Meta-Analysis of Life Cycle Assessment Studies for PET Water Bottle Systems

3. Results and Discussion

A Descriptive Interpretation of the Meta-Analysis Findings

When multiple Life Cycle Assessment (LCA) studies are brought together under a harmonized framework, patterns begin to emerge that are often invisible in isolated research papers. This meta-analysis does exactly that — it transforms fragmented findings into a coherent environmental narrative of the PET water bottle system.

Rather than simply reporting numbers, this section explains what those numbers mean, why they matter, and how they influence sustainable packaging decisions.

Understanding the Research Landscape

After applying strict PRISMA-based screening criteria, 14 studies published between 2010 and 2022 were selected for analysis. These studies originated from different regions, primarily Europe, and applied varying system boundaries and functional units.

This diversity is important.

For example, a PET bottle assessed in a country with a coal-heavy electricity mix will naturally show higher emissions than one produced in a region dominated by nuclear or renewable energy. Similarly, a country with a well-established deposit-return system will report very different end-of-life impacts compared to one relying heavily on landfill.

By harmonizing these variations, the researchers ensured that comparisons were meaningful rather than misleading.

Overall Carbon Footprint of PET Bottle Systems

After standardizing all data to a unified functional unit of 1 kg of PET bottle, the average life-cycle Global Warming Potential (GWP) was found to be:

5.093 kg CO₂-equivalent per kg of PET bottle

To put this into perspective:

• Producing 1 kg of PET bottles emits roughly the same CO₂ as driving a standard gasoline car for approximately 20–25 kilometers.

• A single 0.5 L bottle (weighing ~20 g) would therefore represent about 0.10 kg CO₂-eq.

This provides a tangible sense of scale for consumers and policymakers.

Material Production: The Dominant Hotspot

Across nearly all studies, the Material Production (MP) phase consistently emerged as the largest contributor to emissions.

This stage includes:

• Extraction of fossil-based feedstock

• Production of ethylene glycol and terephthalic acid

• Polymerization into PET resin

• Solid-state polymerization to achieve bottle-grade properties

These processes require high temperatures and substantial energy inputs. Since virgin PET is primarily fossil-derived, its carbon intensity is structurally embedded in the raw material stage.

Practical Example

If a beverage company switches from virgin PET to 50% recycled PET (rPET):

• It directly reduces demand for fossil feedstock.

• It avoids emissions associated with primary polymerization.

• Studies suggest reductions ranging from 12% to over 80%, depending on recycling technology and energy mix.

This explains why increasing recycled content is one of the most effective decarbonization strategies in plastic packaging.

Bottle Production: Energy-Driven Impacts

The second-largest contributor is the Bottle Production (BP) phase.

Here, PET resin is converted into preforms through injection molding and then shaped into bottles using stretch-blow molding at temperatures around 260–280°C.

Electricity use dominates this phase.

Example of Improvement

A lightweighting initiative reducing bottle weight by 20% results in:

• Lower resin demand

• Reduced molding energy consumption

• Lower transport emissions due to weight reduction

In one cited case, a 20% weight reduction led to roughly 21% lower carbon emissions — demonstrating how design innovation directly translates into environmental benefit.

Distribution: Distance Matters

Although not the highest contributor overall, Distribution and Transportation (DT) showed a clear relationship between transport distance and GWP.

The study observed a near-linear relationship (R² = 0.964) between distance traveled and carbon emissions. This confirms that transportation emissions scale proportionally with distance and weight.

Real-World Illustration

Transporting bottled water:

• 60 km → minimal transport emissions

• 750 km → significantly higher GWP

This explains why locally bottled water often has a lower footprint than imported bottled water — even when the bottle design is identical.

It also highlights the importance of:

• Rail over road transport

• Electric fleets

• Regional production facilities

Waste Management: A Story of Variability

Waste Management (WM) showed substantial variability across studies.

Three primary disposal routes were analyzed:

1. Mechanical recycling

2. Incineration (with or without energy recovery)

3. Landfilling

Interestingly, landfill scenarios sometimes appeared to have relatively low GWP within a 100-year time horizon because PET does not biodegrade quickly. However, this does not imply landfill is environmentally preferable — it simply reflects how carbon accounting works within defined temporal boundaries.

Recycling vs Incineration

• Mechanical recycling consistently showed the lowest emissions.

• Chemical recycling had higher emissions but allows higher-quality material recovery.

• Incineration increased GWP significantly, even when energy recovery was considered.

Closed-loop recycling (bottle-to-bottle) produced the greatest environmental benefit because it directly offsets virgin PET production.

This reinforces the circular economy principle: keeping material in use is far more climate-efficient than recovering energy from it.

Environmental Benefits: Credits with Uncertainty

Environmental Benefits (EB) represent avoided emissions due to recycling or energy recovery.

This phase showed the highest coefficient of variation. Why?

Because each study modeled different end-of-life scenarios:

• High-recycling European countries showed strong emission credits.

• Regions dominated by landfill showed minimal environmental benefit.

This variability demonstrates how policy, infrastructure, and consumer behavior directly influence product-level carbon footprints.

Validation Against Market Data

To ensure robustness, the meta-analysis results were compared against national Environmental Product Declaration (EPD) data from Korea.

The EPD system follows internationally recognized standards such as:

• ISO 14040

• ISO 14044

• ISO 14025

The Korean EPD average for PET bottles was:

5.424 kg CO₂-eq per kg

The meta-analysis result:

5.093 kg CO₂-eq per kg

A difference of approximately 6.5% indicates strong methodological reliability.

This alignment suggests that meta-analysis can produce decision-grade insights comparable to certified product declarations.

Bottle Size and Packaging Efficiency

When normalized per 100 mL of water, the average emission was:

17.3 g CO₂-eq per 100 mL

A clear pattern emerged:

• Smaller bottles (e.g., 0.33 L) had higher emissions per 100 mL.

• Larger bottles (e.g., 2 L) had lower emissions per 100 mL.

This is due to packaging efficiency — larger bottles use proportionally less plastic per unit of water delivered.

For example:

• Two 0.5 L bottles require more total plastic than one 1 L bottle.

• Therefore, larger formats are more carbon-efficient per liter.

This insight has implications for retail strategy and sustainable product design.

What This Means for Sustainable Packaging Strategy

The descriptive findings of this meta-analysis reveal a clear hierarchy of action:

1. Prioritize recycled PET integration

2. Invest in lightweight bottle design

3. Decarbonize energy used in production

4. Optimize transport logistics

5. Improve recycling infrastructure

Most importantly, the study demonstrates that the majority of emissions occur before the consumer even opens the bottle.

The climate impact is largely embedded in materials and manufacturing.