High performance ultra- and nanofiltration removal of micropollutants by cyclodextrin complexation

Nanofiltration is a promising solution for the removal of emerging and persistent mi-cropollutants, but it is limited by operating expenses due to high membrane areas and operational pressures, dictated by the membrane's low molecular weight cut-offs (MWCO), and the formation of large amounts of concentrate to be treated, e.g. by ad-vanced oxidation. In this paper, a simple solution is proposed to enhance membrane retention of micropollutants by adding cyclodextrins (CDs) for complexation. Complexation between micropollutants and hydroxypropyl 8-CD resulted in higher re-jections of ibuprofen (99.3%), bisphenol A (94.5%) and phenol (76.4%) compared to filtra-tions without addition of CDs (82.4%, 14% and 4%, respectively) using a 1 kDa MWCO membrane. The CD complexation allowed for filtration with ultrafiltration (UF) mem-branes, where nanofiltration (NF) membranes would normally be the best available membrane to retain the micropollutants. By complexation with 8-CD polymers, retentions of IBU of 97.0 were even achieved using a 5 kDa MWCO membrane. Operation of larger MWCO membranes will potentially lead to less retentate formation, i.e. higher con-centration factors as well as higher operational flux which results in lower membrane area and lower operational expenses. Therefore, the addition of CDs fixated on larger compounds (particles or polymers) may be an efficient and simple solution to increase micropollutant rejection and increase water recovery, while potentially reducing opera-tional treatment expenses. This is of high significance, as it can serve as a simple way to polish contaminated waters by removing micropollutants in large scale wastewater treatment.(c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY license (http://creative-commons.org/licenses/by/4.0/).

Automated summary

This paper proposes a solution to enhance the retention of micropollutants in nanofiltration by adding cyclodextrins (CDs) for complexation. The results show that the addition of CDs significantly improves the rejection rates of ibuprofen, bisphenol A, and phenol compared to filtration without CDs. Furthermore, the complexation of CDs allows for filtration with ultrafiltration (UF) membranes, reducing operational expenses.