Abstract
The pulp bleaching process is mainly responsible for the generation of toxic substances in the whole paper making process. The modification of conventional ECF (elemental chlorine free) bleaching was studied using an oxygen stage, a peracetic acid stage and an oxygen followed by peracetic acid stage in the following bleaching sequences: OD0EOPD, PaaD0EOPD, OPaaD0EOPD and QOPaaD0EOPD. The PaaD0EOPD sequence reduced the COD, BOD, color, TDS and AOX by 36.8, 37.0, 52.4, 39.8 and 53.9%, respectively, in comparison with D0EOPD. Moreover, PaaD0EOPD has better optical effluent properties, compared to the OD0EOPD sequence. OPaaD0EOPD reduced the chlorophenols, chloroguaiacols by 73.3 and 89.3%, and improved the brightness and whiteness by 1.7 and 3.1 units, respectively, in comparison with the D0EOPD bleaching sequence. The QOPaaD0EOPD sequence improved the pulp viscosity by 0.8 units in comparison with OPaaD0EOPD. The amendment of the conventional bleaching sequence was found to be effective for achieving an improvement in optical properties and effluent quality at reduced dose of chlorine dioxide.
Published Version
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