The textile industry has long been associated with significant environmental challenges due to the generation of recalcitrant wastewater, containing complex chemical mixture that pose severe threats to ecosystems and human health. This study focuses on the role of pH adjustment in improving the pretreatment process for direct contact membrane distillation (DCMD) applied to real textile wastewater. By implementing a pH adjustment step (pH 6.14, 7.40, and 9.06) prior to sedimentation and filtration, the pretreatment process was significantly enhanced, reducing wetting, and improving permeate quality. GC–MS analysis identified specific organic molecules causing wetting, including volatile organic acids and alcohol derivatives, revealing that the rejection mechanism is primarily driven by the relationship between the wastewater pH and the pKa of these compounds. Adjusting the pH above the pKa converts these acidic contaminants into ionic, non-volatile forms, effectively preventing their passage into the permeate. This study highlights the importance of pH optimization in advancing DCMD as a sustainable solution for textile wastewater treatment. The proposed approach aligns with circular economy principles, enabling water reuse in textile processes, reducing freshwater consumption, and minimizing environmental discharge.

Hybrid anion exchange adsorbents (HAIX) seem promising to prevent eutrophication and recover phosphate (P). HAIX consist of an anion exchange resin (AIX) backbone, promoting anion physisorption (outer-sphere complex), impregnated with iron (hydr)oxide nanoparticles (NPs), for selective P chemisorption (inner-sphere complex). In this work, for the first time, as far as we know, Zn-doped iron (hydr)oxide NPs were embedded in AIX, and the performances compared with conventional HAIX, both commercial and synthesized. Zn-doped HAIX displayed improved P adsorption performances. Mössbauer spectroscopy (MS) revealed the goethite nature of the NPs, against the “amorphous hydrous ferric oxide” claimed in literature. The P adsorption comparisons, made in synthetic solution and real wastewater, underlined the crucial role of the NPs for selective P adsorption, while improving the understanding on the competition between physisorption and chemisorption. In pure P synthetic solutions, especially at high P concentrations, physisorption can “hide” chemisorption. This depends also on the anion form of the AIX, due to their higher affinity for multivalent anions, which affects HAIX adsorption selectivity and P desorption. In fact, a mild alkaline regeneration over three adsorption–desorption cycles revealed a complex interaction between the regenerant OH⁻ and the adsorbed P. OH⁻ molecules are consumed to transform phosphate speciation, causing (stronger) P re-adsorption and preventing desorption. Finally, Mössbauer spectroscopy revealed NPs agglomeration/growth after the three cycles plus final regeneration at pH 14. This study provides further understanding on the P adsorption–desorption mechanism in HAIX, drawing attention on the choice of experimental conditions for reliable performance assessment, and questioning HAIX consistent P removal and efficient P recovery in the long-term.

In this study, the efficiency of electrocoagulation (EC) with iron electrodes was applied to remove two phosphonates, 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) and nitrilotris(methylene) triphosphonic acid (NTMP) from concentrates. This work provides a detailed description of the experimental procedure and results on phosphonate removal and recovery from different electrolytes, including synthetic and real reverse osmosis (RO) membrane concentrates. This research showed high selectivity of EC, removing 100% and 80% of the NTMP and the HEDP respectively, confirming no competition with sulfates, nitrates, or silica. When experimenting with other electrolytes, calcium showed to be critical in enhancing the flocculation process, while calcium carbonate precipitation contributed to capturing the phosphonates from the concentrate. The produced iron oxide (sludge) was confirmed as goethite and akaganéite, and finally transformed into hematite, indicating the oxidation from Fe2+ to Fe3+ during the EC process. After the iron precipitate collection, an alkaline wash of the sludge was enough to recover 100% of the initial phosphorus from the NTMP phosphonate. However, further research is needed to optimize the recovery procedure and to improve the results with the HEDP. 70 and 140 A·m-2 current densities were optimal to bring HEDP and NTMP concentrations down to 32 μM (1 mg·L-1) in only 30 and 10 min respectively. In these conditions, the operational costs, 1.10 and 0.03 €·m-3 of treated concentrate, were estimated for HEDP and NTMP respectively. Even when EC has been widely studied for phosphate removal, this technique has been barely applied to treat concentrates containing phosphonate-based antiscalants. EC opens new possibilities for phosphonates and phosphorus to be removed and recovered respectively from membrane and other concentrates.

A systematic study on the physicochemical properties of two protic ionic liquids (ILs) {2-hydroxyethylammonium acetate ([Mea][Ac]) and 2-hydroxyethylammonium hexanoate ([Mea][Hex])} and their mixtures with water was performed. The density and viscosity were assessed across the entire range of aqueous dilutions between 278 and 393 K. The conductivities, water activities, and surface tension of the binary systems in water were also assessed, and the influence of anions was evaluated. Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and 1H and 13C nuclear magnetic resonance (NMR) techniques were used to study the systems at different IL compositions. The excess molar volumes (VE) and thermal expansion coefficients were calculated, with negative values for VE across the entire concentration range. Density data were fitted to a polynomial for density prediction, function of temperature, and concentration, with the average deviation percentage not exceeding 0.63%. The viscosities of the binary systems were studied considering six different models and were better predicted by the model of Herráez et al. at IL concentrations higher than 0.25 mole fraction. The systems containing [Hex]- exhibited higher water activities and lower conductivity and surface tension. All studied systems exhibited a glass transition event, which varied according to the IL composition. The FTIR and NMR analysis confirmed the distinct molecular arrangement of [Mea][Ac] and [Mea][Hex] systems.