Yeah, in ecoivent 3.5 we still use (as ecoinvent "itself" does up to today, and e.g. SimaPro too) the double negative waste approach: a process that provides the service of waste treatment has a product on the ouput side (treatment of waste), with a negative sign, and a process that has waste output sent to this process has waste on the input side, also with a negative sign. That is (if I understand correctly) the second picture (where you do not mention the negative sign though).
In openLCA, since version 1.7 or so, you can also use the other approach: model the flow as waste flow, let it be output of the process that has waste output and input of the process that treats it. And do not use negative signs. That is your first picture.
Hope this helps,
- in newer versions of ecoinvent, > 3.5, we always use the second approach, so your first picture.