Assessment of Aox Content in Bleaching Effluent of Eucalyptus Tereticornis Kraft Pulps

Abstract

The research aim is to reduce the organochlorine content in bleach plant effluents by modifying conventional (CEHH) bleaching sequences. Majority of pulp and paper mills generally adopted CEHH or CEH bleaching sequences, using chlorine or chlorinated compounds to remove the color from pulps. Organochlorine compounds are mainly generated from chlorination and alkali extraction stages. The purpose of the study is to substitute elemental chlorine in bleaching with oxygen, chlorine dioxide, or peroxide. Investigations of AOX content of various traditional and innovative ECF bleaching sequences were conducted. In this study, kraft pulps of Eucalyptus tereticornis with kappa numbers of 44.91 and 26.46 and its oxygen-delignified pulps of kappa numbers 21.32 and 13.03 were used. In terms of AOX, various ECF bleaching sequences were compared to the reference sequence (CEHH). AOX value was 4.45, 3.42, 2.27 kg/tp for the pulp bleached adopting OCEH, ODEH, ODEP bleaching sequence and 9.24 kg/tp for the pulp bleached adopting CEHH bleaching sequence for the pulp corresponding to Kappa number 44.91. Similarly, the AOX value was 2.60 , 1.78 1.24 Kg/tp for the pulps bleached adopting the OCEH, ODEH, ODEP bleaching sequence and 5.56 Kg/tp for the pulp bleached adopting the CEHH sequence for the pulp corresponding kappa number 26.46. Due to partial-delignification of oxygen, AOX production was reduced up to 50%.