Reference Flows in a Complex World: Making Appropriate Assumptions

Last post, we introduced the concept of reference flows, which are a measure of the outputs from processes required to fulfill the function expressed by the functional unit of the LCA. We also illustrated how the reference flows are calculated for facial tissues and the facial tissue packaging. Those reference flows were very simple to calculate: they are just the weight of one facial tissue (or the proportion of the packaging for one facial tissue) times the total number of facial tissues used. But to calculate many of the reference flows needed to fully describe the product system as defined by the system boundaries, information from other studies and carefully considered assumptions need to be applied. We at, Ecosystem Analytics, believe that how reference flows are calculated should be fully transparent – all reference sources behind the calculations need to be cited and the assumptions made documented. In the full LCA on facial tissue versus handkerchief use, all reference flows are listed in the Appendix in Tables A1 and A2, and the references and assumptions behind each is listed in the tables or in the footnotes at the end of the tables. We will illustrate an example of how research and informed assumptions helped us calculate reference flows for the end-of-life for facial tissues.

End of Life – Facial Tissue & Packaging

Since this LCA is a cradle-to-grave study, we must quantify the reference flows for the disposal of the used facial tissues and tissue packaging. We have assumed that all used facial tissues and packaging are thrown away instead of being recycled or composted, since used facial tissues would not be accepted in most municipal recycling or composting programs. This LCA is based on the facial tissue or handkerchief use of an average adult American living in New England. Therefore, we used The State of Garbage in America report by Van Haaren et al. (2010) to determine the fraction of trash in New England that is either landfilled or incinerated. For New England, Van Haaren et al. (2010) found that 31% of municipal waste is landfilled, 39% is incinerated, 22% is recycled, and 8% is composted. Since recycling and composting were not considered viable waste options, we determined the relative % of waste that is landfilled and incinerated only:

• Landfilling: 31% ÷ (31% + 39%) x 100% = 44.29% landfilled
• Incineration: 39% ÷ (31% + 39%) x 100% = 55.71% incinerated

Then, the mass of the material was multiplied by the fraction intended for landfilling or incineration:

Facial Tissue:

• Landfilling: 1013 g x 44.29% = 448.66 g
• Incineration: 1013 g x 55.71% = 564.34 g

Cardboard Box:

• Landfilling: 232 g x 44.29% = 102.75 g
• Incineration: 232 g x 55.71% = 129.25 g

PE insert:

• Landfilling: 7.85 g x 44.29% = 3.48 g
• Incineration: 7.85 g x 55.71% = 4.37 g

In the next post, we will explore how unit processes are used to build up the model of how the products are manufactured, transported, and disposed.