Impact of High Chlorine Dioxide Substitution for Chlorine on the Oxygen Delignified Pulp at Espanola, 1990 Environmental Conference Proceedings

With the prime objective of eliminating

polychlorinated dioxins and furans in the bleached pulp and effluent, E. B. Eddy Forest Products Ltd. at Espanola embarked on a mill trial to increase the chlorine dioxide substitution level in the softwood chlorination stage from 10% to 50% of the total equivalent chlorine applied. OCDE0HD is the bleaching sequence used. Four levels of substitution were studied with respect to their impact on pulp quality, effluent characteristics and bleaching cost.

Results indicate that at 50% substitution the polychlorinated dioxins are non-detectable in both pulp and effluent and chlorinated organic compounds measured as AOX have decreased significantly in the bleachery effluent. Total chlorinated phenolics from the bleachery have decreased slightly. The tetra chlorinated catechols decreased significantly.

Secondary treated effluent continues to remain non-toxic to fish and low in BOD, colour, and AOX. Overall bleaching cost has decreased. Pulp viscosity and strength have increased, while thebleached pulp continues to remain clean. These promising results have allowed adoption at 50% chlorine dioxide substitution as the normal operating mode in the softwood bleaching line.