COMPARISON OF EFFLUENTS FROM TCF AND ECF BLEACHING OF KRAFT PULPS

Oxygen-delignified hardwood and softwood kraft pulps were bleached at bench scale with totally chlorine-free (TCF) and elementary chlorine-free (ECF) sequences. Analyses were performed on each individual bleaching stage effluent and on the composite effluent from each sequence. All effluents were very low in color; the TCF effluents were lower than their ECF counterparts. Effluents from TCF bleaching of both hardwood and softwood had much higher TOC and COD values than the corresponding ECF effluents. Aromatic compounds in softwood effluent were more readily degraded by Trametes. versicolor than those from hardwood. Also, aromatic compounds in ECF effluents were more readily degraded than those in TCF effluents. Microtox toxicity was highest in ECF softwood effluent, followed by ECF hardwood and TCF softwood. No toxicity was detected in hardwood TCF effluent. Toxicity was eliminated in all effluents after incubation with T. versicolor for six days.