RESUMO
The European Union has proposed the value of 1 ng L-1 as a drinking water quality standard for estradiol. With conventional technologies only partially removing estradiol, the investigation of novel alternatives is more than ever required. Tagliavini and Schäfer proposed that the use of a thin activated carbon layer combined with a membrane is worth considering. In this work, the process was further advanced through a systematic investigation of the role of activated carbon size, activation and surface chemistry on the removal of estradiol. The use of smaller carbon particles allows reaching the ambitious target value of 1 ng L-1 in a millimetric layer. Further, adsorption kinetic enhancement by increasing the oxygen content on the carbon improves the removal from 96 to 99 % (for a layer of 2 mm) for OH-containing pollutants such as estradiol. High removal, together with low pressure and no by-product formation, are characteristics that make the UF-PBSAC a promising and competitive approach.
Assuntos
Poluentes Químicos da Água , Purificação da Água , Adsorção , Carvão Vegetal , Membranas Artificiais , Polímeros , Ultrafiltração , ÁguaRESUMO
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 (100â¯ngL-1) can be reduced to 20-40â¯ngL-1 via adsorption in a thin layer (2.2â¯mm) of UF-PBSAC at a flux of 120-130â¯Lm-2â¯h-1. Furthermore, during the filtration of 9â¯L (membrane area 38â¯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 11â¯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 2.2â¯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.
RESUMO
Removal and interaction mechanisms of four different steroid micropollutants, estrone (E1), estradiol (E2), progesterone (P) and testosterone (T) were determined for different types of polymer-based spherical activated carbon (PBSAC). Higher than 90% removal and significantly faster kinetics compared to conventional granular activated carbon (GAC) were observed, while performance was comparable with powdered activated carbon (PAC). No influence of pH in the range 2-12 was determined, while the presence of humic acid (HA) reduced both the removal and the kinetic by up to 20%. PBSAC was characterized in terms of morphology and material properties. The low oxygen content was identified as the main cause for the high performance observed. This was attributed to the enhancement of the hydrophobic effect between PBSAC and hormones and the reduced interactions between PBSAC and water. The ratio of micropollutant size (â¼0.8nm) and average pore size (1-2nm) proved ideal for both micropollutant adsorption and HA exclusion. The homogenous size, spherical shape and surface smoothness of PBSAC did not influence adsorption negatively and make PBSAC a very promising sorbent for a vast range of applications, in particular for the removal of micropollutants in water treatment applications.
