Biomedical Engineering Reference
In-Depth Information
Table 8.6
Effects of enzyme treatment on brightness of bagasse mechanical pulp [
33
]
Treated by
xylanase
Treated by ligninolytic
enzymes
Treated by xylanase and
ligninolytic enzymes
Item
Contrast
H
2
O
2
(%)
1:5
1:5
1:5
1:5
Consumption of
H
2
O
2
(%)
0:98
1:06
1:06
0:94
Brightness (%ISO)
46:2
49:8
49:5
50:8
Increased brightness
value
2:6
2:3
3:6
cooking, when the concentration of solution is low, the xylan would be reabsorbed or
deposited on the fiber surface. This part of reabsorbed xylanase cannot be extracted
easily by hot or cold alkaline solutions, which indicates that xylan and lignin form
LCC to reduce the solubility of xylan.
Xylanase can decompose the reabsorbed xylan, increasing the permeability of the
fiber surface, which is conducive to the dissolution of lignin. Furthermore, xylanase
reduces the polymerization of LCC, which is beneficial to the dissolution of lignin.
8.3.3
Efficiency of Xylanase in the Biological Bleaching
Process
8.3.3.1
Reduction of the Consumption of Chemicals in the Bleaching
Process
Treatment of pulp by xylanase is applied in the multistage bleaching process (in
the process, ClO
2
is substituted for Cl
2
). In the test of hardwood, based on the
high brightness, it can greatly reduce the consumption of chemicals (Cl
2
), and in
the chlorinated segment, 50 % ClO
2
is used to replace Cl
2
. To obtain the same
brightness, the consumption of the total available chlorine will be greatly reduced.
8.3.3.2
Reduction of the Harmful Ingredients in Bleaching Liquid Waste
The consumption of Cl
2
is reduced by pretreatment of pulp with xylanase, so the
content of absorbable organic halogens (AOX) decreases in the bleaching waste
liquid, reducing environmental pollution. Twenty percent of ClO
2
is substituted for
Cl
2
in the chlorination section in the multistage bleaching process. When the pulp
brightness is 91 % (ISO), the treatment of xylanase may significantly reduce the
content of AOX in the bleaching waste liquor.
