Effective removal of perfluorooctanoate from groundwater using quaternary nitrogen-grafted granular activated carbon

• DOI: 10.1016/j.jwpe.2020.101416
• Publication Date: 2020-06-12T16:17:18Z
• Authors: Hao Sun; Fred S. Cannon; Xin He
• Keywords: 01 natural sciences; 6. Clean water; 0105 earth and related environmental sciences

Abstract In this study, a quaternary nitrogen-grafted activated carbon (SNQ) was synthesized to remove perfluorooctanoate (PFOA) from a groundwater source. Batch isotherm tests and rapid small scale column tests (RSSCTs) were used to evaluated the performance of these variants in removing PFOA from groundwater. When processing groundwater that had been spiked with 200 ng/L PFOA, the SNQ exhibited 201,000 BV to 60 % breakthrough. This was 1.6 times higher than for the pristine SAC (128,000 BV). The longer bed life was attributed to the tailored carbon’s enhanced positively charged surface properties, which were monitored for this SNQ adsorbent by means of X-Ray Photoelectron Spectrometer, Scanning Electron Microscopy and Incremental surface charge titration analysis. Kinetics and isotherm tests show that the SNQ exhibited higher adsorption rate and adsorption capacity than the pristine subbituminous coal based activated carbon (SAC); and this was attributed to SNQ’s retained pore structure, high quaternary nitrogen ratio (0.89 %) and positive charge (0.47 meq/g). Moreover, the positively charged quaternary nitrogen groups onto the SNQ strongly attracted PFOA and lead to higher effective diffusion rates (12.6×10−10 m2/s). In order to test the nature of PFOA sorption, the authors employed a dynamic regeneration protocol using ethanol as an organic solvent; and this protocol restored 73 % PFOA adsorption capacity of the SNQ. In light of this tailored SNQ carbon’s high PFOA adsorption capacity and regenerability, we anticipated this quaternary nitrogen-grafted activated carbon could serve as an excellent adsorbent for PFOA removal from groundwater.