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

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 SO42- (exchange behavior similar to the one of NO3-) or of HCO3- 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 NO3--loaded SMZ, a complete regeneration (NaBr 1 mol/L, L/S = 10 mL/g, batch system) is achievable after about 6 h.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Nitrate removal from waters on surfactant-modified clinoptilolite. ► Fixed-bed column experiments at laboratory scale. ► Influence of nitrate concentration, flux value and competing anions. ► Material regeneration and uptake of leached surfactant in the effluents.