Biomedical Engineering Reference
In-Depth Information
The high energy consumption and environmental pollution caused by traditional
mechanical and chemical pulp impels the papermaker to attempt a new clean
pulping method. Biopulping gains the attention of many researchers because it is
friendly to the environment. However, only using the microorganism or enzyme
to remove the lignin of lignocellulosic materials cannot reach the same effect
as traditional chemical pulp. So, biological pretreatment is combined with the
traditional mechanical method, chemical method, and organic solvent pulping. The
potential advantages of biological pretreatment for the environment and energy
saving indicate the direction of future clean pulping development [
3
-
6
]. Compared
with mechanical pulp, this can save 30-40 % energy consumption, and under the
same delignification conditions, the lower alkali can improve the physical indicators
of paper compared with chemical pulping [
7
].
The application of biotechnology in the pulp and papermaking industry not
only can improve the pulping properties and slurry performance but also can
fundamentally improve the ecological environment by mitigating or reducing the
generation of pollutants [
8
]. This chapter elaborates the biotechnology regarding
natural lignocellulosic materials in application in the pulp and papermaking industry
from aspects including biopulping, biobleaching, and others.
8.2
Biopulping
Biopulping takes advantage of the decomposing ability of microorganisms on lignin
to remove lignin in the pulp raw material or pulp plant tissue and separate fibers.
According to the ways lignocellulosic materials decompose, the microorganisms
that can corrode plant tissues in nature can be divided into three categories:
brown-rot fungi, soft-rot fungi, and white-rot fungi. White-rot fungi, which are
commonly used in biopulping, are basidiomycetes; there are about 2-3 million in
nature, such as
Phanerochaete chrysosporium
,
Coriolus versicolor
,
Ceriporiopsis
subvermispora
, and so on. The microorganisms used in biopulping must have a
fast reaction rate, high degradability to lignin, and little possibility of decomposing
cellulose. During biopulping, before biological treatment, the raw material usually
requires high-temperature or steam sterilization to ensure that the inoculation of
white-rot fungi is not inhibited by other species.
The research of biopulping includes the following aspects. (1) In the screening of
specific microbial strains, strains with high selectivity for the degradation of natural
lignin compounds, less damage to lignocellulosic materials, and strong antibacterial
activity would be the main breeding strains. The majority of the selected strains are
basidiomycetes, while a small number of strains are ascomycetes or adelomycetes;
brown-rot fungi and bacteria are rarely used. (2) Lignin is completely broken down
by the enzymes in the metabolic process of microorganisms, which is generally
considered to be the inherent mechanism of biopulping. The enzymes involved in
the reaction process at least include lignin peroxidase (LiP), manganese peroxidase
(MnP), and laccase (Lac). It is reported that the enzymes do not directly act on
