A Comparison of Natural and Synthetic Zeolites in Continuous Column-Based Experiments for Removing Ammonia From Wastewater

Ion exchange based processes that use zeolites to remove ammonium from wastewater are relatively resilient to sharp increases in volume or concentration of ammonium beyond usual range or low temperature and could thus nicely complement biological processes. Previous batch-type experiments analysed a range of popular zeolite types to see which would show highest capacity and selectivity toward ammonium and may thus be best suited for removing ammonium from wastewater. Here, as a next step, toward determining real-world applicability, the top three zeolites from these previous batch-type experiments, namely Clinoptilolite, Mordenite and Mesolite, were compared in a column-type experiment, where synthetic ammonium solution was flowing continuously through the zeolite media. This experiment showed substantially longer cycle times with MesoLite relative to the other two zeolites. Cycle time with MesoLite ranged between 3 and 40 days at empty bed contact times (EBCT) of 1.2 minutes and 15 minutes respectively. The resultant capacities to breakthrough of 1 mg/L were 22, 25 and 47 mg/g for Clinoptilolite, Mordenite and MesoLite. Operating the MesoLite column at higher initial ammonium concentration decreased the cycle time at an EBCT of 1.2 minutes from 3672 BV when treating 5 mg/L to 255 BV when treating 30 mg/L. Based on a Thomas reaction model of second order, the maximum capacity for an EBCT of 1.2 minutes was predicted to be 56.8 mg/g. Taken together, these findings show that ammonium removal through zeolite media is feasible in a continuous flow setup at lab-scale with synthetic ammonium solution and that MesoLite compares favourably to two other options for zeolite media. This work can form the foundation for future research into improving process parameters or into applying this setup to conditions that more closely resemble those seen with real wastewater.