Destruction of PCDD and PCDF in bleached pulp by chlorine dioxide treatment

Softwood pulp samples, containing polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins) were treated with chlorine dioxide and analyzed, before and after treatment, for the contents of dioxins. Two separate experiments were carved out under identical bleaching conditions - similar to the elemental chlorine free bleaching of kraft pulp. Each of the two experiments were duplicated, including the analytical determination of the dioxin concentrations. In the first experiments the amount of dioxins in the chlorine dioxide treated pulp was found to be between 39 and 69% of the values found in the original pulp. In the second experiments both the pulp as well as the effluents were analyzed. The results from these duplications proved to be consistent. For 2378-TCDD and 2378-TCDF, 56–63 were found in the pulp sample after chlorine dioxide treatment. The vast majority was found in the pulp while the contribution from the aqueous discharges was negligible. The conclusion is that the levels of the dioxins in the original pulp decreased as a result of the treatment of the pulp with chlorine dioxide. The results are significant since the results of the experiments, including the analytical deternrinations, were highly reproducible.