Reduction of Pollutant from Bleached Kraft Pulp Mills by the Process Conversion to ECF Bleaching (Part III)

We have reported effect of elemental chlorine free (ECF) bleaching for mill effluent in previous paper. As a result of change chemical substances for pulp bleach, the amounts of absorbable organic halogen (AOX) and extractable organic halogen (EOX) decrease to significant lower level when substitution of chlorine dioxide is used. A more recent survey for polychlorinated dioxins and dibenzofurans (Dioxins) are also studied.Effects of ECF bleaching on reduction of dioxins were investigated for 14 bleached kraft pulp mills in Japan, which is a largest study in domestic. Dioxins concentrations in the bleached pulps, bleached filtrates, and whole mill effluents before and after the ECF conversions were measured and compared.After the ECF bleaching process was introduced, the generation of dioxins was dramatically suppressed in all of the mills, and the dioxin levels were decreased by less than 1⁄50 after the ECF conversion. Similarly, the concentrations of dioxins of the bleached filtrates after the conversion also decreased by less than 1⁄20, strongly indicating that the shift of bleaching process to the ECF bleaching effectively suppresses the generation of dioxins.