End of life calculations

The energy and CO₂ footprint associated with a product's end of life are split into two distinct contributions: 'Disposal' and 'End of life (EoL) Potential' (see Figure 1).

'Disposal' includes the cost of: 1) collection of the material/component at end of life and, where applicable, disposal in landfill, and 2) separation and sorting of the collected material, ready for reprocessing by the proposed end of life route.

'EoL Potential' represents the end of life savings or 'credits' that can be realized in future life cycles by using the recovered material or components.

Note: As the 'credit' associated with the recovery and reuse of material/components lies outside the standard system boundaries for a product's life cycle, the 'EoL Potential' is displayed as a separate life phase. This enables:

1. Determination of the environmental footprint of a product over its entire lifecycle (achieved by ignoring the 'EoL Potential' phase)

2. Evaluation of the benefits of the various end of life options (achieved by considering just the 'EoL Potential' phase).

The first of these conforms to the system boundaries used in standard life cycle assessments, while the second enables designers to consider the impact of their design on potential end of life strategies. For example, knowing the benefits that can be achieved by recycling or reusing a material/component at end of life encourages design for disassembly.

'Disposal' calculations

Once a product has reached the end of its intended life, it will be collected and sorted ready for its intended end of life strategy. The energy (H_collect) and CO₂ footprint (CO_2 collect) associated with these operations is determined by the following calculations, using the values in Table 1.

	Collection Energy Hc (MJ/kg)	Primary Sorting Energy Hps (MJ/kg)	Secondary Sorting Energy Hss (MJ/kg)
Landfill	0.2	-	-
Combustion	0.2	0.3	-
Downcycle	0.2	0.3	-
Recycle	0.2	-	0.5
Re-manufacture	0.2	-	-
Reuse	0.2	-	-
None	-	-	-

Note: In certain versions of the tool, there is no option to specify a 'Recovery ratio'. In these cases, it is assumed that all material is recovered and processed by the selected end of life route (i.e. r = 100)

'EoL Potential' calculations

Once collected and sorted, the material is then 'processed' according to the selected end of life strategy. The energy (H_credit) and CO₂ footprint (CO_2 credit) associated with future environmental savings is dependent on both the end of life route and the material type.

In calculating this end of life 'credit', the following assumptions are made:

• The recovered material is used to replace material of the same grade (i.e. credit is only given for recovering the virgin content of the component).

• No credit is given for a material when the Recycled content is set to Reused part.

• In versions of the tool where there is no option to specify a recovery ratio at end of life, it is assumed to be 100% (i.e. r = 100). This leads to a 'best case scenario' as, in practice, not all material will be collected and most recovery processes are not 100% efficient.

The calculations used to determine the credit for each end of life option are detailed below:

Landfill

Landfill is seen as the end of a product's life. As a result, no future energy benefits or costs are associated with this option.

Combust for energy recovery

The aim of this combustion technique is to recover the calorific content of a material. However, some of the benefit in recovering the embodied energy is offset by the carbon dioxide released. The levels of energy and carbon dioxide produced are calculated as follows:

Note: The (-a.Comb_eff.Hcal) term in the CO_2combust equation relates to the CO₂ saving achieved by not having to draw the recovered energy from the national electricity grid.

Downcycle

In downcycling a material is processed into a material of lower quality. Typical examples include the conversion of: PET drink bottles into fibers for fleece clothing, crushing concrete and brick for use as an aggregate replacement, and reprocessing PP packaging as a wood replacement (decking, park benches).

The environmental benefits of downcycling are dependent on both the downcycling technique and the relative reduction in material quality. The eco audit tool considers three main downcycling techniques: reprocessing, comminution (crushing, grinding, and shredding) and metal recovery (see Table 2).

Technique	Applicable Materials
Reprocessing	Metals Thermoplastic polymers & thermoplastic elastomers (TPEs)
Comminution	Ceramics, glasses, natural materials (organic & inorganic), thermoset plastics & elastomers
Metal recovery	Electrical components: Batteries, PCBs…

Downcycle: 'Reprocessing'

The energy and CO₂ footprint calculations used for reprocessing are based on the equations used for recycling. The main difference is that downcycling leads to the replacement of material with lower performance, and lower embodied energy, than the material being downcycled. This is accounted for by applying a downcycling factor (ß).

A lower downcycling factor (ß) has been applied for thermoplastics (0.2 relative to 0.5 for metal) as downcycling of these materials is less established than for metals, leading to the production of lower grade material.

In cases where no data appears on the material datasheet for recycling energy and CO₂ footprint, values are estimated from the primary production data as follows:

Downcycle: 'Comminution' (crushing, grinding, shredding)

The second downcycle route is the size reduction of materials into aggregate or filler replacement. As the energy level required for downcycling material by comminution is similar to that for producing virgin aggregate or filler, the environmental benefit is restricted to savings in transportation costs (i.e. downcycled aggregate is typically used at, or close to, its source).

Downcycle: 'Metal recovery'

Electrical components are generally downcycled by recovering their metal content. This typically uses evaporation and condensation processes which, being energy intensive, lead to little or no reduction in energy or CO₂ footprint. As a result, the eco audit tool defaults the downcycle savings to zero for these products.

Even so, it should be highlighted that metal recovery is both economically and environmentally viable as it conserves resources and reduces the amount of toxic material entering landfill sites.

Recycle

In recycling, material is reprocessed into a material of similar quality. This leads to a saving of the energy and CO₂ footprint associated with the production of virgin material, minus the energy and CO₂ associated with the recycling process. The energy saving is calculated as follows:

Re-manufacture

By re-manufacture, components are recovered from an existing product, cleaned, inspected, repaired (if necessary) and reused in a new product or as a replacement part. It is estimated that, on average, the re-manufacturing process utilizes about 3MJ/kg. This leads to the following savings:

Reuse

Reuse is essentially the extension of a product's life. Examples include: the 'relifing' of aircraft when they reach the end of their intended design life, and items sold on Internet auction sites. As this end of life option involves no additional processing, maximum environmental benefits can be achieved:

None

This option relates to products where there is no disposal at end-of life. For example, the foundations of a building that are left in the ground after demolition. As a result, no future energy benefits or costs are associated with this option.