RESUMEN
It is estimated that Reverse Osmosis (RO) desalination will produce, by 2025, more than 2,000,000 end-of-life membranes annually worldwide. This review examines the implementation of circular economy principles in RO technology through a comprehensive analysis of the RO membrane life cycle (manufacturing, usage, and end-of-life management). Future RO design should incorporate a biobased composition (biopolymers, recycled materials, and green solvents), improve the durability of the membranes (fouling and chlorine resistance), and facilitate the recyclability of the modules. Moreover, proper membrane maintenance at the usage phase, attained through the implementation of feed pre-treatment, early fouling detection, and membrane cleaning methods can help extend the service time of RO elements. Currently, end-of-life membranes are dumped in landfills, which is contrary to the waste hierarchy. This review analyses up to now developed alternative valorisation routes of end-of-life RO membranes, including reuse, direct and indirect recycling, and energy recovery, placing a special focus on emerging indirect recycling strategies. Lastly, Life Cycle Assessment is presented as a holistic methodology to evaluate the environmental and economic burdens of membrane recycling strategies. According to the European Commission's objectives set through the Green Deal, future perspectives indicate that end-of-life membrane valorisation strategies will keep gaining increasing interest in the upcoming years.
RESUMEN
One of the alternative sources to tackle the problem of water shortage is the use of reclaimed water from wastewater treatment plants for irrigation purposes. However, when the wastewater has a high conductivity value, it becomes unusable for crop irrigation and needs a more specific treatment. In this work, recycled nanofiltration (rNF) membranes and anion-exchange membranes (rAEMs) obtained from end-of-life RO membranes were validated to evaluate their application capability in saline wastewater treatment. The use of recycled membranes may represent an advantage due to their lower cost and reduced environmental impact associated with their production, which integrates membrane-based technology into a circular economy model. Both recycled membranes were tested in crossflow filtration and electrodialysis (ED) systems. The results of the rNF membrane showed a high selective rejection of divalent ions (SO42− (>96%) and Ca2+ and Mg2+ (>93%)). In the case of the ED process, the comparison between rAEMs and commercial membranes showed an appropriate demineralization rate without compromising the power consumption. Finally, the quality of both system effluents was suitable for irrigation, which was compared to the WHO guideline and validated by the 7-week lettuce crop study.
RESUMEN
This work explores the application of Reverse Osmosis (RO) upcycled membranes, as Anion Exchange Membranes (AEMs) in Donnan Dialysis (DD) and related processes, such as the Ion Exchange Membrane Bioreactor (IEMB), for the removal of nitrate from contaminated water, to meet drinking water standards. Such upcycled membranes might be manufactured at a lower price than commercial AEMs, while their utilization reinforces the commitment to a circular economy transition. In an effort to gain a better understanding of such AEMs, confocal µ-Raman spectroscopy was employed, to assess the distribution of the ion-exchange sites through the thickness of the prepared membranes, and 2D fluorescence spectroscopy, to evaluate alterations in the membranes caused by fouling and chemical cleaning The best performing membrane reached a 56% average nitrate removal within 24 h in the DD and IEMB systems, with the latter furthermore allowing for simultaneous elimination of the pollutant by biological denitrification, thus avoiding its discharge into the environment. Overall, this work validates the technical feasibility of using RO upcycled AEMs in DD and IEMB processes for nitrate removal. This membrane recycling concept might also find applications for the removal and/or recovery of other target negatively charged species.
RESUMEN
The present work shows a methodology for the preparation of membranes with a high affinity for nitrates. For this purpose, a polymeric mixture containing an anion exchange resin was extended on a recycled pressure filtration membrane used as mechanical support. Different ion exchange resins were tested. The influence in ion fractionation of (i) the type of ion exchange resin, (ii) the use of a recycled membrane as support and (iii) the operating current density during the separation process were studied. Results revealed that the employed anion exchange resin could tune up the transport numbers of the anions in the membrane and enhance the transport of nitrates over sulfates. The use of the recycled filtration membrane as support further increased the transport of nitrates in detriment of sulfates in nitrate-selective membranes. Moreover, it considerably improved the mechanical stability of the membranes. Lowering the operational current density also boosted ion fractionation. In addition, the use of recycled membranes as support in membrane preparation is presented as an alternative management route of discarded reverse osmosis membranes, coupling with the challenging management of waste generated by the desalination industry. These membranes could be used for nitrate recovery from wastewater or for nitrate separation from groundwater.
RESUMEN
In this study, an activation treatment for recycled anion exchange membranes is proposed. Following the circular economy approach, these membranes were prepared by using end-of-life reverse osmosis membranes as mechanical support. The end-of-life membrane was previously used and discarded by desalination plants after overcoming its lifespan. The activation treatment was based on the subsequent immersion of the membranes in diluted acid and alkali solutions. This treatment promoted the complete dissociation of the functional groups in the membrane, making them more reactive to the counter ions. The effects of acid and alkali concentrations and exposition times on the electrochemical properties were studied and the best combination was selected. In such a way, a decrease of 37% in membrane electrical resistance was achieved. The performance of activated and non-activated membranes in brackish water desalination by electrodialysis was compared. The results showed that the proposed activation treatment increased the flux of fresh water more than four-fold (from 1.2 to 4.9 L h-1·m-2), with a considerable reduction of energy consumption (from 5.2 to 3.0 kWh·m-3) and a great improvement in current efficiency (from 38% to 71%). In conclusion, this work shows a simple and low cost methodology for the improvement of the electrochemical properties of recycled electromembranes and thus, their performance in electrodialysis.
