Sustainable exploitation of paper mill wastes: a resource to re-use in the paper factory

In the papermaking industry, billions of tonnes of paper mill wastes are globally produced as wastes every year. These include cellulosic and inorganic sludges, which are traditionally landfilled, leading to environmental and economic issues. For these reasons, it is urgent to develop new sustainable strategies to exploit these fractions. Up to now, these sludges have been exploited i) for land application (as soil amendment/substrate), ii) for energy recovery and iii) for the production of bio-composites. However, the above possibilities involve the direct use of the bulk wastes, without fractionating/exploiting each feedstock component. In the perspective of the valorisation of the different components, the present investigation has considered different strategies: i) a thermal treatment, ii) an alkaline and iii) a mechanical one, aimed at the fractionation and recovery of the two main components of cellulosic and inorganic sludge, cellulose and calcium carbonate, respectively, that could be advantageously reused within the same papermaking process.