Environmental Aspects of Short-Sequence Bleaching, 1990 Environmental Conference Proceedings

Bleaching with short sequences is interesting because of its low cost factor. On the other hand, it requires higher input of bleaching chemicals and therefore produces more halogenated compounds in comparison with longer bleaching sequences.

Low kappa factor chlorination, recommended to decrease the amount of halogenated compounds in the effluent, results in insufficient delignification. The amounts of halogenated compounds and the degree of delignification achieved at different kappa factors is compared with substitution rates for chlorine with chlorine dioxide. The results clearly favor the application of oxygen delignification to achieve lower levels of halogenated compounds and the substitution of chlorine with chlorine dioxide.

An enforcement of the extraction stage with oxygen or hydrogen peroxide is beneficial to compensate for the lower degrees of delignification achieved at high sustitution levels for chlorine.

Very low levels of halogenated compounds are the result of high-intensity oxygen delignification followed by chlorine dioxide and hydrogen peroxide treatment.