Nordahl Sarah L, Scown Corinne D
Energy Technologies Area, Lawrence Berkeley National Laboratory 1 Cyclotron Road Berkeley CA 94720 USA
Joint BioEnergy Institute 5885 Hollis Street Emeryville CA 94608 USA.
Chem Sci. 2024 May 24;15(25):9397-9407. doi: 10.1039/d4sc01340a. eCollection 2024 Jun 26.
Technologies that enable plastic circularity offer a path to reducing waste generation, improving environmental quality, and reducing reliance on fossil feedstocks. However, life-cycle assessment (LCA) methods commonly applied to these systems fall far short of capturing the full suite of advantages and tradeoffs. This perspective highlights inconsistencies in both the research questions and methodological choices across the growing body of LCA literature for plastics recycling. We assert that conducting LCAs on the basis of tonnes of waste managed tonnes of recycled plastics yields results with fundamentally different conclusions; in most cases, analyses of recyclable plastics should focus on the unit of recycled product yielded. We also offer straightforward paths to better approach LCAs for recycling processes and plastics in a circular economy by rethinking study design (metrics, functional unit, system boundaries, counterfactual scenarios), upstream assumptions (waste feedstock variability, pre-processing requirements), and downstream assumptions (closed-loop open-loop systems, material substitution). Specifically, we recommend expanding to metrics beyond greenhouse gases by including fossil carbon balances, net diversion of waste from landfill, and quantity of avoided plastic waste leakage to the environment. Furthermore, we highlight the role that plastic waste plays as a problematic contaminant in preventing greater diversion of all wastes to recycling, energy recovery, and composting, suggesting that plastics may hold a shared responsibility for the system-wide greenhouse gas emissions that occur when mixed wastes are landfilled.
实现塑料循环利用的技术为减少废物产生、改善环境质量以及减少对化石原料的依赖提供了一条途径。然而，通常应用于这些系统的生命周期评估（LCA）方法远远无法全面体现其所有优势和权衡。这一观点突出了在不断增长的塑料回收LCA文献中，研究问题和方法选择方面存在的不一致性。我们认为，基于处理的废塑料吨数与回收塑料吨数来进行LCA会得出截然不同的结论；在大多数情况下，对可回收塑料的分析应关注所产生的回收产品单位。我们还通过重新思考研究设计（指标、功能单位、系统边界、反事实情景）、上游假设（废塑料原料的变异性、预处理要求）和下游假设（闭环与开环系统、材料替代），提供了一些直接的方法，以便在循环经济中更好地对回收过程和塑料进行LCA评估。具体而言，我们建议除了温室气体指标外，还应纳入化石碳平衡、从垃圾填埋场转移的净废物量以及避免泄漏到环境中的塑料废物量等指标。此外，我们强调了塑料废物作为一种有问题的污染物在阻碍所有废物更多地转向回收、能源回收和堆肥方面所起的作用，这表明在混合废物被填埋时，塑料可能对全系统的温室气体排放负有共同责任。
