ecoinvent Forum Archive

Question from Eva Risch via the LCA Discussion List.

I would like to compile consistent inventories with regard to cut-off allocation rules. For recyclable materials such as aluminium, steel or copper: in Ecoinvent v3 database (in “Ecoinvent unit processes”) there are some old v2.2 recycling processes that have been converted (eg "Recycling steel and iron/RER U" and these are empty - which is in line with the cut-off system modelling). But there are also v3 processes describing the waste treatment market (eg "Waste reinforcement steel {CH}| market for waste reinforcement steel | Cut-off, S" - which include recycling activities: “Waste reinforcement steel {CH}| treatment of, recycling | Cut-off, U” that are not empty (contains energy for dismantling); and other end of life activities (treatment in sorting plant and collection for final disposal..):

Why both types of processes are proposed in Ecoinvent v3? How to correctly model the steel used in my inventory, if it is say, recycled at 95%?

Thanks in advance,

Kind regards,

Eva

In the context of the cut-off system model (for more information, please refer to the ecoinvent website) the secondary use cycle of a material starts at the point of waste collection (e.g. steel scrap collected from households), while the point of cut off is the recycling activity. Hence, the supply chain for secondary materials (produced through recycling activities) includes their collection and recovery (sorting and dismantling), which is why secondary products are often not wholly burden free. For steel, this means that the collection and recovery of steel scrap would be included but that the recycling of recovered steel scrap in an electric arc furnace is “cut-off”.

The products “waste reinforcement steel” and “steel scrap”, that you mention in your email, are both wastes. Waste reinforcement steel is treated through one of three activities: “treatment of waste reinforcement steel, recycling”, “treatment of waste reinforcement steel, collection for final disposal” or “treatment of waste reinforcement steel, sorting plant”. The system boundaries of the inventories includes on-site energy use for dismantling and sorting, plus transport and disposal. No bonuses or burdens are given for recycled material and no secondary products are available; i.e. the system boundary cuts off the recycling process entirely. Similarly, “scrap steel” can only be treated by either landfill or incineration; it never goes to recycling.

So how can secondary steel products be included in an inventory? The collection and recovery of ferrous scrap is included in the ecoinvent database through the “iron scrap” recycling chain, not “steel scrap”. This is, obviously, not ideal and can easily lead to confusion: despite being ostensibly the same, “scrap steel” is a waste that is sent for disposal; “iron scrap” is a recyclable that is collected and recovered for recycling.

The collection of “iron scrap, unsorted” is represented by the activity “iron scrap, unsorted, Recycled Content cut-off”. This is then sorted and pressed in the activity “sorting and pressing of iron scrap”, which produces “iron scrap, sorted, pressed”. The sorted iron scrap is then made available, burden-free, for its secondary use cycle by “iron scrap, sorted, pressed, Recycled Content cut-off”. “Iron scrap, sorted, pressed” is consumed, burden free, by the activities “steel production, electric, chromium steel 18/8” and “steel production, electric, low-alloyed”, which represent the production of steel products in an electric arc furnace from ferrous scrap.

How one might include an input of 95% recycled steel: 95% of the steel used in your inventory should be “steel, low-alloyed” or “steel, chromium steel 18/8”, supplied directly from the activity “steel production, electric, low-alloyed” or “steel production, electric, chromium steel 18/8”, respectively. The remaining 5% can come from “steel, low-alloyed” or “steel, chromium steel 18/8” that is supplied directly from “steel production, converter, low-alloyed” or “steel production, converter, chromium steel 18/8”, respectively.

Dear David,

Thank you for your answer and detailed explanations.

Our issue is not about how to include secondary products in our inventory: we use the global market process for steel (“Steel, unalloyed {GLO}| market for | Cut-off, S) that already includes some scrap iron in “Steel production, converter, unalloyed”).

Indeed, our concern is about how to consider the end-of-life of steel, including recycling. In our waste-treatment of steel (outputs to technosphere), we would like to adapt the end-of-life of steel in France by sending e.g. 95% to recycling and 5% to treatment.

1. For treatment we chose “Scrap steel {Europe without Switzerland}| market for scrap steel | Cut-off, U”, which includes transport, landfill and incineration. 
2. For recycling we chose “Steel and iron (waste treatment) {GLO}| recycling of steel and iron | Cut-off, S” which is an empty process (due to cut-off rules).

Also, given the information on the Ecoinvent website and in your reply, we understood that according to cut-off rules, from the waste-producing side (our situation) the recycling process is “cut-off” and we only consider transport to, and dismantling (if necessary, as in “Waste reinforcement steel {CH}| treatment of, recycling | Cut-off, U” for waste reinforcement steel) in a waste treatment facility.

Do you think the above is correct? If so, to ensure consistency with the treatment line 1 (5% of steel), should we add transport in the recycling line 2 (transport to recycling facilities for the 95% of steel)?

Cheers,

Eva 

Dear Eva,

Iagree with your choice of activities in both cases. However, I think there has been some confusion. You write:

"Also, given the information on the Ecoinvent website and in your reply, we understood that according to cut-off rules, from the waste-producing side (our situation) the recycling process is “cut-off” and we only consider transport to, and dismantling (if necessary, as in “Waste reinforcement steel {CH}| treatment of, recycling | Cut-off, U” for waste reinforcement steel) in a waste treatment facility."

To be clear: to be consistent with the philosphy of the cut-off system model, the burdens of collecting, sorting (dismantling) and transporting iron scrap that is collected for recycling are allocated to the consumer of that iron scrap. The producer of the iron scrap that is collected for recycling should not recieve any burdens from producing that by-product.

Based on this, here are some general recommendations for modelling ferrous scrap inputs/outputs in product systems (note that activity and exchange names may vary in SimaPro as they use their own naming convention):

Input from technosphere

"market for iron scrap, sorted, pressed" - where you have an input of iron scrap for recycling (in an electric arc furnace).

"steel, low-alloyed" from "steel production, electric, low-alloyed" - where you have an input of steel produced from recycled iron scrap (note that chromium 18/8 steel is available as well).

By/products/wastes

"iron scrap, sorted, pressed, Recycled Content" - where you have an output of iron scrap for recycling. 

"market for steel scrap" -where you have an output of iron scrap for disposal.

I hope this is helpful to you. Let me know if you have any follow-up queries.

Best,

David

Dear David, 

Thanks for your reply. We certainly understand better the choice in ecoinvent processes. However, we have another follow-up query around the same matter..

Given the postulate in ecoinvent cut-off rules: "The producer of the iron scrap that is collected for recycling should not recieve any burdens from producing that by-product”.

That is why we were surprised to see that the process “Waste reinforcement steel {CH}| treatment of, recycling | Cut-off, U” included in “Waste reinforcement steel {CH}| market for waste reinforcement steel | Cut-off, S” isn’t burden free, it includes energy for dismantling. And it is the same for other recycling cut-off processes as “Waste cement-fibre slab {CH}| treatment of, recycling | Cut-off, U” or “Waste concrete gravel {CH}| treatment of, recycling | Cut-off, U” for instance.

Can you please explain why dismantling is included in these recycling processes (in the producer side of a recyclable material), therefore marking this process with a burden?

Many thanks, 

Eva

Dear Eva,

That is a good question. The various datasets you mention were developed for ecoinvent 2000, adapted for v2.2 and, later, again, integrated into v3. They are based on best available data from Swiss sites, albeit from quite a few years ago, but the modelling approach is clearly more consistent with previous versions of the dabase than it is with the current approach (see my previous posts here). The documentation for these datasets is available in Part V of the report:

Doka G. (2009) Life Cycle Inventories of Waste Treatment Services. Final report ecoinvent v2.1 No. 13. Swiss Centre for Life Cycle Inventories, Dübendorf, CH.

You can access this via our website. The report explains all of the modelling choices and assumptions made by the authors to create these datasets. The system boundaries of the datasets include all waste management activities for collection, recovery and disposal but recycling activities themselves are cut-off. Hence, dismantling is included in these datasets, even for the "for recycling" dataset, which should be burden free. To be consistent with the cut-off system model as implemented in v3, the "for recycling" dataset should be burden free.

We work hard to ensure that all our datasets are up to date and that any issues are resolved but in some cases, inconsistencies like this can slip through the net. Thank you for pointing this out, we will address this as soon as we can. Note that we are currently working on a large project to update the waste management sector in the database, so I'm sure we'll be taking a closer look at these datasets as part of that effort.  

In the meantime, if you need to include outputs of steel for recycling, I would suggest following the recommendations of my previous post rather than using the datasets for reinforcement steel. 

I hope this helps.

Best,

David

Hi David and Eva,

I have read through your discussion with the hope of better understanding how recycling is modelled in ecoinvent. I'm not sure if I'm any wiser, but I give it a try:

I have understood that when following the cut-off system model, the collection, transport and sorting of scrap is allocated to steel scrap, i.e. waste steel at the EoL of a product. The actual recycling process is included in processing of the iron scrap, which comes burden-free from the collection, transpor and sorting. Correct?

What if I wanted to model the actual waste management of steel (or any other material) in order to know the environmental impacts of that phase and compare it to a virgin material that this secondary material might replace? How would it be done for steel? Should I basically sum-up the impacts from scrap steel and scrap iron? How would it be done for other typical types of waste, such as plastics, paper etc.?

Thank you!

Best regards,

Jáchym Judl, Finnish Environment Institute SYKE

Hi Jáchym,

As David Turner is now longer at ecoinvent, I'll do my best to reply to your questions.

First, I just want to clarify the different products related to steel scrap that are available in the ecoinvent database.

There is the product "scrap steel", which is classified as a waste (not recyclable). It gets treated, and whatever burdens are associated with the transport and subsequent treatment of scrap steel are attributed to the activity that produces it.

These treatment activities include some incineration activities. In the underlying Undefined datasets, these have as byproduct "iron scrap, sorted, pressed". This product is classified as recyclable, therefore, the burdens associated with its transportation and recycling are cut off, so none of the associated burdens are attributed to the treatment activity. You'll see in the cut-off system model an input of "iron scrap, sorted, pressed" (with negative amount) supplied by the dataset "iron scrap, sorted, pressed, Recycled Content cut-off", for example in the activity "treatment of scrap steel, municipal incineration".

There is also the product named "iron scrap, unsorted", which classified as recyclable, and is the one that is commonly used for modelling an output of iron-containing waste that is sent to recycling, such as steel scrap. Activities that produce it have a negative input from technosphere that is supplied by the dataset "iron scrap, unsorted, Recycled Content cut-off", which is burden-free. This means that none of the burdens of the collection, transportation and recycling of "iron scrap, unsorted" are attributed to the activities that produce it.

So the answer to your first question is: no, it's not quite correct. The burdens of transportation of the "iron scrap, unsorted" and its sorting and pressing are attributed to "iron scrap, sorted, pressed". These burdens are then attributed to whatever activity turns this sorted scrap into iron and steel products. This is because "iron scrap, unsorted" is classified as recyclable. Your statement is however correct for products classified as waste, such as the product "scrap steel".

Regarding your second question: to model the impacts of steel recycling, in the ecoinvent cut-off system model, you should use the impacts associated with the dataset "sorting and pressing of iron scrap", which produces "iron scrap, sorted, pressed". Then, you would need to add to your model an activity that produces steel from "iron scrap, sorted, pressed". In ecoinvent, for example the activities "cast iron production" and "steel production, converter, low-alloyed" get the iron in part from "iron scrap, sorted, pressed" through the "market for iron scrap, sorted, pressed". This way, consumers of "iron scrap, sorted, pressed" get the burdens of the transportation of "iron scrap, unsorted" to the sorting facility, the burdens of the sorting, and also the burdens of transportation after the sorted iron scrap leaves the sorting and pressing facility.

You would thus have 2 steps that cover the recycling and production of steel, which could be compared to the production of steel purely produced from virgin iron (although as far as I know, most steel produced nowadays always includes a significant fraction of recycled iron).

The description above is also valid for plastics and paper, but you would need to first look for the products that represent plastic or paper that goes to recycling and their corresponding recycling activities.

Please keep in mind that all of the above is only valid for the system model "Allocation, cut-off". It is just one of the possible ways to allocate burdens among multiple products along a supply chain. The other two system models would give different results, due to the different philosophies that are applied.

Best regards,

David FitzGerald

Junior Project Manager

ecoinvent