Removal of bisphenol A and 17α-ethinyl estradiol by combined coagulation and adsorption using carbon nanomaterials and powdered activated carbon

Abstract

In this study, combined coagulation–adsorption treatment using single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and powdered activated carbon (PAC) was employed for the removal of endocrine disrupting chemicals (EDCs) from various water sources. Bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) were the target EDCs used in this study. Natural surface water (BRW) was obtained from Broad River in Columbia, South Carolina. Synthetic seawater (SW) and brackish water (BW) were produced to reflect the typical composition observed in previously published literature. Synthetic landfill leachates were created to replicate the characteristics of leachate produced in young landfills (YLs) and old landfills (OLs). The adsorption capacity of the SWCNTs was greater for EE2 than for BPA for the majority of the aqueous solutions with the exceptions of BW and BRW. The adsorption capacity for BPA observed the following trend: BRW (log Kf=3.18)>SW (log Kf=3.01)>YL (log Kf=2.32)>BW (log Kf=1.96)>OL (log Kf=1.25), while the adsorption capacity of EE2 followed a different trend: SW (log Kf=3.41)>YL (log Kf=3.38)>BRW (log Kf=3.14)>OL (log Kf=2.09)>BW (log Kf=1.38). Molecular modeling was also conducted to determine the binding energies between the EDCs and the SWCNTs in both the gas phase and the liquid phase. The results showed higher binding energies between EE2 and the SWCNTs than between BPA and the SWCNTs in the gas phase and the aqueous phase, which support the higher removal of EE2 than BPA found using adsorption isotherm modeling. Jar testing was conducted with each adsorbent to simulate the combined coagulation–adsorption treatment process. The sole use of coagulation yielded small percentages of BPA removal (<10%) in each aqueous solution but higher percentages of EE2 removal. However, the removal percentages using the combined coagulation–adsorption process were similar to those achieved using only the adsorbent. In these processes, the SWCNTs outperformed the MWCNTs for each combination, while PAC often outperformed both the SWCNTs and the MWCNTs, with more than 90% removal of both BPA and EE2.