I am modelling the use of a domestic washing machine (openLCA, Ecoinvent 3.8). In another thread (https://ask.openlca.org/362/wastewater-model-in-openlca) you stated that the amount of water that is needed for the process must be integrated as wastewater flow with a negative input. However, if I integrate a waste flow as input, I cannot choose a provider. How can I specify the wastewater treatment plant without being able to specify the provider? Consequently, I have tried three options: First, I added the wastewater flow as negative input. Second, I added the wastewater flow as (positive) output. Third, I didn't consider the wastewater flow - to see how the results differ.
The impacts are in all impact categories higher for option 2. The wastewater treatment process is only incorporated in this option. Option 1 and 3 result in the same results.
Could you please explain how to properly account for wastewater in openLCA and why this is the correct option? Thanks in advance.