Ammonium removal from wastewaters using natural New Zealand zeolites

Abstract

Ammoniacal nitrogen (ammonia and ammonium) in agricultural wastewaters can promote eutrophication of receiving waters and be potentially toxic to fish and other aquatic life. Zeolites, which are hydrated aluminum‐silicate minerals, have an affinity for ammonium ions (NH 4 + ) and are, therefore, potentially useful in removing this contaminant from wastewaters. The major objectives of this study were to evaluate the capacity of two natural New Zealand zeolites (clinoptilolite and mordenite) to remove NH 4 + from a range of wastewaters under both batch and flow‐through conditions. Effects of two zeolite particle size ranges (0.25–0.50 mm and 2.0–2.83 mm) on NH 4 + removal performance were also investigated. Results obtained from the batch adsorption experiments indicated that both zeolites tested, regardless of their particle sizes, were equally effective (87–98%) at NH 4 + removal from domestic wastewaters or synthetic solutions containing NH 4 + concentrations of up to 150 gNH 4 ‐N m −3 . However, mordenite showed more effective NH 4 + removal than clinoptilolite for dairy and piggery waste‐waters, and for synthetic solutions containing high NH 4 + concentrations (350–750 g NH 4 ‐N m −3 ). At all equilibrium NH 4 + concentrations tested (0.2–300 g NH 4 ‐N m −3 ), NH 4 + removal by both mordenite and clinoptilolite was significantly ( P < 0.0001) reduced by the presence of competing sodium (Na + ) cations in the synthetic solutions. The maximum amounts of NH 4 + removed by coarse and fine clinoptilolite and coarse and fine mordenite, calculated by the Langmuir model, were 5.77 and 5.74, and 8.09 and 8.28 g NH 4 ‐N kg −1 , respectively. In the slow flow‐through experiment (0.47 mm min −1 ), NH 4 + breakthrough (>1.2 g NH 4 ‐N m −3 ) for both zeolite sources (regardless of their particle sizes) did not occur even after receiving 40 bed volumes (BV) of wastewaters containing 100 g NH 4 ‐N m −3 . The NH 4 + removal at this breakthrough was approximately 99 g NH 4 ‐N m −3 of wastewater throughput, which equates up to 5.8–6.5 g NH 4 ‐N kg −1 zeolite. In contrast, at a faster loading flow rate (15.9 mm min −1 ), the breakthrough was almost immediate (1 BV) for coarse zeolites and after 22 BVs for fine zeolite. The NH 4 + breakthrough capacity for fine mordenite was 2.0–4.4 g NH 4 ‐N kg −1 zeolite. Fine zeolites were more effective than coarse zeolites in removing wastewater NH 4 + (95% and 55% removal, respectively), even after receiving 64 BV of wastewater.