System Boundary Approaches for End-of-Life and Recycling
Master the cut-off, substitution, and circular footprint approaches for handling recycling and end-of-life in LCA system boundaries.
Prerequisites:
System Boundary Approaches for End-of-Life and Recycling
How you handle recycled materials and end-of-life treatment can dramatically affect LCA results. A product using 50% recycled steel could have very different reported impacts depending on which methodological approach you use. This lesson explains the major approaches and when to apply each.
The Core Challenge
Recycling creates a methodological puzzle: recycled materials connect two product life cycles.
Consider recycled aluminum:
- First life: Aluminum can → collected → recycled
- Second life: Recycled aluminum → new product
Which product gets credit for recycling? The first product (that sent material to recycling) or the second product (that used recycled content)?
Different approaches answer this differently, and the choice significantly affects results.
The Three Main Approaches
1. Cut-Off (Recycled Content) Approach
Core principle: Each product system is responsible only for processes within its life cycle. Recycled inputs enter "burden-free."
How it works:
- First product: Bears impacts up to collection point; recycling processes go to second life
- Second product: Receives recycled material with zero upstream burden; bears recycling process impacts
Allocation of burdens:
First product life cycle:
Virgin material → Manufacturing → Use → Collection → [END]
↓
Sorting/Processing
↓
Second product life cycle: [START] ← Recycled material (burden-free)
Key characteristics:
- Simple and transparent
- No credits for recyclability—only for using recycled content
- Encourages use of recycled materials
- Used by ecoinvent "Cut-off" system model
Cut-off is often preferred for its simplicity and because it rewards actual recycled content use, which is verifiable. You know what you put in; you don't know what will happen at end-of-life.
2. End-of-Life (Substitution/Avoided Burden) Approach
Core principle: Products that provide recyclable materials get credit for avoided primary production.
How it works:
- First product: Gets credit for displacing virgin material production
- Second product: Bears full burden of input material (virgin equivalent)
Allocation of burdens:
First product life cycle:
Virgin material → Manufacturing → Use → Collection → Recycling
↓
CREDIT: Avoided virgin production
↓
Second product life cycle:
Virgin equivalent burden → Manufacturing → Use → ...
Key characteristics:
- Rewards design for recyclability
- Requires assumptions about displacement rates
- More complex to calculate
- Sensitive to assumptions about what's displaced
- Used by ecoinvent "APOS" system model (for co-products)
3. Circular Footprint Formula (CFF)
Core principle: Allocate burdens and credits between first and second life based on market dynamics and quality considerations.
How it works: The EU's Product Environmental Footprint (PEF) method uses a formula that shares burdens:
Material burden = (1-R1)×Ev + R1×(A×Erecycled + (1-A)×Ev×Qsin/Qp)
+ (1-A)×R2×(Erecycled,EoL - Ev×Qsout/Qp)
+ (1-B)×R3×(EER - LHV×XER,heat×ESE,heat - LHV×XER,elec×ESE,elec)
+ (1-R2-R3)×Ed
Where:
- R1 = recycled content proportion
- R2 = recycling rate at end-of-life
- R3 = energy recovery rate
- A = allocation factor (default 0.5)
- Q = quality ratios
- E = various environmental impacts
Key characteristics:
- Shares responsibility between life cycles
- Accounts for quality changes (downcycling)
- Default 50/50 split between producer and recycler
- Required for EU PEF studies
Comparing Approaches: Steel Example
Consider a steel product with:
- 50% recycled content
- 90% recycling rate at end-of-life
Virgin steel: 2.0 kg CO₂/kg Recycled steel processing: 0.5 kg CO₂/kg Collection and sorting: 0.1 kg CO₂/kg
Cut-Off Approach
Input: 50% virgin (1.0 kg CO₂) + 50% recycled (0.25 kg CO₂) = 1.25 kg CO₂/kg
Use phase: (as normal)
End-of-life: Collection (0.1 kg CO₂) [recycling goes to next life]
Total input burden: 1.35 kg CO₂/kg
Substitution Approach
Input: 100% virgin equivalent (2.0 kg CO₂)
Use phase: (as normal)
End-of-life: Collection + recycling (0.6 kg CO₂)
Credit: 90% × (2.0 - 0.5) = -1.35 kg CO₂ avoided
Total: 2.0 + 0.6 - 1.35 = 1.25 kg CO₂/kg
Circular Footprint Formula (A=0.5)
The full CFF calculation involves multiple terms for material inputs, energy recovery, and quality adjustments. Rather than provide a simplified calculation that may mislead, we note that CFF typically yields results between cut-off and substitution approaches, as it shares burdens and credits between life cycles using the allocation factor A (default 0.5).
For actual CFF calculations, consult the official PEF method guidance which provides detailed worked examples and parameter values.
The CFF result for this steel example would fall in the range of approximately 1.0–1.3 kg CO₂/kg, reflecting the 50/50 burden sharing between producer and recycler.
Results Comparison
| Approach | Result (kg CO₂/kg) | Notes |
|---|---|---|
| Cut-off | 1.35 | Simple, verifiable |
| Substitution | 1.25 | Credits future recycling |
| CFF (A=0.5) | ~1.0 | Shares credits |
The "right" answer depends on the question you're asking.
Choosing an Approach
Use Cut-Off When:
- Creating EPDs (most PCRs require it)
- Transparency and simplicity are priorities
- You want to reward verified recycled content
- End-of-life fate is uncertain
Use Substitution When:
- Conducting consequential LCA
- Evaluating design for recyclability
- Comparing recycling vs. landfill scenarios
- Product has well-established recycling stream
Use CFF When:
- Conducting EU PEF studies
- Regulatory compliance requires it
- You want to share responsibility across life cycles
- Both recycled content and recyclability matter
Important Considerations
Quality Degradation (Downcycling)
Many materials degrade through recycling:
- Plastics may only be suitable for lower-grade applications
- Paper fiber shortens with each cycle
- Some metals alloy contamination limits reuse
Approaches handle this differently:
- Cut-off: Ignores quality (may overvalue recycled input)
- Substitution: Should account for what's actually displaced
- CFF: Includes quality factors (Qsin, Qsout)
Closed-Loop vs. Open-Loop Recycling
Closed-loop: Material returns to same application
- Example: Aluminum can → aluminum can
- Substitution ratio typically 1:1
Open-loop: Material goes to different application
- Example: PET bottle → fleece fiber
- Substitution ratio may be <1 due to quality
Collection and Recycling Rates
End-of-life approaches depend on assumptions about:
- What percentage is actually collected?
- What percentage of collected material is recycled (vs. downcycled or lost)?
- What material is actually displaced?
These vary by:
- Material type
- Geography
- Time period
- Collection infrastructure
Don't assume 100% recycling rates. Use actual regional data where available. Overstating recycling rates can significantly overestimate credits.
Temporal Considerations
End-of-life happens in the future:
- Recycling infrastructure may improve
- Market for recyclates may change
- Different products have different lifetimes
Current-state assumptions may not reflect future reality.
Documentation Requirements
Regardless of approach, document:
- Which approach and why
- Recycled content percentages (and sources)
- Assumed recycling rates (and sources)
- Quality factors (if applicable)
- What primary material is displaced (for substitution)
- Sensitivity to key assumptions
Approach Summary Table
| Feature | Cut-Off | Substitution | CFF |
|---|---|---|---|
| Recycled input burden | Processing only | Full virgin equivalent | Shared |
| End-of-life credit | None | Full avoided burden | Shared |
| Rewards | Recycled content use | Recyclability | Both |
| Complexity | Low | Medium | High |
| Data needs | Current state | Future projections | Both |
| Common use | EPDs, general | CLCA, design | EU PEF |
Hybrid Approaches
Some studies use hybrid approaches:
Sensitivity testing: Calculate with multiple approaches to show range.
Approach matching: Use cut-off for unknown fate, substitution where recycling is guaranteed.
Conservative choice: Use approach giving least favorable results for claims.
Key Takeaways
- Three main approaches exist: cut-off, substitution, and CFF
- Cut-off rewards recycled content; substitution rewards recyclability
- CFF shares credits between producer and recycler
- Results can differ significantly—approach choice matters
- Match approach to your study's goal and context
- Document assumptions about rates, quality, and displacement
Practice Exercise
A plastic product contains 30% recycled PET and has a 40% recycling rate at end-of-life. Calculate the input-related burden using:
- Cut-off approach
- Substitution approach (assume recycled PET displaces virgin PET 1:1)
Given:
- Virgin PET: 3.0 kg CO₂/kg
- PET recycling process: 0.8 kg CO₂/kg
How do the results differ? Which approach would you choose for (a) an EPD and (b) a design comparison?
Congratulations!
You've completed the Advanced Methods track. You now have deep knowledge of uncertainty analysis, Monte Carlo simulation, consequential LCA, social LCA, and end-of-life allocation methods.
Further Reading
- Allacker, K., et al. (2017). Allocation Solutions for Secondary Material Production and End of Life Recovery. Resources, Conservation and Recycling.
- European Commission (2021). Annex C: Circular Footprint Formula. PEF Method.
- Schrijvers, D.L., et al. (2016). A Review of Methods and Studies on the Environmental Impacts of the Recycling of Metals. Journal of Industrial Ecology.