Environmental sustainability assessment of different end-of-life scenarios for the pulper rejects produced in the paper recycling process

Resource recovery from wastes through recycling processes promotes near-zero-waste residue business models and supports the circular economy's goals by facilitating the closure of loops in industrial systems and reducing energy and resource consumption as well as pollutant emissions. However, the approach is sustainable only when the waste can be valorized, and the environmental impact of the recycling is lower with respect to other end-of-life (EOL) scenarios. Due to the diversity and complexity of wastes streams, these aspects need to be evaluated on a case-by-case basis. This study focuses on a mechanical recycling process for pulper rejects, a mixed waste stream generated during recycled paper production, with two aims: (1) to define a feasible mechanical recycling process and (2) to evaluate its environmental performance through life cycle assessment (LCA) compared to the most common EOL treatments, such as incineration with energy recovery and landfilling. ReCiPe 2016 H method was used to estimate the environmental impacts of all scenarios, adopting both midpoint and endpoint approaches, on a functional unit (FU) defined as 1000 kg of pulper rejects. The LCA results indicate that the pulper rejects recycling is always preferable to landfilling across all impact categories considered. On the contrary, in comparison to incineration, the best environmental option depends on the specific impact category considered. In particular, recycling is the best EOL alternative in terms of impacts on global warming, with an impact 33 % lower, but it is not the most sustainable one in terms of fossil resource consumption, mainly due to the amount of energy required during all steps of the recycling process, while allowing the recovery of materials that would otherwise be lost. Currently, it is not possible to identify an overall ‘winner’ between incineration with energy recovery and recycling for the pulper rejects because the most environmentally sound alternative varies depending on the priority given to different environmental issues. Therefore, further improvements of the pulper rejects recycling pathway performances are required to make the process even more efficient and competitive.