RESEARCH AND ANALYSIS
Figure 1 The paper system.
masses of all flows—gases and water are not included. The con- sumption of five categories of paper, chemical pulp, mechanical pulp, and paper for recycling is based on the Food and Agricul- ture Organization of the United Nations (FAO) (FAO 2016). The flows in each life cycle stage are further specified using parameters from the literature and industry reports (see section SI-1 in the supporting information available on the Journal’s website). Materials referred to as by-products or co-products in the literature are consistently referred to as wastes in this anal- ysis and include black liquor, tall oil, and turpentine. Waste paper that is recycled, sometimes called recovered paper, is re- ferred to as paper for recycling. Pulp from paper for recycling, sometimes called secondary pulp or recovered pulp, is referred to as recycled pulp. The fraction of postconsumer waste paper that is neither recycled nor ends up in the sewer is referred to as residual waste paper. Figure 1 displays the main stages in the life cycle of pa- per from harvest to waste treatment. Paper is produced from wood, non-wood harvest, waste paper, and non-fibrous mate- rial. Wood is converted into mechanical, chemical, and semi- chemical wood pulp. Mechanical pulping consists of grinding wood and is highly energy intensive. Chemical pulping is used for higher-quality products since it removes undesirable lignin from wood. Semichemical pulping combines a grinding stage with chemical treatment, but is split into equal fractions of chemical and mechanical pulping in the further analysis. In addition to wood, a fraction of non-wood pulp from materials such as straw is used, mainly in China and India. Paper for re- cycling is pulped separately and often deinked. The different pulps, together with non-fibrous materials, are used in different combinations for papermaking of different grades (omitted in figure 1). After consumption, paper is either added to stock, recycled, or ends up in incineration (with or without energy
balance helps identify options for reducing virgin material in- puts and associated environmental impacts. An analysis based on the mass balance principle can approximate important but ill-reported flows such as virgin wood inputs, non-fibrous inputs, and waste treatment flows. The material balance is a useful contribution for two rea- sons. First, it is used in this article for comparing and analyzing mass-based performance metrics. Such mass-based metrics are used by governments around the globe to track environmental performance and therefore deserve critical analysis. This arti- cle shows the shortcomings of commonly used recycling and efficiency metrics and makes recommendations for improving them. The article also quantifies the technical recycling poten- tial. Second, the material balance can serve as a basis for more advanced methods that may consider energy, water, emissions, land use, and other environmental impacts. Such life cycle as- sessments (LCAs) require a material balance to start with, and no such balance yet exists for the paper system. The article is structured as follows. The next section explains the data sources, assumptions, and methods used for construct- ing the material balance. This is followed by the results, in the form of a Sankey diagram, and a discussion of recycling met- rics, efficiency metrics, and appraisal of waste reuse. The article concludes by suggesting improvements in environmental per- formance metrics and indicating directions for future research. Data and Methods This study constructs a material balance to indicate the ori- gin, destination, and size of global flows of wood, pulp, paper, and waste paper for 2012. The data are drawn from a variety of sources and the values are calculated using material-balance equations and matrix algebra. The assessment considers the dry
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Journal of Industrial Ecology
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