Natural Zeolites for Sustainable Ammonium Removal in Decentralised Wastewater Treatment: An Experimental Study

Sustainable and efficient removal of nutrients in decentralised wastewater treatment is still challenging. This work focused on the characterisation of natural clinoptilolite and chabasite as low-cost and recyclable ammonium adsorbents. Inductively coupled plasma analysis showed Si/Al ratios of 3.92 and 2.30 for clinoptilolite and chabasite, respectively. X-ray diffraction tests showed different material purities (93% for clinoptilolite and 73% for chabasite). The Brunauer–Emmett–Teller (BET) reported specific areas of 291.6 m2∙g−1 and 29.9 m2∙g−1 for chabasite and clinoptilolite, respectively. Single point pore volume at P/P0 = 0.99 was 0.2 cm3 g−1 and 0.12 cm3 g−1 for chabasite and clinoptilolite, respectively. Adsorption capacities derived from batch adsorption tests were 1.66 ± 0.08 mg∙g−1 and 1.47 ± 0.03 mg∙g−1 for clinoptilolite and chabasite, respectively (Ceq = 10 mg∙L−1). In all column tests, the adsorption capacity of clinoptilolite was higher (2.48 ± 0.3 vs. 2.21 ± 0.2 mg∙g−1), a result inconsistent with its lower exchange capacity and lower specific surface area. Although it is difficult to clearly define the leading mechanism for adsorption, the difference between the two materials is probably due to the slower adsorption kinetics of chabazite, while the purity of the material may also have contributed. Applications of these sustainable materials for ammonium adsorption in decentralised wastewater treatment is promising, although determining their detailed preliminary characterisation is fundamental.