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Bleaching of pulp for papermaking is roughly divided into bleaching with a peroxide, bleaching with a chlorine-containing oxidizing agent, and bleaching with a reducing agent, and these have been employed depending purpose of use in consideration of their bleaching characteristics and effects. The bleaching with a peroxide represented by on the kind of pulp and H2O2 is employed mainly for bleaching of mechanical pulp and for deinking/bleaching of waste newspaper because of its bleaching effect on pulp containing lignin. Since the bleaching with a chlorine-containing oxidizing agent is effective for chemical pulp containing a slight amount of lignin, bleaching with Cl2, NaCIO or CIO2 is mainly carried out in multistage bleaching of kraft pulp, and bleaching with NaCIO in bleaching of waste wood-free or mechanical paper. For example, in the bleaching of waste wood-free or mechanical paper, a 12% NaCIO solution is added to pulp in an amount of about 8% based on the amount of pulp and mixed therewith, whereby the bleaching is carried out. The bleaching with a reducing agent is excellent in decolonization of dye type coloring materials, but it has a limited- bleaching capability for peroxide type chemicals and chlorine-containing chemicals and entails a high cost. For these reasons and the like, it has been employed mainly for bleaching of mechanical pulp demanding a low brightness grade to be incorporated into newspaper, post-bleaching after H2O2 bleaching of mechanical pulp demanding a high brightness grade and post-bleaching after H2O2 deinking/bleaching of waste newspaper. In general, Na2S2O4 or TUDO of the dithionite family has been used as the reducing agent. Of these, Na2S2O4 has been mainly used from the viewpoint of bleaching capability, chemicals cost, etc. However, TUDO bleaching has recently come to be spotlighted as a substitute for NaCIO bleaching in bleaching of waste wood-free or mechanical paper and as a substitute for Na2S2O4 bleaching in post-bleaching after H2O2 deinking/bleaching of waste newspaper, from the viewpoint of the problem of waste water pollution by organic chlorine compounds represented by dioxins, demand for energy conservation, decoloring effect on dye type coloring materials，etc.
From its discovery in the late 18th century, the history of hydrogen peroxide is over 200 years. Hydrogen peroxide is a highly reactive, strong oxidizing. It can be involved in most of the redox reactions of harmful substances with almost no toxicity and is more biodegradable. Solid hydrogen peroxide has been widely recognized in aquaculture due to its ability to reduce the subaqueous content of ammonium and nitrogen, transfer electrons to dissolved oxygen to form superoxide radicals and increase oxygen levels, prevent anaerobe from proliferation and kill nosogenetic bacteria, and enhance water quality. It is also considered as a treatment against ectoparasites of adult fish, improving fish health in aquaculture to support the sustainability of the aquaculture industry.
Hydrogen peroxide is a chemical compound with the Chemical formula H2O2. Pure hydrogen peroxide is a stable substance kept under optimal conditions for years. However, H2O2 easily decomposes when it is exposed to impurities. Hazard Statements： Hydrogen peroxide may cause fire or explosion, releasing a large amount of heat, oxygen, and water vapor. 2H2O2 → 2H2O + O2 + 196.4 kJ/mol
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