Beneficial Improvement of Environmental Impacts by Elemental Chlorine-free Bleaching

Kraft pulp and sulfite pulp bleaching mills using chlorine, chlorine dioxide (D) and other chlorinated compounds are under surveillance of the dioxins regulation in Japan. One of questions is whether water qualities of process sewers in chlorine dioxide bleaching (Elemental Chlorine-free bleaching: ECF bleaching) mills are less than the environmental water quality (1pg-TEQ/L) or not. Objectives of this report are to review studies about the dioxins level of ECF mill sewers and model experiments from an aspect of the environmental water quality. Laboratory bleaching were carried out using a mill hardwood oxygen-bleached kraft pulp (LOKP), chlorine dioxide from a mill R 8 generator in a laboratory high-share mixer. Active chlorine factors were in the range of 0.14-1.14. In all cases, 2, 3, 7, 8-TeCDD and 2, 3, 7, 8-TeCDF were not detected for the pulps and spent liquors. Examination of process water from an ECF bleaching line in Niigata mill of Hokuetsu Paper Mills, LTD. shows that the concentrations of the dioxins in both sewers of the chlorine dioxide stage (D0) and the alkali stage (E/O) were below 1pg-TEQ/L, and that the 2, 3, 7, 8-TCDF concentrations were 0.41pg/L or less. In addition, a main source of 1, 3, 6, 8- and 1, 3, 7, 9-TeCDD in the process water seemed to be an agrochemical in water supplied from a river.In the meantime, Japan revised the Air Pollution Control Law in 1996. The main purpose of the law is to reduce discharge of toxic pollutants such as carcinogenic substances into the air. The Japan Papermaking Association estimated the nationwide chloroform discharge to air for the fiscal year 1996 at 1, 655 t on the basis of field studies, and initiated a reduction of the discharge. As a result, the estimated discharge was reduced to 1, 118 t, which was a reduction of 32%, for the fiscal year 1999. However, further reduction is required because there is still much discharge. We estimated chloroform formation and discharge in the mill having an ECF bleaching line and a chlorine bleaching line as well as an effluent treatment process. It was clarified that the chloroform formation in ECF bleaching was approximately one eightieth of that in chlorine bleaching.