Expanded polystyrene (EPS) is a synthetic plastic used in various industrial and commercial applications. EPS is popular for its unique physical properties, specifically insulating capabilities and low density. These properties become problematic at the end of its useful life as EPS cannot be recycled with other conventional plastics. Though possible, recycling EPS often is practically or economically prohibitive and the material typically is consigned to landfill after a single use. This study investigates the EPS handling system and several disposal alternatives using the methodology of life cycle assessment. The results are applied to evaluate the environmental impacts and economic tradeoffs of a recycling program for EPS shipping boxes at the University of Wisconsin-Madison. The approach in this study pertains to infrastructure sustainability through exploring the challenges and lack of existing infrastructure for managing EPS. The four disposal scenarios under consideration in this study are (1) consignment to a sanitary landfill, (2) a closed-loop reuse arrangement with a biotechnology company, (3) a conventional open-loop recycling arrangement with a specialty recycler, and (4) a novel open-loop recycling arrangement with an on-campus lab. While a closed-loop reuse system for EPS was most environmentally desirable, the study results indicate that conventional recycling of EPS is the only disposal scenario that generates net environmental benefits while also being logistically feasible. Thus, the study results contribute to the body of knowledge related to post-consumer EPS management and can inform decision-making at comparable institutions that generate large quantities of EPS waste.
1.Introduction
Expanded polystyrene (EPS) is a paradoxical substance. It is both beneficial and problematic, it is convenient but also a nuisance, and it is cheap yet costly. Furthermore, EPS products frequently are mistaken for Styrofoam. In fact, Styrofoam is a registered product of Dow Chemical and is specific to the trademarked brand of extruded blue foam insulation (Cansler 2018). Conversely, 'Styrofoam' products such as packaging inserts, foam coffee cups, and insulated shipping boxes actually are made from EPS (Insulation Company of America 2018).
By whatever name, EPS is more than paradoxical. In 2018, the robust EPS industry had a global market value estimated at USD 15.5 billion and this value is projected to exceed USD 20 billion by 2023 (Markets and Markets 2018). The material is popular for its physical characteristics: it is inexpensive to manufacture, lightweight yet rigid, does not degrade, provides good thermal insulation and shock absorption, and can easily be molded to fit custom shapes and designs. EPS exists in a range of products such as bike helmets, to-go containers, and automotive parts, but is most commonly utilized in building insulation, shipping boxes, and packaging products (EPS Industry Alliance 2013). EPS is manufactured from polystyrene (PS), a petroleum-based polymer comprised of styrene monomer (Tan and Khoo 2005). By injecting PS pellets with pentane and applying steam heating as an expansion medium, the plastic can be 'blown' or expanded into a foamy substance that is over 95% air with a density between 20–30 kilograms per cubic meter (kg m−3) (Tan and Khoo 2005, Bribián etal 2011). By comparison, conventional PS has an approximate density of 1000kgm−3 (Material Properties.org 2022). Accordingly, EPS shares several qualities common to plastics but with a fraction of the density. This lightweight feature makes EPS attractive in various applications but also makes it notoriously problematic to responsibly manage at the end of its useful life.
Though many plastics are recyclable, increased efforts to improve recycling practices nationwide have yet to be realized. In 2014, over 75% of plastic waste was landfilled in the United States (U.S. EPA 2016). Equal to 25 million tons or 18% of municipal solid waste (MSW), plastics represented the highest landfill rate of any material tracked by the United States Environmental Protection Agency (EPA). These trends create long-term issues of space as plastics are inert and persist indefinitely. Estimates indicate that plastics account for 25%–30% of total landfill volume in the United States (Earth Resource Foundation 2016).
1.1.Review of the literature
Assessments of post-consumer plastic waste management populate the literature, and consensus generally suggests that recycling is preferable to landfill or incineration in closed-loop scenarios where the recycled material directly replaces virgin plastic. However, EPS presents additional challenges unique to plastic recycling. Post-consumer EPS is expensive to store and transport, and materials recovery facilities that use automation to mechanically sort MSW will not accept EPS due to its density (Earth Resource Foundation 2016). Thus, EPS cannot be included with other plastics among conventional curbside recycling products. The material must be recycled at specialized facilities that densify and either remanufacture EPS or produce new PS products (EPS Industry Alliance 2017). These factors make EPS recycling prohibitively expensive and do not necessarily mitigate demand for virgin material. Accordingly, EPS products typically are consigned to landfill after a single use.
Most peer-reviewed life cycle assessment (LCA) studies of EPS focus on insulation from cradle-to-gate, finding EPS preferable to other synthetic materials but not natural alternatives (Bribián etal 2011, Purgana etal 2014, Dylewski and Adamczyk, 2016). Among the few end-of-life assessments of EPS in the literature, studies tend to either reinforce the cradle-to-gate comparisons of EPS with natural and synthetic alternatives (Tan and Khoo 2005; Franklin Associates 2011) or explore the impacts from techniques that extend the useful life of EPS (Ross and Evans 2003). Studies that explore the quality and performance attributes of recycled EPS in applications involving replacement of or integration with virgin EPS or PS tend to observe slight degradations in properties such as density (Acierno etal 2009, Hattori 2015) and thermal insulation (Tittarelli etal 2016); however, these studies also suggest that the recycled alternatives retain much of the mechanical properties of the virgin alternatives. Despite the need for additional research, industry affiliates, academics, and advocates alike acknowledge that post-consumer EPS has value and that recycling is a preferable alternative to landfill (PWC 2001, EPS Industry Alliance 2013). For additional discussion of EPS LCA studies in the literature, please see Marten and Hicks (2018).
The end-of-life crossroads for EPS remains an underexplored case for industrial ecology (IE), where the tool of LCA can be used to evaluate changes in the supply chain of products (Hicks 2017). The published LCA literature on EPS has favored cradle-to-gate studies on insulation. Building upon that work, this study uses LCA to evaluate the life cycle impacts of EPS shipping boxes with four distinct end-of-life scenarios. The LCA results are then applied to evaluate the impacts of an EPS recycling program at the University of Wisconsin-Madison (UW-Madison). The study pertains to IE through the emerging concept of the circular economy, which seeks to employ waste flows as feedstocks for alternative processes and mitigate unusable byproducts or unwanted material (Zink and Geyer 2017). Additional literature review is provided in the supporting information (SI) (https://stacks.iop.org/ERIS/2/031001/mmedia) online.
2.Methods
The LCA is conducted using the International Organization for Standardization (ISO) framework established in the ISO 14040 standards (ISO 2006). These standards divide LCA methodology into the sections of goal and scope, inventory analysis, impact assessment, and interpretation. The LCA uses SimaPro (version 8.4) (Pré Consultants 2016) to conduct the assessment and the environmental impacts are reported using the tool for the reduction and assessment of chemical and other environmental impacts (TRACI) (version 2.1) (U.S. EPA 2012). TRACI is a midpoint life cycle impact assessment (LCIA) method that allows for assessment of first-order or direct impacts in ten categories: ozone depletion, global warming potential, smog, acidification, eutrophication, human health carcinogenics, human health non-carcinogenics, respiratory effects, eco-toxicity, and fossil fuel depletion. The LCA relies upon data from two life cycle inventory (LCI) databases: (1) the United States life cycle inventory (US LCI) curated by the National Renewable Energy Laboratory (2013), and (2) ecoinvent v3.3, an aggregation of LCI data related to European markets (Weidema etal 2013). Additional site-specific data have been gathered experimentally and in consultation with actors involved in the EPS system modeled in this study. The electricity mix utilized in this work is based on the US grid average.
2.1.Goal and scope
The goal of the LCA is to determine the life cycle environmental impacts of EPS shipping boxes with four end-of-life disposal alternatives. The setting is UW-Madison, a large public research university in the Midwestern United States. Two factors contribute to the significance of the study site. First, research institutions contribute large volumes of EPS waste associated with laboratory shipments (Murchie 2012). The UW-Madison campus has over 3000 wet labs, and a 2013 survey estimated a monthly throughput of nearly 14 500 EPS shipping boxes. Second, the concentrated nature of a university campus means that labs can collectively be viewed as large point-sources of EPS waste rather than small and diffuse sources that characterize residential or commercial zones in a city. These factors contribute to the feasibility and practicability EPS recycling on university campuses that other settings may not possess.
Moreover, as microcosms of society, university campuses serve as living laboratories where sustainable solutions to societal problems are developed, tested, and evaluated (Trombulak etal 1998, Sharp 2002). Indeed, campuses can be proving grounds for new ideas or techniques for reducing the environmental impacts of business-as-usual practices. These efforts often begin as bottom-up initiatives bringing students and staff together in collaborations spanning research, operations, and solutions-based learning. Successful initiatives might catalyze top-down mandates and effect campus-wide shifts in practices (Cole and Srivastava 2013). At UW-Madison, an EPA grant (U.S. EPA 2020) funded a 2013 pilot project to recycle EPS shipping boxes from select labs. EPS recycling has since seen campus-wide adoption and continues as part of the standard practices of laboratory staff and facilities employees. By evaluating the environmental impacts of this shift in practices, the study results contribute to the body of knowledge related to EPS recycling and inform decision-making or management strategies at comparable institutions that generate large quantities of EPS waste. These could include universities, private or government labs, or even densely-populated urban areas.
Although this study primarily concerns the end-of-life disposition of EPS, the system boundaries comprise all life cycle phases (figure1). This provides a holistic view of the materials, waste, and impacts present throughout the EPS life cycle so that the significance of end-of-life disposition may be evaluated against hotspots elsewhere. Since EPS boxes come in varying sizes, this study uses a mass-based functional unit of 1 kilogram EPS.
The raw materials phase of the life cycle includes the extraction and refinement of petroleum and natural gas into ethylene and benzene which provides the source material for the production and transformation of PS. In the manufacturing phase, PS pellets are processed into EPS foam (EPS Industry Alliance 2013). Transportation occurs throughout the life cycle, including between the extraction site, refinery, manufacturing site, distribution center, point of use, and ultimately the site of final disposition. The use phase resembles other products meant to safely transport items to consumers. In fact, the use phase can be considered synonymous with transportation from a distribution center to a consumer. Upon arrival, EPS becomes obsolete and is discarded. The four disposal scenarios under consideration in this study are (1) consignment to a sanitary landfill, (2) a closed-loop reuse arrangement with a biotechnology company, (3) a conventional open-loop recycling arrangement with a specialty recycler, and (4) a novel open-loop recycling arrangement with an on-campus lab.
2.2.Inventory analysis
This section discusses the assumptions and sources of data used to create the LCI for the EPS system with four disposal scenarios. The SI provides additional content, including a table of the partial LCI for EPS.
2.2.1.Raw materials and manufacturing
The environmental impacts from the cradle-to-gate stages of EPS primarily are associated with petroleum refining and plastics manufacturing (Tan and Khoo 2005). Petroleum is extracted and refined to produce ethylene and benzene, which are reacted to produce styrene monomer. Styrene is polymerized into PS pellets, which are injected with pentane and steam-heated in forming molds to manufacture EPS. The inventory for EPS production largely has been taken from the US-EI 2.2 database (Long Trail Sustainability 2018), a hybridized database for North American regions that supplements gaps in US LCI data with ecoinvent 3.3 data. The resulting inventory is associated with 1 kilogram of EPS production and expansion.
2.2.2.Transportation
Transportation is allocated between three life cycle stages: materials acquisition and manufacturing (i.e. production), use, and end-of-life. The production stage is modeled using the US-EI 2.2 database (Long Trail Sustainability 2018) and EPS industry data (PWC 2001). Additional transport data was obtained on-site and is provided in the SI.
2.2.3.Use
EPS shipping boxes are used to transport temperature and shock-sensitive materials. The boxes are shipped to UW-Madison laboratories from Promega Corporation, a biotechnology company in Fitchburg, Wisconsin. Upon arrival, the box reaches the end of its useful life and is designated for disposal. Thus, transport is the only factor considered in the use phase of EPS.
2.2.4.End-of-life
This study considers four end-of-life scenarios for EPS boxes. In the first scenario, EPS is transported to the Dane County Sanitary Landfill and modeled as inert waste. In the second scenario, EPS is transported back to Promega to be reused as a shipping box in a closed-loop arrangement. Thus, it is assumed that a reused EPS box displaces the demand for a new box manufactured from virgin materials. It also is assumed that since the box would have otherwise been sent to landfill, the associated impacts are avoided and thus can be discounted.
In the third scenario, EPS is transported to Uniek Incorporated, a specialty recycler in Waunakee, Wisconsin. At Uniek, EPS is recycled using a four-step process. The inventory associated with recycling has been compiled through communication with a Uniek representative (Duzan 2017). This scenario discounts landfill impacts using the same assumption stated in the reuse scenario, and it also is assumed that recycled EPS displaces an equal mass of virgin PS. However, a Uniek representative indicated that their source material includes scrap PS and the company has not relied on virgin material for a decade (Duzan 2018). The degree to which recycled EPS displaces virgin PS and the resulting effects on environmental impacts are addressed in the sensitivity analysis.
In the fourth scenario, EPS is recycled via a novel process observed in the literature whereby the material is dissolved in a solution and electrospun into PS nanofibers that can be used as enhanced filtration media or biomedical mesh devices among other applications (Shin 2005, Shin and Chase 2005). As in the other non-landfill scenarios, it is assumed that recycling EPS circumvents the production of virgin materials and that the avoided impacts of landfill can be discounted. The SI provides additional details regarding both the conventional and novel recycling methods.
2.3.Impact assessment
The impacts of the EPS life cycle are assessed using TRACI, which comprises ten impact categories quantifying damages both to humans and the environment (U.S. EPA 2012). The TRACI impact assessment is designed for the United States, which is relevant to the system and setting under consideration in this study. Then ten impact categories include ozone depletion (OZ), global warming potential (GW), smog (SM), acidification (AC), eutrophication (EU), human health carcinogenics (CN), human health non-carcinogenics (NC), respiratory effects (RE), eco-toxicity (ET), and fossil fuel depletion (FF). The usage of this suite of multiple factors allows for tradeoff analysis to occur among the different impact categories.
2.4.Interpretation
The LCA results are analyzed both from a process life cycle and an end-of-life perspective. First, the process life cycles are evaluated for each scenario to assess the impacts at each stage and determine the relative significance of the end-of-life impacts. Second, the disposal scenarios are evaluated across the TRACI impact categories to determine the tradeoffs inherent in different disposal methods. The results also are applied to the UW-Madison EPS recycling program to determine the net impacts associated with the cumulative mass of recycled EPS. Uncertainty and sensitivity analyses also are performed to assess the significance of variability in certain data and ascertain the extent to which changes in variables affect the outcomes of the LCA (see SI).
3.Results
The cumulative life cycle impacts were determined for each of the four scenarios (landfill, reuse, conventional recycling, and novel recycling). The impacts are shown in figure2 and are displayed as normalized percentages allocated to each life cycle stage.
3.1.Landfill
In the landfill scenario (figure2(a)), the impact categories differ between those primarily influenced by the cradle-to-gate stages of the EPS life cycle and those primarily influenced by the disposal stage. For example, production and manufacturing comprise the vast majority of impacts (>94%) in seven categories (OZ, GW, SM, AC, CN, RE, and FF). Of the seven, GW (4.36kg CO2e/kg EPS), FF (13.36 MJ surplus/kg EPS), and SM (0.18kg O3e/kg EPS) present the largest impacts while OZ, SM, AC, CN, and RE all present less than 0.01 characterized units per kg EPS. These cradle-to-gate influenced impact categories relate to the petroleum-derived nature of EPS and the heavy industry inherent in manufacturing the material. The disposal stage dominates the remaining three categories (EU, NC, and ET). Of these, only ET (53.35 CTUe/kg EPS) presents impacts greater than 0.02 characterized units. In the case of these disposal influenced impact categories, TRACI assigns to EPS a large share of the ecosystem effects associated with a landfill. Like all scenarios in this study, transportation does not significantly contribute to any environmental impacts due to the low density and subsequent mass of EPS.
3.2.Reuse
The reuse scenario results are influenced by the prior assumptions stated in section2.2, leading to the discounting both of virgin EPS manufacturing and the landfill impacts described in section3.1. When this discounting is applied, the disposal stage impacts effectively offset those from production and manufacturing. This explains the nature of the histogram bars in figure2(b), where the disposal stage often appears as a mirror image of the combined production and manufacturing stages. Consequently, the results in each impact category are negative and indicate net beneficial environmental impacts with respect to a single-use landfilled box as a baseline (figure2(b)). Though all categories show environmental benefits, only ET (−43.71 CTUe/kg EPS) presents a large negative result due to the value associated with avoided landfilling of EPS. The remaining impact categories present small negative results, with GW (−0.12kg CO2e/kg EPS) being the only impact larger than −0.02 characterized units.
3.3.Conventional recycling
In the conventional recycling scenario, EPS is transported to Uniek where the material is densified and remanufactured into PS picture frames in an open-loop recycling system.
The results in figure2(c) resemble those in the reuse scenario as the disposal stage largely offsets the impacts of production and manufacturing. Only for OZ does disposal add to the impact total, indicating that the energy required to recycle EPS contributes to ozone depleting substances in the upper atmosphere. The effects of the electricity fuel mix on ozone depletion and other impact categories are addressed in the sensitivity analysis. The disposal stage does not entirely offset production and manufacturing for six impact categories (GW, SM, AC, CN, RE, and FF). Of those, FF (1.59 MJ surplus/kg EPS) presents the largest impacts which suggest that the energy required for recycling is worth considering. The remining three categories (EU, NC, ET) present negative (beneficial) scores, the largest of which again is ET (−39.51 CTUe/kg EPS).
3.4.Novel recycling
In the novel scenario, EPS is transported to a UW-Madison laboratory where the material is dissolved in dimethylacetamide (DMAc) and electrospun into PS nanofibers based on the experimental process described by Shin (2005). This scenario was chosen to include a unique EPS recycling method among the disposal alternatives.
Figure2(d) shows that the novel recycling method incurs impact scores that dominate every category even after discounting EPS landfilling and virgin PS production. The disposal stage accounts for between 65% (FF) to nearly 100% (EU) of the life cycle impacts. These results are attributed to two factors in the electrospinning process: the volume of DMAc solvent (4.23 L) and the electricity demands (28.76 kWh) required to respectively dissolve and electrospin 1 kilogram EPS. Correspondence with the laboratory that conducted the research indicated that 20 wt% EPS was the ideal solution for electrospinning PS nanofibers with desired morphology and that electrospinning rates can vary between 1–10 ml hr−1 (Pan 2018). Furthermore, the power supply fixed to the needle runs at intervals of 5, 10, or 20 watts. The corresponding electricity demands were taken from midpoint values of 5 ml hr−1 and 10W. The effects of different electrospinning and power rates as well as different electricity fuel mixes are addressed in the sensitivity analysis, which also explores the effect of replacing DMAc with the natural solvent d-limonene.
It is relevant to consider that the novel technology is still at the laboratory level. It is anticipated that due to economies of scale that if this technology was analyzed at the operational scale, that it could be a great deal more efficient than what is presented in this work. Piccinno etal (2016) presented a scale up format for chemical process in LCA. While Parvatker etal (2019) modeled the cradle-to-gate greenhouse gas emissions for twenty anesthetic active pharmaceutical ingredients based on process scale-up and process design calculations. In general, as was found in other work, economies of scale are anticipated with this recycling process, and there is an expectation that the environmental impact will decrease as the technology matures.
3.5.End-of-life results
The remaining discussion of the midpoint LCA results focuses on the end-of-life disposition of EPS as the cradle-to-gate models in each scenario are identical. In order to more easily compare the four disposal scenarios, the results are displayed in table1 using shading to indicate the relative magnitude of impacts across each scenario.
Table 1.LCA results showing the end-of-life impacts per kilogram EPS across four life cycle scenarios and the percent difference of impacts relative to landfill as the baseline scenario.
| Landfill | Reuse | Recycling | Novel | ||
|---|---|---|---|---|---|
| Ozone depletion | kg CFC-11 eq | 5.78 × 10−9 | −1.49 × 10−7 (−2686%) | 2.49 × 10−8 (331%) | 1.44 × 10−6 (24 872%) |
| Global warming | kg CO2 eq | 0.140 | −4.34 (−3199%) | −3.37 (−2511%) | 11.43 (8068%) |
| Smog | kg O3 eq | 5.96 × 10−3 | −0.180 (−3129%) | −0.125 (−2202%) | 0.444 (7347%) |
| Acidification | kg SO2 eq | 2.16 × 10−4 | −0.015 (−6853%) | −0.010 (−4780%) | 0.047 (21 605%) |
| Eutrophication | kg N eq | 0.016 | −0.018 (−217%) | −0.016 (−201%) | 0.691 (4318%) |
| Ecotoxicity | CTUe | 43.73 | −53.33 (−222%) | −49.14 (−212%) | 40.22 (−8%) |
| Carcinogenics | CTUh | 5.06 × 10−9 | −1.37 × 10−7 (−2803%) | −7.76 × 10−8 (−1631%) | 5.84 × 10−7 (11 425%) |
| Noncarcinogenics | CTUh | 9.97 × 10−7 | −1.15 × 10−6 (−216%) | −9.81 × 10−7 (−198%) | 2.18 × 10−6 (118%) |
| Respiratory effects | kg PM2.5 eq | 2.76 × 10−5 | −1.04 × 10−3 (−3879%) | −7.26 × 10−4 (−2727%) | 3.60 × 10−3 (12 914%) |
| Fossil fuel depletion | MJ surplus | 0.066 | −13.31 (−20 174%) | −11.70 (−17 743%) | 25.30 (38 062%) |
The environmental impacts of landfilling 1kg EPS tend to be small, measuring less than 0.5 characterized units in every category except ecotoxicity. This result necessitates two qualifying statements. First, even a slight derivation from the landfill values can produce strikingly large percent differences in the alternative disposal scenarios. This effect occurs frequently, and percent differences should be assessed in tandem with the magnitude of the impact scores to evaluate their significance. The second reiterates a finding from the process life cycle results; namely, that in the context of the entire system, the end-of-life impacts generally are small relative to the impacts incurred from cradle-to-gate.
The end-of-life disposition of EPS affects environmental impacts to varying degrees (table1). For example, five categories (OZ, AC, CN, NC, RE) present impacts measuring smaller than +/−0.05 characterized units across every disposal scenario while SM (+/−0.2 units) and EU (+/−0.02 units) display minimal impacts apart from the novel scenario. The predominant factor is the production of DMAc solvent with the electricity demands of electrospinning playing a secondary role in SM.
Of the remaining three impact categories, GW and FF display parallel trends. Namely, the reuse and recycling scenarios show meaningful reductions with respect to baseline due to avoided landfill impacts and discounted virgin PS manufacturing. Conversely, the novel scenario shows a marked increase with respect to landfill for both GW and FF. In the case of GW, landfilling EPS resulted in 0.14kg CO2e/kg compared with 11.40kg CO2e/kg for the novel scenario, an increase of over 8000% with respect to baseline. The novel scenario also resulted in 25.30 MJ surplus/kg EPS, a 38 000% increase over landfilling EPS at 0.06 MJ surplus/kg. In each case, the impacts of the novel scenario are due to DMAc production and electricity demands throughout the electrospinning process. Only ET displays sizeable impacts across all scenarios (larger than +/−40 units). This again stems from the large impact factor that TRACI places on ecosystem effects from a product in a landfill that does not decompose. For additional discussion of the end-of-life results, please consult the SI.
4.Discussion
EPS is a confounding substance that remains popular for its physical characteristics but problematic to responsibly manage at the end of its useful life. This study primarily evaluated the environmental impacts of different EPS disposal scenarios through a midpoint LCA conducted in SimaPro (Pré Consultants 2016) and using the US-EI 2.2 LCI database (Long Trail Sustainability, 2018) and the TRACI LCIA method (U.S. EPA 2012). The results are used to evaluate end-of-life management alternatives for post-consumer EPS at the UW-Madison, the setting of the study. Further discussion of EPS and UW-Madison impacts is provided in the SI online.
The midpoint results can be interpreted both by what is beneficial and what is feasible. For example, the reuse scenario effects the most beneficial environmental outcomes as characterized by the impact scores (figure2 and table1). Indeed, EPS ought to be reused in a closed-loop system when environmental outcomes are prioritized. However, anecdotal evidence from UW-Madison suggests a takeback arrangement with a biotechnology company is not feasible. The novel scenario also has feasibility issues relating to proof of concept at laboratory scale which results in the most detrimental environmental outcomes.
Thus, the conventional recycling scenario emerges as the most desirable alternative when compared with landfill as the business-as-usual scenario. Conventional recycling of EPS is the only disposal scenario considered that generates net environmental benefits while also being logistically feasible. With respect to UW-Madison, recycling EPS requires additional resources in financial and human capital. However, the university may accept these additional costs to pursue business practices considered ethically and socially desirable while contributing to additional (albeit tangential) economic activity. From the broader standpoint of this study, UW-Madison is pursuing a strategy that realizes an optimal balance of institutional and societal impacts by utilizing a circular economy approach to managing EPS waste.
5.Conclusions
While conventional recycling emerged as the preferred disposal method for EPS shipping boxes, the UW-Madison recycling program exists largely because of the favorable proximity of the campus to Uniek, Inc. At 20 miles roundtrip (32 kilometers), transportation to Uniek was not a limiting factor to a sustained EPS recycling program. In December 2019, Uniek representatives informed Brad Schenkel that they no longer would be accepting waste EPS and would be selling their recycling equipment to Madison-based Reynolds Urethane Recycling, Inc. (Schenkel 2019). In a seamless transition, Reynolds has agreed to receive waste EPS from UW-Madison at no charge and facilities staff anticipate continued service without interruption. Institutions or entities not situated near a specialty recycler may find that transporting a material with the density of EPS is economically prohibitive. In such cases, one solution may be to purchase or rent an on-site densifier that will reduce the volume of the material and allow for more efficient use of cargo space.
This study also identified limitations to evaluating the EPS life cycle and further areas of inquiry. The limitations primarily concern lack of transparency regarding both cradle-to-gate processes and the non-electrical processes of conventional EPS recycling. The study used an average manufacturing-to-distribution transport value from a European study but was unable to obtain transport data upstream from the factory gate in order to model specific distances related to the UW-Madison EPS supply chain. The study also modeled EPS recycling exclusively via electricity consumption and did not account for additional transport or processing. Future research should focus on improved supply chain transparency and explore potential impacts on the EPS manufacturing industry should recycling or reuse practices become more widespread.
Finally, EPS waste management strategies ultimately must be contextualized for the magnitude of impacts relative to the rest of the life cycle. While this study focused on end-of-life management, the entire EPS system was included to identify impactful stages as compared with disposal. The results showed that the cradle-to-gate stages accounted for the majority of deleterious impacts in the landfill, reuse, and conventional recycling scenarios (figure2). These results suggest that while marginal benefits can be realized through circular economy approaches to EPS waste management, more substantive benefits can be realized by focusing on upstream effects of the EPS life cycle.
Thus, a sense of scale can be applied to this study from two perspectives. On one hand, the scale of environmental benefits realized by responsible EPS disposal practices pale in comparison to that of the impacts attributed to producing and manufacturing the material. There remains enormous potential for benefits in rethinking and redesigning this system to utilize alternative materials. On the other hand, the concrete benefits of a circular economy approach to EPS identified in this study also have enormous potential if scaled up from a single higher education institution in the United States. Were analogous institutions worldwide to employ similar tactics—whether by utilizing a local specialty recycler, an on-site densifier, or other creative means—the resulting environmental benefits and the message sent to the adjacent systems and their supply chain actors could be transformative.
Acknowledgments
The EPS pilot collection and recycling project at UW-Madison was funded by a grant from the People, Prosperity and the Planet (P3) Student Design Competition administered by the EPA. Professors Craig Benson and Cathy Middlecamp served as PIs for the grant. This work has not been formally reviewed by the US EPA, and the views expressed are those of the authors alone. The authors acknowledge UW-Madison postdoctoral student Andrew Markley and undergraduate Brooke Marten for their early work in establishing and maintaining the EPS recycling program. The authors are further grateful to the UW-Madison Office of Sustainability for supporting this research and to Buildings and Grounds Superintendent Bradley Schenkel for managing the EPS recycling program and for sharing collection and recycling data. The authors also would like to note that any references to companies or brand name products are not an endorsem*nt of the product or industry but are provided to aid in the specificity of this work.
Data availability statement
All data that support the findings of this study are included within the article (and any supplementary information files).
Conflict of interest
The authors declare no conflict of interest.
