Plastic Recycling and Impact on CO2 Emission
Two forms of waste processing make it possible to stop plastics being released into nature: incineration and recycling. What are the respective environmental impacts of these two methods for managing end-of-life plastics? Shown below are estimates of these impacts, made by comparing net greenhouse gas emissions (GHG) for each method. The waste management process that emits the least, assuming that variables are comparable, is judged the most environmentally friendly. Net GHG emissions for a process are expressed as follows:
Net GHG emissions (metric tons of CO2e/metric tons of plastic) = Actual GHG emissions (1) - Credits (2)
CO2e = CO2 equivalent
1. Actual emissions are the sum of direct emissions relating to transportation and energy use during processing, and processing rejects in the case of recycling. Actual emissions vary according to the type of polymer processed, the distance raw materials are transported, the quantity of energy used, the local energy mix and energy efficiency. For example, it takes more energy to recycle PET than to recycle PE/PP.
2. Credits are GHG emissions avoided thanks to recycling, for example by avoiding emissions linked to the production of new products made from raw plastic, or thanks to incineration, producing energy that is not generated from the carbon-sourced energy mix. These credits vary as a function of the polymer, the local energy mix and the cogeneration performance of the incinerators.
Example: Net emissions relating to recycling polyethylene in the EU
1. Actual GHG emissions are shown in gray and are equivalent to approx. 0.5 kg CO2e/kg PE.
2. GHG emissions avoided thanks to recycling are shown in red and are equivalent to approx. 1.5-1.8 kg CO2e/kg PE. Net emissions are the difference between the two, a net saving from recycling of 1-1.3 kg CO2e/kg.
Similarly, a calculation is made to determine net emissions from incinerating PE using current technologies: the energy recovery benefits (-2 kg CO2e/kg) do not sufficiently outweigh the environmental impact (3 kg CO2e/kg), i.e., surplus emissions of 1 kg CO2e/kg.
This shows that recycling PE in the EU is not the most environmentally friendly option.
Life cycle analysis demonstrates that recycling is always the most environmentally friendly option with current processing technologies, whether processing PP/PE or PET, in France or Asia, irrespective of whether the energy performance is low or high (assuming use of current incineration facilities). The same analysis shows that using recycled plastic in place of raw plastic can cut GHG emissions by 20–50%.
However, if we look at a theoretical “optimal” case where incinerators become more efficient in terms of energy recovery (heat and electricity), then incineration can deliver fewer negative environmental impacts than recycling in regions with a very high-carbon energy mix:
· optimized incineration of HDPE would be the preferred solution in China, the USA and Europe, except in France, as the French energy mix is overwhelmingly nuclear;
· in China, optimized incineration of PP would emit less GHG than recycling, but the two solutions would be equivalent in the rest of the world;
· however, recycling is the best solution everywhere for PET, even assuming the optimized incineration scenario (except in China, which has a very high-carbon energy mix).