process, denim used to be washed with pumice stones. However, this abrasive
process was cost incurring due to machine repair and high energy consumption.
Moreover, the abrasion can damage the fabric and hence lower the quality of the
fabric. Thus, it was necessary to develop an alternative method that gives the same
effect. The use of enzymes, specifically cellulases, emerged as replacement for
the stone washing, and the process is named biostoning [83, 84]. The action of the
cellulase on the cellulosic fibers results in certain indigo dye loss which gives the
garment a uniform aged look under mild conditions. Neutral and acid active cellulases have been used in biostoning process. However, the low pH biostoning suffers
from the undesirable effect of the indigo dye back staining. On the other hand, denim
biostoning at alkaline conditions diminishes the indigo back staining effect, and
hence, the use of alkaline active cellulases in biostoning process has been
recommended [85]. Alkaline active cellulases which are potentially suitable for
this application have been reported from different alkaliphiles [69, 85–87].
4.1.3 Paper and Pulp Processing
Pulp and paper production has been a multibillion-dollar business, and its market
value for 2019 was estimated to be about 63 billion USD [88]. In the year 2017, the
world has produced about 184 million metric tons of pulp [89] and close to
420 million metric tons of paper and cardboard [90]. To process such large volume
of products, the input it takes and the effluent it discharges are expected to be high.
Thus, if the process involves the use of hazardous chemicals, its pollution impact can
be significant and poses a serious threat. Pulp and paper production had been using
different potentially hazardous chemicals, and bleaching was one of the major
pollution sources.
Unbleached pulp has brownish color primarily due to the residual lignin and
lignin derivatives which are covalently attached to the hemicellulose fraction.
Removal of this lignin involves a multistage bleaching process, which used to
involve elemental chlorine. Although chlorine-based bleaching of pulp is effective,
it is also associated to formation of chlorinated organic by-products which are
known to have highly persistent toxic and mutagenic effects. Because of the growing
public concern about environment and strict legislations regarding pollution, the
search for alternative ways to reduce or avoid the release of chlorogenic compounds
with pulp mill bleaching effluent has been promoted. Different environmentally
friendly bleaching chemicals like H 2 O 2 , O 2 , and O 3 have been substituting the
toxic chlorine-based bleaching chemicals [91]. Currently, the oxidizing agent, chlorine dioxide, is the major bleaching chemical and being used widely in what is
known as elemental chlorine-free (ECF) bleaching process [92]. On the other hand,
the total chlorine-free (TCF) bleaching, which is the most environmental benign
process, accounts only for a tiny fraction of pulp bleaching.
ECF substituted the elemental chlorine-based bleaching and is accepted by the
United Nations Environment Programme, the International Joint Commission, the
Alkaliphiles: The Versatile Tools in Biotechnology
15
process was cost incurring due to machine repair and high energy consumption.
Moreover, the abrasion can damage the fabric and hence lower the quality of the
fabric. Thus, it was necessary to develop an alternative method that gives the same
effect. The use of enzymes, specifically cellulases, emerged as replacement for
the stone washing, and the process is named biostoning [83, 84]. The action of the
cellulase on the cellulosic fibers results in certain indigo dye loss which gives the
garment a uniform aged look under mild conditions. Neutral and acid active cellulases have been used in biostoning process. However, the low pH biostoning suffers
from the undesirable effect of the indigo dye back staining. On the other hand, denim
biostoning at alkaline conditions diminishes the indigo back staining effect, and
hence, the use of alkaline active cellulases in biostoning process has been
recommended [85]. Alkaline active cellulases which are potentially suitable for
this application have been reported from different alkaliphiles [69, 85–87].
4.1.3 Paper and Pulp Processing
Pulp and paper production has been a multibillion-dollar business, and its market
value for 2019 was estimated to be about 63 billion USD [88]. In the year 2017, the
world has produced about 184 million metric tons of pulp [89] and close to
420 million metric tons of paper and cardboard [90]. To process such large volume
of products, the input it takes and the effluent it discharges are expected to be high.
Thus, if the process involves the use of hazardous chemicals, its pollution impact can
be significant and poses a serious threat. Pulp and paper production had been using
different potentially hazardous chemicals, and bleaching was one of the major
pollution sources.
Unbleached pulp has brownish color primarily due to the residual lignin and
lignin derivatives which are covalently attached to the hemicellulose fraction.
Removal of this lignin involves a multistage bleaching process, which used to
involve elemental chlorine. Although chlorine-based bleaching of pulp is effective,
it is also associated to formation of chlorinated organic by-products which are
known to have highly persistent toxic and mutagenic effects. Because of the growing
public concern about environment and strict legislations regarding pollution, the
search for alternative ways to reduce or avoid the release of chlorogenic compounds
with pulp mill bleaching effluent has been promoted. Different environmentally
friendly bleaching chemicals like H 2 O 2 , O 2 , and O 3 have been substituting the
toxic chlorine-based bleaching chemicals [91]. Currently, the oxidizing agent, chlorine dioxide, is the major bleaching chemical and being used widely in what is
known as elemental chlorine-free (ECF) bleaching process [92]. On the other hand,
the total chlorine-free (TCF) bleaching, which is the most environmental benign
process, accounts only for a tiny fraction of pulp bleaching.
ECF substituted the elemental chlorine-based bleaching and is accepted by the
United Nations Environment Programme, the International Joint Commission, the
Alkaliphiles: The Versatile Tools in Biotechnology
15