**4. Conclusions**

In this work, the application of polymer-assisted ultrafiltration (PAUF) for selective retention and separation of Cu(II) from MSWI fly ash extracts was investigated at laboratory and pilot scale. The following conclusions can be drawn from these investigations:


**Supplementary Materials:** The following are available online at http://www.mdpi.com/2227-9717/8/12/1662/s1: Figure S1. Schematic illustration of laboratory ultrafiltration system. Figure S2. pH dependent metal retention using fly ash extract from MVA Ingolstadt without addition of polymer. Table S1**.** Average metal concentrations (>1 mg L<sup>−</sup>1) of fly ash extracts from MVA Ingolstadt and KEBAG Zuchwil. Chloride concentration of both extracts is approximately 60 g L<sup>−</sup>1.

**Author Contributions:** Conceptualization, C.H. and S.F.; methodology, C.H. and S.F.; experimental investigation, C.H. and S.F.; data curation, C.H. and S.F.; writing—original draft preparation, C.H. and S.F.; writing—review and editing, C.H., S.F. and M.S.; visualization, C.H. and S.F.; project administration, M.S.; funding acquisition, M.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF), grant number 033R140.

**Acknowledgments:** The authors would like to thank Anton Perfoll and Michael Funk (MVA Ingolstadt) and the staff members of KEBAG Zuchwil for providing fly ash extract samples for our research. The authors would also like to thank BASF SE for providing the polymers used in this study.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study, in the collection, analyses or interpretation of data, in the writing of the manuscript or in the decision to publish the results.
