Evaluating the effectiveness of using ClO2 bleaching as substitution of traditional Cl2 on PCDD/F reduction in a non-wood pulp and paper mill using reeds as raw materials

Abstract

The effectiveness of ClO2 bleaching as a replacement for conventional Cl2 bleaching, which is intensively practiced in developing countries, to reduce polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in non-wood pulp and paper mills has not been field tested. The first field study was performed to investigate PCDD/F variations when ClO2 bleaching was used as a substitute for conventional Cl2 bleaching in a non-wood pulp and paper mill. It was found that the PCDD/F toxic equivalents (TEQs) in solid and effluent samples were approximately 1.3–14.9 times lower when ClO2 bleaching was used instead of the conventional Cl2 bleaching. 2,3,7,8-Substituted tetrachlorinated dibenzofurans (2,3,7,8-TCDF) were the dominant contributors to total PCDD/F TEQs in samples from the investigated mill when using conventional Cl2 bleaching. The formation amounts of 2,3,7,8-TCDF were reduced from 1.56–2.76 pg TEQ/g to 0.02–0.32 pg TEQ/g in solid samples when ClO2 bleaching was used instead of the conventional Cl2 bleaching. The replacement of Cl2 with ClO2 might decrease the chlorination reactions of dibenzofuran as potential precursors, and thus reduce the formation amounts of 2,3,7,8-TCDF. The results could provide important knowledge for suggesting the best available technique for PCDD/F reduction for non-wood pulp and paper mills in developing countries. Keywords: PCDD/Fs, Pulp and paper mill, ClO2 bleaching, Cl2 bleaching, Persistent organic pollutants