Post on 06-Apr-2018
8/2/2019 Deinking With Cellulase
1/5
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: josep.puig@udg.es (J. Puig).
Process Biochemistry 38 (2003) 1063/1067
www.elsevier.com/locate/procbio
0032-9592/02/$ - see front matter# 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 2 - 9 5 9 2 ( 0 2 ) 0 0 2 3 7 - 6
mailto:josep.puig@udg.esmailto:josep.puig@udg.es8/2/2019 Deinking With Cellulase
2/5
8/2/2019 Deinking With Cellulase
3/5
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
8/2/2019 Deinking With Cellulase
4/5
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
M.A. Pelach et al. / Process Biochemistry 38 (2003) 1063/10671066
8/2/2019 Deinking With Cellulase
5/5
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