Research

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

Read the article

Abstract

Nanofiltration is a promising solution for the removal of emerging and persistent micropollutants, 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 advanced 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 β-CD resulted in higher rejections of ibuprofen (99.3%), bisphenol A (94.5%) and phenol (76.4%) compared to filtrations 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) membranes, where nanofiltration (NF) membranes would normally be the best available membrane to retain the micropollutants. By complexation with β-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 concentration 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 operational 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.