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

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.