Nitrate sorption from water on a Surfactant-Modified Zeolite. Fixed-bed column experiments

Abstract This study concerns fixed-bed column experiments performed at a laboratory scale in order to remove nitrate ions from water using a surfactant-modified (HDTMA +  = hexadecyltrimethylammonium) clinoptilolite as adsorbent. The influence of the initial nitrate concentration (0.32–2.42 mmol/L), the flow rate or flux (1.6–47.2 cm/min) and the presence of competing anions chloride, sulphate and bicarbonate, is examined. At the beginning of each experiment, removal rates R are very high, larger than about 95%, and then decrease progressively during filtration. As expected, the higher the initial nitrate concentration and/or the flow rate are, the earlier the column becomes completely inefficient. In comparison to corresponding batch-wise experiments, the performances of the Surfactant-Modified Zeolite are better in the column in particular larger exchange rates values at complete breakthrough (≈60%). In the presence of competing anions, the nitrate uptake performances are variously affected, being significantly or slightly reduced in the presence of SO 4 2 - (exchange behavior similar to the one of NO 3 - ) or of HCO 3 - respectively, whereas chloride, with no affinity towards SMZ, has practically no influence. Some leaching of HDTMA + ions occurs continuously upon filtration (concentration ≈ 10 −4 –10 −5  mol/L). In relation to the ecotoxicity of these species (concentration limit ≈ 10 −7  mol/L), a treatment of the effluents is necessary and was successfully performed by filtration through an activated carbon bed. Finally, from a 45 mmol/kg NO 3 - -loaded SMZ, a complete regeneration (NaBr 1 mol/L, L/S = 10 mL/g, batch system) is achievable after about 6 h.