Optimization of AOX formation during the first chlorine dioxide bleaching stage (D0) of soda AQ bagasse pulp

Abstract

The first chlorine dioxide stage (D0) in the ECF bleaching of a soda AQ bagasse pulp has been investigated using response surface methodology (RSM) for experimental design. The effects and interactions of the available chlorine dosage, the reaction temperature and the pH value, on the adsorbed organic halogen (AOX) content of wastewater as well as the brightness and viscosity of the pulp were examined. The optimal reaction conditions to achieve a balance of reduced AOX content, higher brightness and higher viscosity were: available chlorine dosage of 3.7%, reaction temperature of 76 degreesC and pH 8.8. Under these conditions, AOX content of 14.7 mg/L, brightness of 52.4% ISO and viscosity of 929 mL/g were observed. To the authors' knowledge these results provide the only detailed study of AOX formation in ECF bleaching of Soda AQ pulp from bagasse. By and large the effects of process variables were similar to those seen in ECF bleaching of kraft pulps.