Calculating tied up and consumed plastic for a reuse system and a single-use system for PET bottles

In this report, we estimate the amount of tied up plastic and plastic consumption in the single-use system (the current system in Norway) and a reuse system for PET bottles as beverage packaging. We calculate and compare the consumed and tied up plastic for PET bottles both isolated and when accounting for Transport Items such as plastic crates, trays, and bags that are used in shipping and storing of the bottles. Tied up plastic is calculated from the number of bottles (and corresponding Transport Items) that at all times must exist in order to keep the circular material system operational. Here we find that the number of bottles that are tied up is greater in the reuse system than in the single-use system, which is due to a higher sensitivity to seasonal variation and logistical imbalance. As the bottles weigh more in the reuse system, the effect is further reinforced when we consider the amount of plastic instead of the number of bottles. We estimate more than twice as much tied up plastic in the reuse system as in the single-use system. If we also take into account Transport Items in the form of plastic crates, trays, and bags, the difference between the systems becomes even greater. Plastic consumption is here defined to be the amount of virgin plastic that must be put in to the system to cover the loss of plastic. Here we find that consumption is greater in the reuse system than in the single-use system for small PET bottles, and smaller for large PET bottles. This is partly due to the fact that the DRS collection rate by unit is higher for large PET bottles than for small PET bottles. In total the reuse system has the highest plastic consumption when we take into account the consumption of plastic crates, trays, and bags. Plastic consumption from PET bottles in the reuse system decreases as the DRS collection rate by unit increases. In the single-use system there is a limiting factor in terms of the proportion of recycled plastic that can be utilized in new bottles. Hence, after a certain threshold of high DRS collection rate by unit we do not see a decrease in plastic consumption from PET bottles despite further increase in the DRS collection rate by unit.