Examination of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in process water of kraft pulp bleaching mill using chlorine dioxide from the aspect of environmental water quality

Abstract

Process water of a pulp mill with extended kraft cooking, two-stage oxygen delignification, and chlorine dioxide bleaching was examined from the aspect of a new standard for environmental water quality in Japan. According to the new standard, the concentration of dioxins – polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, coplanar polychlorinated biphenyls – in environmental water is restricted to less than 1 pg TEQ/l. We clarified that the concentrations of the dioxins in sewers in the chlorine dioxide stage and the alkali stage were less than 1 pg TEQ/l and that the 2,3,7,8-tetrachlorodibenzofuran concentrations were 0.5 pg/l or less. In addition, a main source of 1,3,6,8- and 1,3,7,9-tetrachlorodibenzo-p-dioxins in the process water seemed to be an agrochemical in water supplied from a river.