The Battle of Emissions: Waste vs. Recycling

When you think of plastic pollution, what comes to mind? Harm to the environment, disruption of habitats, toxicity, damage to the body? With all these issues, it’s easy to overlook plastic’s enormous carbon footprint. In an estimate outlined by Zheng and Suh in 2019, the amount emitted globally due to the production and disposal of plastic products is 1780.46 Mt CO2eq. (Zheng and Suh 2019). For comparison, the UK’s carbon footprint has been calculated to be 329.58 MtCO2 in 2020 (Our World in Data 2020). Therefore, we can conclude that recycling plastic instead of producing virgin plastic would lead to a dramatic reduction in these emissions. However, the question we want to answer is: by exactly how much are we reducing the emission of carbon dioxide by recycling plastic instead of producing it anew?  

 

To determine the carbon dioxide emissions that will be avoided due to the recycling of a certain plastic type, you need to decide on a method to calculate this. This is open to interpretation. We decided on the following method.

 

Consider the lifetime emissions of two separate kilograms of a certain plastic type: one of these kilograms is produced, used and then incinerated, the other kilogram is produced, used, recycled, the remaining material is then used and then finally incinerated. Each step in the lifetime of both these materials will lead to the emission of some carbon dioxide. If recycling didn’t create emissions, then you would expect these lifetime emissions to be the same since the same amount of material was produced and the same amount of material was incinerated. Recycling does lead to the emissions of CO2 though and so the lifetime emissions of the recycled kilograms will be higher. This could lead you to conclude that recycling was, in fact, worse for the environment. However, this would not take into account the fact that the material is used more throughout the lifetime of the recycled kilogram. To account for this, we compared the emissions we could attribute to the initial kilogram of plastic throughout the entire lifetime of the material of which the kilogram is made. For the unrecycled kilogram, this will be 100% of the lifetime emissions. For the recycled kilogram, this will be the proportion of the initial kilogram’s mass compared to the total mass of material used multiplied by the lifetime emissions[1] The ‘Avoided Emissions’ is then the difference between these two emissions.

 

To calculate the lifetime emissions of the two separate kilograms of plastic, we need to determine the emissions from this plastic’s production, use and disposal. A report by the European Environment Agency gave us the values for the carbon emissions due to the production, recycling and incineration of different types of plastic (Vanderreydt et al. 2021, 12). This report included analysis of the crude oil extraction, refinery, cracking, polymerisation, conversion into plastic, use, transportation to waste disposal facilities, the sorting process, incineration, energy generated during incineration and landfill emissions. Notably, this report only includes transportation emissions in the post-consumer phase and none in the pre-consumer phases (ie., the only time emissions from transportation are accounted for is when taking plastic waste from people’s houses to waste disposal facilities). This report also concludes that the use of plastic leads to no emissions. Furthermore, this report focuses on plastic use in the EU. In addition, we decided to carry out a similar process for Aluminium. A study by European Aluminium gave us the value for emissions due to Aluminium production and recycling (European Aluminium 2019, 4). Using the method described above for getting the avoided emissions we get the following table.

Note that the Aluminium cannot be incinerated. So we instead compare two forms of disposal – landfill and recycling. Landfill leads to no further carbon emissions. Also, bear in mind that this is the Avoided Emissions when comparing material that has been recycled just once with material that hasn’t been recycled at all. The Avoided Emissions when comparing material that has been recycled twice would be different but a similar process would be used.

Using the values derived from the calculation outlined above, we have been able to determine roughly what the emissions avoided through plastic recycling are. Therefore, by knowing this, we can add to the many ways Nozama allows people to measure and reduce their environmental impact.


 [1] That is, Effective emissions = lifetime emissions * (1 kg / (1 kg + mass of material remaining after recycling))

References

European Aluminium. 2019. CIRCULAR ALUMINIUM ACTION PLAN: A STRATEGY FOR ACHIEVING ALUMINIUM’S FULL POTENTIAL FOR CIRCULAR ECONOMY BY 2030. N.p.: European Aluminium. https://european-aluminium.eu/media/2931/2020-05-13_european-aluminium_circular-aluminium-action-plan_executive-summary.pdf.

Our World in Data. 2020. “Annual CO2 Emissions (UK).” Our World in Data (United Kingdom: CO2 Country Profile). https://ourworldindata.org/co2/country/united-kingdom?country=~GBR.

Vanderreydt, Ive, Tom Rommens, Anna Tenhunen, Lars Fogh Mortensen, and Ida Tange. 2021. Greenhouse gas emissions and natural capital implications of plastics (including biobased plastics). N.p.: European Environment Agency. https://www.eionet.europa.eu/etcs/etc-wmge/products/greenhouse-gas-emissions-and-natural-capital-implications-of-plastics-including-biobased-plastics/@@download/file/ETC_2.1.2.1._GHGEmissionsOfPlastics_FinalReport_v7.0_ED.pdf.

Zheng, Jiajia, and Sangwon Suh. 2019. “Strategies to Reduce the Global Carbon Footprint of Plastics.” Nature Climate Change 9 (5): 374-378. https://doi.org/10.1038/s41558-019-0459-z.

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Johnny Hilditch

Sustainability Research and Applied Physics

As Sustainability Technician at Nozama, Johnny, a Physics graduate from Oxford University where he specialised in Orbital Mechanics, is leading Nozama's Research department on the Carbon Footprint of Cryptocurrencies. His department is working with the development team to come up with a Cryptocurrency Carbon Footprint Tracker.