Organic matter interference with steroid hormone removal by single-walled carbon nanotubes - ultrafiltration...

Composite adsorbent-ultrafiltration membranes for micropollutant removal are an interesting concept, although water matrix compounds, such as organic matter (OM), may interfere with micropollutant adsorption. To prevent this interference, the adsorbents such as single-walled carbon nanotubes (SWCNTs) can be deposited on the permeate side of an ultrafiltration membrane (UF) that can retain OM. In this study, the 'shielding' effect by different UF MWCOs of such an SWCNT-UF composite was evaluated for nine different types of OM. All nine OM types competed with 17β-estradiol (E2) for adsorption to varying extents, and tannic acid (TA, 1.7 kDa) reduced E2 adsorption by SWCNT-UF most drastically. TA interference mechanisms included direct competition with hormones for adsorption sites, and indirect competition via TA-hormone interactions. TA was not fully retained by the composite membrane with an MWCO range of 3-100 kDa, resulting in ineffective shielding. In contrast, humic acid was mostly retained by the composite with low MWCO of 3-10 kDa and allowed high E2 adsorption. This study demonstrates that tailoring composite membranes by carefully choosing UF MWCO can prevent interference of OM types in micropollutant adsorption by permeate-side adsorbents.