Dioxins Levels in Chlorine Dioxide Bleaching of Hardwood Oxygen-bleached Kraft Pulp (I)

Abstract

Kraft pulp and sulfite pulp bleaching mills using chlorine, chlorine dioxide (D) and other chlorin-ated compounds are under surveillance of the dioxins regulation in Japan from 15 January 2000. The bleaching mills are regarded as “notified establishments” which may pollute water quality. According to it. the dioxins are composed of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzo-furans (PCDFs). and coplanar-polychlorinated biphenyl (Co-PCI3s). The limit for the dioxins emissions to environmental water from the mills is 10 pg-TEQ^WHO1998/L. The limit should be considered ten times as that of the environmental water quality level (1 pg-TEQ/L). One of questions is whether water qualities of process sewers in chlorine dioxide bleaching (ECF) mills are less than the environmental water quality (1 pg-TEQ/L) or not. Objectives of this study are to clarify the dioxins level of ECF mill sewers and to know more about mechanism of the dioxins formation during ECF bleaching of hardwood oxygen-bleached kraft pulp (LOKP) on a basis of the analysis level for the environmental water quality. Laboratory bleaching was carried out using a mill LOKP (kappa number 9. 8), chlorine dioxide from a mill R 8 generator and drink water in a laboratory high?share mixer. Active chlorine factors were in the range of 0. 14-1. 14. The total TEQs of pulps are less than 15 ppq for both the D-treated pulps and D and alkali-extracted (E) pulps. Those of spent liquors are less than 0. 0057 pg-TEQ/L for both the D and E spent liquors. In all cases, 2, 3, 7, 8-TeCDD and TeCDF were not detected.