Optimizing ammonium adsorption on natural zeolite for wastewaters with high loads of ammonium and solids

Ion exchange (IE) has been so far limited to treating waters and wastewaters low in solids (TS) and ammonium (NH4 (+)). This study provides a new insight into the application of IE for NH4 (+) removal from wastewaters with high NH4 (+) and TS, using natural zeolite as adsorbent medium. Assays were carried out in continuously stirred batch reactors to study the effect of initial NH4 (+), pH, TS, contact time, and zeolite pore size (0.2-0.5 and 0.6-2.0 mm). Results confirmed the suitability of this zeolite to remove NH4 (+) from wastewater with high amounts of solids (up to 2%TS) and NH4 (+) (up to 2500 mgNH(4) (+)-N/L). Ammonium adsorption capacity (q (t) ) was faster with 0.2-0.5 mm size because of the greater specific surface area and shorter diffusion path than 0.6-2.0 mm zeolite. Both zeolites showed increasing q (t) with increasing initial NH4 (+) due to the higher driving force produced by higher concentrations. The process followed a pseudo-second order kinetic and was best described by the Freundlich isotherm. Varying the pH (6-8.5) of the wastewater had no effect on NH4 (+) removal capacity. In conclusion, this natural zeolite showed high affinity for NH4 (+) in wastewater with high loads of NH4 (+) and solids, returning a viable treatment method when other techniques are not applicable.