Abstract

This study aimed to improve the sustainability of the kraft pulp production process by recovering Pinus radiata and Eucalyptus grandis wastewater generated during the bleaching process. The effluents were obtained from the first alkaline extraction stage (E0) of the ECF bleaching sequence used to produce white Kraft cellulose, considering that this stage is where the highest contamination by phenolic compounds occurs and the effluent exhibits an intense color. A photochemical oxidation system, utilizing TiO2/S2O8 2- /UV, was implemented to generate in situ two highly oxidizing radical species, with high redox potential, a hydroxyl radical (HO• 2.8 eV) and a sulfate radical (SO4 •-2.5-3.1 eV), which promote rapid degradation of contaminants. To obtain the optimal response, we employed the 2n model to construct a matrix of 15 experiments, utilizing the Box-Behnken design. According to the experimental variables studied, phenolic compounds were completely removed from the Eucalyptus effluent (0.0312 min-1) and 80% of them were removed from the pine effluent (0.0102 min-1), at pH 5.0 with 0.6 gL-1 of persulfate and 1.0 gL-1 of titanium dioxide. Under these conditions, the bioavailability of effluents from Pinus radiata and Eucalyptus grandis increases from 0.16 and 0.26 to 0.90, after the treatment. The excellent bioavailability of the effluents obtained after the treatment demonstrates that the process used is efficient in recovering wastewater from the pulp industry and that the treated water could be reused in the same process or returned to the ecosystem, without harming the environment. © 2024, Publishing House of the Romanian Academy. All rights reserved.