Steroid hormone micropollutant removal from membrane bioreactor effluents using single-walled carbon nanotube composite nanofiber membranes

Waterborne micropollutants can persist in wastewater effluents even after advanced treatment processes, such as membrane bioreactors (MBRs), posing significant risks to aquatic organisms and human. The incorporation of ultrafiltration (UF) membranes with adsorbents, such as single-walled carbon nanotubes (SWCNTs), provides a low-energy barrier against micropollutants, but water matrices can compromise function. Removal of steroid hormone 17(3-estradiol (E2) micropollutants in synthetic water and MBR effluent is investigated with SWCNT;- UF composites with different configurations of feed-and permeate-side adsorption. Feed-side deposition of SWCNTs at a loading of 2.1 g/cm2 in nanofiber mats achieves 96 % removal of E2 from synthetic water, while permeate-side deposition yields a lower removal of 73 % due to uneven SWCNT distribution in the non-woven UF support. With feed-side adsorption, E2 removal is limited by hydraulic residence time (12-30 milliseconds) rather than SWCNT loading (0.5-5.3 g/m2). The removal of E2 that is spiked into MBR effluent was significantly lower, at around 47 %. This can be attributed to the direct and/or indirect competition of other micropollutants and organic matter in the MBR effluent for the adsorption sites of SWCNTs. The removal of other micropollutants that were identified in the MBR effluents was low. These results highlight the strong interference of MBR effluent organic matter and potentially other micropollutants to steroid hormone adsorption by composite membranes, and suggest permeate-side deposition of adsorbents may be a strategy to partially mitigate this interference.