How system boundaries expansion with substitution is done in openLCA?

Question

Hi all,

I am currently working in openLCA using the Ecoinvent cut-off unit processes database, and I’m trying to understand how to model substitution correctly.

For example, I have a cheese production plant that generates cheese and whey as co-products. In my case, whey is intended to substitute animal feed (barley), meaning it should be used as an input in another process.

However, in openLCA, selecting the “avoided product” option appears to perform system expansion, which instead links to another system that produces whey as an alternative supply route. In my situation, since whey is produced within my system, I would like it to act as a substitute for feed in another process.

Could someone please clarify how this type of substitution can be modelled properly in openLCA?

Thank you in advance for your help.

Answer 1

I am maybe not fully following but openLCA models indeed system expansion so that an avoided product and its supply chain is substracted from the original system, in line with ISO 14040. You can select any process that produces the byproduct you like, also a process that is already in your system. Does that answer your question?

Comments

Dear Andreas,

Many thanks for your reply.

I intend to apply system expansion by substitution. My system produces cheese and whey as a co-product. I would like the whey to be used in another process (a feed production process) where it substitutes another feed, such as barley.

However, in openLCA, when I select the avoided product, the processes that appear are those that produce whey as a by-product, which I think is different from what I need in this case.

Similarly, if we assume that the whey goes to an AD plant for biogas production, and this biogas then replaces, for example, natural gas, how should this be modelled in openLCA so that the cheese plant is credited for these substitutions?

---

Ah, if the process providing the product for system expansion is again a multi-functional process you need to get rid of the other product(s) by system expansion or allocation.