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Separation of nitrate from contaminated water using recycled membranes

​Researchers from IMDEA Water, in collaboration with the School of Science and Technology of NOVA University Lisbon, have recently published the paper Nitrate Removal by Donnan Dialysis and Anion-Exchange Membrane Bioreactor Using Upcycled End-of-Life Reverse Osmosis membranes in Membranes, the open access journal (A. Lejarazu-Larrañaga et al., 2022).

In this study, anion exchange membranes prepared from recycled reverse osmosis membranes have been used to separate nitrate from contaminated water to achieve concentrations suitable for consumption. In this way, it is intended to give a second life to discarded reverse osmosis membranes currently accumulated in landfills (>840,000 membranes are discarded per year [1]). On the other hand, nitrate is harmful to human health, so the World Health Organization (WHO) limits its concentration below 50 mg L-1 in water for consumption while recommending keeping it below 25 mg·L-1 [2].

Donnan dialysis is a spontaneous process without any energy input, through which nitrate can be separated from water (through an anion exchange membrane) and exchanged for a non-toxic ion (chloride, in this case). This transport is achieved thanks to the concentration gradient established between the contaminated water compartment and the receiving compartment, which contains a high concentration of sales. In addition, the integration of a bioreactor in the receptor compartment allows the simultaneous removal of nitrate by biological denitrification [3].


Image: Diagram representation of the Donnan dialysis system and its integration with a bioreactor (denitrification reaction represented in grey italics), using anion exchange membranes prepared from discarded reverse osmosis membranes [4].

This study showed that recycled membranes could be used in these processes for the separation of nitrate with a minimum energy input (only when pumping the solutions through the system).

This research is part of grant CTM2015-65348-C2-1-R funded by MCIN/AEI/10.13039/501100011033/ and by ERDF `A way of making Europe ´; grant RTI2018-096042-B-C21 funded by MCIN/AEI/10.13039/501100011033/ and by ERDF `A way of making Europe ´; grant CTM2015-74695-JIN funded by MCIN/AEI/10.13039/501100011033/ and by ERDF `A way of making Europe ´; grant BES-2016-076244 funded by MCIN/AEI/10.13039/501100011033 and by `ESF Investing in your future´; by the Portuguese Foundation for Science and Technology (FCT) and the Portuguese Ministry of Science, Technology and Higher Education (MCTES) UIDB/50006/2020 (FCT/MCTES).

Author: Amaia Lejarazu-Larrañaga

References:

[1] J. Landaburu-Aguirre, R. García-Pacheco, S. Molina, L. Rodríguez-Sáez, J. Rabadán, E. García-Calvo, Fouling prevention, preparing for re-use and membrane recycling. Towards circular economy in RO desalination, Desalination. 393 (2016) 16–30. https://doi.org/10.1016/j.desal.2016.04.002.

[2] World Health Organization, Guidelines for drinking-water quality, Fourth Edi, World Health Organization, 2017.

[3] J.G. Crespo, S. Velizarov, M.A. Reis, Membrane bioreactors for the removal of anionic micropollutants from drinking water, Curr. Opin. Biotechnol. 15 (2004) 463–468. https://doi.org/10.1016/j.copbio.2004.07.001.

[4] A. Lejarazu-larrañaga, J.M. Ortiz, S. Molina, S. Pawlowski, Nitrate Removal by Donnan Dialysis and Anion-Exchange Membrane Bioreactor Using Upcycled End-of Life Reverse Osmosis Membranes, Membranes. 12 (2022) 101.