Sustainability 2023 , 15 , 6915
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forestation. Additionally, the PPI discharges wastewater that can pollute water bodies. Furthermore, the waste produced by this industry includes paper waste and sludge, which require proper management. These wastes are usually burnt or dumped in landfills, which causes a variety of health and environmental issues. Therefore, the recovery aspect of sustainable waste management is of great importance, which is based on a hierarchy of prevention, reuse, recycling, recovery, and disposal. After prevention and reuse, paper recycling is crucial, which significantly lowers greenhouse gas emissions because fewer trees are cut down, and it also lowers manufacturing costs. Paper can be recycled up to seven times, after which the cellulose fibers are considered unsuitable. The other possible sustainable ways to deal with paper waste emphasized in this review are based on the concept of converting paper waste into energy and high-value materials. Under this concept, biofuel production is possible, as paper is an important source of sugars that can be fermented to bioethanol—an alternate energy source. Other than biofuel production, biohydrogen and biomethane can be produced from paper waste as sources of energy. Heat and electricity can also be generated from the incineration of paper waste. Paper waste and sludge can also be converted into high-value materials minimizing the issues related to paper waste disposal. Paper waste can be used as raw materials for the production of cellulose nanoparticles, which have very advantageous properties and applications. Paper sludge also contains organic fractions that are suitable for hydrothermal carbonization. This process involves the conversion of wet biomass into a high carbon-containing solid product known as hydrochar, which can be used as a solid fuel, low-cost adsorbent, catalyst, and contaminant remover. Another sustainable use of paper waste and sludge is the production of construction materials such as insulation materials, plasterboard, and bricks. The large fraction of inorganic substances in paper mill sludge makes it ideal for the production of construction materials. Finally, paper waste and sludge can be composted for the production of soil amendments, which can decrease soil acidity, increase its organic matter, and provide essential nutrients. The composting of paper sludge or waste that is rich in organic matter can be the most useful disposal method, as this process can return the micro- and macronutrients back to the environment. Overall, the aforementioned processes and possibilities toward the sustainable management of paper waste and sludge have both pros and cons. Therefore, future research should focus on the optimization of the available paper waste utilization processes and on the development of new conversion technologies in order to improve the environmental sustainability of the pulp and paper industry. Author Contributions: Conceptualization, H.A., M.A.M., S.T.G. and J.M.; formal analysis, H.A., M.A.M., S.T.G. and J.M; investigation, H.A., M.A.M., S.T.G. and J.M.; writing—original draft prepa- ration, H.A., M.A.M., S.T.G. and J.M.; writing—review and editing, H.A., M.A.M., S.T.G. and J.M.; supervision, H.A. and J.M.; project administration, H.A. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded through an internal grant offered by Abu Dhabi University to Dr. Hatem Abushammala (PI) and Dr. Jia Mao (Co-PI) and an external grant offered by Mubadala to Dr. Hatem Abushammala (PI). Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.
References 1. Bajpai, P. Biermann’s Handbook of Pulp and Paper: Raw Material and Pulp Making ; Elsevier: Amsterdam, The Netherlands, 2018; Volume 1. 2. Latha, A.; Arivukarasi, M.; Keerthana, C.; Subashri, R.; Vishnu Priya, V. Paper and Pulp Industry Manufacturing and Treatment Processes—A Review. Int. J. Eng. Res. Technol 2018 , 6 , IJERTCON011. [CrossRef]
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