Simultaneous removal of phosphate and ammonium using salt–thermal-activated and lanthanum-doped zeolite: fixed-bed column and mechanism study

Abstract

Assessment of breakthrough performance of NaCl–Thermal–LaCl₃ synthetic modified zeolite continuous flow fixed-bed column on the simultaneous removal of phosphate and ammonium from simulated municipal wastewater was conducted. Variable parameters, including solution pH, bed depth, effluent flow rate, and input concentration, were examined for this study. The results indicated that the adsorption capacity increased with the increase in bed depth and input concentration and decrease of effluent flow rate for both phosphate and ammonium. Thomas and Yoon–Nelson models were found to give the better fitness to experiment data of the whole breakthrough curves, whereas Adams–Bohart model could only predict the initial part of the breakthrough using linear regression analysis. The bed depth service time model of breakthrough data showed that the time for the movement of the mass transfer zone increased with the increase in bed height and flow rate and decrease in initial concentration. Best fixed-bed column performance was obtained at high fixed bed depth, low effluent flow rate, and low initial concentration. Successful desorption and regeneration were achieved with 0.2 M HCl and 0.1 M NaOH. BET, scanning electron microscopy, energy dispersive X-ray spectroscopy, and FTIR and X-ray photoelectron spectra analyses confirmed that ammonium removal was mainly ascribed to exchanging with sodium in the adsorbent, and phosphate adsorption mainly followed the surface complexion mechanism; the surface hydroxyl groups played the key role. All the results proved that the column could be promising option for the simultaneous removal of phosphate and ammonium at lower concentrations.