I am currently working with the ecoinvent 3.6 database in Brightway and I have a question about the end of life treatment processes. I found out that some of these treatment processes have a negative production amount and give negative results when tested. For the same processes opened in Simapro, the production amount is positive and the LCA score is also positive. Screenshot of an activity details in Brightway
Screenshot of the result for this activity in Brightway
Screenshot of the activity details in Simapro
Screenshot of the result for this activity in Simapro
Is there an explanation for this ? And is it possible to know which processes are concerned ? Than you very much for your answer.
it is a thorny sign convention issue. One needs to be aware of these conventions because different LCA softwares and databases can have different conventions.
if you look into the same dataset in ecoinvent website you'll see that the reference product is -1 waste polypropylene. What that means is that it treats 1 kg of polypropylene.
Following the same convention the production flow of that activity on brightway is -1 (unlike normal "production" activities that have a positive production). To be consistent, the use of waste treatment services has also a negative amount (if you look into technosphere exchanges you'll see waste with - sign).
I think simapro treats them differently, and flips the sign of waste treatment activities, that is why you see it positive. It then flips the sign at some point in the calculation.
A good explanation is probably buried in the LCA mailing list somewhere, but I could not find it.
