ABSTRACT
This paper provides an update on the environmental aspects of elemental chlorine free (ECF) vs. totally chlorine free (TCF) pulp bleaching with an emphasis on literature published during the last two years. In general, there is no evidence of any adverse effects related to the use of chlorine dioxide, i.e., the trace amounts of chlorinated organics formed during ECF bleaching have no environmental effects and resemble naturally formed organochlorines. TCF pulp bleaching is less well documented, but it seems that the environmental effects of a pulp mill operation cannot be deduced from knowing the bleach sequence of the mill. One will have to know about the pulping operation, spill control, brownstock washer loss, etc. Biological data are mostly logarithmic by nature. Therefore, when comparing toxicity emission factors (TEF) between mills we suggest that logTEF = Q × logTU is used (where Q is the amount of effluent per tonne of pulp produced and TU is the toxic units, ECxx−1 instead of the hitherto used TEF = Q × logTU. Bleaching sequences based on peroxide generally result in lower energy demand than those based on ozone, which in turn are more energy efficient than those based on chlorine dioxide. However, mill operating conditions, product specifications and operator skill can have just as much of an effect on energy consumption. The agenda is thus not whether to use ECF or TCF as the choice of bleaching sequence, but rather to modernize the pulping operation itself.
