Effect of process modifications on AOX emissions from kraft pulp bleaching, using Chilean pine and eucalyptus

This paper reports experimental results on the effect of prebleaching lignin content and chlorine load on chlorinated organic (AOX) formation from Chilean pinewood and eucalyptus kraft pulp bleaching. Unbleached pulp with kappa number in the range 14–30 and 7–22, for pine and eucalyptus, respectively, were assayed. Bleaching sequences based on Cl2/ClO2, ClO2 and oxidative alkaline extraction, were studied here. Residual chlorinated organics were found in the range 0.8–7.0 (kg AOX/ton dry pulp) and 0.6–4.2 (kg AOX/ton dry pulp), for pine and eucalyptus, respectively. AOX in effluents were linearly correlated with the unbleached pulp lignin content and the ratio between Cl2 and ClO2 used in bleaching. It is concluded that around 8.6% and 7.9% of added chlorine is bounded to soluble organic compounds, for pine and eucalyptus, respectively. Investment requirements and reductions in operating costs associated with upgrading conventional pulp mills are presented here. In all cases, economic benefits off-set investment costs.