Treatability of effluents from eucalyptus kraft pulp bleaching with acid hydrolysis/hot chlorine dioxide technologies / Tratabilidade dos efluentes de branqueamento de polpa kraft de eucalipto com tecnologias de hidrólise ácida/dióxido de cloro à quente

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The aim of this study was to evaluate the impact of D, D*, A/D* and AD technologies on characteristics and treatabilities of eucalyptus kraft pulp ECF bleaching effluents, of low and high COD, and a full brightness 89-90% ISO. Two samples of eucalyptus kraft pulp pre-delignified in oxygen, a well washed one with COD 6,4 kg/t.a.s. and another not well washed with COD 25,5 kg/t.a.s., were treated, in a first bleaching stage, using the technologies D, D*, A/D* and AD, and subsequently bleached up to 89 and 90% ISO, with the sequences EpDD e EpD, respectively. It was determined the bleachability and quality of fully bleached pulp. The bleaching effluents were characterized as for color, TOC, COD, BOD5 and AOX loads and biologically treated in an activated sludge system. The efficiency of the biological treatment was certain for the removal of the appraised parameters. It was concluded that the pulp of high COD shows low bleachability in relation to the high COD. The pulps of high COD bleached by the various technologies showed brightness reversion about 2,5 times bigger than those of low COD. The technologies containing acid / hot chlorine dioxide stage (D*, A/D*, AD) resulted in bleached pulps with greater brightness stability, less viscosity, minor kappa and HexAs tenor than the reference (D), being the impact more significant for the pulp of high COD. Regarding the bleaching and reagents costs, the only technology to the conventional stage Do that justify is the stage D *, even so for pulp of low COD. The technology AD is efficient when the wash of the pulp is deficient, however it should be avoided, therefore it requests high capital cost. The technology A/D * is not recommended for the kraft pulp of eucalyptus, because it presents the largest reagents cost, for pulp with low and high COD. The bleaching effluents of high COD pulp presented substantially higher values of COD, BOD5 and AOX than those of pulp of low DQO, but the treatability of the two effluents, measured by the removal percentages of these parameters in the biological treatment, was similar. The greatest part of organic load and organic allogenous from the pulp effluent of low COD (65-99%) is generated during pre-bleaching. The technologies D *, A/D * and AD increase the organic load of the effluent, however it is easy to treat, in spite of larger treatment cost. The discharge of AOX in the effluent due to technology D * it is smaller in relation to conventional D, however that benefit disappears in the treated effluent. In practice, any alternative justification to the stage D is justified to reduce the tenor of AOX in the effluent. The technologies D *, A/D * and AD result in more colored effluents than conventional D and the biological treatment accentuates the effluent color.

ASSUNTO(S)

celulose kraft hydrolysis efluentes hidrólise treatment effluents bleaching dióxido de cloro tratamento kraft pulp branqueamento tecnologia e utilizacao de produtos florestais chlorine dioxide

ACESSO AO ARTIGO

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