Sustainability of kraft pulp mills: Bleaching technologies and sequences with reduced water use

Abstract

The Kraft pulp industry is a relevant industrial sector in many countries with a considerable social, economic, and environmental impact. Thus, sustainability is the adequate framework to address this activity sector. This work presents a review of the literature, with a particular focus on the bleaching area and its relevance in reducing water use. The sustainability reports of the most prominent pulp and paper companies were analyzed, considering their specific water utilization and the sustainability targets they have outlined. The most industrially applied bleaching sequences were also addressed and the stages of the state-of-the-art sequences were analyzed (elemental chlorine free – ECF bleaching). Moreover, in this review, a detailed analysis of a sequence used on an industrial scale was carried out, highlighting the washing steps and the measures that are taken to minimize water use. The main limitations to the minimization of water use were identified, being deposit formation the major problem. Measures to overcome these limitations, as well as future perspectives were discussed. Due to the shortage of freshwater nearby some pulp and paper production sites, there will continue to be great pressure in the future to reduce water utilization, especially in the bleaching area.