**5. Summary**

A 4D-μCT approach to assess removal of fatty oil from sponge has been developed. A sample holder with a flow channel and the capability to squeeze and flush the sample was designed to follow the dynamic processes inside the sponge during oil removal. Two contrast agents were assessed to improve visualization of the fatty oil absorption, emulsification and removal. Magnetite particles provided contrast but the stability of the magnetite dispersion in olive oil and the magnetite adsorption onto the sponge inner surfaces were identified as the major problems with this approach. On the other hand, mixing brominated vegetable oil with olive oil was identified as the better approach as it forms a solution with olive oil. This fatty oil solution does not phase separate and does not adsorb strongly to the sponge inner surfaces thus behaving like olive oil. Washing the sponge with a dishwashing solution almost completely removed the oil indicating deep down cleaning and can help minimize bacterial growth inside the sponge.

**Author Contributions:** Conceptualization, M.N.B., V.C., E.R.; Methodology, A.S., M.N.B., E.R., K.B., P.E.P.-M., V.C., L.V.H., I.J.; Software, A.S., F.V.A., S.V.; Validation, A.S., P.E.P.-M., E.R., M.N.B.; Formal Analysis, A.S.; Investigation, A.S.; Resources, A.S., I.J., F.V.A., S.V., P.E.P.-M.; Data Curation, A.S.; Writing—Original Draft Preparation, A.S., M.N.B.; Writing—Review and Editing, all authors; Visualization, A.S., M.N.B.; Supervision, M.N.B., E.R., V.C., L.V.H.; Project Administration, E.R., M.N.B., V.C.; Funding Acquisition, E.R., V.C., M.N.B., L.V.H., K.B.

**Funding:** This work is funded by the European Union's Horizon 2020 research and innovation programme under gran<sup>t</sup> agreemen<sup>t</sup> No. 722871 in the scope of the Marie Skłodowska-Curie Action ITN BioClean. The Ghent University Special Research Fund (BOF-UGent) is acknowledged for the financial support to the Centre of Expertise UGCT (BOF.EXP.2017.000007).

**Acknowledgments:** Philippe Van Auwegem (Ghent University, Department Physics and Astronomy) is acknowledged for his assistance in building the flow cell and Daniëlle Schram (Ghent University, Department Geology) for helping in purchase and procurement of the materials.

**Conflicts of Interest:** This work presents a methodology to investigate deep-down cleaning using in-situ experiments. The results of this work do not reflect any value measurement of any P&G product and as such do not pose a conflict of interest. Any dishwashing liquid can be used for this purpose.
