Water Reuse Within the Paper Industry

Pulp and paper industry is still an intensive water consumer, although fresh water use by this sector has decreased by 90% along the last three decades, which currently shows its long water reuse tradition. Sustainable water management has been achieved by following the principle of water fit for use, which has mainly been developed through the optimization of water circuits, the cascade use of water, the implementation of internal water treatments, the optimal treatment of effluents to be reused and the use of alternative water sources, such as reclaimed water from municipal wastewater treatment plants. In fact, this sector is nowadays regarded as a reference for water reuse. Paper mills need to use fresh water to compensate evaporation losses and in critical applications. In addition, the final degree of circuit closure depends on the quality of the final product. For example, whereas unbleached paper grade mills may work with highly closed circuits, this is not usually possible for virgin pulp and bleached paper grade mills. Filtration and dissolved air flotation are the most common treatments applied to internal water reuse. Otherwise, the combination of physicochemical, biological and filtration technologies is generally considered to enable the reuse of mill effluents. Finally, tertiary effluent from municipal wastewater treatment plants must be further treated by filtration technologies and disinfection stages to be finally reused within the papermaking process safely.