Comparative toxicity of effluents from ECF and TCF bleaching of eucalypt kraft pulps

The toxicity of elemental chlorine free (ECF) and totally chlorine free (TCF) effluents from laboratory scale bleaching of eucalypt kraft pulps was compared using a suite of marine bioassays developed by the National Pulp Mills Research Program. The ECF bleaching sequence was D(EO)DD and the TCF sequences were Z(PO), (PA)P and (XQ)(EOP)(EPN)P. The effluents were tested before and after secondary treatment using Microtox, a phytoplankton growth inhibition test, a macroalgal fertilization test, a sea urchin fertilization test, a scallop larval abnormality test and a fish larval survival test. The untreated TCF effluents were more toxic than the ECF effluent, possibly due to residual peroxide in the TCF effluents. While secondary treatment reduced toxicity, both the ECF and one of the TCF effluents were still found to be toxic in the sensitive sea urchin fertilization and scallop larval abnormality tests. Environmental implications of these improvements in bleaching technology are discussed.