RESEARCH AND ANALYSIS
lost in the sewer or added to stock. The lower and upper bound is based on variability in additions to stock. In addition, pa- permaking generates 21 tonnes of paper for recycling. The total potential quantity of paper for recycling implies a collection rate of 90% to 96%. This large supply of paper for recycling can only be used with improved control of contamination. Pivnenko and colleagues (2015) show that 51 contaminants currently found in paper can pose challenges for recycling. Contamination may exclude certain uses of paper for recycling or lead to lower pulp- ing yields. The most effective measure is not source separation or removal, but to phase out the use of chemicals altogether (Pivnenko et al. 2016). The maximum value of the more desirable RIR can be calculated assuming a fixed non-fibrous content fraction and a fixed ratio between mechanical and chemical pulp for virgin fibrous inputs. The calculation assumes the lower recycled pulping yield ratio of 0.73 to reflect the increased need for deinking. Under these assumptions, the technical limit of the RIR is 67% to 73% (see section SI-4 in the supporting information on the Web). In other words, only 67% to 73% of fibrous inputs can be supplied by waste paper, the rest needs to be virgin fibers. The current performance for the metric is 38%, which is just over half of the technical potential. The inclusion of a technical potential in the reporting of recycling metrics can support better decision making. It would be useful for policy makers and industry to know how much more recycling is possible. An LCA would be required to assess the environmental merit of maximizing recycling. Material Efficiency Metrics Another way to improve paper production is by increasing the material efficiency of conversion processes since it reduces input requirements. The overall material efficiency (or yield ratio) of paper production strongly depends on the paper grade and required pulp inputs. For example, mechanical pulping has a much higher yield (0.90 to 0.95) than chemical pulping (0.40 to 0.55). However, the wastes from chemical pulping are used for energy recovery and can be sufficient to meet the energy demand of the mill. Low yield in chemical pulping therefore does not necessarily represent an undesirable inefficiency. The beneficial use of waste materials needs to be captured when discussing material efficiency. Basic material efficiency calculations ignore the role of waste reuse. The standard metric for material efficiency is the ratio be- tween material used in the product (M p ) and material supplied to it (M s ) (Lifset and Eckelman 2013).
are skewed toward higher values because of the distribution of company performance. Despite the uncertainty, the material balance is useful for comparing the relative sizes of flows and analyzing potential improvements. Over time, the balance may be updated and improved with new data. The following sec- tions discuss recycling and efficiency metrics and waste reuse appraisal based on the material balance. Recycling Metrics Current recycling metrics provide only a distorted image of the paper system. Recycling is commonly calculated by dividing paper for recycling by total production of paper and cardboard (Ervasti et al. 2015). For the global paper system, this results in a collection rate of 54%. However, this metric is both inconsis- tent and lacks meaning. It is inconsistent because it compares a quantity from the pulping stage (paper for recycling inputs) with a quantity from the papermaking phase (total production or consumption). The metric omits the losses that occur in be- tween the two stages and ignores that not all paper is discarded and therefore not available for recycling. The metric also lacks meaning because its value does not reflect the purpose of recy- cling. The main goal of recycling is the reduction of impacts by displacing virgin production (Geyer et al. 2016). A recycling metric can only reflect the avoidance of virgin inputs by focus- ing directly on the harvest stage of the life cycle. A recycling metric that is both consistent and meaningful should compare waste paper inputs (paper for recycling) with total inputs (paper for recycling plus virgin fibrous harvest). Such a metric was dis- cussed by Graedel and colleagues (2011) and named the recycled input rate (RIR). The value of the RIR is 38% while the collection rate is 54%. The difference reflects the relatively high yield ratio of recycled pulping compared to chemical pulping. In other words, an increase in paper for recycling inputs does not imply a pro- portional decrease in virgin input requirements. Due to the differences in pulping efficiencies, 1 mass unit of paper for re- cycling may either displace 0.9 units of wood for mechanical pulping or 1.7 units of wood for chemical pulping. When paper for recycling substitutes virgin inputs without affecting the ra- tio between mechanical and chemical pulp inputs, the average global substitution rate is around 1.5. In practice, it depends on the desired properties of the final product whether recycled pulp will substitute mostly mechanical or chemical pulp. The RIR should be used with care because it can be inflated through inefficient use of secondary material (Chen 2013). The met- ric is also sensitive to the fraction of non-fibrous inputs since these could also substitute virgin pulp. It is beyond the scope of this article to discuss desirable levels of substitution of fibers by non-fibrous material. Recycling metrics expressed as percentages may create the false impression that 100% recycled paper is technically possi- ble. It is therefore important to report the technically achievable maximum performance alongside actual performance. At 2012 consumption levels, 351 tonnes ( ± 12 tonnes) of paper for recy- cling can be collected. The rest of consumption is irretrievably
M p M s
η m =
Allwood and colleagues (2011) show how energy use and carbon emissions associated with conversion processes can be included in this equation. However, the example of the paper industry shows that energy needs can also be met by energy recovery from wastes from the same conversion process. In ad- dition, wastes can be used for non-energy recovery. Material
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Journal of Industrial Ecology
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