Removal of steroid micropollutants by polymer-based spherical activated carbon (PBSAC) assisted membrane filtration

Effective micropollutant removal requires energy intensive advanced treatment processes. A novel hybrid membrane configuration - consisting of both ultrafiltration (UF) and nanofiltration (NF) - with permeate-side polymer-based activated carbon (PBSAC) was developed and investigated for the removal of natural hormones with a particular focus on estradiol (E2). The UF-PBSAC process offers significantly enhanced water permeability and hence energy efficiency, while NF-PBSAC was anticipated to reduce residual micropollutant concentration. Realistic micropollutant concentration in the feed (100 ngL^-1) can be reduced to 20-40 ngL^-1 via adsorption in a thin layer (2.2 mm) of UF-PBSAC at a flux of 120-130 Lm^-2 h^-1. Furthermore, during the filtration of 9 L (membrane area 38 cm²), the micropollutant concentration was constant and no saturation could be achieved. Hormone removal was shown to further increase both at lower pressure (and hence flux) and thicker PBSAC layer (until 11 mm). In both cases, this effect was correlated to the increased contact time between estradiol and the PBSAC adsorbent. NF coupled with a PBSAC layer of 2.2 mm achieved a higher overall removal than the UF-PBSAC due to the intrinsic retention of NF. However, the residual NF permeate concentration was similar with and without PBSAC. Thus, the retention of hormones by NF and the adsorption inside the PBSAC layer were demonstrated to be two dependent processes. Overall, the combination of UF with PBSAC absorbent layers is a promising approach for the efficient removal of micropollutants.