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I want to look at the Impact of waste treatment and I have numbers on how many kg of wood, plastic, paper, etc. is disposed of. I am creating a process using the Opposite Direction Approach but am unsure where to put the input and output (waste flows or reference flows) and where to use a negative sign. I’m sending a screenshot as well. Looking forward to your help!

in openLCA by (120 points)

1 Answer

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by (90.7k points)
In the opposite direction approach, you must use product flows not waste flows (unless you are using a really old openLCA version). Then, simply set a negative sign for waste input (the process that has in reality waste output), and for waste output (the process that treats the waste) a negative sign as well. Hth, and I would rather recommend the waste flow modeling ;)

Best wishes,

by (120 points)
Thanks a lot for your answer! Im my screenshot, I am using waste flows of Ecoinvent 3.8. Should there be product flows also in this Database? How would I model the waste flows as you suggest accordingly?

Thanks a lot!
by (90.7k points)
You are welcome, thank you.
For using waste flow modeling, just
- have waste treatment processes that consume waste, i.e. have waste on the input side
- have processes that produce waste, add for these waste flows on the output. No minus signs, just the amounts from the processes in reality. That's it!
by (120 points)
So waste flows on input side and for output I create a flow for the disposed waste? Another problem I am having, is that I cannot choose a provider for waste flows on the input side, only on output side. Any tips in that regard?
by (90.7k points)
To your first sentence: correct. "Another problem": this is not a problem but comes with waste flows. You will need to specifiy where your waste output is treated (incineration plant, e.g.) but you will not want to specify where all the waste that goes into the incineration plant is coming from -> for waste flows, you specify the provider on the output side.
by (120 points)
I see!

So I have the reference waste flow that I created manually  on the input side, which is the sum of the mass of all waste disposed by the company.

On the output side I have waste flows for each category of waste and their respective mass with the according provider.

Is that correct?