Deinking With Cellulase

8/2/2019 Deinking With Cellulase

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Enzymic deinking of old newspapers with cellulase

M.A. Pelach a, F.J. Pastor b, J. Puig a,*, F. Vilaseca a, P. Mutje a

a Laboratori dEnginyeria Paperera i Materials Polmers, Departament dEnginyeria Qumica, Agraria i Tecnologia Agroalimentaria, Escola Politecnica

Superior, Universitat de Girona, Girona 17071, Spainb Departament de Microbiologia, Universitat de Barcelona, Barcelona, Spain

Received 18 May 2001; received in revised form 2 August 2002; accepted 12 August 2002

Abstract

Paper recycling industries are oriented towards re-use and sustainability. These effects are combined in different ways to achieve

the requirements on printing and writing papers. Biodeinking is an alternative analysed in this study. Cellulase uses improve ink

detachment from old newspapers giving similar or better results when cellulase is used in place of classical chemicals. Cellulase needs

an optimal contact time with the pulp suspension. Ink detachment can also be optimised by means of defibering efficiency and

specific energy consumption. Increasing the consistency and decreasing the repulping time enhance savings and therefore

sustainability. These two parameters are analysed in terms of shear factor l .

# 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Biodeinking; Repulping; Ink detachment; Cellulase; Old newspaper; Shear factor

1. Introduction

Sustainability requires proper management of both

natural resources and energy, as well as feasible

recycling of wastes and methods for increasing produc-

tion without environmental concern.

Paper recycling represents a subsection of the paper

industry that is being oriented towards re-use and

sustainability. The main implications of this process

are the preservation of important woodland resources

and energy saving. Moreover, with the recycling of this

kind of waste, two significant purposes are attained: (i)

the elimination of large quantities of residual materials

and (ii) the added value of the pulp.In the paper recycling industry, deinking is necessary

to achieve minimum brightness values required for

printing and writing papers. A typical deinking process

starts with disintegration of recycled paper. This step is

generally carried out by the addition of chemicals in a

strong alkaline medium in order to promote defibering

and ink particle detachment. Subsequently, washing or

flotation technologies, generally in mild alkaline media,

allow ink removal from the suspension.Biodeinking is proposed as an alternative to the use of

chemical products at the disintegration stage. The

proposed methodology uses a neutral medium, which

allows the reduction of the contaminant charge and is

comparatively more suitable for the maintenance of the

environment. Different kinds of cellulase enzymes are

used to facilitate ink detachment, essential in the

deinking process for the removal of the ink later [1,2].

The application of cellulase in deinking is a recent

methodology and contradictory results have been pub-

lished. In addition, the proposed mechanisms of cellu-

lase functioning in deinking are different. According toWodward et al. [3], cellulase binding on pulp fiber may

result in surface fiber alteration, sufficient to favour

detachment during repulping. Nevertheless, other

authors reported that the main effect is the hydrolysis

and superficial degradation of cellulose that implies ink

removal from fibers [4/6]. It has also been reported that

enzymic and mechanical actions are basic in the process

[7]. Enzymic deinking increases in effectiveness on

increasing the disintegration consistency caused by a

higher friction between fibers. Conversely, Putz et al. [8]

minimise the importance of the mechanical action in the

enzymic process.* Corresponding author. Fax: '/34-972418399

E-mail address: [email protected] (J. Puig).

Process Biochemistry 38 (2003) 1063/1067

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0032-9592/02/$ - see front matter# 2002 Elsevier Science Ltd. All rights reserved.

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To compare enzyme application with traditional

chemicals added in the disintegration stage, additional

experiments using sodium hydroxide and hydrogen

peroxide were carried out. Disintegration consistency

was maintained constant and the ratio of sodium

hydroxide to hydrogen peroxide was 1:1.

3. Results and discussion

The literature consulted on the topic of study reports

that enzyme application to deinking is usually at a rate

of 0.05 and 0.1%. In the first experiment, this was rather

ineffective and did not show hopeful results. Conse-

quently, the applied enzyme percentage was increased to

0.75 and 2.25%. Table 2 shows the results of ink

detachment (InkD, %) as a function of concentration

of enzyme, type of enzyme, disintegration consistency

(cD) and contact time between enzymes and pulp

suspension.

The results indicate that there was a substantial

improvement in ink detachment by enzyme application.

Nevertheless, in addition to the enzyme percentage

activity, two other variables may affect the interpreta-

tion of results such as repulping consistency and contact

time. The significance of both variables was corrobo-

rated by statistical analysis (Table 3).

Values obtained for the two disintegration consisten-

cies without enzyme application indicate that increasing

contact time produced better values of InkD. These

findings indicate that previous contact of the old news-papers with hot water may favour the subsequent release

of the ink from the paper. It is possible that soaking time

either weakens the ink binding property on the old

newspaper or favours its disruption thereby improving

overall ink detachment. The magnitude of improvement

was similar in 6 and 10% formulations.

Values of detachment factor (InkD) in enzyme-less

experiments increased considerably from 6 to 10% of

consistency. This finding was attributed to the shear

strength factor (l) of the suspension under the operating

conditions that shifts from 0.35 Pa s at 6% consistency

to 2.44 Pa s at 10% consistency. The term l represents

the global quantification of the strengths involved in a

detachment process such as mechanical impact on the

rotor, pulper baffles and walls, and both acceleration

and viscosity [13,14]. The increase of InkD is therefore

logical when the consistency also increased, because the

higher shear strength between the fibers produced a

higher detachment.

It was also observed that InkD did not vary signifi-

cantly with increasing soaking time when no enzyme

was added to pulp suspension even at higher consis-

tency.

Referring to the enzyme activity, results obtained and

statistical analysis applied have shown that it is not

significant. ERICHW results obtained with different

enzymes were compared with classical chemicals (Table

4). The detachment degree obtained with a mixture of

1% NaOH'/1% H2O2 was of the same order or smaller

than that obtained with the application of E1 and E2

under the same operating conditions. This indicates thatproducts such as enzymes considered more sustainable

could substitute classical chemistry.

Results of E1 and E2 trials did not allow decisive

conclusions because the difference in activity was rather

small as was shown in the preliminary trials on non-

printed newspaper. Moreover, values were considerably

different from those obtained with other substrates

(Table 1) where a marked difference between E1 and

E2 was found. This may mean that the evaluation of

enzymic activity or enzyme behaviour must be evaluated

using similar substrates.

On the other hand, very promising results of ERICfrom hyperwashing were found (Table 5). By comparing

InkD values with results obtained with conventional

deinking (Table 4), a significant improvement in the

Table 2

Values of InkD (%) obtained as a function of concentration and type of

enzyme, disintegration consistency (cD, %) and contact time (t , min)

between enzymes and pulp suspension

cD (%) t (min) InkD (%)

E1 E2

0% 0.75% 2.25% 0% 0.75% 2.25%

6 30 65.2 79.4 76 65.2 77.1 80.2

120 67.7 79.4 78.4 67.7 77.3 79.6

10 30 74.2 76.1 81.8 74.2 79.6 82.1

120 80.4 81.9 84.5 80.4 80.9 85.1

Table 3

Effect test ofvariables over InkD

Variables D.F. Sum of squares F-ratio PF

Enzyme type 1 0.81 0.11 0.75

Enzyme concentration 2 364.84 24.09 0.00

Disintegration consistency 1 192.67 25.44 0.00Contact time 1 43.20 5.70 0.03

Influence of enzyme type, enzyme concentration (%), disintegration

consistency (%), and contact time (min).

Table 4

Values of ERIC (ppm) of hyperwashing handsheets obtained with

conventional disintegration stage

ERICHW (ppm)

1%NaOH'1%H2O2 250

2%NaOH'2%H2O2 310

Disintegration consistency: 6%; contact time: 30 min.

M.A. Pelach et al. / Process Biochemistry 38 (2003) 1063/1067 1065


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repulping step was observed. This may be beneficial for

the whole suspension in order to obtain a high-quality

deinking either through washing or flotation.

Ink detachment was strictly related to defibering

efficiency and specific energy consumption. Optimisa-

tion of ink detachment and environmental protection

could be analysed by these two concepts.The main purpose of defibering is the individualisa-

tion of the flakes so as to obtain a suitable suspension

for subsequent paper production, and the overall

objective was to produce at minimum cost with possibly

low energy consumption. In addition, by controlling the

defibering time (energy consumption) it is possible to

avoid the excessively fragmented ink, which may

reprecipitate into the fibers, a phenomenon that may

make complete elimination impossible.

The study of disintegration as a function of time

provides the pulping kinetics. These show that the

evolution of Sommerville index (ISV) fitted a first-orderkinetic equation. The evolution of ISV as a function of

time for 6 and 10% consistency with 18.33 s(1 rotor

speed and 50 8C temperature was determined. Using

this kinetics, it is possible to determine the repulping

time corresponding to ISV5/0.1% which in this case was

4 and 14 min for 6 and 10% consistency, respectively.

Higher values of repulping time may be detrimental for

complete ink removal, either due to an excessive

fractionation that leads to lower-sized particles, or by

redeposition into the lumen fibers.

Table 6 shows the evolution of energy consumption of

6 and 10% suspensions and the energy consumption in

empty conditions. With these results, it is possible to

calculate the net power. Values achieved were 728.6 W

for 6% and 1113.3 W for 10% consistency. Substituting

these values in expression (2) together with the respec-

tive densities and the frequency of the rotor gives the

following shear factor values: 0.35 Pa s for 6% and 2.44

Pa s for 10%. Specific energy consumption (kJ/ton) is

calculated by considering the tD and the energy con-

sumption values. Results corresponding to 6 and 10%

consistency (tD, 14 and 4 min, respectively) were 782.5

and 189.0 MJ/ton. This shows the advantages when

experiments were carried out with high consistencies

during repulping where the defibering and energetic

efficiency were higher as a consequence of l increase

with consistency.

4. Conclusions

The use of cellulase-type enzymes may represent an

alternative to conventional chemicals in repulping of old

newspaper. With low consistency (6%) and reasonable

contact time (30 min), the enzyme efficacy was equiva-

lent or higher to that obtained by means of conventional

deinking. For this same consistency and 120 min of

contact time, the efficacy did not improve.

For a medium consistency (10%) and 30 min of

contact time the efficacy decreased, although the

absolute detachment values improved. This behaviour

was similar for a contact time of 120 min.

Despite the different activities of the two investigated

enzymes on the diverse substrates, this difference was

not observed in deinking. Nevertheless, these results

coincide with the observed activity on the non-printed

paper. As a final conclusion, it can be stated that the

behaviour of the two enzymes in deinking was similar

and that the results improved slightly on increasing both

the contact time and the enzyme amount. From an

energetic point of view, increasing the consistency

because of the decrease in the repulping time enhancedsavings. Moreover, the effect of a higher consistency on

the ink detachment was very positive because of the

shear forces increase. This effect was also observed

without enzymes.

Acknowledgements

The authors would thank G. Pardini and M. Font for

their contribution and also to Cromogenia S.A.

Table 5

Results of effective residual ink concentration (ERICHW, ppm) of

hyperwashing handsheets as a function of concentration and type of

enzyme and contact time at constant disintegration consistency (10%)

t (min) ERICHW

E1 E2

0.75% 2.25% 0.75% 2.25%

30 218 166 198 174

120 147 165 185 145

Table 6Total energy consumption (kJ) in function of time (t , min) at different

disintegration conditions (cD, %)

t (min) Total energy consumption (kJ)

cD00% cD06% cD010%

2 50 152 201

4 100 280 378

6 147 416 554

8 194 549 720

10 237 676 892

12 280 807 1054

14 327 939 1229

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References

[1] Carre B, Galland G, Saint Amand FJ. Third Research Forum on

Recycling, 1995. p. 73/88.

[2] Bennington CPJ, Sui OS, Smith JD. The effect of mechanical

action on waste paper defibering and ink removal in repulping

operations. J Pulp Paper Sci 1998;24(11):341/8.

[3] Wodward J, Stephan LM, Koran LJ, Wong KKY, Saddler JN.

Enzymatic separation of high-quality uninked pulp fibers from

recycled newspaper. Biotechnology 1994;12(9):905/8.

[4] Eom TJ, Ow SSK. German patent GB 3,934,772 (1990).

[5] Lee SB, Kim KH, Ryu JD, Taguchi H. Structural properties of

cellulose and cellulase reaction mechanism. Biotechnol Bioeng

1983;25:33/52.

[6] Kim TJ, OW SSK, Eom TJ. Enzymatic deinking of wastepaper,

TAPPI Proceedings, 1991. p. 1023/30 (1991 Pulping Conference).

[7] Jeffries TW, Klungness JH, Sykes M, Rutledge-Cropsey KR.

Comparison of enzyme enhanced with conventional deinking of

xerographic and laser-printed paper. TAPPI J 1994;77:173/9.

[8] Putz HJ, Gottsching L, Renner K, Jokinen O. Enzymatic

deinking in comparison with conventional deinking of offset

news, TAPPI Proceedings, 1994. p. 877/84 (1994 Pulping

Conference).

[9] Vilaseca F, Gou M, Pelac h MA, Mutje P. Aspectos energeticos y

calidad de desfibrado en la desintegracion de papeles viejos.

Investigacion y Tecnica del Papel 2000;137(145):423/38.

[10] Spiro RG. The Nelson/Somogyi copper reduction method:analysis of sugars found in glycoprotein. Meth Enzymol

1966;8:3/26.

[11] Mandels M, Andreotti R, Roche Ch. Measurement of sacchar-

ifyng cellulase. Biotechnol Bioeng Symp 1976;6:21/3.

[12] Metzner AB, Otto RE. Agitation of non-Newtonian fluids.

AIChE J 1957;3(1):3/10.

[13] Pelach MA. Proces de destintatge del paper per flotacio,

Avaluacio de leficacia deliminacio de tinta, Tesis Doctoral,

Universitat de Girona, 1998.

[14] Paraskevas S. High consistency repulping: benefits and draw-

backs. Pulping Conference Proceedings. Atlanta: Tappi Press,

1983. p. 129/32.

M.A. Pelach et al. / Process Biochemistry 38 (2003) 1063/1067 1067

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