Testing adsorption properties of natural zeolites for nutrients in wastewater

Low-cost and efficient removal of nutrients in decentralized wastewater treatment plants is still challenging. The installation of supplementary adsorption systems may, in some cases, be appropriate. This work focused on two types of untreated natural zeolites, clinoptilolite and chabasite, with the objective of their characterization and testing of the adsorption properties. Characterization tests were first made on the samples. Inductively coupled plasma analyses showed a Si/Al ratio of 4.09 and 2.40 for clinoptilolite and chabasite respectively. X-ray diffraction tests showed different material purity (93% for clinoptilolite, and 73% for chabasite). The Brunauer–Emmett–Teller (BET) test showed that the specific area of the chabasite was 10-fold than clinoptilolite. Batch adsorption tests were conducted by introducing a known mass of sample in a mixing rotative reactor and measuring the contaminant equilibrium concentration. Column adsorption tests were done by introducing the water-ammonium solution into a PMMA column. Experimental measurements were compared to a general adsorption model. In all tests, the adsorption capacity of clinoptilolite was higher, despite the lower Si/Al ratio and higher specific area of chabasite. Such a result is attributed to the purity of the material. Natural zeolites confirm to be good candidates for ammonium adsorption in decentralized wastewater treatment plants, although their detailed preliminary characterization is fundamental.