How to take into account processes for by-products?

Question

Hi,

I have a product system (see below) where a by-product (B) is formed that goes to a "side-process". There water and other flow (B) are separated. The B flow goes to another factory for further treatment, and the system boundary ends before the treatment in other factory, so it is not considered in results.

If I create the product system and calculate the results, it does not consider the impacts of the by-product B and its side-process inside the system boundary. How can I take the process for by-product B into account?

I am using the ecoinvent cut-off unit process database.

-Ilmari

Answer 1

I think this would be considered a problem with allocation. in the parameters, you can set the allocation to a ratio or number that you think is correct. Say your product is lamb meat, but the side product of bone is created, which can be used in other products, you would then add whatever percent you think is acceptable to the production of lamb meat. Economic allocation can be zero, if the by products have close to zero value.

Comments

Yes that is one option.
I also found another option that makes it possible to do processes for by-products that are considered in the results. So from the process where the by-product is formed (process A), I just modelled the by-product (B) as waste which goes to a by-process (process C). In process A I choose the provider for the by-product B, as process C. So the output by-product B has a provider in outputs because it is waste (this is different than typically where the provider is usually only in inputs). As a result, I get the by-process and by-product included in the whole process and in the results. I discovered this "technique" in ecoinvent case-study of cups were similar technique was used. The by-process (process C) is not seen in the model graph but is still included there. Very complicated answer but hopefully you understand :)

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ahhhh, i misunderstood your question set up. I think the other method I have seen for doing this is placing providers of upstream processes in the inputs, but giving them a negative value.  I think I see this most often for waste streams.