Use of secondary condensates from evaporation as washing liquid in kraft pulp bleaching

This study investigates the role of secondary condensates in the pulp and paper industry’s journey to minimize its water footprint. The integration of secondary condensates, traditionally less explored in bleaching processes, is examined for its potential in reducing freshwater demand. Condensates with different organic content (chemical oxygen demand, COD) and their mixtures were tested as washing liquid after the alkaline extraction stage ( E P ) of eucalyptus globulus kraft pulp and compared to hot water. Two subsequent chlorine dioxide stages were applied to evaluate the impact of the washing liquid COD on pulp properties and chemicals consumption. Despite its higher organic content, the condensates can be used as a partial or total substitute for hot water without substantial compromises in the pulp properties, such as brightness, reversion, and viscosity. The calculated correlation between ClO 2 consumption and COD in the washing liquid can be applied for assessing economic and environmental trade-offs, providing a roadmap for optimizing processes and reducing environmental impacts.