Removal of Organoselenium from Aqueous Solution by Nanoscale Zerovalent Iron Supported on Granular Activated Carbon

Nanoscale zerovalent iron particles (nZVI) immobilized on coconut shell-based granular activated carbon (GAC) were studied to remove organoselenium from wastewater. A chemical reduction technique that involves the application of sodium borohydride was adopted for the adsorbent preparation. The texture, morphology and chemical composition of the synthesized adsorbents were analyzed with a scanning electron microscope (SEM), nitrogen adsorption–desorption isotherms and X-ray diffraction (XRD). Batch experiment with various pHs and contact times were conducted to evaluate nZVI/GAC adsorption performance. The results showed that nZVI/GAC has a strong affinity to adsorb selenomethionine (SeMet) and selenocysteine (SeCys) from wastewaters. The maximum removal efficiency for the composite (nZVI/GAC) was 99.9% for SeCys and 78.2% for SeMet removal, which was significantly higher than that of nZVI (SeCy, 59.2%; SeMet, 10.8%). The adsorption kinetics were studied by pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. Amongst the two, PSO seemed to have a better fit (SeCy, R2 > 0.998; SeMet, R2 > 0.999). The adsorption process was investigated using Langmuir and Freundlich isotherm models. Electrostatic attraction played a significant role in the removal of organoselenium by nZVI/GAC adsorption. Overall, the results indicated that GAC-supported nZVI can be considered a promising and efficient technology for removing organoselenium from wastewater.