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Meetings & Symposia 
Environmental performance of modern ECF bleaching 
Axegård, P; Bergnor, E 
In 1996 AET (1) stated that complete replacement of elemental chlorine with chlorine dioxide results in virtual elimination of 2, 3, 7, 8-TCDD and that 2, 3,7, 8-TCDF cannot be detected if the level of dibenzofuran in the pulp does not exceed 10 ppb. Concerns regarding dioxins in coastal fish in the Bottnia Lake were raised 2005 by the Swedish EPA, SEPA and the role of ECF bleaching discussed (2). During 2007/2008, Innventia carried out a screening laboratory study to clarify, if a modern first chlorine dioxide bleaching stage can be considered a contributor to the formation of chlorinated dioxins and furans. The study showed that the content of PCDD/Fs in O2-delignified, D-bleached and Q(PO)-bleached pulp are extremely low and are of the same magnitude as in the blank samples. The pH in the D-stage or the presence of carry over had no significant influence on the formation of PCDD and PCDF. The purity of the chlorine dioxide solution, on the other hand, is a prerequisite for dioxin-free bleaching. When the content of elemental chlorine in the chlorine dioxide increased above 5% (as active chlorine) increased levels of PCDD/F could be observed. A chlorine impurity level of 5% is far above the level from modern chlorine dioxide generators, i.e. possible to obtain a chlorine dioxide that contains less than 0.8% elementary chlorine. The overall conclusion from this study is that with modern bleaching technology there is no formation of dioxins during the bleaching of industrially produced softwood kraft pulps.