Life cycle implications of managing plastic wastes Ming Xu, Ph.D. Associate Professor School for Environment and Sustainability Department of Civil and Environmental Engineering University of Michigan, Ann Arbor mingxu@umich.edu www.mingxugroup.org @MingXuUMich

Agenda What is life cycle assessment (LCA)? What can LCA offer in managing plastic wastes? What do we know in the plastics-LCA space? What are the challenges and possible solutions?

1. What is life cycle assessment (LCA)?

LCA in environmental policymaking Identify key processes contributing to the environmental footprint to guide technology development Evaluate system-wide environmental impacts of consumption to avoid shifting environmental burdens from one process to another Inform consumer choices and public policy

2. What can LCA offer in managing plastic wastes? The war on plastics is not new Plastic is criticized for its end-of-life impact on ecosystems A symbol of environmental literacy in the 1970s

Paper and plastics from life cycle perspective Life cycle of paper Life cycle of plastic

Life cycle energy use and air emissions It depends! What are included in the life cycle What environmental impacts are concerned … Hocking, M. B. Science 1991, 251 (4993), 504-505.

What LCA can offer? Compare environmental impacts of different end-of-life pathways for plastics www.epa.gov

Characterization factors How does LCA work? Hellweg and Milà i Canals (2014) 3. Impact assessment: Characterization factors 2. Inventory analysis Unit process data kg GWP (kg CO2 eq.) Damage to ecosystem (species.yr) CO2 1 8.73E–06 CH4 28 2.44E–04 N2O 265 2.31E-03 … Plastic film (kg) Polyethylene 1.02 kg Electricity 0.66 kWh Wastewater 0.027 m3 …

3. What do we know in the plastics-LCA space? Three main application areas: Comparison With bio-based plastics With other materials Identifying “hotspots” for improvement Life cycle cost analysis Key words = “life cycle assessment” & “plastics” in Scopus

Compare bio-based plastics with fossil fuel-based plastics: GHG emissions Upcycling carbon dioxide into polymers 11-20% reductions in GHG emissions and the depletion of fossil resources From plants to plastics 20-50% reduction in GHG emissions Zhu, Y., Romain, C., & Williams, C. K. (2016). Nature, 540 (7633), 354.

Compare bio-based plastics with fossil fuel-based plastics: GHG emissions Global carbon footprint of fossil fuel-based plastics produced in 2015: 1.8 GtCO2e or 3.8% of global emissions Dominated by resin production (61%) and conversion (30%) stages For strategies to reduce plastic carbon footprint: Using renewable energy Bio-based plastics Recycling Reducing demand Zheng, J., & Suh, S. (2019). Nature Climate Change, 9, 374.

Compare bio-based plastics with fossil fuel-based plastics: Other environmental impacts Main impacts: ozone depletion, acidification, eutrophication, carcinogens, and ecotoxicity Causes: farming and fertilizer use Fossil fuel-based Main impacts: fossil fuel depletion, global warming Causes: oil refining, chemical process Tabone, M. D., Cregg, J. J., Beckman, E. J., & Landis, A. E. (2010).  Environmental Science & Technology, 44 (21), 8264-8269.

Compare plastics with other materials Conclusion: for identical transportation distances, plastic pots have smaller environmental burdens in almost all impact categories compared to glass jars Humbert, S., Rossi, V., Margni, M., Jolliet, O., & Loerincik, Y. (2009).  The International Journal of Life Cycle Assessment, 14 (2), 95-106.

Identify “hotspots” for improvement Lean manufacturing opportunities are identified in plastic injection moulding process guided by LCA Lean manufacturing improvements can reduce the life cycle environmental impacts by approximately 40% in climate change, human toxicity, photochemical oxidant formation, acidification, and eco-toxicity. Cheung, W. M., Leong, J. T., & Vichare, P. (2017). Journal of Cleaner Production, 167, 759-775.

Life cycle cost assessment of plastic waste Three scenarios: simple mechanical recycling advanced mechanical recycling feedstock recycling Conclusion: all scenarios achieved net financial revenues in case of market substitution factor above 0.7 (price of recycled material = 70% of price of virgin material) sMR: simple mechanical recycling aMR: advanced mechanical recycling FR: feedstock recycling Faraca, G., Martinez-Sanchez, V., & Astrup, T. F. (2019). Resources, Conservation and Recycling, 143, 299-309.

Case study: life cycle assessment of end-of-life treatments for plastic film waste landfill Incineration Recycling Requires a large amount of space One of the major sources of CH4 emissions Reduce the need for landfill Recover energy from combustion of waste Hazard air pollutants Make new products Collection and transportation consume energy Hou, P., Xu, Y., Taiebat, M., Lastoskie, C., Miller, S. A., & Xu, M. (2018). Life cycle assessment of end-of-life treatments for plastic film waste. Journal of Cleaner Production, 201, 1052-1060.

Goal and scope definition Functional unit: Film waste in 1 metric ton of either recyclable or mixed waste Recyclable: 0.6% by weight Mixed: 2% Collection scenarios Urban, mixed or recyclable Rural, mixed or recyclable Consumer drop-off, recyclable End-of-life scenarios Landfill in mixed stream Incineration in mixed stream Recycling in mixed stream Recycling in recyclable stream Weights from NIST Building for Environmental and Economic Sustainability (BEES) used for relative importance of each impact category

Life cycle environmental impacts of different end-of-life scenarios based on the same collection scenario (rural, mixed) avoidance of virgin material production Mixed > recyclable: larger mass fraction of film waste

End-of-life stage dominates

decrease by 72% if using solar energy instead of US average grid Sensitivity analysis Parameters change by 1% LCA result changes Collection distance 0.02% Electricity and diesel fuel consumption at MRF 0.01% Recycling rate at MRF 1.22% Utilization rate of recycled plastic films Waste-to-energy conversion rate at incinerators 0.81% Mass fraction of films in the waste 1.99% Type of electricity replaced at incinerators decrease by 72% if using solar energy instead of US average grid Strategies for reducing environmental impacts of plastic: Improve recycling rate at MRF  technology innovations Improve utilization rate of recycled plastic films  incentives Increase mass fraction of films in waste stream  source separation Low-carbon electricity  energy system transition

Data challenges in plastics-LCA, and LCA in general Laboratory test Onsite investigation Literature review Questionnaires, surveys Expensive & Time Consuming More Efficient Methods

Data science helps fill data gap in LCA datanami.com

Life cycle inventory (unit process) data is a network Paper (g) Pulp 2.3 g Water 1 L … ? Waste-water 0.8 L ? ? Estimate missing data in a unit process database Predict missing links in a network =

Use online shopping recommendation system to estimate missing data in life cycle inventory ? We can estimate missing data in ecoinvent database with very high accuracy (<5% error) if missing less than 10% of data Hou, P., Cai, J., Qu, S., & Xu, M. (2018). Estimating missing unit process data in life cycle assessment using a similarity-based approach. Environmental Science & Technology, 52(9), 5259-5267.

Summary LCA offers a holistic and system-based evaluation of the environmental impacts of the plastic system: Identify environmental hotspots for improvement Avoid shifting environmental burdens to different processes Inform consumers Data gaps are large; Data science can help with “generating” data from data

Resources, Conservation & Recycling Special issue on Sustainable Cycles and Management of Plastics Deadline: May 15, 2019 http://bit.ly/plastics-rcr http://www.elsevier.com/locate/resconrec Guaranteed social media coverage http://www.linkedin.com/groups/12038300 @RCRjournal http://www.facebook.com/groups/333217667089759 WeChat