Sustainability 2023 , 15 , 6915
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strategies for reducing this effect aim to increase the efficiency of printing techniques and the utilization of recycled paper [6]. The PPI is considered a major water polluter because it releases massive amounts of toxic substances into water bodies. The wastewater from the PPI contains more than 250 toxic chemicals resulting from various processes in wood pulping and papermaking, including organic, sulfur, and chlorinated compounds and heavy metals, such as chlorophenols, sulfides, iron, zinc, and manganese [7,8]. The PPI also generates various types of waste, such as wood rejects, black liquor, paper rejects, and sludge [9]. The large amounts of waste present a challenge for waste disposal and can result in significant damage to water, air, and soil. Furthermore, the organic matter in wastewater sludge, if discharged into water bodies, increases biochemical oxygen demand (BOD), causing eutrophication [10]. Waste combustion can also cause health problems in nearby communities. Recently, advanced incineration technologies have been developed and used, which emit less harmful gases, but the health effects of incinerators can still be difficult to evaluate because of the simultaneous pollution from many other sources, such as automobiles and industries [11]. The PPI is also energy intensive, which can be improved by implementing energy conservation technologies, using renewable energy, and utilizing the biomass rejects of the industry as bioenergy [9]. The increased awareness of environmental issues and the rapid depletion of natural resources has promoted the interest of industries to reuse the waste generated in their manufacturing processes [12–16]. In addition, strict governmental regulations have been enacted to facilitate the utilization of wastes (reuse, recycling, or conversion), which were formerly burnt or disposed of in landfills, to reduce their environmental impact on air, soil, and water resources [17]. Sustainable waste management is a basic part of sustainable de- velopment, as multiple benefits in the public health, safety, and environmental sectors can be gained. Sustainable waste management reduces greenhouse gas emissions, improves the quality of life, preserves natural resources, and reduces soil and water contamination [18]. Moreover, modern waste management has a major goal of effectively recovering energy from waste before safely disposing of it. For example, organic waste has a high energy re- covery potential [19], and municipal solid waste is listed as a renewable energy resource by the United States Environmental Protection Agency [20]. The recovery aspect of sustainable waste management is based on a hierarchy of waste prevention, reuse, recycling, recovery, and disposal. It is therefore important to mention that, before incineration and disposal, no efforts should be spared to convert paper waste and rejects into materials that can function as starting materials or finished products for all possible kinds of applications [21]. Several reviews are available in the literature about paper waste. Some discussed specific paper waste management techniques, including sorting and recycling [22,23], while others focused on the conversion of paper waste into a specific product, including construction materials and nanocellulose [24,25]. Our review comprehensively discusses the possible routes for the efficient conversion of paper waste and rejects into both high- value materials and energy. First of all, the review starts by explaining paper production from wood, including wood pulping and papermaking, and its impact on the environment while describing possible emissions, effluents, and wastes. It then continues to describe the process of recycling paper waste and rejects and the environmental and economic advantages. It then discusses the possible routes to convert paper waste into energy and high-value materials when it is not possible to further recycle paper into high-quality paper products. Finally, it economically and environmentally compares these routes with a focus on composting, anaerobic digestion, and incineration. Overall, this review provides a comprehensive overview of paper’s lifecycle—from wood to paper to energy and other useful products—towards a circular economy. 2. Wood Pulping and Papermaking The PPI requires four main inputs for papermaking: cellulose fibers, chemicals, energy, and water. In the past, the industry utilized cotton and linen rags as cellulose sources but later shifted to wood for increased paper production and quality [26]. Cellulose is the most
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