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 mgNH₄ ⁺-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.