Module D net (output) flow calculation using Ecoinvent EN 15804 GD

Question

I am interested in your take on the practical modelling of secondary material (SM) inputs and Material For Recycling (MFR) outputs when using the EN 15804 (GreenDelta implementation) system model of Ecoinvent.

The database (correctly) accounts for these indicators not only in the foreground system, but also in the background system. The result is that both indicators are likely not 0 even if my product contains no recycled material and is not sent for recycling at end-of-life.

My problem comes when modelling the net flow of materials leaving the product system (stages A-C) to be considered in module D. To account for processes in module D, the net flow (MFR minus SM, in kg) needs to be separated out for each material, but the indicator results from the life cycle inventory are aggregated. SM and MFR can thus both be a mix of e.g. iron scrap, aluminium scrap, waste cardboard, and there is no feasible way to model module D.

I cannot find any rules in the standard or PCR that would allow me to disregard from these flows just because they arise from the background system.

How have other LCA practitioners solved this? Are you tracking the use of "Recycled content cut-off" processes for each type of material and doing the net flow calculation manually? Are you manually changing names of elementary flows in the database to "SM (iron scrap"), etc., or are you simply disregarding the SM and MFR flows from the background system in your module D calculations?

I checked but this specific topic does not seem to have been addressed in the white paper Ciroth and Hamed (2025) Module D in Environmental Product Declarations (EPDs).

Answer 1

Dear Kristian,

You raise an important point that there is still no clear guidance if the input (SM/RSF/NRSF) and output inventory indicators (MFR/MER/CRU) should be calculated over the foreground only or over foreground+background. I have the feeling that the trend is going towards foreground only, even though this is not really a life cycle perspective. Of course, it has the advantage that results are easier to grasp and not mixed with the background, but it also has the disadvantage that background datasets with e.g. high recycled content will contribute with lower e.g. greenhouse gas emissions to the foreground, but all this is not reflected in the overall recycled content used in the whole product system.

If over the foreground only, as you said, module D inputs can be directly taken from MFR minus SM. There would be no contributions from the background database and all results are only manually inserted by the practitioner into the foreground.

If over the foreground+background: What do you think about the idea that we split all 6 indicators (SM/RSF/NRSF/MFR/MER/CRU) into the indicators from background and into the indicators that are manually inserted by the practitioner in the foreground only? For example, "Secondary materials" will be split into "Secondary materials (background)" and "Secondary materials (foreground)". The total result will be still the same as before, but practitioners can directly see how much stems from the background only and how much stems from the foreground only and how much stems from the sum of the two.

Best wishes,
Conrad

Comments

I'll try to explain my thinking in slightly different words:

I don't see a differentiation made in the standard or PCR between MFR and SM "in foreground processes" vs. "in background processes". Or between "material in the product" vs. "material not in the product". The system boundary and end-of-waste definition apply to all flows, including those in generic data. This means that:

– If the net output flow from the product system is > 0, I have to assign loads from processing + benefits for this material flow in modul D. A conservative approach is to assume that this is zero.

– If the net output flow from the product system is <0 (more recycled material used as input than is generated as an output), I have to assign "avoided loads from processing" + "avoided benefits" in module D for this material flow. Assuming zero in module D is not a conservative approach in this case.



I tried your suggestion regarding the contribution tree > inventory indicator flow: This does give me the possibility to dig down into where the contribution comes from. An even better solution is probably to use the Impact analysis by process view. This gives me the aggregated contribution from each process. This is not perfect, however, as the SM indicator can contain multiple material inputs aggregated together.

A better solution to consider the database level might be to create different inventory flows:
– Secondary materials (iron scrap)
– Secondary materials (waste aluminum)
– etc.

These can then all be classified and characterized in a joint "LCIA" method for Secondary materials with the value of 1 kg/kg. This would give the practitioner the possibility to both have the aggregated indicator, as well as a possibility to do the manual calculations of MFR minus SM for each material flow for consideration in module D.