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The use of low-cost inorganic sorbents as a new sustainable strategy to enhance the valorization of nutrients (N-P-K), from the urban water cycle (e.g., side streams from sewage sludge anaerobic digestion), in agriculture applications is presented. The simultaneous recovery and stabilization of ammonium and phosphate by using a mixture of two reactive sorbents (Na and K zeolites and magnesium oxide) was evaluated. The nutrients stabilization process, favoured at alkaline pH values, is carried out by a) the precipitation of phosphate ions with magnesium and/or ammonium ions and b) the sorption of ammonium by Na- and K-zeolites. MgO(s) promoted the stabilization of phosphate as bobierrite (Mg(PO)(s)) or struvite (MgNHPO(s)) depending on the applied dose. Doses with the stoichiometric molar ratio of Mg/P promote the formation of bobierrite, while molar ratios higher than 3 favour the formation of struvite. Na zeolites (NaP1-NA, NaP1-IQE) demonstrated efficiency on ammonium stabilization between 60±2 (for 15gZ/L) to 90±3% (for 50gZ/L). The ammonium recovery efficiency is limited by the zeolite sorption capacity. If the target of the fertilizing criteria should include K, then the use of a K-zeolite (e.g., 5AH-IQE) provides a good solution. The optimum pH for the precipitation of struvite and bobierrite is 9.5 and the optimum pH for ammonium removal is between 4 and 8.5. N is present in higher concentrations (up 0.7-1gNH/L) when pH is ranged between 8.2 and 8.6. The ammonium recovery ratios were better than those previously reported using only magnesium oxide or even a more expensive reagent as newberrite (MgHPO(s)). The recovery mechanisms described generate low-solubility stabilized nutrients forms that potentially can be applied as slow-release fertilizers in agriculture. Thus, the use in agriculture of blends of digested sludge with low-solubility stabilized nutrients forms will improve soils quality properties in terms of organic matter and nutrients availability.

Nanofiltration (NF) membranes can be used in different configurations. The aim of this work was to determine the reliability of the data obtained using flat-sheet (FS) laboratoryscale configuration when NF membranes are implemented at industrial scale level using spiral wound (SW) configuration. Ion rejections in salt mixtures with the two configurations types were analysed, modelled, evaluated and compared. In both cases of the study, the\ud operation was carried out in cross-flow mode and with recirculation of permeate and concentrate streams into the feed tank. Different feed synthetic salt solutions were used based on a dominant and a trace salt. In both cases, the operating temperature was kept constant (21.5 ± 2.5°C), and the trans-membrane pressure range varied from the osmotic pressure to 20 bar. The same NF membrane was used for both configurations: NF270 (Dow Chemical).\ud The solution–diffusion–electromigration–film model was employed to describe the experimental results. Comparing both membrane configurations, the trans-membrane flux obtained with the FS configuration was higher than that observed with the SW configuration under the same operating conditions. In general, it is proved that ion rejection curves for both membrane configurations were fairly similar. Moreover, the membrane permeances\ud with respect to each ion in both configurations were quantitatively similar.Peer ReviewedPostprint (published version

In this work, the rejection of two ions associated with fertilizer pollution of ground water (NH4and NO3) by a polyamide nanofiltration (NF270) membrane was studied. Sodium chloride was selected as the dominant salt and the effect of its concentration on the NH4 and NO3 rejections was evaluated. Filtration experiments were carried out in a cross-flow setup with a rectangular spacer-filled feed channel. The solution-diffusion-electro-migration-film model (SDEFM), previously developed to model the pressure-driven trans-membrane transfer of electrolyte mixtures consisting of a single dominant salt and (any number of) trace ions, was used to obtain membrane ion permeance from the experimental data. In this way, the membrane permeances with respect to single ions (Na,Cl,NH4,NO3) were obtained for various concentrations of both dominant (0.05–0.3 M NaCl) and trace salts (0.001–0.003 M NH4Cl/NaNO3). It was observed that when the dominant salt concentration increased, the rejections of dominant salt and trace ions decreased, whereas the membrane permeances to ions increased. This information can be useful for developing design tools for nanofiltration of mixed electrolyte solutions in water-treatment applications.Peer ReviewedPostprint (author's final draft