp; Wastewater; Stickies, Bentonite; Coagulation

1. Introduction

Increased consumption of recycled fiber in paper indus-

try not only reduced the dep endence on for e s t resource

require ments, but also the pollution of environment. On

the ot her ha nd, the impurities from the waste paper bring

about more and more serious problems, and the accumu-

lation problems of stickies are especially paid attention.

The accumulation of stickies in waste paper stock and

follow-up white water system will make drainage in the

wet-end of the paper machine become uneven, resulting

in paper flaws such as paper hole and stain. Sorting of

waste paper, flocculation deinking, screening of pulp,

dispersion, process water treatment, chemical agent ap-

plication and b io-treatment, all these technologies can be

used to control the stickies troubles of recycle fiber pulp

[1-5]. All these mentioned technological measures aimed

at recycle fiber pulp and pulping process, but reducing

the stickies content of pulping wastewater is useful and

helpful to control the stickies troubles, too. In this artic le,

a bentonite & PAM particle flocculation system was em-

ployed in recycled fiber pulping wastewater treatment.

Bentonite, clay, coke, activated sludge and some other

materials were used as adsorption aids to improve floc-

culation efficiency [6, 7 ]. Bentonite, which is available in

large quantities, can be used as an adsorbent for the re-

moval of dissolved organic compounds from pulp & pa-

per mill effluent with appreciably lower cost [8].

2. Material and Methods

The wastewater was collected at a laboratory installation,

include wastewater from pulping, floatation deinking. It

was stor ed in a refri gerator until use. Its i nitial prope rties

were shown in Table 1. The bentonite (800 mesh,

Na-bentonite) and the PAM (medium cationic, MW

about 10 million daltons) were obtained from YaGuang

Development Co., Ltd, Ningbo, Zhejiang province of

China.

Put appropriate amount recycled fiber pulp wastewater

liquor into a beaker and the pH and temperature of the

wastewater sample were first adjusted. Then put into

Table 1. Index of routine analysis for original wastewater

and those after treatment.

wastewater Treated water Removal (%)

CODcr (mg/L) 3020 312 89.67

SS (mg/L) 860 38 95.58

Turbidity( NTU) 108.00 1.03 99.56

pH 6.4 7.9 -

color (C.U.) 867.4 58.2 93.08

MTBE extract ( mg/L) 236.8 20.7 91.26

CD (μmol/L) 1065.4 150.0 85.92

pa r t icle size(μm) 40.95 0.51 -

T. Z. LIU ET AL.

315

appropriate amount bentonite and Stiring at 150 rpm for

30 min for adsorption. After adsorption reaction, put

PAM int o beake r and stri ng for a few minute s, then con-

tent settle for 30 min, the supernatant in the b eaker was

taken out and used for the analyse s .

The chemical oxygen demand (CODcr) of the water

sample was determined by colorimetric methods. The

turbidity of the water sample was measured by an ASN

2000 turbidity meter [9]. The MBTE extract of effluent

was determined according to the method described in an

article [10]. And the Cationic demand (CD), mean di-

ameter of particles of wastewater were measured by

PCD-03 particle charge analyzer (Mütek). The color of

wastewater was determined by spectrophotometer at 465

nm and convert s to Pt -Co C.U.

3. Results and Discussion

The op timal conditions of recycled fiber pulp wastewater

treatment were studied. This article was focused on ef-

fects of bentonite, PAM dosages, pH, temperature of

wastewater and the stir speed and time on removal of

pollutions. The CD, SS, turbidity and OD of 465 nm

were determined to optimize the treatment conditio ns.

Table 1 offered an index of routine analysis for original

wastewater and those after treatment under the optimal

conditions. As shown in Table 1, the results of routine

tested of recycled fiber pulp wastewater were: The

CODcr was 3020 mg/L, pH was 6.4. The average particle

size was 40.95 μm and the turb idity was 108.0NTU. The

contents of SS and MTBE extract were 860 mg/L and

236.8 mg/L, respectively. The CD of the wastewater was

as high as 1065.4 μmol/L. These anionic constituents

were related to the content of stickies i n wa st e wate r [11].

3.1. Effect o f the Bentonite Dosage

As sho wn i n Figure 1, the tur bidity and SS of t he treated

wastewater were reduced with the increase of bentonite

dosage, and reached the minimum at the same dosage

which was about 250 mg/L. It is because that the SS of

the treated water was devoted by fines concentration. The

light beam will be scattered and reflected by the small

particles. This is exactly corresponds with the determina-

tion theory of turbidity. So the turbidity of the water in

this stud y was linear with the content o f SS. T he CD and

465 nm OD of the treated water were decreased with the

increase of bentonite dosage, and reached the minimum

at about 150 mg/L dosage, but increased at the dosage of

250 mg/L, then drop again while the dosage reached at

400 mg/L. This was most likely caused by that the re-

moval of CD and color substances due to the two ways:

adsorption and coagulation mechanism.

Figure 1 further showed that the removal of the four

index were significant only when the dosage from 50

mg/L to 150 mg/L, and the maximum color and CD re-

movals were observed at about 150 mg/L. So the 150

mg/L was the optimal bentonite dosage.

3.2. Effect o f the PAM Dosage

The Figure 2 showed that the curve trends of turbidity

and SS of the treated wastewater were similar with the

increase of PAM dosage. The SS and turbidity of treated

water reached the minimum points at the same dosage

which was about 50 mg/L PAM, and then increased

while the PAM dosage increased to 100 mg/L, the max-

imum dosage of this study. The similar result of SS and

Turbidity removal with the increase of PAM dosage was

also reported by Angela C.R while they used a Fe- culant

to treated pulp effluent [12]. The CD of the treated water

reduced sharply with the increase of PAM dosage while

the dosage lower than 10 mg/L, then increased slightly

with the dosage from 20 mg/L increased to 100 mg/L.

The changes of color of the treated water with the

150

200

250

300

350

400

050100 150 200 250 300 350 400

200

250

300

350

400

SS(mg·L

-1

)

OD of 465nm

Turbidity

Dosage of bentonite(mg.L

-1

)

CD(umol

-1

)

0. 0

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7

0. 8

0. 9

1. 0

Turbidity( NTU)

465nm O D

Figure 1. Effect of the bentoni te dosage on adsorption & coag ulation t r e atment .

T. Z. LIU ET AL.

316

increase of PAM dosage were far more complicated than

the other three indexes. The 465 nm OD of the treated

water decreased sharply with the increase of the PAM

dosage from 2 to 10 mg/L, and then increased from 10

mg/L to 100 mg/ L. The OD had a minimum at the PAM

dosage about 10 mg/L and a maximum at about 100

mg/L. This confused c urve tre nd can be explained through

understanding ho w t he objects of PAM flocculation. As a

kind o f macromolecular flocculant, the function of P AM

in the waste water treatment is mainly due to the reaction

of adsorption bridging mechanism. This can be explained

the sharply decreasing with the increase of the PAM do-

sage from 2 to 10 mg/L. When the dosage of PAM was

too big, the positive electricity charges of the excessive

PAM (medium cationic PAM) will adsorb and coagulate

the fines concentration by compression of double

charged. It was very difficult to precipitate and demix,

because there was so much substantial macromolecular

floc in the treated water. It was also explained why the

SS, CD, turbidity and 465 nm OD of treated water in-

creased with the PAM from 50 mg/L to 100 mg/L. Con-

clusions as a result, the 10 mg/L was the choice dosage

of PAM.

3.3. Effect o f the Initial pH

Figure 3 Showed the effects of initial pH on the bento-

nite treatment of recycled fiber pulp wastewater. As a

whole, all of CD, SS, 465 nm OD and turbidity of the

treated water were increased with the initial pH value

increased. The color and CD of the treated water in-

creased slightly with the increased of pH, the acidic

property of water becomes stronger, the CD and color of

treated water will become smaller. It is different that the

color of the treated water altered little with the pH from 2

to 6 to that of raw material puling ef fluen t. The color of

raw material puling effluent will change very signifi-

cantly because the acidic precip itation of lignin that con-

tributes to the color of these effluents. The SS of the

treated water increased slightly with the pH from 2.0 to

6.0, and from 8.0 to 12.0, but decreased at the pH8.0.

The turbidity of the treated water shows two inflection

points at pH value 4.0 and 8.0. The turbidity decreased

with the pH from 2.0 to 4.0, and then increased fro m pH

4.0 to 8.0, after pH 8.0, with the increase of pH value, the

turbidit y increased significantly. It was ma ybe due t o the

good dispersion of bentonite at alkaline environment.

The dispersion of absorbed water and expanded bentonite

in water caused the increasing of turbidity.

The above mentioned factors should be under consid-

eration choice of pH value. Except for the SS of the

treated water, the other three indexes are good enough

for the treatment at pH6.0. Choose the pH 6.0 as the op-

timal value was under consideration not only the treated

efficiency but also the cost of the treatment, because the

pH value of the origin water was about 6.0.

3.4. Effect of the Wastewater Temperature

The temperature of wastewater will affect the adsorption

and coagulation efficiency of bentonite. As shown in

Figure 4, the CD, 465 nm OD, SS and turbidity of the

treated water decreased with the increase of the tempera-

ture from 30˚C to 60˚C, and reached a desired treated

effect at 60˚C. The n the C D, 4 65 nm OD, SS and turbid-

ity of the treated water increased with the increase of the

temperature from 60˚C to 80˚C. Figure 4 also shows that

the temperature affects the index of SS and turbidity

more weakly than those of CD and 465 nm OD. The CD

value of the water was to indicate the negative electric

charge. Another perspective reflects the content of nega-

tive substances. These substances are mainly composed

120

130

140

150

160

170

180

190

200

010 20 30 40 50 60 70 80 90100110

150

160

170

180

190

200

210

220

230

240

250

SS(mg

L-1)

O D of 465nm

Turbi dity

Dosage of PAM(mg.L-1)

CD(umol

L-1)

0. 10

0. 12

0. 14

0. 16

0. 18

0. 20

Turbidi ty( NTU)

465nm O D

Figure 2. Effect of the PAM dosage on bentonite adsorption & coagulat ion tr e a tme nt.

T. Z. LIU ET AL.

317

100

200

300

400

2 4 6 810 12

100

200

300

400

SS (mg·L

-1

)

O D of 465nm

Turbidity

CD(umol·L

-1

)

0. 0

0. 2

0. 4

0. 6

0. 8

1. 0

Turbidi ty( NTU)

465nm O D

Figure 3. Effect of the initial pH on bentonite adsorption & coagulation treatment.

140

150

160

170

180

190

200

5. 0

5. 5

6. 0

6. 5

7. 0

7. 5

8. 0

8. 5

9. 0

30 40 50 60 70 80

100

110

120

130

140

150

160

SS(mg

-1

)

O D of 465nm

Turbidity

Temperature(℃)

CD(umol

-1

)

0. 06

0. 08

0. 10

0. 12

0. 14

Turbidity(NTU)

465nm O D

Figure 4. Effect of the w ast ewater temperature on bentonite adsorption & coagulati on treatme nt.

of soluble and collo idal constituents. The color is mainl y

contributed by these soluble and colloidal constituents

too. Except effect of adsorption & coagulation of the

bentonite, the temperature of water also affects the ener-

gy of motion of these soluble and colloidal constituents.

The energy of motion of the se soluble and co lloidal con-

stituents was up to the status in adsorption & coagulation

treatment. So the temperature of water affects the CD

and 465 nm OD strongly than those of SS and turbidity.

By contrast, the components that influence the detec tio n s

of SS and turbidity index were composed of colloidal and

dispersive constituents. The energy motion of these col-

loidal and dispersive constit uents will be affected slightly

by temperature change than it of soluble and colloidal

constituents. So tha t the force of gravity and volume fac-

tors of these colloidal and dispersive constituents affect

the status settlement and separation much more impor-

tantly. So 60˚C was the optimal temperature for adsorp-

tion & coagulat ion treatment.

3.5. Effec t of the Stir Speed

As Figure 5 shown, the CD and 465 nm OD of treated

water decreased and then increased with the increase of

stir speed, and they all reached the maximum color and

CD removals at 200 rpm speed. Figure 5 also s hows that

the curve trends of turbidity and SS of the treated waste-

water were similar to these of the CD and 465 nm OD

with the increase of stir speed. However, the lowest

points of the SS and turbidity of the treated water were

observed at the 150 rpm. The appearance of the maxi-

mum removal speed of CD and 465 nm OD different to

that of SS and turbidit y attribu tes to the d ifferent removal

mechanism of them. For the removal of CD and color

T. Z. LIU ET AL.

318

constituents, the fast Stir not only enhances the mass

transfer cap ability of the water but also gives those more

chance to come into contact with the others. So the

minimum points of the CD and color reached at more

fast s tirri ng spe ed tha n tho se of t he SS and tur bidi ty. Bu t

over—rapid stirring will broke up the floc and disperse

the co nstitue nts into the water again, t his ca n explain t he

increases of CD and 465 nm OD with the speed from 200

rpm to 300 rpm. Stir speed affects the turbidity and SS

not o nly o n ca pab ilit y o f ma ss tr ans fer, but also o n sta tus

of the floc. A sli ght over stirri ng will give t he floc app re-

ciable damage effects, so the ideal stir speed for turbidity

and SS removal was lower than it of CD and 465 nm OD,

it was 150 rpm. Figure 5 also sho ws that the turbidity

changed slightly with the speed from 50 rpm to 100 rpm,

but significantly when the speed is over 100 rpm, and

will increase while the speed is more than 150 rpm.

Many researchers had obtained the same rule on the

effect of speed on turbidity in their studies [12,15].

3.6. Effec t of the Stir Time

Figure 6 showed that a short time stirring could o btain a

very good effect of SS, turbidity and 465 nm OD remo-

val. From Figure 6, the SS, turbidity and 465 nm OD

decreased significantl y with the stirri ng time fo rm 0 pro-

long to 2min, and reached to the good removal point at 2

- 5 min, then increased with the stirring time extended

again. It was different to the other three inde xes, the CD

of the treated water increased stably with the stirring time

extended. Removal of the material that indicated CD of

the water mainly depends on the adsorption of the bento-

nite. Before the addition of PAM, t he bentonite has been

added into the water and adsorbed the material for 30min,

so the content of CD materials has reduced to a limited

status. When the stirring beginning, the materials of CD

resolved into the water, so the CD incre ased.

100

110

120

130

140

150

160

170

180

190

200

5.0

7.5

10.0

12.5

15.0

17.5

20.0

50100 150 200 250 300

100

120

140

160

180

200

220

240

SS(mg

-1

)

O D of 465nm

Turbidity

Stir(rpm)

CD(umol

-1

)

0.0

0.1

0.2

0.3

0.4

0.5

Turbidi ty( NTU)

465nm O D

Figure 5. Effect of the stir speed on bentoni te adsorption & coagulati on treatment.

120

140

160

180

200

220

05 10 15 20

120

140

160

180

200

SS(mg·L-1)

OD of 465nm

Turbidity

S tir time( min )

CD(umol

L-1)

0. 10

0. 15

0. 20

0. 25

0. 30

Turbidi ty( NTU)

465nm O D

Figure 6. Effect of the stir time on bentonite adsorption & coa gulation treat ment

T. Z. LIU ET AL.

319

3.7. The Removal Efficiency of Bentonite

Adsorption & Coagulation Treatment

Through the studies of influence factors we draw up the

optimal conditions for recycled fiber pulp wastewater

treatment. The optimal co nditi ons were: bentonite dosage

was 150 mg/L, PAM dosage was 10 mg/L, the adsorption

reaction temperature was 60˚C, pH value was 6.4, the

original pH of the wastewater, after PAM additio n, stir-

ring at the speed of 150 rpm for 2 - 5 min. Table 1 shows

an index of routine analysis for original wastewater and

those after treatment under the optimal cond itions.

From Table 1, under these optimal conditions, the

COD of the wastewater from 3020 mg/L reduced to 312

mg/L, and the removal rate reached about 90%. The tur-

bidity and the SS of the waste water red uced from 108 .00

NTU and 860 mg/L to 1.03NTU and 38 mg/L, and the

removal of them were 99.56%, 95.58%, respectively.

The color of the wastewater from 867.4 C.U. reduces to

58.2 C.U., and the removal rate was 93.08%. All these

lead up to the conclusion that the particle flocculation

system was effective for the treatment of recycled fiber

pulp wastewater. Figure 6 also shows that the average

particle size in the treated wastewater pollutants is re-

duced from 40.95 μm to 0.5 μm. It shows that the ad-

sorption coagulation aid treatment which is mainly used

to remove larger particles and colloids suspended materi-

al. It is worthwhile noting that the removal of MTBE

extract reached 91.26%. The stickes materials are mainly

composed of these constituents that can be e xtracted by

orga nic so lve nts. T he removal of organi c sol vent s extract

always reached to about 90% [13-15]. But those studies

were almost though the biological treatment to reach the

removal rate. And the removal of CD of the waste water

was about 87% reflecting that the bento nite adsor ption &

coagulation T r eatment wa s a very good treatment and the

removal of stickies was very efficiently.

4. Conclusion

The bentonite, which is available in large quantities, can

be used as an adsorbent for the removal of dissolved or-

ganic compounds from pulp & paper mill effluent with

appreciably lower cost. Und er the optimal condition s, the

removal of MTBE extract and cationic demand reached

91.26% and 86.93%. The results show that the particle

flocculation system is effective for the treatment of re-

cycled fiber pulp wastewater, and the control of stickes

of recycle fiber pulp wastewater is very efficien t.

5. Acknowledgemen ts (Heading 5)

Financial support from National “Twelfth five-year”

Science & Technology Key Project of China

(2011BAC11B04) and Science & Technology Develop-

ment Grants Planning Projects for Tianjin High Educa-

tion Colleges (SW 20080001).

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