Development of a Conceptual Framework for Plastic Waste Management in a Small Island Developing State

Introduction

Mauritius, a Small Island Developing State (SIDS), with an area of 2040 km² is situated in the Indian Ocean. According to the Central Statistics Office [1], the population of the island was around 1.3 million in 2022, with a population density of 626 persons/km² and the estimated GDP growth rate in 2022 was 7.8%. The island is currently addressing a pressing issue related to the sustainable management of solid waste, given that the sole sanitary landfill at Mare Chicose is already saturated. The Government of Mauritius has devised a number of initiatives to improve resource recovery for recyclers. For instance, the development of a pilot composting unit and a sorting unit for the separation of dry and wet waste resources, as well as the introduction of a framework to encourage the composting of green waste from households, markets, parks and gardens. The Waste Management And Resource Recovery Act, 2023 and the Government Gazette of Mauritius No. 32 was promulgated on 20 April, 2023. This Act provides the regulatory framework to ensure the environmentally safe and sound management of solid and hazardous waste and a sustainable waste management system through the adoption of a circular economy approach focusing on waste reduction, reuse, material recovery and recycling.

Plastic waste represents 14% of domestic waste produced annually in Mauritius, while just 3–4% of plastics are recycled [2]. To date, there are only a few recycling facilities available in Mauritius but are not economically feasible as the amount of waste generated is insufficient for the recycling facilities to operate efficiently. Therefore, to tackle the issue of plastic waste disposal, the Government put forward a waste minimization strategy in 2010 that includes the three R principle; reducing, reusing and recycling through awareness campaigns. In addition, as of May 2019, the Government has also put in place a Rs 2.00 tax on plastic products especially on plastic carry bags and PET bottles to discourage the use of plastic products [2, 3]. Moreover, in 2020–2021, the Ministry of Environment reinforced the plastic regulations under Environment Protection Regulations, 2020 where it is prohibited to import, produce or distribute fossil-fuel based plastic products [4, 5]. This has prompted the manufacturers to shift to bio-alternatives (Bioplastics) such as polylactic acid (PLA), polyhydroxalkanoate (PHA) and starch blend plastic products like corn, wheat or potatoes.

PLA is currently one of the most promising green plastic alternatives available on the market [5, 6]. Hence, shifting to bioplastics is likely to promote a circular economy [7–9] with the aim of achieving the Sustainable Development Goals (SDGs), such as reducing the dependence on fossil fuels, setting forth novel approaches for degradation, recycling and reducing the release of toxic chemicals during manufacturing [10]. ‘Sustainable development is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs’ [11]. Nevertheless, the environmental impact of PLA products, especially their end-of-life scenarios, requires further investigation to ensure their sustainability.

Studies on the LCA (Life Cycle Assessment) of plastic waste have yielded important insights regarding the environmental effects of PET and PLA bottles throughout different phases of their life cycle. Desole et al. [12] studied the LCA of PET and PLA bottles used for fresh pasteurized milk and determined that PLA bottles had a lower overall environmental impact than PET bottles, especially in categories related to GHG emissions and fossil fuel depletion. The study highlighted the importance of end-of-life situations, as the environmental advantages of PLA were significantly reliant on appropriate industrial composting or recycling conditions. Similarly, Lucchetti et al. [13] evaluated the performance of conventional PET, bio-based PET, and PLA bottles with regard to radon emission during water storage. Their results revealed that PLA bottles had different permeability characteristics relative to PET, potentially affecting their appropriateness for long-term storage uses. Cubeddu et al. [14] assessed the potential of PLA bottles for high-pressure processing of apple juice. Their findings indicated that although PLA bottles maintained sufficient structural integrity during processing, they showed shortcomings in mechanical durability and shelf-life performance, highlighting the necessity for enhancements in material formulation. Horowitz et al. [15] carried out an LCA of bottled water products such as Green2O and showed that although bioplastic alternatives reduced dependence on fossil fuels, their disposal methods had a significant effect on their overall environmental impact.

Although these studies offer important perspectives on the environmental performance of PET and PLA bottles, challenges persist. Several studies  [12–15] faced obstacles such as limited data on evaluating the long-term environmental consequences, concerns about the economic viability of recycling processes, and inconsistencies in material degradation rates depending on different conditions. Moreover, gaps in understanding the consequences of these materials within the specific framework of SIDS still persist. The distinct challenges that SIDS encounter are limited land space and restricted access to advanced waste management systems [16, 17]. Therefore, to tackle these challenges, further research is necessary to optimize bioplastic waste management, enhance local recycling systems [18], and develop policies to promote sustainable waste disposal with customized strategies for managing plastic waste [19].

Worldwide, there is an increasing emphasis on creating conceptual frameworks that integrate circular economy principles into waste management systems [20, 21]. These frameworks prioritize waste reduction, material recovery, and improve end-of-life management strategies for both conventional plastics and bioplastics. However, the application of these frameworks to the unique circumstances of SIDS has not been thoroughly examined.

This study aims to fill this significant gap by formulating a conceptual framework specifically for plastic waste management in Mauritius. By using LCA with IMPACT 2002+ framework, this study delivers an in-depth assessment of the environmental effects linked to the disposal and treatment of PET and PLA bottles. The evaluation included 14 categories of environmental impact and 4 damage categories, providing a detailed understanding of the tradeoffs involved in various waste management approaches.

This study specifically examines the relationship between traditional plastics and bioplastics within a circular economy model. The suggested framework incorporates approaches for minimizing waste, recycling, composting, and landfilling, guided by quantitative assessment of environmental effects, offering practical recommendations for policymakers and waste management professionals.

Materials and methods

The methodological approach adopted was based on assessing the environmental impacts associated with the following scenarios:

Scenario 1 (Landfilling of PET bottles)—PET bottles are often discarded in landfills, particularly in areas where there is a lack of recycling facilities. This situation illustrates the current state of plastic waste management, in which PET, a non-biodegradable plastic sourced from fossil fuels, builds up in landfills.

Scenario 2 (Landfilling of PLA bottles)—In contrast to PET, PLA bottles are both biobased and biodegradable under specific industrial composting conditions. However, under landfill circumstances, PLA may not break down effectively and could act similarly to PET, potentially releasing harmful substances and contributing to long term environmental issues.

Scenario 3 (Composting of PLA bottles)—The composting of PLA bottles in industrial composting facilities offers an alternative approach to managing PLA waste. This possibility is included to evaluate the potential advantages and drawbacks of composting as a waste management strategy for PLA bottles.

PET bottles are made from polyethylene terephthalate, a polymer derived from petroleum, whereas PLA bottles are made from polylactic acid, a bio-based polymer sourced from renewable materials like corn starch or sugarcane. The bottles examined in this study were typical single- use bottles particularly used as water bottles. It is worth noting that the bottles were produced through a preform method. Initially, a preform is created from either PET or PLA, which is then reheated and shaped into the final bottle form using specialized machinery. This two- step manufacturing process was not incorporated into the environmental evaluation due to limitations in data availability. Nevertheless, it shows the differences in resources between PET and PLA, which are avenues for future research.

2.1.

Life cycle assessment

This study followed a cradle-to-grave analysis. However, the unit processes falling outside the system boundary have not been considered due to missing data and confidentiality of manufacturers. Hence, in this life cycle study, LCA software 9.4.0, Analyst version was used as a supportive tool since LCA is well suited for better assessment and evaluation of the plausible environmental impacts based on ISO 14040. Additionally, LCA software can be applied for decision making by comparing the various options to better understand the outcomes and make the most appropriate decision. Furthermore, IMPACT 2002+ was applied as an impact assessment method to evaluate each scenario in terms of midpoint and damage categories. IMPACT2002+ was chosen over other approaches like IMPACT World+ or ReCiPe 2016, as it is well-suited for regionalised assessments, helping to meet the objectives and scope of this study. Moreover, IMPACT 2002+ is mostly suitable for assessing waste disposal implications such as landfilling and composting, as long-term environmental impacts are taken into consideration. Hence, providing a comprehensive framework to characterise and link results of LCI to assess 14 impact categories and 4 damage categories, makes it well-suited to compare different plastic waste management scenarios. In addition, it has received widespread validation for research on small, geographically constrained regions like Mauritius.

The functional unit was defined as disposal and treatment of 1000 Units plastic (PET/PLA) bottles. The respective flowchart for scenario 1, 2 and 3 can be found at Figures 1, 2 and 3 and the inventory data for scenario 1, 2, 3 can be found at Tables 1, 2 and 3. It is important to note that the cap was not integrated in the analysis as it is not biodegradable. Hence, only the final product (i.e., the finished bottle) was considered for the analysis.

The functions of the product system, system boundary and assumptions are defined in ISO 14044:2006, an internationally recognized standard to perform LCA by covering essential phases like Goal and Scope Definition, LCI analysis, LCIA and interpretation of results are as follows:

Unit processes	Unit	Amount
Transportation 1
Diesel	L	Ecoinvent database
Distance	t-km	0.4644
PET bottle manufacturing
Inputs
PET granules	kg	25.8
Crude oil	kg	29.5
Natural gas	M3	14
Energy input from electricity	MJ	1068
Water (cooling)	kg	113
Outputs
Emissions to air
Carbon monoxide	kg	0.74
Carbon dioxide	kg	403
CxHy	kg	0.32
Dust	kg	0.27
Methane	kg	5.28
Non-methane VOC	kg	2.03
NOX (as NO2)	kg	1.48
SOX (as SO2)	kg	3.9
Emissions to water
Anorg. Dissolved substances	kg	1.73
BOD	kg	4.167
Chlorate ions	kg	0.0012
Chlorate ions	kg	3.02
COD	kg	0.16
Suspended substances	kg	0.27
TOC	kg	0.51
Wastewater	M3	76.67
Emissions to soil
Pb	mg	61.5
Cd	mg	15.13
Hg	mg	3.95
Transportation 3
Diesel	L	Ecoinvent database
Distance	t-km	0.645
Landfill site
Inputs
Disposal of PET bottles	kg	25.8
Outputs
Mineral waste (mining)	kg	1.19
Waste bioactive landfill	kg	0.62
Waste in inert landfill	kg	0.0097

Table 1

Scenario 1—Inventory data.

Note: Based on Foolmaun et al. [22], information was retrieved and adapted for scenario 1.

Unit processes	Unit	Amount
Transportation 1
Diesel	L	Ecoinvent database
Distance	t-km	0.693
PLA bottle manufacturing
Inputs
PLA granules	kg	38.5
Electricity	kWh	62.31
Water	g	35.29
Outputs
Wastewater	g	36.58
SO2	g	139.24
NMVOC	g	9.34
Transportation 3
Diesel	L	Ecoinvent database
Distance	t-km	0.9625
Landfill site
Inputs
Disposal of PLA bottles	kg	38.5
Outputs
Mineral waste (mining)	kg	1.19
Waste bioactive landfill	kg	0.62
Waste in inert landfill	kg	0.0097

Table 2

Scenario 2—Inventory data.

Note: Based on Guo et al. [23], information was retrieved and adapted for scenario 2.

Unit processes	Unit	Amount
Transportation 1
Diesel	L	Ecoinvent database
Distance	t-km	0.693
PLA bottle manufacturing
Inputs
PLA granules	kg	38.5
Electricity	kWh	62.31
Water	g	35.29
Outputs
Wastewater	g	36.58
SO2	g	139.24
NMVOC	g	9.34
Transportation 3
Diesel	L	Ecoinvent database
Distance	t-km	0.9625
Composting site
Inputs
Disposal of PLA bottles	kg	38.5
Outputs
CO2 emissions	kg	65.3
Compost waste	kg	231

Table 3

Scenario 3—Inventory data.

Note 1: Based on Guo et al. [23], information was retrieved and adapted for scenario 3. Note 2: For scenario 3, aerobic biodegradation under controlled composting conditions, at thermophilic conditions was performed over 45 days at 58 °C as per the American Society for Testing and Materials (ASTM) D 5338 standard where 65.3 kg of CO₂ emissions were obtained for 1000 units of PLA bottle.

• The primary functions for scenarios 1, 2 and 3 were to reduce landfilling of plastic bottles.

• Their respective secondary functions were as follows:

  • Scenario 1: Disposal of PET bottles after single-use and reduce landfill space use.

  • Scenario 2: Disposal of PLA bottles after single-use and reduce landfill space use.

  • Scenario 3: Treatment (e.g. composting) of PLA bottles instantly after their disposal and reduce landfill space use.

• The system boundary for scenarios 1, 2 and 3 were defined as follows:

  • Scenario 1: The PET bottles were manufactured with the assumption that they would be discarded immediately after their use. They were then transported to Mare Chicose landfill site.

  • Scenario 2: The PLA bottles were manufactured with the assumption that they would be discarded immediately after their use. They were then transported to Mare Chicose landfill site.

  • Scenario 3: The PLA bottles were manufactured with the assumption that they would be discarded immediately after their use. They were then transported to a composting/treatment site.

• The general assumptions made in this study are as follows:

  • The manufacturing processes were not accounted for in the analysis due to lack of data. All PET bottles were imported for use. PLA bottles were produced in Mauritius but this unit operation was beyond the scope of this study.

  • The use phase of plastic bottles falls outside the boundary.

  • The single-use plastic bottles were assumed to be directly transported to the disposal/treatment site accordingly.

  • The waste scenarios such as recycling, re-use and incineration were not considered.

  • The timeframe for all scenarios (landfilling & composting) was defined to be over 45 days.

  • For transportation within Mauritius, trucks with a capacity of less than 10 tons that use diesel were considered, from collection of PET/PLA granules to plastic bottles manufacturing plant and from collection of plastic bottles to disposal/treatment site.

  • The average transport distances covered were retrieved as follows [8]:

  • The average distance to transport PET/PLA granules to a plastic bottles manufacturing plant was 18 km.

  • The average distance travelled from collection of plastic bottles to disposal/ treatment site was 25 km.

  • The disposal site was assumed to be located at Mare Chicose landfill station. The treatment site was considered to be in the vicinity of Mare Chicose landfill station.

Results and discussion

3.1.

Life cycle impact analysis (LCIA)

The LCA study was assessed using IMPACT 2002+ for each scenario and the following were determined: (i) percentage contribution in terms of impact categories; (ii) percentage contribution in terms of damage categories; (iii) comparative analysis in terms of damage category to assess whether scenario 1, 2 or 3 one has the highest environmental impact.

3.1.1.

Analysis of results for midpoint categories

The initial analysis was done for each scenario based on 14 midpoint categories modelled in IMPACT 2002+, excluding long-term emissions.

Scenario 1: Figure 4 shows that PET bottle manufacturing had the highest percentage contribution (>99.3%) for all impact categories supported by Foolmaun et al. [22] and showed 90% contribution under impact category based on Eco-indicator 99 method. Ionizing radiation, ozone layer depletion, respiratory inorganics, land occupation and mineral extraction showed 100% contribution under PET bottle manufacturing. It was noted that raw copper contributed the most to mineral extraction with 2.68 MJ surplus for Scenario 1. This contribution for scenario 1 resulted from cobalt production where cobalt is an effective blueing agent used for producing neutral PET bottles [24, 25].

Scenario 2: Figure 5 shows that PLA bottle manufacturing contributed the most with 99.6% for all 14 impact categories compared to Transportation. Moreover, ozone layer depletion, land occupation, respiratory inorganics and mineral extraction contributed 100% under PLA bottle manufacturing. For example, contribution from land occupation arose during production of maize grain used to produce PLA granules required to manufacture PLA bottles. This contribution was also supported by Tamburini et al. [26] showing that PET bottles had a lower environmental impact during manufacturing process compared to PLA bottles based on the ReCiPe method.

Scenario 3: As illustrated in Figure 6, PLA bottles manufacturing contributed to all 14 impact categories, of which ozone layer depletion, respiratory inorganics, land occupation and mineral extraction represented 100% contribution under PLA bottles manufacturing. Nevertheless, it can be seen that composting sites do contribute to global warming resulting from emissions of CO₂ with 65.3 kg CO₂ eq while 150.7 kg CO₂ eq of CO₂ emissions falls under PLA bottles manufacturing. Baldowska-Witos et al. [27] conducted a study on PET and PLA bottles using CML method and determined that aquatic ecotoxicity was most significant during bottle manufacturing.

3.1.2.

Results and discussion

Scenario 1: Figure 7 illustrates that more than 99.4% of all damage categories were attributed to PET bottle manufacturing. Amongst all 4 damage categories under PET bottle manufacturing, climate change impact was 0.54% higher than ecosystem quality.

Scenario 2: As shown in Figure 8 shows that PLA bottle manufacturing contributed greatly (>99%) to all damage categories. Nevertheless, the impact on human health, climate change and resources was 99.8% and 0.48% more than ecosystem quality, respectively.

Scenario 3: Figure 9 shows that PLA bottle manufacturing contributed significantly to human health (99.8%), although the impact on climate change by composting site cannot be ignored (28.7%).

3.1.3.

Comparative analysis of damage categories

Comparisons of damage categories revealed the following insights (Figure 10):

• Human health: Scenario 1 impacted human health category 35.5% more than scenarios 2 and 3. This can be attributed to the dominating substances (NO_x) being 2.2 times higher in scenario 1 compared to scenarios 2 and 3. This resulted from the release of toxic fumes from electricity production, particularly during the manufacturing stage. Exposure to NO_x causes significant health issues by irritating the respiratory system, which may result in diseases such as asthma, bronchitis, and other chronic respiratory conditions. Prolonged exposure increases the likelihood of respiratory infections and worsens existing health problems. Moreover, NO_x plays a role in creating ground- level ozone, which further deteriorates air quality and endangers human health [28].

• Ecosystem quality: Scenarios 2 and 3 showed quasi-similar values with 100% contribution towards ecosystem quality that represented 21.1% higher than that of scenario 1. This contribution was due to the presence of Al (in soil), 1.18 times higher for scenarios 2 and 3 compared to scenario 1. The main contributor of Al (in soil) was caused due to the drilling operations for oil and gas production. During this process, drilling waste produced contained contaminated substances [29]. AI poses a threat to ecosystem quality, especially to soil and aquatic environments, when present in excessive amounts. Prolonged and increased levels of aluminium in the soil can alter its pH, making it more acidic, which subsequently interferes with nutrient availability for plants. This deterioration results in decreased soil quality, diminishing agricultural yields and negatively affecting plant growth. Furthermore, aluminium can leach into bodies of water, where it can accumulate in aquatic life, compromising their health and biodiversity. Additionally, long-term exposure to high aluminium concentrations can also have adverse effects on the reproductive systems of aquatic species, leading to long-term ecological harm.

• Climate change: The contribution of scenario 1 to climate change was 78.8% higher than scenario 2 and 70.3% higher than that of scenario 3. This can be attributed to the high contribution of CO₂ due to the biodegradation process from composting of PLA bottles. While PLA is made from renewable resources, its breakdown in composting facilities still produces CO₂. During the composting process, microorganisms decompose the organic material in PLA, utilize oxygen, and emit carbon dioxide as a byproduct. If the composting process is not properly managed (e.g., lack of aeration or inadequate temperature regulation), this could result in inefficient degradation, further increasing CO₂ emissions. Subsequently, emissions of CO₂ fossil (in air) also referred to as anthropogenic emissions lead to an increase in GHG emissions [27] and contribute to global warming. Nikolic et al. [30] demonstrated that the net global warming potential can be reduced by 30.9%, if PLA granules are used.

• Resources: Scenarios 2 and 3 showed 78.5% lower contribution compared to scenario 1, as relatively less crude oil was required in PLA bottle manufacturing, leading to a reduced impact on mineral extraction and non-renewable energy. Nikolic et al. [30] concluded that non-renewable energy would decrease by 32%, if PLA granules are used. Vink et al. [31] demonstrated that 25–55% fossil energy was used for PLA production.

• It can be inferred that scenario 1 significantly contributed to human health, climate change and resources. Moreover, from comparative analysis, it can be inferred that the contribution of scenarios 2 and 3 was lower compared to scenario 1, although scenario 3 contributed more than scenario 2 to climate change. Baldowska-Witos et al. [27] determined that the impact of PET bottles was 10 times more than that of PLA bottles.

3.2.

Developing a sustainable waste management system

PET bottles: It was determined that PET bottles had an overall negative environmental impact. Therefore, to reduce these impacts,recycling is best suited for used PET bottles, by virtue of circular economy [32, 33] which reduces plastic waste that interferes with the environment and also offers economic value through recycling facilities for plastics. For instance, in Mauritius, PET bottles are recycled [2] and the recycling rate was 40% (Jankee [34]).

Therefore, increasing the recycling rate by 20% would meet the indicators set for SDGs 12 and 13. This could be achieved by setting sensitization campaigns by the Ministry of Environment to ensure that manufacturing plants are aware of the practice of recycled PET bottles. Hence, 60% recycling and 40% landfilling for disposal of PET bottles is recommended. Additionally, a closed-loop cycle for PET bottles can be found at Figure 11. Previous studies [31] have proposed 50% recycling, 30% incineration and 20% landfilling for disposal of PET bottles.

PLA bottles: Compared to PET bottles, PLA bottles are designed to be durable, chemically and biologically resilient [22]. Besides recycling of PLA products, composting is achievable to some extent via commercial composting facilities. For example, in industrial facilities, PLA products can decompose within 3 weeks [35]. Additionally, PLA showed biodegradability properties particularly by biotic degradation process [36]. Havstad [35] showed that depending on the size and shape of PLA products, it has the potential to degrade in the environment within 6 months to 2 years.

Based on LCA study, PLA bottles showed a lower overall environmental performance. In spite of the lower performance, a circular economy approach can be applied to further reduce waste generation and GHG emissions to meet the indicators set for SDGs 12 and 13. Moreover, PLA bottles degraded up to 91.8% over a period of 45 days under biodegradability study and composting can aid in reducing landfill space. Therefore, it is suggested that 40% recycling, 50% composting and 10% landfilling be followed for disposal and treatment of PLA bottles. Figure 12 shows a closed-loop cycle for PLA bottles. Gironi et al. [37] recommended 40% recycling, 30% composting, 15% landfilling and 15% incineration.

Conclusions

This study evaluated the environmental impacts of PET/PLA bottles within the Mauritian context. Life cycle assessment study was conducted using IMPACT 2002+. The main findings were; scenario 1 contributed 35.5% more than scenarios 2 and 3 towards human health category. Scenario 1 showed a 21.1% higher contribution to ecosystem quality compared to scenarios 2 and 3. Scenarios 2 and 3 contributed 78.8% lower than that scenario 1 under the climate change category. For resources, scenarios 2 and 3 both showed 78.5% lower contribution than scenario 1.

Based on these findings, the recycling rate of PET bottles was recommended to be increased by 60% and 40% to be landfilled. For PLA bottles, a waste management strategy was proposed where 50% of bottles can be composted, 40% recycled while the remaining 10% can be disposed of to Mare Chicose landfill site.

The study’s findings show the pressing need to enhance Mauritius’s plastic waste management strategies. Hence, to achieve a sustainable and effective framework, the following suggestions are proposed: (i) Improve recycling infrastructure by investing in modern recycling facilities to manage increasing volumes of PET and PLA bottles. (ii) Establish modernized sorting facilities to improve the recycling process. (iii) Implement tax incentives for companies using recycled materials in their manufacturing. (iv) Encourage community involvement in recycling activities through corporate social responsibility (CSR) programs. (v) Incorporate industrial composting facilities for handling PLA bottles. (vi) Establish a national database to track waste generation, recycling rates and landfill capacities to inform adaptive policy measures.

Acknowledgments

This work was supported by University of Mauritius.

Author’s contributions

Dr. Somaroo, Geeta: Conceptualization, Funding Acquisition, Resources; Letoah, Marie-Antoinette Elsa: Fomat Analysis, Methodology, Writing - Original draft; Rambojun-Ruchaya, Sanjana: Investigation, Writing - Review & editing.

Funding

This research did not receive external funding from any agencies.

Ethical statement

Not applicable.

Data availability statement

Source data is not available for this article.

Conflict of interest

The authors declare no conflict of interest.