AMMONIUM REMOVAL FROM WASTEWATERS USING NATURAL NEW-ZEALAND ZEOLITES

Ammoniacal nitrogen (ammonia and ammonium) in agricultural wastewaters can promote eutrophication of receiving waters and be potentially tox ic to fish and other aquatic life. Zeolites, which are hydrated alumin um-silicate minerals, have an affinity for ammonium ions (NH4+) and ar e, therefore, potentially useful in removing this contaminant from was tewaters. The major objectives of this study were to evaluate the capa city of two natural New Zealand zeolites (clinoptilolite and mordenite ) to remove NH4+ 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 NH4+ removal performance were also invest igated. Results obtained from the batch adsorption experiments indicat ed that both zeolites tested, regardless of their particle sizes, were equally effective (87-98%) at NH4+ removal from domestic wastewaters or synthetic solutions containing NH4+ concentrations of up to 150 g N H4-N m(-3). However, mordenite showed more effective NH4+ removal than clinoptilolite for dairy and piggery wastewaters, and for synthetic s olutions containing high NH4+ concentrations (350-750 g NH4-N m(-3)). At all equilibrium NH4+ concentrations tested (0.2-300 g NH4-N m(-3)), NH4+ 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 NH4+ removed by coa rse 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 NH4-N k g(-1),respectively. In the slow flow-through experiment (0.47 mm min(- 1)), NH4+ breakthrough (>1.2 g NH4-N m-3) for both zeolite sources (re gardless of their particle sizes) did not occur even after receiving 4 0 bed volumes (BV) of wastewaters containing 100 g NH4-N m-3. The NH4 removal at this breakthrough was approximately 99 g NH4-N m(-3) of wa stewater throughput, which equates up to 5.8-6.5 g NH4-N kg(-1) zeolit e. In contrast, at a faster loading flow rate (15.9 mm min(-1)), the b reakthrough was almost immediate (1 BV) for coarse zeolites and after 22 BVs for fine zeolite. The NH4+ breakthrough capacity for fine morde nite was 2.0-4.4 g NH4-N kg(-1) zeolite. Fine zeolites were more effec tive than coarse zeolites in removing wastewater NH4+ (95% and 55% rem oval, respectively), even after receiving 64 BV of wastewater.