Olive leaf and olive mill wastewater are wastes which are produced in olive industry and can be used to obtain value-added products such as polyphenols. In this work, extracts of polyphenols from olive mill wastewater and olive leaf in an aqueous medium are obtained and their composition in polyphenols were determined and compared with those obtained using the conventional extract agent (methanol–water). The antioxidant capacity of the aqueous extracts of olive mill wastewater and olive leaf were also analysed. It was observed that the olive mill wastewater extracted in water provides a similar content of phenolic compounds in the final extract compared to extraction with methanol–water, with the main polyphenols being hydrotyrosol and tyrosol (20.1 and 6.61 mg gdw⁻¹). In the case of leaf extraction, the methanol-free extract (recovery in water after extraction with methanol–water) had a lower total phenol content compared to the methanolic extract, with the main polyphenol being oleuropein (22.73 and 9.05 mg gdw⁻¹, for the methanol and methanol-free extract, respectively). However, both extracts obtained in aqueous solution present a similar antioxidant capacity at very diluted concentrations of the original extract, with IC50 values (half-maximal antioxidant concentration) of about 20 mg TS L⁻¹. The antioxidant capacity of the extract in aqueous solution facilitates its application as an antioxidant in biological systems, like animal food, where the use of extracts based on organic solvents, like methanol, are not suitable.

In this work, poly(vinyl chloride)-based polymeric ionic liquid inclusion membranes were used in the selective separation of Fe(III), Zn(II), Cd(II), and Cu(II) from hydrochloride aqueous solutions. The ionic liquids under study were 1-octyl-3-methylimidazolium hexafluorophosphate, [omim⁺][PF₆⁻] and methyl trioctyl ammonium chloride, [MTOA⁺][Cl⁻]. For this purpose, stability studies of different IL/base polymer compositions against aqueous phases were carried out. Among all polymer inclusion membranes studied, [omim⁺][PF₆⁻]/PVC membranes at a ratio of 30/70 and [MTOA⁺][Cl⁻]/PVC membranes at a ratio of 70/30 were able to retain up to 82% and 48% of the weight of the initial ionic liquid, respectively, after being exposed to a solution of metal ions in 1 M HCl for 2048 h (85 days). It was found that polymer inclusion membranes based on the ionic liquid methyl trioctyl ammonium chloride allowed the selective separation of Zn(II)/Cu(II) and Zn(II)/Fe(III) mixtures with separation factors of 1996, 606 and, to a lesser extent but also satisfactorily, Cd(II)/Cu(II) mixtures, with a separation factor of 112. Therefore, selecting the appropriate ionic liquid/base polymer mixture makes it possible to create polymeric inclusion membranes capable of selectively separating target metal ions.

The implementation of a microbial fuel cell for wastewater treatment and bioenergy production requires a cost reduction, especially when it comes to the ion exchange membrane part and the catalysts needed for this purpose. Ionic liquids in their immobilized phase in proton exchange membranes and non-noble catalysts, as alternatives to conventional systems, have been intensively investigated in recent years. In the present study, a new microbial fuel cell technology, based on an ionic liquid membrane assembly for CoCu mixed oxide catalysts, is proposed to treat animal slurry. The new low-cost membrane–cathode system is prepared in one single step, thus simplifying the manufacturing process of a membrane–cathode system. The novel MFCs based on the new low-cost membrane–cathode system achieved up to 51% of the power reached when platinum was used as a catalyst. Furthermore, the removal of organic matter in suspension after 12 days was higher than that achieved with a conventional system based on the use of platinum catalysts. Moreover, struvite, a precipitate consisting of ammonium, magnesium, and phosphate, which could be used as a fertilizer, was recovered using this membrane–cathode system.

In recent years, the quest to advance fuel cell technologies has intensified, driven by the imperative to reduce reliance on hydrocarbon-derived fuels and mitigate pollutant emissions. Proton exchange membranes are a critical material of fuel cell technologies. The potential of ionic liquid-based polymer inclusion membranes or ionogels for proton exchange membrane fuel cells (PEMFCs) has recently appeared. Thermal stability, SEM-EDX characterization, NMR and IR characterization, thermogravimetric analysis, ion exchange capacity, and water uptake are key properties of these membranes which need to be investigated. In this work, ionogel based on quaternary ammonium salts, such as [N_8,8,8,1⁺][Cl⁻], [N_8,8,8,1⁺][Br⁻], and [N_{8-10,8-10,8-10,1}⁺][Cl⁻] in various compositions with poly(vinyl chloride) are extensively studied and characterized based on those key properties. The best properties were obtained when a quaternary ammonium cation was combined with a bromide anion. Finally, ionogels are tested in microbial fuel cells. Microbial fuel cells based on the ionogel reach a maximum of 147 mW/m², which represents 55% of the reference membrane (Nafion 212). These results indicate that we still have the possibility of improvement through the appropriate selection of the cation and anion of the ionic liquid. Overall, the promise of ionogel membranes as a viable alternative in fuel cell applications has been demonstrated.

Microbial fuel cells (MFCs) and microalgae–bacteria consortia represent two renewable and promising technologies of growing interest that enable wastewater treatment while obtaining high-value-added products. This study integrates MFCs and microalgae production systems to treat animal slurry, aiming to remove and recover organic and inorganic components while generating energy and producing biomass. The MFCs effectively eliminated Chemical Oxygen Demand (COD), organic nitrogen, and a portion of the suspended solids, achieving a maximum voltage of 195 mV and a power density of 87.03 mW·m⁻². After pre-treatment with MFCs, the slurry was diluted to concentrations of 10%, 50%, and 100% and treated with microalgae–bacteria consortia. The results showed a biomass production of 0.51 g·L⁻¹ and a productivity of 0.04 g·L⁻¹·day⁻¹ in the culture fed with 10% slurry, with significant removal efficiencies: 40.71% for COD, 97.76% for N-NH₄₊, 39.66% for N-NO₂⁻, 47.37% for N-NO₃⁻, and 94.37% for P-PO₄⁻³. The combination of both technologies allowed for obtaining a properly purified slurry and the recovery of nutrients in the form of bioelectricity and high-value biomass. Increasing the concentration of animal slurry to be treated is essential to optimize and scale both technologies.

In this paper, microbial fuel cell technology with heterotrophic anodic denitrification, based on a new membrane-cathode assembly, was tested for slurry treatment and bioenergy production. Slurry is used due to its high chemical oxygen demand and a high content of nutrient compounds of nitrogen which can contaminate soil and water. The new membrane-cathode assembly systems were based on different ammonium and phosphonium cations combined with chloride, bistriflimide, phosphate, and phosphinate anions and a non-noble catalyst composed of copper and cobalt mixed-valence oxides. The influence of ionic liquids on the catalytic membrane was studied. The best membrane-cathode assembly was based on the ionic liquid catalyst [MTOA⁺][Cl⁻]-CoCu which achieved 65% of the energy reached with the Pt-Nafion^® system. The [MTOA⁺][Cl⁻]-CoCu system improved the water purification parameter, reducing the COD by up to 35%, the concentration of nitrates by up to 26%, and the organic nitrogen by up to 70% during the experiments. This novel membrane-cathode system allows for easier manufacturing, lower costs, and simpler catalysts than conventionally used in microbial fuel cells.