Regenerating Spent Zeolites with UV and UV/H2O2 To Enhance Removal of Endocrine Disrupting Compounds
Erik J. Rosenfeldt
Endocrine disrupting compounds (EDCs) have become contaminants of emerging concern due to their potential for harmful effects on human and ecological health, at low concentrations (ppb). As an alternative to conventional adsorption media, activate carbon, this study investigates feasibility of using high-silica, hydrophobic zeolites for the removal of EDCs through adsorption process. Zeolites are crystalline, porous alumino-silicate with well defined pore structures, and tetrahedral framework.
While traditional media regeneration processes are energy and cost intensive, evidence has been found that zeolites can be regenerated multiple times through relatively inexpensive methods using direct ultraviolet (UV) photolysis and advanced oxidation process (AOP). The regeneration process not only presents potential for multiple uses of the sorption media, but provides the additional benefit of oxidative treatment of back wash water produced from zeolite regeneration, potentially generating less hazardous waste.
Bench scale adsorption studies were performed to collect baseline adsorption data for three EDCs; estrone (E1), 17-β Estradiol (E2) and 17-α Ethinylestradiol, on three zeolites; CBV-400, CBV-780 and CBV-901. Freundlich and Langmuir isotherms models were considered to estimate the adsorption capacity and strength of each of these zeolites for the selected EDCs.
CBV-400 showed minimal adsorption of all three EDCs and hence was disregarded for kinetic and regeneration experiments. For CBV-780 and CBV-901, results obtained showed that equilibrium was reached within an hour, and over 90% of the EDCs were typically removed within 10 minutes of the reaction time.
Polychromatic, Medium Pressure Ultraviolet (MP UV) energy was used for the regeneration experiment due to the relatively high quantum yield of the EDCs being studied as compared to monochromatic, Low Pressure UV (LP UV). Results showed that regenerating zeolites with UV and UV/H2O2 treatment can more than double their adsorption capacity after four regeneration cycles when compared to untreated zeolites. Regeneration using advanced oxidation process with peroxide (UV/H2O2) did not significantly improve regeneration efficiency of zeolites compared to UV photolysis.
Studies were also conducted to evaluate the adsorption capacity of the zeolites in natural water. Lower adsorption of EDCs was achieved in natural water than in deionized water which was attributed to interference of various anions, cations and other precipitate salts depositing on the surface of zeolites.